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Wetting and drying of masonry walls: 2D-resistivity monitoring of driving rain experiments on historic stonework in Oxford, UK
Abstract
2D resistivity methods can provide useful information about moisture distributions within porous historic stonework, especially when used in conjunction with simulated driving rain. Moisture is known to be a highly important factor in the deterioration of porous stone. We report here on a series of experiments on historic walls within the centre of Oxford, UK, which illustrate varying degrees of deterioration (including the formation of gypsum-rich black crusts and exfoliating hollows). Using medical electrodes we have been able to carry out non-invasive and non-destructive 2D resistivity surveys before and after simulated rainfall to investigate the progress of wetting and drying. We have applied tentative calibrations to convert resistivity values to moisture contents. Our results show that rainfall penetrates in predictable ways, with clearly defined wetting and drying fronts. Stone blocks with highly weathered surfaces exhibit the most rapid and high levels of water uptake, but also dry out more quickly than crusted or sound blocks. Thus, positive feedbacks may be encouraged whereby more water is cycled through damaged blocks, thereby enhancing the potential for further damage.
... Periods of deep wetting: Prolonged periods of wetness can result in sub-surface wetting of porous building materials and encourage biological growth (Smith et al. 2011a;McCabe et al. 2013). Deep wetting can drive salt penetration into the stone (Sass and Viles 2010). While this process may delay the onset of surface decay, the severity can be greater due to increased surface or substrate heterogeneity (Sass and Viles 2010). ...
... Deep wetting can drive salt penetration into the stone (Sass and Viles 2010). While this process may delay the onset of surface decay, the severity can be greater due to increased surface or substrate heterogeneity (Sass and Viles 2010). Here, we consider a prolonged period of wetness to be ≥ 4 days of rainfall ≥0.2 mm. ...
... The variability in rainfall event characteristics poses a challenge within a heritage context as the same monthly total of rainfall could drive two very different processes of deterioration depending on how the rain fell, e.g. short isolated spells of heavier rain can drive surface deterioration, while prolonged rainfall with little drying time between spells will promote deeper wetting of the stone, with deeper areas requiring longer to dry out (Sass and Viles 2010). Furthermore, drying of walls will likely take longer in months with lower temperatures and higher humidities. ...
Changes in climate will exert increasing pressure on heritage, so standard climate metrics need to be tuned to heritage threats. Historical meteorological records are commonly available as monthly summaries, with few offering daily observations as daily readings may not have been taken or yet digitised. As data averaged over longer intervals misses short weather events, we investigate the extent to which temporal resolution is important for assessing climate pressures on façades. The Radcliffe Meteorological Station, Oxford, UK, provides the longest continual record of daily temperature and precipitation measurements in the UK. We use this record to assess the role of temporal scale in heritage climate parameters relating to (i) sunshine and warmth, (ii) rainy days and (iii) freezing events. Where there is a linear relationship between daily and monthly scale data, monthly observations can be interpolated as heritage climate parameters. However, for the majority of parameters, daily data was required to capture the variability in the datasets. We argue for the increased availability of daily observations to help assess the threat of climate to heritage.
... Due to the high surface area of porous stone, the drying rate of the materials can be higher than the evaporation rate of a free water surface [53]. Surface sealing by misplaced treatments or by crust formation can inhibit the drying out of the stone and cause prolongation of periods of dampness under the surface [54,55]. ...
... The electrical resistance of porous samples changes with water content by several orders of magnitude [55,58,68]. Problems occur due to the salinity of the pore water which is generally unknown. ...
... The use of numerous (up to 50 and more) electrodes together with a control unit [66] allows to calculate the 2D-or 3D-distribution of electrical resistivity. The results can visualize water absorption and desorption of stonework [55], the level of capillary rise [69] and the salinity of groundwater [70]. Infrared thermography (IR) can be used for moisture detection as wet surfaces are usually cooler due to evaporation. ...
Water plays a vital role in the deterioration and conservation of built and rock-hewn heritage and it is generally agreed that climate change is significantly changing the environmental controls on stone decay. We here introduce the framework of heritage hydrology as a holistic way of conceptualising the flows and stores, processes and impacts of water interacting with building materials. We distinguish the basic types of stone-built buildings, ruins and free-standing walls, and rock-hewn sites. Analogous to catchment hydrology, heritage hydrology can be subdivided into water fluxes and water reservoirs, further subdivided into inputs (e.g. wind-driven rain, capillary rise), throughputs (e.g. runoff down façade), storages (moisture content) and outputs (evaporation and runoff). Spatial patterns of moisture are different between buildings and rock-hewn sites, both presenting hydrological complexities. The interaction between mean and short-term precipitation, wind, radiation and resulting evaporation may lead to very different impacts at different heritage sites. We here differentiate between the detail scale, the façade scale and the building or site scale. Patterns at different sites can be very variable on different scales due to the multitude of influencing parameters and it is not clear which scale of moisture variations is actually relevant for decay processes. Temporal patterns are equally scale-dependent and include short-term fluctuations in temperature and rainfall, high-magnitude episodic events such as floods and storms, and longer-term changes as a result of seasonality, interannual variability and secular trends or climate change. Based on the outlined framework we advocate a research agenda for heritage hydrology in the future. This should focus on (1) finding the best combinations of methods to measure and model spatio-temporal patterns in moisture; (2) researching the major factors controlling spatio-temporal patterns in moisture; (3) figuring out which spatio-temporal patterns are most important for driving deterioration and how their respective scales interact.
... All other methods are indirect and use either chemical or physical parameters of the stone that are influenced by dampness. Electrical resistivity (ER) is a frequently used proxy (Sass and Viles, 2010;Kawaai and Ujike, 2018) because it changes with water content by orders of magnitude. However, the salt content of pore water, the total porosity, and temperature are influencing factors that may thwart the application of simple resistance-humidity relationships at rock or building sites and may complicate the interpretation. ...
... was done in earlier works that used ERT in similar settings (e.g. Sass and Viles, 2010;Sass, 2022) and the amount of water is insignificant compared to the total water volume within the stone. When this procedure did not work in the drying phase, we occasionally added a few drops of NaCl solution, which turned out to be a mistake (see Discussion section). ...
... The use of ERT was limited by extremely low electric conductivities at the top side of the stone which was very dry for most of the time. The methodology used in this study, but also in other studies (e.g., Sass and Viles, 2010) when water drops are applied between the rock and the electrode, influences the undisturbed moisture situation in the rock (Sass, 2022). The use of NaCl solution for this purpose reduces the amount of water needed but causes far-reaching problems in a smallscale experiment like this (see Section 4.2.1). ...
Surface geomorphological processes and the decay of heritage buildings are amplified by rock weathering, which mostly either requires water or is augmented by its presence. Measuring of water content in rock is, however, challenging and different scientific aims require different approaches. To find the most suitable rock moisture investigation methods, we conducted an experiment using eight types of moisture measurement (1D resistivity, 2D resistivity, TDR, borehole humidity, microwave reflectance, capacitance, IR thermography, and uranine-probes) under controlled conditions in a sandstone block that was subject to a slow wetting and drying cycle and to a series of freeze-thaw cycles. Critical evaluation of methods shows that measurement of dielectric properties as a proxy of rock water content can be recommended for most research aims whether for long-term monitoring, non-destructive measurement of surface moisture patterns, or for applications in deeper areas of rock. Moreover, observation of moisture dynamics in deeper subsurface requires either drilling inside the rock or the use of ERT. To determine the location of the subsurface evaporation front, uranine-probes and borehole humidity sensors are recommended. Lastly, the specific nature of freeze-thaw environments shows that the use of 1D resistivity and TDR can outperform other methods tested, with TDR being more reliable than resistivity but lacking in defined depth moisture fluctuations. To challenge the disadvantages of tested methods, a combination of techniques should always be considered.
... Due to the high surface area of porous stone, the drying rate of the materials can be higher than the evaporation rate of a free water surface [53]. Surface sealing by misplaced treatments or by crust formation can inhibit the drying out of the stone and cause prolongation of periods of dampness under the surface [54,55]. ...
... The electrical resistance of porous samples changes with water content by several orders of magnitude [55,58,68]. Problems occur due to the salinity of the pore water which is generally unknown. ...
... The use of numerous (up to 50 and more) electrodes together with a control unit Sass and Viles Heritage Science (2022) 10:66 [66] allows to calculate the 2D-or 3D-distribution of electrical resistivity. The results can visualize water absorption and desorption of stonework [55], the level of capillary rise [69] and the salinity of groundwater [70]. Infrared thermography (IR) can be used for moisture detection as wet surfaces are usually cooler due to evaporation. ...
Water plays a vital role in the deterioration and conservation of built and rock-hewn heritage and it is generally agreed that climate change is significantly changing the environmental controls on stone decay. We here introduce the framework of heritage hydrology as a holistic way of conceptualising the flows and stores, processes and impacts of water interacting with building materials. We distinguish the basic types of stone-built buildings, ruins and free-standing walls, and rock-hewn sites. Analogous to catchment hydrology, heritage hydrology can be subdivided into water fluxes and water reservoirs, further subdivided into inputs (e.g. wind-driven rain, capillary rise), throughputs (e.g. runoff down façade), storages (moisture content) and outputs (evaporation and runoff). Spatial patterns of moisture are different between buildings and rock-hewn sites, both presenting hydrological complexities. The interaction between mean and short-term precipitation, wind, radiation and resulting evaporation may lead to very different impacts at different heritage sites. We here differentiate between the detail scale, the façade scale and the building or site scale. Patterns at different sites can be very variable on different scales due to the multitude of influencing parameters and it is not clear which scale of moisture variations is actually relevant for decay processes. Temporal patterns are equally scale-dependent and include short-term fluctuations in temperature and rainfall, high-magnitude episodic events such as floods and storms, and longer-term changes as a result of seasonality, interannual variability and secular trends or climate change. Based on the outlined framework we advocate a research agenda for heritage hydrology in the future. This should focus on (1) finding the best combinations of methods to measure and model spatio-temporal patterns in moisture; (2) researching the major factors controlling spatio-temporal patterns in moisture; (3) figuring out which spatio-temporal patterns are most important for driving deterioration and how their respective scales interact.
... These vary in rigour, affordability, spatial resolutions and factors that after their signals. ert is attuned to the characteristics of natural stone and has been employed to successfully monitor short-term moisture regimes in historic masonry [12], [13]. ...
... As such, it was expected that a measurement schedule such as t ={0 . . . 12,15,18,21,24,30, 36, 48} h should capture the integral features of the desorptive drying processes. ...
... enabling comparison between monoliths and the masonry constructions at depths Block uncertainties were greater for the pre-wetting states, and also tended to increase over the duration of the drying process. This is likely exacerbated by the software's skepticism of the geological realism of inversions of dry stone, which has been addressed previously [12]. This complicated obtaining appropriate values of ρ pw ; however, the benefit of the lognormal normalisation is that the pre-wetting denominator induces only a vertical shift of ρ ′ in the lognormal dimension. ...
Detecting the presence of moisture in historical masonry is essential to understanding how a structure interacts with the environment, and diagnosing the potential for damage from a range of physical, chemical, and biological processes. In-situ, non-invasive diagnostic techniques have been developed in preference to methods that require irreversible modifications to a structure. These techniques include: electrical resistivity, microwaves, and infrared thermography. Independently, these approaches provide limited snapshots of surficial and internal moisture regimes; this project sought to assess the comparability of multiple techniques. Simulated post-rain spell drying was monitored over 48 h on limestone and sandstone monoliths in a controlled laboratory environment and also in ambient conditions on purpose-built masonry located in Oxfordshire, UK. Repeat measurements were taken using electrical resistance tomography (ERT), electrical and microwave moisture meters, and infrared thermography. Three aspects of comparability are discussed: i) data transformations and geological comparability, ii) depth-resolving meter readings, iii) the localised benefits of employing multiple technologies and instruments.
... This method is simple but it is invasive and it depends upon the exact location of the dowels and may affect the water movements within the masonry [19]. Electrical resistivity measurements have received more attention and have given valuable results on water movement in porous media such as rock [19,[30][31][32] or concrete [33][34][35][36][37][38]. This method is based on the variation in electrical resistance (or resistivity) of the system 'solid porous material + liquid water' in which the solid porous material has a high electrical resistance and the liquid water has a low electrical resistance. ...
... The reasons are related to both the material and to the practical manipulation of the techniques themselves, which may be destructive (e.g. sampling) or invasive, their sensitivity, their accuracy, their complexity for fieldwork, and the negative effect of implanting probes which may influence the measurement environment and can capture more moisture [30]. Thus, only electrical resistance measurement seems to be the most sensitive and the simplest method to use both in the laboratory and on site. ...
... This model does not match very well with our experimental measurements (regression coefficient of r 2 = 0.63 for tuffeau and r 2 = 0.56 for Richemont stone). Based on Archie's law, Sass et al. [30] determined a relationship between moisture content w and electrical resistivity of stone q by ''w = q À1  q W  D w  D st À1 " in which q, q w , D st , D w are the resistivity of stone, the resistivity of water, the density of stone, the density of water, respectively. The authors grouped together the results of a set of rocks, with a very low porosity (1-4%), in a single calibration curve [28]. ...
Electrical resistance can be a relevant indicator for the assessment of water transfer in porous materials. The aim of this work was to establish a relationship between electrical resistance and water saturation in the case of two limestones used as building stones in the Château de Chambord in France: tuffeau and Richemont stone. For this purpose, firstly the electrical resistance matching different values of degree of saturation was investigated. Experimental measurements were performed to determine a relationship between the electrical resistance and the degree of water saturation, with high sensitivity. Secondly, using this relationship, the capillary imbibition curves and imbibition coefficients of the two stones were precisely determined by electrical resistance measurement.
... In other cases, NDT can be used to gather empirical data and linked to specific material properties. This demands more rigorous and robust protocols (e.g., [33,43]). An in-depth approach may benefit from combining two or more NDTs in order to triangulate results (e.g., [27,38]), and calibration with laboratory tests (e.g., [44]). ...
... Trials were also made using moisture meters based on conductivity measurements. Conductivity/resistivity measurements can be taken at different depths and used to construct moisture profiles but are highly susceptible to salinity (e.g., [43]). Capacitance devices are less susceptible but can be affected by moisture gradients and decrease in accuracy at high MC [35]. ...
The correct choice of pointing mortar is considered crucial to the conservation of historic masonry. A proliferation of cement and eminently hydraulic lime mortars since the late 19th century has accelerated the deterioration of built cultural heritage in many parts of the world. Whilst the use of softer, lime-based mortars in stone conservation is now common practice, their role in the overall conservation strategy of highly vulnerable building stones such as Reigate Stone requires assessment. In this paper non-destructive testing (NDT) is used across a two-year period to investigate the impact of different pointing mortar types in situ. NDT data on surface hardness and moisture are interpreted at different scales to assess moisture regulation of Reigate Stone masonry at the Wardrobe Tower, a ruined structure at the Tower of London, following repointing carried out in Spring 2017. Joints repointed using a hydraulic lime mortar (NHL3.5) are shown to regulate moisture in adjacent Reigate Stone blocks less well than those repointed using a lime putty mortar. However, despite an initially inappropriate recipe, older hydraulic lime mortars are in some instances shown to perform similarly to the lime putty mortar, suggesting that NHL can weather sympathetically. The results also indicate that, whilst pointing mortar type does play a role in the moisture regulation of individual stones, its effect is outweighed by both properties of the stone itself, such as strength and past decay, and by wider micro-contextual factors, such as exposure or adjacent topography. Findings from the Wardrobe Tower indicate that pointing mortar only plays a part in overall moisture regulation; to enable its effective functioning and minimise the need for repeated interventions, it may be necessary to take additional protective measures to mitigate moisture ingress, such as water run-off and channelling following heavy rainfall. The overall implication is that in vulnerable historic masonry such as Reigate Stone, sustainable conservation strategies must incorporate a broad appraisal of, and tailored response to, specific decay mechanisms. With careful calibration across repeated survey campaigns, data collected in situ using NDT can inform the role of pointing mortar within such strategies.
... The electrode to electrode distance was 8 or 10 cm depending on the wall structure. A more comprehensive description of the approach including references is provided by Sass and Viles (Sass and Viles 2010a). Wenner and Schlumberger configurations were applied for the 2D-survey. ...
... Methodological: The combination of ERT, MM, and PPP is well suited to detect patterns of moisture and salts. Electrical resistivity (ERT) can respond to wetness (base of garden side, middle of road side), to salts (upper road side) or both; however, the response is complicated by porosity and microstructure (cavernous weathering zone) (Sass and Viles 2010a). ...
Boundary walls are neglected but important parts of historic urban environments, and they are often prone to serious deterioration. Understanding moisture and salt dynamics within boundary walls can help infer the causes and dynamics of deterioration. This investigation investigates the patterns of moisture, salt, and deterioration on a 300 year old limestone boundary wall in Worcester College, Oxford. Multiple methods to assess moisture and salts within and across the wall (electrical resistivity tomography, handheld resistivity-based moisture meter, paper pulp poultices, scanning electron microscopy, inductively coupled plasma optical emission spectrometry, and ion chromatography of small scale sampling of deteriorated limestone) were used in conjunction with decay mapping of both sides of the wall. The salt weathering strongly correlates with severely weathered zones at the wall and salts, mainly sulfates, seem to be the main agent of decay processes. The combined results demonstrate that the environmental influences driving stone decay can differ on a very small scale even at a comparatively simple structure like a boundary wall, and that repairs can have adverse effects if the patterns of salt and moisture dynamics are not sufficiently known.
... Water and dissolved salts are among the most important factors in physical and chemical weathering (Goudie et al., 1970;Doehne, 2002;Ollier, 1984). Excessive moisture and salinity are also major causes of deterioration in historic buildings (Winkler, 1994;Turkington & Smith, 2000;Sass & Viles, 2010;Oguchi & Yu, 2021). Porous materials with low strength, such as mortars, bricks, and some types of rocks, are particularly susceptible to the destructive effects of water and salts (Vasanelli et al., 2022). ...
The article highlights the importance of medieval churches with embedded millstones as geocultural objects with a great geotouristic and educational potential. In the lowland areas of Northeastern Poland, 79 millstones and their semi-finished products were inventoried. Their sizes ranged from 70 to 100 cm in diameter. The majority of them were made of erratic boulders, mainly granitoids of Fennoscandian origin. Additionally, gneisses, sandstones, pegmatites, and basaltoid were also identified. An attempt was made to determine the degree of weathering of the millstones over several hundred years of exposure to external conditions. Measurements of moisture content and salinity of the walls surrounding 10 millstones embedded in the walls of 8 churches were taken three times (in spring, summer, and winter). Lower wall moisture was observed in the vicinity of the millstones, but only in the case of three walls, the salinity of the mortar binding the bricks and stones was at a low level. A weak but statistically significant negative correlation was found between the age of the churches and the hardness of the millstones measured with a Schmidt hammer.
... The results of the calibration (Fig. 4) show that the conductivity-RWC relation follows a root function (cf. [29,41]). For fitting a curve we gave more attention to the 0% and 100% values since the intermediate saturation (50%) is likely to be less reliable. ...
Knowledge of salt and moisture distribution is a key factor for understanding rock decay at cultural heritage sites. The cave town of Uplistsikhe in Georgia, carved from sandstone in late bronze age to medieval times, suffers from progressive scaling and flaking processes. Multi-method investigations of rock moisture and salt distribution were carried out in order to better understand the patterns of decay. Salt distribution was investigated using drill dust samples and paper pulp poultices; moisture was determined by 2D-resistivity and handheld microwave sensors, supplemented by infrared thermography. The combined results from the different methods revealed a complex pattern of salt and moisture distribution. At most sites, K2SO4 (arcanite) and its hydrates dominate, sometimes in combination with CaSO4 (gypsum). At one site (Grandhall), halite (NaCl) and niter (KNO3) prevail. Sulphates are assumed to be a legacy of air pollution; origin of halite and niter remains unsolved but might be due to concrete reinforcements. Two main sources of moisture were evidenced depending on season and spatial situation: (1) Condensation of air humidity at cool cave backwalls in spring (combined with and aided by salt hygroscopicity), evidenced by 2D-resistivity and infrared thermography; (2) seepage along joints particularly at the cave backwalls and roofs, evidenced by handheld microwave sensors. Further investigations should focus on identifying seepage pathways and on clarifying the origin of destructive halite and nitrates.
... A relatively small number of studies also used ERT and EMI to detect the shallowest ground layers, although results obtained in this way are relatively easy to interpret. So far, high-resolution geoelectrical imaging has been applied in studies of small-scale weathering forms of bedrock (Roqué et al., 2013), deterioration of stone monuments (Mol and Viles, 2010;Saas and Viles, 2010), stability of embankments (e.g., Jones et al., 2014), and pattern grounds (Kasprzak, 2015;Way et al., 2017). In addition, the ERT was successfully used to image the soil properties under treethrow pit-mound topography and within the root zone of dead and living trees (Pawlik andKasprzak, 2015, 2018). ...
Forested hillslopes are zones of specific surface hydrology and geomorphic activity regimes. Their distinct properties , namely terrain microrelief (<10 m in diameter and height), are often a result of past disturbances that control forest stand conditions, soil formation processes, and superficial processes. A clear bioindicator of the past forest disturbance is pit-mound topography, which, however, is challenging to study because of its complexity and relatively small sizes of individual forms (usually <5 m in diameter). The present study analyzed the spatial representation, geomorphometric, and geophysical evaluation of the rare pit-mound topography in the Karkonosze Mountains National Park, SW Poland, Central Europe. For this task, two digital terrain models (DTMs) have been considered and were based on different quality point clouds collected during airborne and terrestrial laser scanning (ALS and TLS, respectively). The first data allowed the production of the DTM in 1 × 1 m spatial resolution, while the second data offered the DTM in 0.025 × 0.025 m resolution. Various geomorpho-metric derivatives (Terrain Ruggedness Index, Geomorphons, Topographic Wetness Index, Valley Depth, and Negative Openness) were applied and compared based on these models. In the further part of the study, we applied electrical resistivity tomography (ERT) and electromagnetic induction (EMI), assisted by shallow soil sampling and analyses to support the interpretation of geophysical models. Our TLS-based DTM offered higher-quality models and a better representation of pit-mound topography. The high-quality TLS-based DTM elevation model can support close-to-reality hydrological and geomorphic model-ing. The geophysical investigation allowed us to isolate a critical difference between treethrow pits and mounds better represented by ERT models than shallow EMI models. The differences were partly supported by soil properties , namely lower electrical resistivity in treethrow pits were related to higher moisture conditions, organic matter, organic carbon, and silt content in pits. As a general property, pit-mound topography resulting from tree uprooting adds to the complexity of forested hillslope hydrology and geomorphic activity. The surficial hetero-geneity in hillslope topography was also evident in soil properties with sharp changes in short distances between treethrow mounds and pits.
... The results of the calibration (Fig. 3) show that the conductivity-RWC relation follows a root function (cf. [27,39]). For tting a curve we gave more attention to the end members 0% and 100% since the intermediate saturation (50%) is likely to be less reliable due to uneven pore water distribution within the sample. ...
Knowledge of salt and moisture distribution is a key factor for understanding rock decay at cultural heritage sites. The cave town of Uplistsikhe in Georgia, carved from sandstone in late bronze age to medieval times, suffers from progressive scaling and flaking processes. Multi-method investigations of rock moisture and salt distribution were carried out in order to better understand the patterns of decay. Salt distribution was investigated using drill dust samples and paper pulp poultices; moisture was determined by 2D-resistivity and handheld microwave sensors, supplemented by infrared thermography.
The combined results from the different methods revealed a complex pattern of salt and moisture distribution. An most sites, K2SO4 (arcanite) and its hydrates dominate, sometimes in combination with CaSO4 (gypsum). At one site (Grandhall), halite (NaCl) and niter (KNO3) prevail. Sulphates are assumed to be a legacy of air pollution; origin of halite and niter remains unsolved but might be due to concrete reinforcements. Two main sources of moisture were evidenced depending on season and spatial situation: (1) Condensation of air humidity at cool cave backwalls in spring (combined with and aided by salt efflorescence), evidenced by 2D-resistivity and infrared thermography; (2) seepage along joints particularly at the cave backwalls and roofs, evidenced by handheld microwave sensors. Further investigations should focus on identifying seepage pathways and on clarifying the origin of destructive halite and nitrates.
... Therefore, the in situ determination of moisture content using non-destructive and non-invasive instruments has emerged as an alternative approach. Electrical resistivity is commonly used as a proxy for water content, but the relationship between electrical resistivity and water content can be influenced by salts in the pores (Sass and Viles 2010;Lopez-Gonzalez et al. 2016;Kawaai and Ujike 2018). A microwave moisture system is another beneficial device that analyses the moisture of materials based on their dielectric constant (Jamil et al. 2013). ...
Water plays a vital role in deteriorating stone heritage, especially those carved into vertical rock slopes. Southeast China is home to numerous limestone rock-hewn heritages, many of which showcase diverse deterioration patterns on their facades. Nevertheless, due to the large scale of this heritage and the limitations imposed by the principle of minimal intervention in practices, there is still a lack of practical strategies for understanding moisture distribution. Therefore, this study aims to analyse the moisture distribution of limestone rock-hewn statues via in situ detection employing a portable hygrometer and laboratory calibration based on the gravimetric method and regression analysis. The in situ determination was conducted in the Ciyunling statues niche 1 (World Heritage Site), which was hewn in the Wuyue states (942 CE). Thirty-six measuring areas were evenly planned on the niche's façade, with 20 moisture readings obtained from each measuring area. Additionally, the surface hardness of the typical area of statues was examined using a non-invasive Leeb hardness tester and Kruskal–Wallis H test to assess the impact of moisture on deterioration. The findings reveal that the statues' moisture content is higher than the background wall between the statues, signalling a greater potential for deterioration on the surface of the limestone statue. The primary source of moisture appears to be gaseous water in the atmosphere, which accumulates in the micropores through capillary condensation. Furthermore, the statistically significant differences in surface hardness between the chest/shoulder of statues and the root of the façade highlight the softening effect of moisture on the foundation of the limestone statues. Hence, the methodology utilised in this study serves as a viable approach for examining moisture levels and the extent of deterioration in rock-hewn heritage structures.
... Works that apply these methods research the distribution of humidity on masonry walls and also; the ones that research monitoring the filtration of water through antique walls, creating measurements in 2D and 3D [23,24]. One of the main reasons the ERT method was accepted, in the last years is because of its easy management of equipment and the adaptation of electrodes, causing few affectations on the surface of walls [25]. ...
Diagnosis of historic buildings is relevant because it contributes to their preservation in adequate and safe conditions; in the present work, the Electrical Resistivity Tomography (ERT) technique is applied on horizontal and vertical planes to study aspects of humidity, to recognize the internal geometry of elements, and to detect resistivity anomalies in two old buildings in the state of Aguascalientes, Mexico; these buildings are the Temple of the Inmaculada Concepción and Terán House. In the first, the electrical profiles obtained from the subsoil show a zone of low resistivity associated with a saturated layer that damages the wall due to rising dampness. On the second, the resistivity images obtained from measurements on two walls with humidity problems show the source and define some flow patterns. It could be concluded that using the obtained results ERT technique generates valuable information for the preservation of built heritage and, therefore, is viable for the diagnosis of historical buildings, mainly in the study of humidity and discontinuities in walls.
... Works that apply these methods research the distribution of humidity on masonry walls and also; the ones that research monitoring the filtration of water through antique walls, creating measurements in 2D and 3D [23,24]. One of the main reasons the ERT method was accepted, in the last years is because of its easy management of equipment and the adaptation of electrodes, causing few affectations on the surface of walls [25]. ...
Diagnosis of historic buildings is relevant because it contributes to their preservation in adequate and safe conditions; in the present work, the Electrical Resistivity Tomography (ERT) technique is applied on horizontal and vertical planes to study aspects of humidity, to recognize the internal geometry of elements, and to detect resistivity anomalies in two old buildings in the state of Aguascalientes, Mexico; these buildings are the Temple of the Inmaculada Concepción and Terán House. In the first, the electrical profiles obtained from the subsoil show a zone of low resistivity associated with a saturated layer that damages the wall due to rising dampness. On the second, the resistivity images obtained from measurements on two walls with humidity problems show the source and define some flow patterns. It could be concluded that using the obtained results ERT technique generates valuable information for the preservation of built heritage and, therefore, is viable for the diagnosis of historical buildings, mainly in the study of humidity and discontinuities in walls.KeywordsNon-Destructive Testinghistorical buildingsElectrical Resistivity TomographyTemple of the Inmaculada ConcepciónTerán House
... They are manufactured by doping normal clay bricks with conductive or semi-conductive impurities. Such inclusions, however, must be able to endure the high baking temperatures that the brick is subjected to throughout the production process, for instance, titanium dioxide (titania) and micro-or macrofibers made of certain metals that resist oxidation at high temperatures [120,123,124]. ...
Masonry structures dominate cultural heritage sites worldwide. Public authorities ought to preserve and safeguard such structures for future generations. However, precise evaluation of the current condition of such historical inheritance is crucial to appraise the need for adequate restoration and preservation work. Yet, ambiguity related to the absence of design and construction information and lack of data on the materials used makes this task a daunting challenge. Therefore, there has been considerable research into developing pertinent methodologies and technologies. Evaluating the safety of such heritage masonry structures typically requires in-situ inspections and surveys, sampling and testing, and balancing data from multiple diagnosis activities to select the best strategy for conservation and protection. Despite its operational benefits, this approach is costly, laborious, requires a high degree of professional skill, is unable to unveil hidden defects, and may escalate future maintenance costs. A promising alternative solution is structural health monitoring (SHM) systems. Accordingly, this paper systematically reviews damage detection and SHM techniques for masonry structures. The different measurement methods for SHM are classified into sensor-based and remote sensing methods, while the analyses methods are divided into signal and image processing techniques, artificial intelligence, and numerical techniques. The advantages and disadvantages of the various methods are discussed and compared. The related knowledge gaps are identified, recommendations for best practice are formulated, and the need for future research is identified.
... ERT has been used extensively over the past few decades for archaeological purposes to find and identify ancient structures, as well as to distinguish the local geological features and provide useful information about the building's hidden foundations [35][36][37][38][39][40][41][42][43]. This comparatively recent geophysical method has also been applied to stone exposures [44][45][46]. This paper aims to prove the effectiveness of the integration between geochemical and geophysical investigations in detecting the hidden paleochannel linking the cenotaph of Seti I and the Nile River. ...
The scientific controversy among archaeologists about the existence of paleochannels under the Abydos archaeological site, Sohag, Egypt connecting the Osirion (cenotaph of Seti I) with the Nile River has been explained in this study. This study is an attempt to address this issue using integrating a near-surface geophysical approach with stable isotopic geochemistry on this site. Particularly, the stable oxygen and hydrogen isotopes on the water samples collected from the surface and the groundwater in the study area were analyzed and interpreted. The isotopes result showed that the Osirion water is a mixture of three different types of water: Old Nile Water (ONW) before the construction of the High Dam, Recent Nile Water (RNW) after the construction of the High Dam, and Paleowater (PW) from deeper aquifers. Field observations of the Osirion and nearby water cannot explain the presence and direction of this water. Therefore, the next step in this study is determining the location and the direction of the paleochannel connecting the Osirion with the Nile River which was proven using the electric resistivity tomography (ERT) technique. By using the results of the isotope of all types of water near the Osirion and its surrounding wells and the water of the Nile River, in addition to the near-surface geophysical measurements, the results indicated that the 3D view of the ERT data revealed a prospective paleochannel in the direction of the northeast and its location, where this channel is in charge of providing groundwater from the Nile River to the Osirion location.
... This technique is used to determine the resistivity of a material, i.e., its resistance to the flow of electrical current across its length [56,57]. Resistivity is related to a number of parameters, including moisture content, the presence of soluble salts or other ionic compounds transporting electric current, permeability or porosity, and the presence of other materials [58][59][60][61][62]. Broadly speaking, a high moisture content in combination with a high ionic load and considerable porosity favours current flow and decreases the electrical resistivity of a material. ...
This study refers to the inclusion of phase change materials (PCMs) in porous building materials as an alternative means of improving their thermal behavior, assessing the changes caused in their physical–mechanical and durability properties. Specifically, an organic paraffin wax was selected for direct incorporation into lime mortars using different concentrations by weight. The results show that PCMs improve the thermal properties of the mortar while reducing its accessible porosity. This increases the mortars’ resistance to water and soluble salts. However, excessive PCM content causes stresses within the mortar that can jeopardize its structure.
... This technique is used to determine the resistivity of a material, i.e., its resistance to the flow of electrical current across its length [56,57]. Resistivity is related to a number of parameters, including moisture content, the presence of soluble salts or other ionic compounds transporting electric current, permeability or porosity, and the presence of other materials [58][59][60][61][62]. Broadly speaking, a high moisture content in combination with a high ionic load and considerable porosity favours current flow and decreases the electrical resistivity of a material. ...
The characterization of both surface and subsurface pathologies (position, depth, width,...) that affects the porous materials used in building constructions, once in service, is important to establish the most suitable intervention strategy. In this sense, the use of non-destructive techniques allows the analysis of different properties without affecting the material. The present study shows the accuracy of different non-destructive in situ techniques, such as: electrical conductivity and capacitance, infrared thermography, ultrasonic pulse velocity, sound absorption, and electrical resistivity tomography, applied on dolostone ashlar stones outer façade of a sixteenth-century belltower, affected by moisture and salt induced decay. The joint analysis of the results obtained with different techniques substantially improves the interpretation and characterization of the detected pathologies, as they complement each other perfectly. Electrical resistivity tomography, which delivers resistivity cross-sections, yields very good results in detecting subsurface pathologies, and sound absorption is particularly useful for stone surfaces. In both cases, the frequency of the electric field and that of the acoustic emission to detect the extent of damage must be established in advance. The joint study of electrical conductivity and capacitance determines the degree of moisture/salts, both at the surface and subsurface, in the materials tested, one of the main causes of scaling and flaking in stony materials. However, the petrological characteristics of the materials used and the identification of the saline phases present must be known in advance to make a correct interpretation of the results.
... The in situ measurements on ancient monuments (Souffaché et al., 2016) using a decimetric sized instrument showed over two different depth of investigation (approximately 10 cm and 20 cm) significant variations of both the real and imaginary components of the effective permittivity over the whole volume of masonry stones belonging to the facings. It is worth noting that in the older monuments, i.e. having exceeded a half-century of existence, the water content of the stone is constant beyond two to three centimetres whatever the weather conditions (Sass and Viles, 2010). Where constructions are protected by roofs, weather fluctuations only lead to pellicle variations of the stone water content, conversely a significant water content would evidence a lack of protection. ...
Lutetian limestones have been widely used in historical monuments in the Paris Basin in the course of medieval and modern periods. Among the physical properties that can be used to assess the evolution of the limestones in situ in the buildings and their present health, the complex effective permittivity in the 10 kHz – 100 kHz frequency range is easy to measure and reflects the stone internal structure with also the dependence on the water content. To improve the knowledge about this property, a laboratory study on four samples collected in the relevant quarries has been undertaken along the 100 Hz – 10 MHz frequency range. Except close to zero water content, the observed results exhibit a quasi-absence of variation of the real effective permittivity with the water content. The frequency variation fairly fits with a model taking into account a Jonscher's decrease, a direct current conductivity, a high frequency dielectric permittivity and losses, and a relaxation phenomenon. When fitted by a Cole-Cole model, the magnitude of the corresponding relative permittivity change always stays close to 30 but the time constant varies from 1 to 0.1 μs as the water content increases.
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... The moisture content of a building wall has great significance in the material durability, health of the indoor environment, and building energy consumption. In addition to the traditional weighing method, researchers have also tried the electrical resistance method [26,27], capacitance method, dielectric constant method [28], microwave method, infrared thermal imaging method, X-ray detection method, portable nuclear magnetic resonance method, and so on. However, at present, there is no ideal method for a non-destructive, rapid, and accurate measurement method of moisture content on site that can automatically and continuously monitor the moisture content of porous materials as simple as measuring the air temperature and humidity [29]. ...
The occurrence of rising damp in historical buildings results in material deterioration, energy waste, water-related damage, uncomfortable indoor air, and mould growth. The rising process in a real wall is influenced by the construction types, masonry details, environmental conditions, physical properties of brick and mortar. To clarify the features of rising damp influenced by the construction types in blue-brick masonry walls, a solid wall and a cavity wall made of clay blue bricks and lime mortar with a size of 3 m (high) × 1.2 m (wide) × 0.24 m (thick) were constructed to perform a water rising experiment for 600 days in a closed laboratory. The results demonstrated that the construction types directly affected the rising speed and the height of sharp fronts, which were 192 cm in the cavity wall and 168 cm in the solid wall after 600 days. The calculation model of the moisture rising in the solid wall and cavity wall obeyed the sharp front model of a homogeneous wall; however, the environmental conditions affect the rise of sharp front and moisture distribution. The research expands the understanding of the rising damp in real masonry and provides data supporting the moisture simulation, energy consumption, and heritage conservation of brick masonry.
... Some field studies (e.g. Sass and Viles, 2006;Sass and Viles, 2010;Mol and Viles, 2013) use electrical resistivity (ER) as a proxy to measure water content and its distribution in porous media. Using the ER tomography, Mol and Viles (2013) reported a sharp increase in resistivity in near sub-surface of a drying sandstone block, which can be interpreted as a VP. ...
The vaporization plane, a narrow zone of subsurface evaporation often present in porous rocks, separates the region where water flows due to capillary forces from the dry zone where moisture moves in gas phase only. The knowledge of its depth and geometry is critical for estimating water flux in rockatmosphere interphase, for understanding moisture distribution and for localization of damaging salt crystallization. Yet, an easy-to-use method applicable in the exterior has been missing. This strongly limits interpretation of moisture-related measurements as moisture content differences in the abovementioned zones are often immeasurable by currently used field techniques. We have introduced a new micro-destructive method to measure the vaporization plane depth using an instrument consisting of a rod, adhesive, and dye powder, reacting with moisture, that is inserted into porous materials in 2 mm diameter holes. We tested different rods, adhesives, and dyes, and the best combination of these has been used in >500 experiments to determine the vaporization plane depth in porous rocks and building materials. The knowledge of vaporization plane depth enables more reliably to interpret the moisture and suction data obtained from numerous existing techniques. This new uranine-probe method should be thus of interest to many scientific disciplines: evaporation, unsaturated hydrology, weathering, or geobiology.
... The unique systemic qualities of stone masonry (units and joints) has either been considered negligible, i.e. measurements are interpolated across joints and masonry units (e.g. [24][25][26]) or the joints are omitted from the survey, i.e. measurements are taken on individual masonry units alone [16]. This disregards the potential benefit of capitalising on the spatial geometries of non-destructive techniques to assess the dynamic behaviour of masonry systems, as represented by interactions between masonry units and joints. ...
Water is a fundamental control on the deterioration of historic stone masonry, of which wind-driven rain (WDR) is an important source in the UK. Non-destructive testing methods for moisture measurement can characterise the response of masonry to short (but intense) periods of wind-driven rain. An important part of this response is how masonry functions as a system of stone units and mortar joints, in which mortar can act as a conduit for moisture. While non-destructive techniques are common in moisture surveying of built heritage, there are no agreed best practice methods for collection, handling, and visual representation of data. This study explores the comparative advantages of microwave and radar measurements in two field experiments of exposure to short (but intense) simulated wind-driven rain exposure to demonstrate when and how they are most effectively employed. A novel method of representing data as percentiles is explored to facilitate effective communication of moisture measurements. In the case of the granite wall (e.g. with components of strongly contrasting hygric properties), microwave and radar provided similar information. The average travel time of the radar signal (from the back wall reflection) demonstrated that radar can non-destructively identify water penetration through mortar joints. In the sandstone tower, the microwave measurements were able to clearly identify four different moisture regimes as a result of different intensities of WDR exposure. The radar measurements were suited to identifying distinctions between localised moisture contents within masonry units and mortar joints, which characterised how the masonry was functioning as a holistic system. The measurements on both the granite wall and the sandstone tower demonstrated that the radar is influenced by environmental conditions which influence surface condensation and equilibrium moisture contents. Representing the measurements as percentiles improved visual representation of measurements with colour scales and minimised potential skewing of normalisation and scales from extreme values/outliers. This paper demonstrates that both microwave and radar techniques can be useful for monitoring moisture in stone masonry systems. Material characteristics of the masonry system and the objective(s) of the investigation should be considered during selection of the appropriate technique(s).
... Hughes et al. have tested several compositions of mortar for repointing granite, which included using quicklime [13]. Moreover, understanding the response of a masonry system to driving rain, comprising masonry units, mortar joints, but also a core filled with loose stones, rubble and mortar, is complex [30,31]. Therefore some studies have used test walls to understand the effect of water ingress and compare conservation treatments [3] and to evaluate the response of a specific material to driving rain, mainly focusing on brick walls [25,32] and stone [33]. ...
When rain impacts a building façade, it is essential that once it has entered, it leaves by evaporation to help the building dry out. Accumulation of moisture can lead to internal dampness, mould and decay of valuable masonry by salt weathering. In a solid masonry wall where the stone is of low permeability, such as granite which is found in many historic buildings, rain water mainly enters and leaves through mortar joints. If granite stone masonry needs repointing, the repair mortar must allow the overall masonry to dry out. This study evaluates the drying response of various lime-based repointing mortars mixes in small granite stone masonry constructions (test walls) subjected to a simulated intense short rain event and then left to dry. It determines the moisture movement through mortar joints, the influence of materials, joint types and workmanship, and whether repointing could mitigate moisture ingress and help masonry dry out. This study developed a novel experimental protocol which allowed comparison of the drying response of different mortar types in a low-porosity stone masonry system and the effect of repointing. Five test walls were built of Cornish granite with five different lime mortar mixes combining NHL 3.5 (St Astier) gauged with non-hydraulic quicklime (Shap), quartz and calcitic sand and biomass wood ash as additives. Simulated intense rain was sprayed on each wall over a 3.25 h spell. Drying was monitored over a week with a microwave moisture device (MOIST350B). Measurements were done at surface and depth on both mortar joints and granite units. Each wall was then repointed with the same mortar mix initially used when built and the same rain simulation was performed to evaluate differences repointing could make to the moisture dynamics. The importance of mortar in dealing with moisture movements in the test wall and absorbing moisture from the stones was demonstrated. Gauged binder and wood ash additives decreased the capillary absorption capacity of mortars while retaining a good drying rate. This study has also showed that after repointing water did not penetrate as deep under the same conditions. Therefore repointing reduces the threat of water ingress and shows that it could be a suitable conservation intervention to mitigate water ingress and accelerate drying.
... Some field studies (e.g. Sass and Viles, 2006;Sass and Viles, 2010;Mol and Viles, 2013) use electrical resistivity (ER) as a proxy to measure water content and its distribution in porous media. Using the ER tomography, Mol and Viles (2013) reported a sharp increase in resistivity in near sub-surface of a drying sandstone block, which can be interpreted as a VP. ...
In coarser porous materials (e.g. in natural sandstone bodies, buildings made of porous materials, or sandy soils), evaporation of pore water often occurs several mm to cm below the actual surface, at the so-called vaporization plane. The knowledge of the depth of this vaporization plane is critical for prediction of material disintegration, e.g. by salt or frost weathering. It also influences the presence of various organisms (mosses, lichens, fungi, etc.), and influences the evaporation rate, a critical process in the earth-atmosphere water balance. In the field, the vaporization plane depth can be determined by several proxy methods, the most common of which is the electrical resistivity tomography. Recently, a direct dye visualization method has been developed (Weiss et al., 2018). The methods currently being used have, however, either low spatial resolution, require special devices, or are too invasive. Here, we present the needle method (patent pending), a direct visualization field method that is simple-to-use, cost-effective and minimally invasive. The measuring device used is composed of a needle, glue and a dye in powder form, preferably uranine. This device is inserted into a hole previously drilled in the material of interest, left for some time so that the dye can react to the pore water, and later taken out and visually interpreted. The needle changes its appearance (especially colour) depending on the wetness of the material and we can, when following a suggested methodology, directly identify the vaporization plane depth with accuracy of several mm. The results using this method correspond to the dye visualization method, and in materials without substantial amount of salts in pore water also to the electrical resistivity method. We believe that this new method will find use in the scientific fields of geomorphology, heritage site protection, pedology, and porous material engineering.
... A escolha e utilização de um método depende da finalidade e características do projeto. Assim, a deteção de fraturas pode utilizar GPR [19] e tomografia de ultrassons [20], enquanto a investigação de patologias, como humidade em paredes, pode recorrer a tomografia elétrica [21,22] que também pode ser usada para a caracterização de terrenos e fundações sob edifícios [23,24]. ...
The characterization of the Monastery of Batalha included the use of the geophysical method of ground-penetrating radar (GPR), a non-destructive and indirect method that provides high-resolution 2D/3D images of the structures to investigate. Owing to the nature and aims of the survey, appropriate measurement grids, acquisition parameters and adapted data processing techniques were used. The GPR survey provided important information about the Monastery foundations, construction and conservation. GPR high-resolution images allowed to locate recent and ancient infrastructures, columns foundations and structures of historical-archaeological interest. The characterization of the Monastery walls was also carried out using GPR on the surface of walls of the Cloister of D. João I and of the Church. These results contribute for the proposal of an inner structure model of the walls. GPR proved to be an efficient and expeditious method that allowed obtaining information to be used in the preservation, recovery and rehabilitation of the Monument.
... According to research carried out employing Non Destructive Testing (NDT) Methods in the built heritage [6][7][8][9][10], the seismic, electric and GPR methods shown useful results in the analysis of the deterioration of the elements in historical structures. Particularly, the ERT technique has been used in the characterization of structural elements in historical buildings. ...
... This technique has been also applied to the south wall of the Acropolis of Athens, showing a selective route of the rainwater flow through the infill materials behind the wall (Tsourlos and Tsokas, 2011). In conjunction with simulated driving rain and conversion from resistivity value to moisture content, the rainfall penetrates in predictable ways, with clearly defined wetting and drying fronts (Sass and Viles, 2010). Cases studies from Hertford College (Oxford, UK) and Neolithic rock art (Golden Gate Reserve, South Africa) proved that ERT can be used as a vital tool for understanding hydrology and weathering processes within different rock types (Mol and Preston, 2010). ...
... In a study of sandstones, Hale and Shakoor (2003) found that larger and more numerous pores make material more susceptible to weathering, and that the cycles produced a cumulative loss of compressive strength in the material. The deeper the water penetrates, the deeper below the surface that recrystallized salts can damage the stone (Coombes, 2011;Heinrichs, 2008;Karatasios et al., 2009;McCabe et al., 2012;Ruedrich et al., 2011;Sass and Viles, 2010). Waragai (2016) surveyed sandstone temples in Cambodia and found that the main contribution to their physical weathering was the wet-dry cycles that they were subjected to as result of the extreme seasonality. ...
Subaerial weathering is a taphonomic process that affects many archaeological and paleontological bone assemblages and is characterized by surface bleaching, loss of organic component, and progressive cracking and splintering of the bones. Although the mechanisms of such changes are not well understood, previous research has indicated that multiple processes contribute to weathering, including ultraviolet exposure, mineral leaching, mineral recrystallization, thermal expansion/contraction, freezing/thawing, and wetting/drying. In order to examine specifically how wetting/drying cycles can contribute to weathering, a laboratory sample (n= 100) of ribs, phalanges, vertebrae, and distal tibiae from white-tailed deer (Odocoileus virginianus) were subjected to 150 cycles of complete wetting and drying. The bone surfaces developed the characteristic surface cracking of subaerial weathering, with weathering stage 1 (WS 1) reached by 50 cycles on three bones. By 150 cycles, 27 bones had reached WS 1, with all but 15 bones exhibiting some kind of new cracking damage. One bone reached WS 2 by 125 cycles, with additional bones exhibiting beginning surface delamination. Wet-dry cycles in some environments are a potentially important component of the overall osseous subaerial weathering process and can on their own weather bone.
... This concept extends the potential of electrical resistance measurements within masonry elements. Currently, resistance tests are used to identify wetting and drying cycles along with structural inconsistencies in masonry structures [13,42]. ...
The paper proposes the novel concept of smart bricks as a durable sensing solution for structural health monitoring of masonry structures. The term smart bricks denotes piezoresistive clay bricks with suitable electronics capable of outputting measurable changes in their electrical properties under changes in their state of strain. This feature can be exploited to evaluate stress at critical locations inside a masonry wall and to detect changes in loading paths associated with structural damage, for instance following an earthquake. Results from an experimental campaign show that normal clay bricks, fabricated in the laboratory with embedded electrodes made of a special steel for resisting the high baking temperature, exhibit a quite linear and repeatable piezoresistive behavior. That is a change in electrical resistance proportional to a change in axial strain. In order to be able to exploit this feature for strain sensing, high-resolution electronics are used with a biphasic DC measurement approach to eliminate any resistance drift due to material polarization. Then, an enhanced nanocomposite smart brick is proposed, where titania is mixed with clay before baking, in order to enhance the brick’s mechanical properties, improve its noise rejection, and increase its electrical conductivity. Titania was selected among other possible conductive nanofillers due to its resistance to high temperatures and its ability to improve the durability of construction materials while maintaining the aesthetic appearance of clay bricks. An application of smart bricks for crack detection in masonry walls is demonstrated by laboratory testing of a small-scale wall specimen under different loading conditions and controlled damage. Overall, it is demonstrated that a few strategically placed smart bricks enable monitoring of the state of strain within the wall and provide information that is capable of crack detection.
... Electrical resistivity imaging is more often applied to the study of small scale structures of geologic bedrock. For example, if the imaging resolution is suitable, it can be used to study bedrock outcrops (Roqué et al., 2013), monument deterioration (Mol and Viles, 2010;Saas and Viles, 2010), the stability of flood banks (e.g., Jones et al., 2014) and to recognize the internal properties of patterned grounds (Kasprzak, 2015). The method was also pioneered and satisfactory applied to study pit-and-mound microtopography (Pawlik and Kasprzak, 2015). ...
Following previous findings regarding the influence of vascular plants (mainly trees) on weathering, soil production and hillslope stability, in this study, we attempted to test a hypothesis regarding significant impacts of tree root systems on soil and regolith properties. Different types of impacts from tree root system (direct and indirect) are commonly gathered under the key term of “biomechanical effects”. To add to the discussion of the biomechanical effects of trees, we used a non-invasive geophysical method, electrical resistivity tomography (ERT), to investigate the profiles of four different configurations at three study sites within the Polish section of the Outer Western Carpathians. At each site, one long profile (up to 189 m) of a large section of a hillslope and three short profiles (up to 19.5 m), that is, microsites occupied by trees or their remnants, were made. Short profiles included the tree root zone of a healthy large tree, the tree stump of a decaying tree and the pit-and-mound topography formed after a tree uprooting.
In spite of a very complex picture of the resistivity of regolith and bedrock, the long profiles showed that through the presence and action of roots, trees add to this complexity. Trees change soil and regolith properties directly through root channels and moisture migration and indirectly through the uprooting of trees and the formation of pit-and-mound topography. Within tree stump microsites, the impact of tree root systems, evaluated by a resistivity model, was smaller compared to microsites with living trees or those with pit-and-mound topography but was still visible even several decades after the trees were windbroken or cut down.
The ERT method is highly useful for quick evaluation of the impact of tree root systems on soils and regolith. This method, in contrast to traditional soil analyses, offers a continuous dataset for the entire microsite and at depths not normally reached by standard soil excavations. The non-invasive nature of ERT studies is especially important for protected areas.
... Therefore, ERT is rarely employed for 71 structural monitoring, even though the use of ERT for archaeological application on 72 masonries is not infrequent (e.g. Mol and Preston, 2010;Sass and Viles, 2010;Tsourlos 73 and Tsokas, 2011;Cardarelli et al., 2016). 74 4 Furthermore, the investigation of existing masonry buildings, widespread the historic 75 centres, is requested because of their high seismic vulnerability highlighted by the recent 76 earthquakes occurred in Central Italy ( Summer and Autumn 2016), in order to understand 77 potential and limits of reinforcements applicable to these structures. ...
This paper aims to explore potential and limits of the combined use of ground penetrating radar (GPR) and electrical resistivity tomography (ERT) investigations for the characterization of reinforced masonry samples. To this aim, both techniques were applied on two laboratory small-scale wall samples before and after the application of a shear-compression diagonal load. Laboratory samples (1 × 1 × 0.25 m) are made of bricks and tuff respectively and reinforced with a thin high-strength and high-conductive fibre fabric. In order to improve the sample-antenna coupling in presence of conductive reinforcements, a Plexiglas plate was added underneath the 2 GHz antenna. GPR data were acquired along profiles spaced 0.1 m apart and ERT measurements were executed on a 0.1 m regular spaced grid with a dipole-dipole array operating in a three-dimensional configuration. GPR datasets were also analysed in non-conventional mode, by means of the picking of the reflection time of the EM wave from the rear face of the samples.
... Inversion uncertainties were greater for the pre-wetting states, tending to increase over the duration of the drying process: this is likely caused by the software's difficulty with handling the geological realism of inverting very dry stone (Sass and Viles 2010). This complicated obtaining appropriate values of í µí¼ í µí±í µí±¤ ; however, the benefit of lognormal transformation is that the pre-wetting denominator induces only a vertical shift of í µí¼′ in the lognormal dimension. ...
Detecting the presence of moisture in historical masonry is essential to understanding how a structure interacts with the environment, and diagnosing the potential for damage from a range of physical, chemical, and biological processes. In-situ, non-invasive diagnostic techniques have been developed in preference to methods that require irreversible modifications to a structure. These techniques include: electrical resistivity, microwaves, and infrared thermography. Independently, these approaches provide limited snapshots of surficial and internal moisture regimes; this project sought to assess the comparability of multiple techniques. Simulated post-rain spell drying was monitored over 48 h on limestone and sandstone monoliths in a controlled laboratory environment and also in ambient conditions on purpose-built masonry located in Oxfordshire, UK. Repeat measurements were taken using electrical resistance tomography (ERT), electrical and microwave moisture meters, and infrared thermography. Three aspects of comparability are discussed: i) data transformations and geological comparability, ii) depth-resolving meter readings, iii) the localised benefits of employing multiple technologies and instruments.
Keywords: moisture mapping, drying processes, non-destructive testing (NDT), instrument comparability, stone masonry
In the history of our civilization, masonry structures date back thousands of years. Considering the different types, geometries, and arrangements of masonry components, as well as the mortar properties, defining “masonry” precisely is challenging. Construction of masonry structures relies on layering single components and binding them using mortar or crafting them with stones without mortar. Despite many advantages, masonry structures remain one of the most vulnerable construction types. Many of these structures have not been designed to withstand seismic loads. Generally, their structural systems have been designed primarily to withstand gravity loads. Consequently, moderate earthquakes can cause extensive damage and destroy entire cities. Therefore, the assessment, repair, and retrofitting of these structures is vital to society’s well-being. First, this study describes masonry structures and their mechanical and structural characteristics. Next, methods for detecting and classifying common types of damage are presented. Subsequently, a comprehensive review of assessment, repair, and retrofitting methods for masonry structures is provided. Machine learning (ML) techniques have proven to be exceptional tools for providing accurate and reliable information. In this paper, descriptions and recent advances in ML techniques for the assessment, repair, and retrofitting of masonry structures are presented. These models can be utilized for several predictive applications, such as determining possible damage scenarios in heritage buildings, assessing seismic vulnerability, detecting superficial surface damage, and selecting mortar compositions for optimal mechanical properties. Furthermore, structural health monitoring (SHM) methods applicable to masonry structures are discussed. The study concludes with case studies, and an extensive discussion of existing methods, challenges, and recommendations for future work.
Moisture plays a key role in rock decay in the built and natural environments. Rock-cut sites are particularly vulnerable to moisture-related weathering as they are carved into rock outcrops and do not have impermeable foundations or roofs to retard the flow of moisture. To characterise the moisture dynamics and its influence on weathering of rock-cut sites, we undertook a moisture monitoring campaign using a non-destructive Microwave Moisture Measurement System (MMMS) at two monolithic rock-cut churches in Lalibela, Ethiopia. The results showed that the walls were more saturated at depth than on the surface during the wet season. This suggests that low surface temperature and higher moisture content at depth will lead to constant-rate drying and accumulation of salts on the surface of the walls during the wet season. In the dry season, there was higher saturation near the surface than at depth (falling-rate drying). High rock surface temperature during the dry season contributes to subsurface drying and accumulation of salts below the surface. This seasonally shifting moisture dynamics will lead to a complex and dynamic damage profile. This study highlights the significant wetting facilitated by a lack of impermeable roofs and foundations at rock-cut structures during rainy periods.
Moisture is one of the most important factors causing building stone decay and rain penetration is one of the leading factors. Particularly, wind-driven rain spells, which are becoming increasingly common and seasonal as a result of climate change. Historic buildings' sometimes intricate design features can be a factor multiplying meteorological anisotropy, either shielding walls or increasing the surface that is affected by wind-driven rain spells. This paper aims to identify the effect of pilasters and tower buttresses on the wetting dynamics of a listed 9th Century historic building during a rain spell by means of electrical resistivity methods coupled with GIS mapping, paying special attention to how data representation and map algebra can improve the interpretation of several data sets of non-destructive testing. Results show how building features can modify deeply moisture dynamics and maximise local anisotropy. In the present case, a compound of an external tower buttress and an internal pilaster decreases moisture ingress through ground infiltration while increasing moisture retention into the wall due to its larger mass. This, in turn, multiplies the incidence of moisture-related processes inside the building. The presented data also highlight the usefulness of mapping over time (4D mapping) and of GIS to improve interpretations through map algebra.
Dans un contexte environnemental qui demande à pérenniser la durée de vie des structures, les gestionnaires d’ouvrages doivent être accompagnés dans la maintenance des ouvrages existants. Des démarches d’inspection périodique et de surveillance d’ouvrage reposent sur le développement de méthodes de contrôle non destructif afin d’avoir un retour, tout au long de la vie des ouvrages, sur des variables clés traduisant l’état mécanique et pathologique des structures. Dans le domaine des matériaux de construction hygroscopique, la surveillance de l’humidité interne demande à développer des outils spécifiques permettant d’identifier les profils hydriques dans les sections structurelles. La méthode étudiée dans ce travail de thèse concerne la tomographie électrique. Elle est basée sur la mesure de résistivité apparente aux bornes de quadripôles. Un multiplexage permet de multiplier les lignes de courant afin d’avoir un échantillonnage recouvrant la totalité d’une section transversale. L’ensemble de ces données est confronté à une modélisation par éléments finis de la conduction électrique en régime établi, et ce, en employant une méthode d’optimisation numérique basée sur les méthodes inverses de Gauss Newton et de Levenberg-Marquadt. Le matériau employé est la terre crue, ce qui permet d’avoir des régimes hydriques transitoires rapides. L’ensemble expérimental a permis de mettre en œuvre et de tester les algorithmes de mesures et d’inversion sur des champs hydriques homogènes et hétérogènes en phase de désorption. Ainsi, les profils 2D permettent, pour une section donnée, d’estimer le champ d’humidité interne en tout point et de proposer ainsi un suivi dans le temps des profils hydriques. Des inversions sur des champs hydriques simulés permettent de mettre en avant la robustesse de la démarche avant d’être confrontée à des champs réels.
Surface geomorphological processes and the decay of built heritage are amplified by rock weathering, which mostly either requires water or is augmented by its presence. Measuring of water content in rock is however challenging and different scientific aims require various approaches. To recommend the most suitable rock moisture investigation, we have conducted an experiment using eight types of moisture measurement (1D resistivity, 2D resistivity, TDR, borehole humidity, microwave reflectance, capacitance, IR thermography, and uranine-probes) under controlled conditions in a sandstone block that was subject to a slow wetting and drying cycle and to a series of freeze-thaw cycles. The critical evaluation of methods shows that measurement of dielectric properties as a proxy of rock water content can be recommended for most research aims being it long-term monitoring, non-destructive measurement of surface moisture patterns or applications in deeper areas of rock. Moreover, observation of moisture dynamics in deeper subsurface requires either drilling inside the rock or the use of ERT. To determine the location of the subsurface evaporation front, uranine-probes and borehole humidity sensors are recommended. Lastly, the specific nature of freeze-thaw environments shows that the use of 1D resistivity and TDR can outperform other methods tested, with TDR being more reliable than resistivity but lacking in defined depth moisture fluctuations. To challenge the disadvantages of tested methods, a combination of techniques should always be considered.
High moisture is one of the main factors favouring the growth of algae and other organisms on stone surfaces. However, little is known about the specific effects of subsurface moisture on this process. Some regions will be exposed to longer periods of humidity and rainfall as a result of climate change. Understanding the role and internal dynamics of moisture in stone is therefore essential to enable development of mechanisms for controlling biological colonisation and thus preventing biodeterioration. The present case study is a preliminary investigation of the role of subsurface moisture in the biocolonisation process and was conducted on the walls of the Guard House of Stirling Castle. Moisture was measured at depth (up to 3, 11 and 30 cm) in both interior and exterior walls of the building with a portable device based on non-destructive microwave technology. Data were analysed in relation to the orientation of the walls, type of stone and biocolonisation. The subsurface moisture between 3 and 11 cm was found to play an important role in supporting colonising organisms on the building by modulating bioreceptivity.
The common goal of researchers and practitioners in conservation of monuments is to stretch as much as possible the lifespan of built heritage. However, despite this common target, work carried out in the laboratory and on the field are all too often disconnected. In the context of stone consolidation, for example, practitioners are often skeptical about treatment recommendations emerging from laboratory studies, due to the often-questionable representability of the tests employed.
To improve this situation, we describe the development of a research approach that would allow researchers to more pragmatically assist conservators in their decision-making, while also achieving a broader scientific significance.
In particular, we discuss the application of this strategy for conservation treatments applied to swiss monuments built out of molasse sandstones. These stones contain swelling clays, which makes them particularly susceptible to weathering. The difficulty in preserving such substrates is exacerbated by the lack of effective consolidation treatments, since common ethyl silicate-based products (TEOS) tend to lose their effectiveness shortly after application. A possible solution lies in using swelling inhibitors that have been shown in laboratory to potentially extend the durability of consolidation treatments. However, it is still not clear in which specific conditions these treatments would be worth applying.
We used a Design of Experiment (DOE) to analyze the simultaneous effects of varying environmental conditions and treatments procedures on the effectiveness of TEOS-based consolidation and swelling inhibition treatments for swiss molasses. We showed that the application of ethyl silicates at high relative humidity and low temperature greatly decreases their curing time, without compromising their effectiveness. We also demonstrated that swelling inhibitors effectively improve the durability of ethyl silicate consolidation treatments.
In terms of accelerated testing, we developed an automated machine for simulating “critical events” (i.e., a specific combination of damaging conditions leading to the most damage) in the laboratory.
We attempted to identify critical cycles at the cathedral of Lausanne, by characterizing wetting and drying conditions at the façade depending on orientation, and monitoring the materials response to the weathering conditions through measurements of the water movement throughout the depth of the stone.
At orientations typically presenting severe damage, a critical distribution of water can be observed at a depth of 6 cm during the winter months, suggesting that freezing might play a crucial role in the initiation of contour scaling. This water profile is not created by individual critical events, but results from an overall cumulation of events. Once established, it remains probable that degradation is caused by specific events, but these still remain to be clearly defined and reproduced in laboratory.
Ongoing laboratory experiments under simulated on-site conditions are presented, which aim at clarifying the mechanism of accumulation of water at those depths.
Adobe constructions are widely used worldwide as low-cost vernacular buildings and also as monuments and historical constructions. Beside low cost these materials have excellent thermal and acoustic properties. Some challenges of this material involves durability and high vulnerability to seismic motions due to its relatively high weight and brittleness. To improve safety levels of existing adobe structures it is often necessary to strengthen or retrofit them based on a structural characterization. The structural characterization requires assessment of the in situ condition, geometry, engineering properties of existing adobe construction and buildings using minimal to no intrusion. In this chapter we present a general overview of commonly used NDT and MDT methods for the assessment of existing adobe construction to obtain information such as: detailed geometry information, damage mapping, and multi-scale mechanical and physical characterization. Additional to literature review summarizing different applications of NDT and MDT, this chapter presents four case studies related to projects in Peru recently performed by the research group led by the first author. The descriptions and results of NDT and MDT tests carried out at these case studies highlight how the use of several NDT and MDT methodologies complement each other and allow a suitable multi-scale characterization of existing adobe structural systems, that can successfully be used for the diagnosis, and design of intervention and retrofit measures as needed.
Freeze-thaw weathering is an important surface process and the complex underlying processes can be understood as an interplay between rock properties and its dynamic environment. Multiple researchers coming from different scientific disciplines have contributed to the present-day knowledge on the matter and misconceptions still prevail. In a changing climate, the multidisciplinary insights into freeze-thaw action are crucial for a better understanding of rock weathering in natural and anthropogenic environments. In this review, a series of laboratory and in-situ field tests are presented to illustrate the present-day methods to assess freeze-thaw weathering. Over the last century, these methods led to insights and the development of theories on damage mechanisms. Presently, it is accepted that crystallization pressure is responsible for the majority of stresses in the material’s pores. Damage is induced when these stresses overcome the local tensile strength. Since most of the methods used to derive and validate stress build-up theories are indirect observations of parameters related to the phase transition, it is hard to reach a consensus on the exact explanation for stress development. Direct observations, which require actual real-time observation of the pore space during a freeze-thaw cycle, are therefore favoured to reach agreement. Eventually, the goal is to achieve a better insight on which processes potentially occur, how these vary with different environmental, temporal and spatial conditions and under which circumstances damage is inflicted.
Geophysical investigations could provide a valid tool for the identification of possible causes of settlement phenomena that affect civil buildings. They provide a non-invasive method of obtaining high-resolution information about the subsoil, saving time and money. However, uncertainties related to the accurate interpretation of the acquired data could potentially reduce the value of these methods. For this reason, the integration of non-invasive tests with direct measurements to support geophysical data interpretation is strongly recommended. This is a fundamental step in the process of defining a sufficiently reliable geological model to explain the cause of failure. Among the various geophysical techniques, electrical resistivity tomography and ground penetrating radar offer significant advantages for monitoring the status of the conservation of civil engineering structures and infrastructures. This paper presents the most recent and beneficial advances of the use of electric and electromagnetic geophysical methods in the field of civil engineering, with particular attention to their applications for monitoring subsidence and settlement phenomena. Finally, the possibilities of the joint use of resistivity and electromagnetic methods for studying the causes of the structural decay that affects two precast buildings are monitored and discussed. The results demonstrate the capability of combining non-destructive geophysical techniques with direct data, for evaluating the safety of building constructions and solving geotechnical problems.
In the current changing climate historic timber frame buildings are exposed to ever more severe and frequent extreme weather conditions such as floods and wind driven rainstorms. These structures are especially vulnerable to moisture ingress and subsequent decay. In light of this there is a need to better understand and quantify the impact of this exposure on the mechanical behavior and capacity of such systems. Here an experimental investigation is presented which sets out a novel test method for measuring the impact of cyclic wind driven rain and flood exposure on the lateral stiffness and strength of masonry infilled timber frames. Empirical data presented here indicates losses in elastic stiffness exceeding 75% as a result of exposure, whilst analytical assessment confirms the failure mechanism that describes yielding of the system in weathered and unweathered states. This work has measured the extent of structural decay in direct relation to the meteorological parameters wind speed and precipitation accumulation, giving deeper, understanding of the vulnerability of the structural system of masonry infilled timber framing to these climate phenomena.
As a result of increased rainfall and flooding the building fabric of historic structures in exposed areas are likely to be subject to higher and more sustained moisture content levels, along with experiencing an increased frequency and severity of wetting and drying cycles. This study aims to evaluate the impact of such cyclic wetting and drying on the mechanical behaviour of historic brick masonry. The reported results are obtained from a series of weathering and mechanical tests carried out on clay bricks and masonry specimens. The weathering test regime derives from analysis of observed weather data, combined with review of similar existing test protocols. Similarly, a modified mechanical test procedure is applied to simulate fatigue observed in the field. The results indicate that exposure to the weathering tests results in a reduction of masonry shear strength. This is discussed within the context of wider work carried out at a case study location, and highlights the value of designing a weathering regime that can more closely replicate the in-situ weathering processes. In this way the data collected in this experimental programme is shown to be suitable for use in contextual analysis of individual historic masonry case studies, with respect to climate change and the associated alteration of wetting regimes.
Many pre- to late-nineteenth century brick masonry structures encountered by conservation professionals are constructed with hygroscopic, porous brick that has been attacked by the combination of moisture and salt. The presence of these enabling factors of deterioration accelerates damage to a brick. Professionals need an affordable nondestructive tool that does not require extensive calibrations to highlight dangerous levels of moisture in the presence of soluble salts at a macroscopic scale prior to evident material loss. The infrared camera has been proven to display a visual image of moisture anomalies in a brick wall, but quantification requires spot readings with a moisture meter and accurate quantification requires sampling and laboratory testing. This paper investigates whether an infrared camera can be used to quantitatively determine in situ moisture content of a porous brick wall. In achieving this, a testing procedure was developed and performed on thirty-two hand-molded colonial face brick cuboid samples conditioned to four equilibrium moisture contents. The results of this test concluded that infrared thermography can distinguish different levels of moisture content with the thermal images. Secondly, there exists a linear relationship between ∆T surface center point and measured moisture content as well as a similar relationship between ∆T average surface and measured moisture content when room %RH is lower than equilibrium %RH for the sample. The linear relationship of measured moisture content and ∆T may be consulted for determining moisture content readings in different ambient conditions; however, nearly saturated samples require further study.
The results of a study of the effect of marine salt crystallization on the physical and mechanical properties of Plio-Pleistocene calcarenites cropping out in southern Italy are presented here. Owing to their workability, aesthetic appeal and availability, the calcarenites have been widely used as building stones in many historic monuments. Samples of medium-grained packstones and fine-grained packstones-wackestones were prepared for the salt crystallization test defined by EN 12370, using sea water instead of a 14% solution of Na(2)SO(4) center dot 10H(2)O. To determine the effect of imbibition alone on the performance of the calcarenites, the same procedure was followed with distilled water without soluble salts. Microfabric analysis, evaluation of index parameters and grain-size distribution were carried out as well. Particular attention was given to pore-size distribution by mercury intrusion porosimetry (MIP), loss of weight and uniaxial compressive strength determined before and after the tests, and after every five cycles of complete immersion in sea water and distilled water. The results suggest that detailed information on fabric and pore network are indispensable to predicting the weatherability of rocks. Crystallization tests that involve the complete immersion of the samples in a saline solution are not effective for an understanding of the real importance of salt damage on soft and porous calcarenites owing to a significant incidence of imbibition in accelerating deterioration rates and in influencing patterns and intensity of weathering.
We analyse rising damp using the concepts and methods of unsaturated flow theory. A simple first-order Sharp Front model i developed which uses clear physical principles and includes the effects of evaporation and gravity. We find that the simpl model captures well the observed features of capillary rise in walls and is supported by the underpinning nonlinear capillar diffusion theory. For most cases, capillary forces are dominant and the effects of gravity can be neglected.
Since pharaonic times local limestones have been used in Cairo for monument construction. Weathering damage on many historical stone monuments in Cairo is alarming. Studies on properties and weathering behaviour of the limestones were carried out by means of laboratory tests and in situ investigation of many historical monuments. The laboratory studies reveal considerable petrographical variations for the Middle Eocene limestones. The limestone weathering was assessed with respect to weathering forms, weathering products and weathering profiles. A classification scheme of weathering forms and their intensities was tailored to optimal applicability for all Cairo historical monuments constructed from limestones. Monument mapping has been applied for the detailed registration of weathering forms and as a basis for the quantitative rating of stone damage by means of damage categories and damage indices. For the historical monuments in the centre of Cairo the combined evaluation of weathering forms, weathering products and weathering profiles shows clear correlations between the development of weathering damage and salt loading of the limestones as a consequence of air pollution and rising humidity. They demonstrate the need and urgency for monument preservation measures.
Die Art und den Grad einer Salzbelastung in feuchten Baustoffen festzustellen, gehört zu den schwierigsten Aufgaben im Bereich der zerstörungsfreien Prüfung. Die vorliegende Arbeit beschäftigt sich mit dem möglicherweise ungenutzen Potential komplexer Leitfähigkeitsmessungen (complex resistivity - CR, Frequenzbereich1mHz -100Hz). Dazu wurde erstens eine umfangreiche Experimentreihe an unterschiedlichen Baustoffen mit vier Salzen (NaCl, Na2SO4, CaCl2 und MgSO4) in variierenden Konzentrationen durchgeführt, um die Sensitivität der Methode der für den Baubereich relvanten Salzmengen zu untersuchen. Zweitens wurde der Einfluß der Sättigung für verschiedene Ausgangsfluide nachvollzogen. Darüberhinaus beschäftigt sich die Arbeit mit dem Versuch, chemisch von strukturell bedingten Impedanzänderungen unterscheiden zu lernen. In einer FD Modellierung wurden die effektiven Impedanzen synthetischer Mikrostrukturen berechnet und die Auswirkungen von Strukturunterschieden untersucht. Liegen Kalibrationsdaten vor, kann im Fall eines gesättigten Baustoffes anhand der Widerstandsamplitude eine verlässliche Einschätzung des Salzgehaltes vorgenommen werden. Die Phase des komplexen elektrischen Widerstands enthält Informationen über das dominante Kation in der Porenfluidlösung. In porösen, feuchten Baustoffen, in denen Polarisation als Folge komplexer Grenzflächenleitfähigkeit auftritt, bestimmen generell das Matrixmaterial, der Porendurchmesser und die innere Oberfläche seine Aufladbarkeit. Diese Größen können aber nur bedingt aus elektrischen Messungen abgeleitet werden. Liegt die durchschnittliche Porenhalsgröße eines Baustoffs zwischen 20 und 100 Mikrometer, kann i.d.R. eine deutliche Aufladbarkeit beobachtet werden. In feinporigen Baustoffen (Tonziegeln) sind die Porenhalsgrößen kleiner als 5 Mikrometer, und die Aufladbarkeit liegt oft nur noch im Bereich der Messgenauigkeit. Die hier vorgestellte Datenbasis untermauert den theoretisch vorhergesagten exponentiellen Zusammenhang zwischen der Cole-Cole (CC) Relaxationszeit und einer materialbedingten, charakteristischen Relaxationslänge - im Fall von Festmaterialien der Porenhalslänge. Der Imaginärteil der Leitfähigkeit reagiert sensitiv auf den Chemismus der Porenlösung. Ausschlaggebend sind wahrscheinlich Veränderungen in der elektrischen Doppelschicht (EDL). Dies liegt wahrscheinlich an der fortschreitenden Ionensättigung des EDL. Ist eine gewisse Sättigungsstufe erreicht, führt eine weitere Ionenzufuhr zu zunehmenden elektrostatischen Wechselwirkungen und schließlich abnehmenden Ionendiffusionskoeffizienten. Auch der Wassergehalt spielt eine wesentliche Rolle für das CR-Verhalten. Für die meisten Baustoffe nimmt mit dem Wassergehalt der Imaginärteil der Leitfähigkeit stärker ab als der Realteil. Vermutlich sind Tongehalt und Zementationsgrad eines Materials ausschlaggebend für ein solches, nicht der bisherigen Theorie entsprechendes Verhalten sind. Darüberhinaus zeigen die Ergebnisse, daß der kürzlich von anderen Autoren aufgezeigte Zusammenhang von CC Relaxationszeit und hydraulischen Eigenschaften nicht bedingungslos gültig ist und weiterer Forschungsbedarf besteht. Um die Eigenschaften der EDL in Abhängigkeit der Porenfluidchemie zu untersuchen, wurden Zetapotentialmessungen durchgeführt. Die verwendeten Partikelsuspensionen wurden in gleicher Weise mit den Schadsalzen versetzt wie zuvor die Baustoffproben in den elektrischen Messungen. Die Auswertung der elektroakustischen Messungen deutet zwar generell einen positiven linearen Zusammenhang zwischen Zetapotential und dem Imaginärteil der Leitfähigkeit an, dieser ist jedoch schwächer als erwartet. In der Literatur wird davon ausgegangen, daß die komplexen elektrischen Eigenschaften eines Materials außer vom Chemismus des EDL auch von der Geometrie des Porenraumes. In einem neuartigen Versuch, diese beiden Phenomäne zu trennen, wurde eine Parameterstudie mittels einer FD Impedanzmodellierung durchgeführt, in der gezielt Längenverhältnisse und Leitfähigkeiten verändert werden konnten. Generell konnten die experimentellen Ergebnisse der Salinitätstudie nachvollzogen werden; die wenigen Fälle, in denen sie abweichen, sind vermutlich auf chemische Umstrukturierungen im EDL zurückzuführen. Die Beobachtungen der Entsättigungsexperimente konnten ebenfalls erklärt werden. Falls die hier verwendeten, stark vereinfachten Modelle die komplexen elektrischen Eigenschaften wahrheitsgemäß abbilden, bieten sie die Möglichkeit eines erweiterten Verständisses des Leitfähigkeitsverhaltens teilgesättigter Medien. Komplexe Widerstandsmessungen bieten Potential für die Anwendung im Bereich der zerstörungsfreien Bauwerksanalyse, es handelt sich zum gegenwärtigen Zeitpunkt jedoch noch um eine Methode im Forschungsstadium. In jedem Fall sind a-priori Informationen und -sofern quantitative Aussagen getroffen werden sollen- auch Klibrationsdaten erforderlich. Das Verfahren sollte nicht allein angewendet werden.
Ecological Insulation materials are getting more and more popular, but until now their share of the insulation market is e.g. in Europe below 10 %. One of the reasons is, that architects, engineers or designers are not well informed about the advantages of their use. With the use of advanced hygrothermal building simulation tools, like WUFI-ORNL/IBP the realistic heat and moisture performance of a wall or roof assembly can be predicted easily. Unfortunately the needed material properties for the ecological insulation materials are not completed or even unknown. This work is focused on the measurement of the hygrothermal material properties. Afterwards the results are used in order to calculated the hygrothermal performance for a roof construction under real climatic conditions. With the information about the stochastical deviation of the measured data and the help of the computational sensitivity analysis, one can study how sensitive the solution of a problem based on the data confidence input and its reaction to a single parameter of uncertainty. It may also provide us the basis for simplifying some of the hygrothermal analyses by allowing us to use material properties that are representative to materials with similar but not exactly the same properties.
Despite decades of study of stone decay phenomena and practical stone conservation experience, there are still great gaps in our knowledge, and it is still difficult to predict how stone decay and soiling will respond to changes in air pollution and other environmental changes. Nonlinear behavior and chaotic system dynamics have been recognized in many earth surface systems and are also relevant to stone decay phenomena. Identification of nonlinear behavior in stone decay systems should help interpret, model, and manage such systems. Several examples indicate the presence of nonlinear, and sometimes chaotic, behavior in stone decay systems. A review of sources of nonlinearity in stone decay systems illustrates that nonlinearities are common and important, with chaotic behavior sometimes resulting. Such findings illustrate the potential dangers of applying linear damage functions and the need for management efforts to take seriously nonlinearities in stone decay, due to the often complex and chaotic responses of deteriorating stonework to environmental changes.
In this paper the results of a trial application of 2D-geoelectrical soundings ("ERT") are presented. The aim of the field work was to examine the small-scale moisture distribution in rockwalls and its temporal variations, and thereby to establish the presence or lack of water for weathering processes. To achieve this object, the 50 electrodes of a GeoTom ERT unit were replaced by steel nails sunk into the rock with an electrode spacing of 0.04 m (total length of the survey line: 1.96 m). The measured resistivity values range from 100 Ωm to more than 100 kΩm, which are equivalent to a moisture content of 7.5% to < 0.1%. The highest moisture content for each survey site corresponds well with the pore volume of the rock investigated, while the comparison with moisture data derived from dried and weighed rock pieces collected shows only poor correlation. The moisture distribution in the rock investigated is extremely variable. In most locations, the deeper parts of the rock are predominantly saturated, while the outer 10-15 cm are more or less dried out. Therefore, shallow frost cycles with a penetration depth of less than 10 cm may be insignificant for frost weathering in large parts of the rock. The most important factor controlling the moisture content seems to be the micro-topography of the sites. Joints, ledges or less inclined parts of the rock allow water to soak in and cause moister conditions in their sphere of influence. In addition, south-facing sites are mostly drier than north-facing sites, though micro-topographic differences may cause exceptions to the rule. The spreading of moisture within the rock seems to take place mainly from the damper inside to the outer parts. The weather conditions in the weeks before measurement are of greater importance for the moisture content than the weather on the day of measurement itself.
An attempt is made in this article to provide a readable summary of the bases for and problems encountered with the resistivity and induced polarization methods in gencrat application. The article commences with a discussion of aqueous electrolytic conduction in rocks including consideration of the effects of temperature, rock texture, rock type, geological processes, and of the presence of clay minerals. Doth electrode and membrane polarization in soils and rocks are described in simple terms. The elementary theory for the rcsistivity and induced polarization methods are next described in terms of formulas for electrodes on a homogeneous and layered half-space. The notion of apparent resistivity is introduced. Vertical electric sounding is described in relation to curve types, inversion, equivalence, anisotropy, and correlation. ProfXug with resistivity is briefiy described while combined sounding-profiling is treated in more detail for both the resistivity and induced polarization methods. The parameters used to describe the induced polarization phenomena are next introduced. A brief discourse follows on data acquisition and processing including design considerations for transmitters and receivers, electrodes, and wire logistics.
Sinkholes are commonly utilized for agriculture, and are thus subject to application of fertilizers, including animal manures and biosolids. Because sinkholes are hydrologically connected to underlying aquifers, fertilizer application within sinkholes may adversely impact groundwater quality. Few scientific data are available to support effective management of fertilizer application that will minimize karst groundwater contamination. Our research aims to characterize the hydrogeology and recharge mechanisms in agricultural sinkholes. Initial work includes physical characterization of several sinkholes at the Virginia Tech Kentland Experimental Farm, Whitethorne, VA. Nearly 100 2-D Electrical Resistivity Tomography (ERT) profiles, topographic mapping, and physical observations were used to generate 3-D sinkhole models of the shallow subsurface. Preliminary results generally show a clear resolution of changes in soil composition, and in some cases, the bedrock-soil interface. We conducted an experiment utilizing 2-D Differential ERT to monitor vadose water movement and to delineate preferential flowpaths during a recharge event. Repeated measurements in the same location before, during, and after a large storm, show significant resistivity differences interpreted to be related to changes in soil moisture due to infiltration. Similar experiments using 3-D Differential ERT are underway that will attempt to model infiltration and delineate preferential flowpaths over larger areas. 3-D Differential ERT results will be compared with simultaneous soil moisture measurements collected using down-hole Time Domain Reflectometry (TDR). If modeled ERT values can be correlated with the TDR soil moisture values, this technique has the potential to provide high resolution 3-D soil moisture data that can be used to greatly improve the visualization of vadose flow in shallow sinkholes.
A fast technique for the inversion of data from resistivity tomography surveys has been developed. This technique is based on the smoothness-constrained, least-squares method, and it produces a 2-D subsurface model that is free of distortions in the apparent resistivity pseudosection caused by the electrode array geometry used. A homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically. Tests with a variety of models and data from field surveys show that this technique is insensitive to random noise, provided a sufficiently large damping factor is used, and that it can resolve structures that cause overlapping anomalies in the pseudosection. -from Authors
We present electrical conductivity measurements (at a fixed frequency of 1 kHz) performed on three directions on limestone samples from the quarry of Meriel, during uniaxial tests of deformation up to failure. Samples were saturated from 100 to 80 per cent by drainage. The samples showed brittle fracture with Young's modulus in the range 10–13 MPa. Formation factor (sample resistivity divided by water resistivity) values range between 2 and 4. In saturated conditions the electrical measurements reflect the initial rock compaction, followed by dilatancy due to new axial cracks formation and finally crack coalescence, fracture localization and failure. The conductivity increase is related to the crack porosity Φc, which starts to increase at relatively low stress (31 per cent of strength). The magnitude of the electrical conductivity variation is 1–4 per cent of the initial value. We show that when saturation is decreased the conductivity increase occurs earlier during the deformation process, from 68 to 17 per cent of strength for 100 to 80 per cent of water saturation, respectively, so that the decrease in conductivity at low stress is less and less present. The induced relative rock conductivity variation in non-saturated and undrained conditions is the result of two competing effects: the relative porosity variation and the relative saturation variation during the deformation process. During compaction the electrical conductivity can show either a small decrease or a small increase; since the size of the partially saturated pores and cracks is reduced, the water occupies a larger percentage of the pore space, and then conductivity can be increased at this stage. We show a continuous increase of the conductivity both during the compaction and the dilatancy phases when the initial saturation is about 80–85 per cent. Finally a power law is shown between conductivity and stress, so that the relative electrical conductivity increase is larger as one goes along the compression process.
Just before failure, at 90–95 per cent of strength, the rate increase in horizontal conductivity drops, so that the anisotropy between axial and radial conductivity is about 0.5–2 per cent. At failure a drastic increase of this anisotropy can be seen, up to 5–6 per cent (CME21, CME24 and CME13 samples).
Laboratory measurements of elastic wave velocities, attenuation, and electrical resistivity of sandstones all show distinct changes in the measured properties at very low levels of water saturation. Velocity decreases, attenuation reaches a maximum, and electrical resistivity decreases over a limited range in saturation. We assume that all the water at low saturations is present in the rock as a layer of uniform thickness covering the entire internal surface area of the sample. With this model, we calculate the thickness of surface water that corresponds to the distinct low saturation region. In all cases, for both the seismic and the electrical data, the thickness is equal to one to four monolayers of water. This is interpreted as marking the transition in the behavior of water in a sandstone from that of a surface adsorbed phase to a bulk water phase. The changes in seismic properties can be modeled by considering the effect of adding surface and bulkwater to grain contacts. In a similar treatment, the role of contacts is shown to be a dominant factor in the electrical resistivity of sandstones at low saturations, such that the addition of water to the contact area causes a dramatic decrease in the electrical resistivity.
Moisture in walls provides a key control on decay processes, but has proved difficult to measure. As part of a larger study investigating the ability of soft wall capping (soil and vegetation) to help conserve ruined monuments we have investigated moisture contents of walls at two ruined abbeys. Two methods of moisture measurement were used, i.e. a novel adaptation of 2D electrical resistivity surveys and the well-established wooden dowel method. Medical ECG electrodes were utilised to provide a completely non-destructive resistivity measurement. At Hailes Abbey wooden dowel and 2D resistivity measurements were made of soft capped vs. uncapped wall sections. The wooden dowels showed drier conditions in the core of the capped sections, although the resistivity surveys were influenced by a different stone structure in the wall core. At Byland Abbey, resistivity surveys indicated drier stone blocks and wetter mortar in the near-surface zone, and illustrated the success of the soft-capping technique in reducing water contents in the core of the wall in comparison with hard-capping with mortar. The 2D resistivity technique is shown to be a useful and fast non-destructive technique with the capacity to provide good spatial and temporal resolution information on moisture distribution in walls.
Rocks were subjected to wetting and drying cycles with de-ionized water under real time conditions. Using tidal simulators, one-third of the samples experienced 11 h of exposure and 1 h of inundation over a 12-h tidal cycle (representing high tidal conditions), one-third experienced 6 h of exposure and 6 h of inundation (representing mid-tidal conditions), and one-third experienced 1 h of exposure and 11 h of inundation (representing low tidal conditions). We obtained 324 cores from igneous, metamorphic, and sedimentary rocks from Ontario, which were exposed to more than 930 wetting and drying cycles over 16 months. We obtained 675 cores and cubes from basalts, sandstones, and argillites from shore platforms in eastern Canada, which were exposed to about 700 cycles over 12 months. Many of the cores and cubes experienced very little to no breakdown, particularly those from the igneous and metamorphic rocks of Ontario. Sandstones from a sloping platform in the macrotidal Bay of Fundy and argillites from a horizontal, mesotidal platform in Gaspé, Québec, were the most susceptible rock types, with equivalent surface downwearing rates ranging from 0 to 4 mm year−1. The results suggest that downwearing rates decrease with elevation within the intertidal zone, probably because rocks require much longer to desorb than to absorb water. The experiments demonstrated that wetting and drying can be an important process on shore platforms in some types of rock, helping to lower the height and reduce the gradient of sloping macrotidal platforms and to reduce the height of horizontal micro- and mesotidal platforms.
Understanding the hygrothermal behaviour of exposed building components is a first step in avoiding damage or undue heat loss from constructions. Since experimental investigations are rather expensive and of limited transferability, there is an urgent need for reliable heat and moisture transfer calculations applicable in building practice. Such a calculation method, which is based on physical evidence concerning vapour and liquid transport and new experimental results, is presented and the required material and climatic data are described. To validate the model the calculation results for the moisture behaviour of a facade exposed to driving rain and solar radiation are compared to well documented measurements. As a consequence of this comparison it appears that the described model provides accurate results despite simplifications concerning the material properties. Copyright © 1996 Elsevier Science Ltd.
In Budapest damage due to atmospheric pollution on many public buildings is severe. Black encrustations, white crusts and other decay features of a soft oolitic limestone have been studied in detail by using field measurements and laboratory analyses. Limestone weathering was assessed by description of weathering forms, by on-site petrophysical tests (Duroscope, Schmidt hammer, water absorption) and by laboratory mineralogical assessment and thermoanalysis (X-ray diffraction, Derivatograph). There is a clear correlation between the organic carbon content in stone and location of the site, particularly in the polluted city centre. Gypsum, which is not an indigenous mineral in the limestone, can contribute up to 70% of the crust composition and indicates the importance of air-derived SO 2. This mineralogical change in stone composition leads to changes in physical properties, by strengthening laminar black crust and white case hardened crusts and weakening the host rock.
In this paper, we propose a noninvasive method for monitoring three-dimensional (3-D) spatial and temporal variations of soil water content in the field, soil moisture tomography. The basic idea of the method originates from Archie's relationship between soil resistivity and water content. Initially, 88 electrodes were densely buried within a 3.5m×3.5m square area, and potentials at the electrodes were measured by pole-pole and Wenner array methods at given time intervals. An inversion calculation of the 3-D soil resistivity was then conducted based on these potential data. Next, 46 soil samples were taken at representative positions in the square, and the parameters in the Archie's relationship were measured in the laboratory. Then, the 3-D distributions of the parameters were obtained by a distance weight interpolation method. Finally, based on Archie's relationship and the 3-D distribution of the soil resistivity and the related parameters, 3-D distributions of soil water content were calculated. To evaluate the obtained water content, the calculated water contents were compared with those measured by heat-probe-type soil moisture sensors, and a comparison between the spatial distribution patterns of calculated water content and soil bulk dry density was conducted. The 3-D variations of the calculated water content during a rainfall event were also analyzed. The results show that there are +/-0.10 cm3/cm3 errors in the calculated water content, but between the calculated and the measured water content there exists a good linear relationship. It is possible to use the calculated water content to analyze the very general 3-D distribution characteristics of the soil moisture and investigate the 3-D rainfall infiltration process, the redistribution of soil water after rain, and other hydrological processes in the field. The proposed method is preferred for porous media where the water resistivity is relatively stable.
The understanding and modelling of the process of water imbibition is important for various applications of physics (e.g. building or soil physics). To measure the spatial distribution of the water content at arbitrary times is not trivial. Neutron radiography provides an appropriate tool for such investigations with excellent time and spatial resolution. Because of the high sensitivity to hydrogen, even small amounts of water in a porous structure can be detected in samples with dimensions up to 40 cm. Three different porous stones found in Indiana, USA, have been investigated (Mansfield sandstone, Salem limestone and Hindustan whetstone). The imbibition of deionized water and a NaCl solution in up- and downwards directions has been tracked during several hours and radiographed at regular intervals. A correction method to reduce the disturbing effects due to neutron scattering is applied. This allows a quantitative evaluation of the water content in addition to the visualization of the water distribution. The results agree well with theoretical models describing water infiltration and reproduce the water content with a pixel resolution of 272 µm in time steps of 1 min. The comparison with the radiographed structure of the dry stone explains variations in the conduction or retention of the water, respectively. The experimental and correction procedures described here can be applied to other porous media and their uptake and loss of fluids.
A series of experiments on sandstone and dolerite was undertaken in an attempt to better understand the wetting and drying weathering process. As rock samples are frequently subjected to wet–dry cycles within the simulation of other weathering mechanisms (e.g. freeze–thaw), three common methods of moisture application were used and the influences of these evaluated. It was found that the method of moisture application could affect the nature of the weathering products resulting from wetting and drying. It was also observed that there were changes in the internal properties of the rock (e.g. porosity/microporosity) and that these could influence the synergistic operation of other weathering processes. Although not all of the observations could be explained, it is apparent that wetting and drying has both a direct and an indirect effect on the weathering of rock that has not been taken into account in simulations. Greater cognizance needs to be given to the role of this process both in the field and in laboratory simulations.
In this paper we describe a new electrical tomography technique which has been theoretically developed and finally tested in ancient walls and floors. The technique is based on the simultaneous acquisition of a number of potentials (up to 256 channels) and a successive back-projection of the data, using normalized sensitivity coefficients, in order to obtain 3D electrical imaging of the internal structure. A successive filtering technique has been in addition developed to increase the contrast of the images taking as a reference sharp-boundary electrical models. Finally some results are presented which have been obtained on a floor and a wall of the Steri palace, in Palermo.
Rock moisture is an important factor for the intensity and distribution of frost weathering processes. However, quantitative measurements are scarce, which is partly due to the lack of reliable measurement techniques. This paper presents five different techniques for obtaining rock moisture data. While collecting rock pieces and two-dimensional geoelectric measurements allow determination of the spatial moisture distribution, the temporal variability can be derived from conductivity and time domain reflectometry records. Computer simulations, using rock properties and climatic records as input data, render it possible to clarify the important aspects that are responsible for the moisture distribution. It proved to be advisable to use several methods to check and validate the results.
The results, obtained in study areas in the Bavarian Alps, make it clear that direct rainfall is the main source of rock moisture. The influence of snow is limited to the immediate vicinity of the snow fields and is not equally pronounced at different times and positions. Rock moisture levels are higher in summer than they are in winter, since in winter less water is supplied in liquid form. Northerly exposed rockwalls are generally more moist than those exposed in a southerly direction, which is due to the different insolation as well as to the wind direction during rainfall. In every position the rock is, on average, wetter on the inside than it is on the surface. This means that shallow frost cycles, as typical for south-exposed sites, are not affecting weathering, since they take place at a depth level that is mostly dried out.
Numerous spatial and temporal patterns of rockfall found in the same study areas can be explained through variations in rock moisture. Thus, the moisture content of the rock is considered to be one of the major controlling factors of the frost-shattering rate. Copyright
A methodology was developed to clean geo-electrical measurements on masonry structures from geometrical and other disturbing factors such as moisture and salts.
Only relevant information about the internal structural situation of the masonry remains.
This paper shows the practical applicability of cement grout consolidation as well as its control by means of resistivity measurements. A plain brickwork test wallet is used in the experiment. Controlled cracking is made in the initially sound wallet and repair is done by cement grout injection. Resistivity values are measured in the sound, cracked and repaired situation. Relative difference mapping of these resistivity measurements shows a clear picture of the internal situation in the masonry and can serve as a basis for design decisions.
In the natural environment, temperature and moisture are very important parameters in stone degradation. Therefore, on 28 samples from different lithologies (magmatic, metamorphic and sedimentary rocks) thermal and hygric expansion measurements were performed in order to constrain their behaviour related to environmental changes. It was shown that marbles, even those that are dolomitic, are sensitive to temperature impacts. For rocks with clay minerals the effect of temperature may be responsible for shrinking. Finally the amount of residual strain, i.e. the formation of microcracks due to temperature action controls the rate of stone degradation. For most sedimentary rocks no residual strain after heating was observed. In contrast to most magmatic and metamorphic low-porosity rocks, sedimentary rocks contain swelling minerals (like smectite and even phyllosilicates), which are very sensitive to hygric attacks. The cycles of wetting and drying, i.e. the natural environmental effects, may significantly control the deterioration velocity caused by hygric expansion.
Geophysical techniques offer the capability to non-invasively investigate engineering structures, both in terms of their spatial variability, and the prediction of properties of interest to the engineer from the ‘pixel’ values of the geophysical tomograms. The combined use of different geophysical methods provides a means of identifying the signature of salient engineering conditions. The response of seismic, radar and electrical resistivity tomography to simple targets within masonry structures is demonstrated. The benefits of combining rapid standard radar surveys with more detailed tomography is discussed and strategies for investigating typical structures developed. The response of the three methods, acoustic, electrical and radar to changes in the condition of masonry, such as reduction in strength and ingress of water, are discussed, with particular reference to a case study utilising the Ribblehead viaduct as an example. The corresponding responses to changes in ground conditions are also presented and shown to be important in understanding possible further applications of these methods, such as investigating behind retaining walls.
Both ground-penetrating radar and the resistivity method have proven to be useful tools for exploring water content variations, since related parameters such as dielectric constant and the resistivity of rocks and sediments are highly dependent on moisture content. These methods were used independently to estimate volumetric water content in the unsaturated zone and porosity in the saturated zone in a 100-m sandy section. Two sample sites along the profile were also chosen for a shallow geophysical investigation and soil sampling, to enable the calibration and verification of the indirect geophysical methods. The grain distribution at these sites is dominated by medium-sized sand (0.25–0.5 mm). The water content was 6.9 vol.% and calculated porosities are 37% and 40% respectively. At each of these sites the mean water content values calculated from resistivity are within one percentage unit of measured water content while those calculated from ground-penetrating radar give higher values by as much as 2.9 percentage units. The water contents in the unsaturated zone in the section, estimated from resistivity and ground-penetrating radar, show very similar trends, although that deduced from ground-penetrating radar is generally somewhat larger, consistent with the results from the sample sites. The mean porosity values obtained from the two methods in the saturated zone are in good agreement.
Electrical resistivity is a physical parameter linked to both texture and moisture content of the investigated bodies; therefore, its study provides reliable information about the internal structure and eventual degradation state of the elements generally used for construction purposes, like walls, columns, etc. Recent advances in hardware and software allow to acquire resistivity information of the investigated body in a ‘tomographic’ manner. This technique, called Electrical Resistivity Tomography (ERT), furnishes detailed two (2D) and three (3D) dimensional models of electrical resistivity distribution of the portion of the subsurface being investigated.In this work, the application of the ERT technique, to evaluate restoration quality of the building foundations after being consolidated, is described throughout a test site, located in Venice (Italy). The reconstructed 3D images of the resistivity distribution before and after consolidation provided details about the internal structural of the foundation itself as well as the volumes which have been occupied by the mortar after consolidation. Direct field test confirmed the diffusion of the mortar in the foundation and further laboratory analyses, conducted on a specimen taken at 80 cm, showed that cracks of 40 mm width had been completely filled with mortar.
The flow and transport of a non-reactive tracer and melt water was monitored in a heterogeneous coarse sandy unsaturated zone in southeastern Norway, during the snowmelt of 2001. Electrical resistivity tomography (ERT) as well as conventional suction cup techniques was employed. A frozen solution of NaBr in water was supplied as a line source on the ground surface above two parallel vertical profiles monitored by the two measurement systems prior to the onset of snowmelt. The two monitored vertical profiles were separated by approximately 1 m. The results were analysed by visual comparison of images and by the use of spatial moments analysis. The two measurement approaches showed that the system was affected by the presence of preferential flow paths during the early stages of the snowmelt, perhaps due to ice near the surface, but the major part of the plume moves uniformly later in the snow-melting period. After most of the tracer plume has reached the depth monitored by both systems (i.e. below 0.4 m depth) there is a good consistency between the two datasets. Spatial moment calculations on the basis of ERT cannot be used to describe the movement of tracer alone, as the resistivity is affected by changes in both saturation levels and tracer concentration. Nevertheless, ERT appears to be an appropriate method to characterise regions of localised high infiltration in this type of soil. The method therefore constitutes a possible alternative and supplement to suction cups in a monitoring system.
We investigate the problem of internal fracturing of the columns of a building of cultural importance (the Crypt of the “Cattedrale di Otranto”, Apulia, Italy), using a multi-disciplinary approach, integrating different non-destructive techniques (Microclimatic and Geophysical). In fact historic buildings, over centuries, may accumulate a high concentration of water and/or moisture that increases significantly the deterioration rate, diminishing the mechanical resistance.It is well known that the distribution of moisture within stone strongly depends on ambient conditions, i.e. temperature and relative humidity. No suitable environmental condition in the Crypt and the presence of wet buried structures in the ground involved in the process of deterioration have been indeed assessed in previous surveys.Actually we perform a ground penetrating radar (GPR) investigation, in reflection mode, in order to reveal the existence of fractures inside the columns, because of the important rising of water from pavement.The reconstruction of the fracture distribution is fundamental to plan the safeguard and the restoration of the columns themselves and also the stability of the Crypt and of the uppermost Cathedral. Such survey was performed on seven columns using GPR technique. Moreover the electrical resistivity tomography (ERT) and GPR traveltime tomography (TT) methods were applied on the most damaged column.The results obtained with these different methodologies are in good agreement, however, the 2D electrical resistivity tomography seems to be less resolutive than GPR. While the GPR traveltime tomography is more time expensive than GPR reflection mode method. The GPR method, in reflection mode, allows to reconstruct the main fractures inside the columns also in virtue of its penetration power.We think that the joining of different methodologies permits to better understand the complex physical mechanisms in the phenomenon of deterioration of the cultural heritage, in order to achieve useful information for possible, future, restoration works.
This paper describes a series of experiments that tested the ability of the electrical resistivity tomography (ERT) method to locate correctly wet and dry fractures in a meso-scale model. The goal was to develop a method of monitoring the flow of water through a fractured rock matrix.
The model was a four by six array of limestone blocks equipped with 28 stainless steel electrodes. Dry fractures were created by placing pieces of vinyl between one or more blocks. Wet fractures were created by injecting tap water into a joint between blocks. In electrical terms, the dry fractures are resistive and the wet fractures are conductive. The quantities measured by the ERT system are current and voltage around the outside edge of the model. The raw ERT data were translated to resistivity values inside the model using a three-dimensional Occam's inversion routine. This routine was one of the key components of ERT being tested.
The model presented several challenges. First, the resistivity of both the blocks and the joints was highly variable. Second, the resistive targets introduced extreme changes the software could not precisely quantify. Third, the abrupt changes inherent in a fracture system were contrary to the smoothly varying changes expected by the Occam's inversion routine. Fourth, the response of the conductive fractures was small compared to the background variability.
In general, ERT was able to locate correctly resistive fractures. Problems occurred, however, when the resistive fracture was near the edges of the model or when multiple fractures were close together. In particular, ERT tended to position the fracture closer to the model center than its true location. Conductive fractures yielded much smaller responses than the resistive case. A difference-inversion method was able to correctly locate these targets.
Enhancement of geo-electrical techniques for NDT of masonry
- R Keersmaekers
- D Posen
- M Knapen
- M Leus
- D Van Gemert
Keersmaekers, R., Posen, D., Knapen, M., Leus, M., Van Gemert, D., 2008. Enhancement
of geo-electrical techniques for NDT of masonry. In: D'Ayala, D., Fodde, E. (Eds.),
Structural Analysis of Historical Constructions. London, Bath, pp. 1053-1060.
Die Steuerung von Steinschlagmenge und -verteilung durch Mikroklima, Gesteinsfeuchte und Gesteinseigenschaften im westlichen Karwendelgebirge (Bayerische Alpen)
- O Sass
Sass, O., 1998. Die Steuerung von Steinschlagmenge und -verteilung durch Mikroklima,
Gesteinsfeuchte und Gesteinseigenschaften im westlichen Karwendelgebirge (Bayerische Alpen). Münchener Geographische Abhandlungen B 29, 175 p. (PhD thesis).
The electrical resistivity log as an aid in determining some reservoir characteristics. Transactions of the American Institute of Mining and Metallurgical Engineers/Petroleum Division 146
- G E Archie
Archie, G.E., 1942. The electrical resistivity log as an aid in determining some reservoir
characteristics. Transactions of the American Institute of Mining and Metallurgical
Engineers/Petroleum Division 146, 54-62.
Deciphering the impacts of traffic on stone decay in Oxford: some preliminary observations from old limestone walls
- Antill
Antill, S.J., Viles, H.A., 1998. Deciphering the impacts of traffic on stone decay in Oxford:
some preliminary observations from old limestone walls. In: Jones, M.S., Wakefield,
R.D. (Eds.), Aspects of Stone Weathering, Decay and Conservation. Imperial College
Press, London, pp. 28-42.
High-resolution micro-geophysics: electrical tomography for walls
- P L Cosentino
- R Martorana
Cosentino, P.L., Martorana, R., 2002. High-resolution micro-geophysics: electrical
tomography for walls. Proceedings of the Asamblea Hispano-Portuguesa de
Geodesia y Geofísica, Valencia, pp. 1794-1797.
Rising damp: capillary rise dynamics in walls
- Hall
Enhancement of geo-electrical techniques for NDT of masonry
- Keersmaekers