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Ethyl silicate for surface treatment of concrete – Part I: Pozzolanic effect of ethyl silicate
Abstract
Despite the widespread use of ethyl silicate for stone consolidation, the investigation of its reactivity with the different supports is still in progress. In this paper, the pozzolanic behaviour of ethyl silicate is investigated, by means of experimental mixtures of commercial ethyl silicate and slaked lime, and the occurrence of C–S–H formation is shown. The ability of ethyl silicate to penetrate in porous building materials as a liquid solution and, only after curing, to give rise to a pozzolanic material encourages the application of ethyl silicate for the consolidation and protection of reinforced concrete, as well as for the consolidation of modern cement-based mortars having artistic value (Art Nouveau cement-based mortars, etc.). The pozzolanic effect of ethyl silicate can be exploited also for the formulation of new consolidating materials (e.g. with nanolime).
... Among consolidants, TEOS (tetraethoxysilane, Si(OEt) 4 ), also known as ethyl silicate, is one of the most commonly used products for consolidating siliceous-based construction materials such as sandstone, tuff stone, cement mortars and other concrete structures [2,7,10,11,12,13,14]. The popularity of TEOS products is due to their ample commercial availability and reasonable price, and their proven general high physical and chemical compatibility with siliceous materials, leading to a reduction in porosity and strength increase with minimal alteration in substrate appearance [7,13]. ...
... Although the same group tested this strategy on several substrates using different treatment protocols, the underlying chemistry behind this combined treatment remains poorly understood. Advances in cement and concrete composites have evidenced improved performance of ethyl silicate consolidants in combination with slaked lime [11] or nanolime particles [25] through the precipitation of additional calcium silicate hydrate (C-S-H) gel upon pozzolanic reactions between ethyl silicate and Ca(OH) 2 (nano)particles, as well as with portlandite crystals formed during cement hydration [26,27]. As a result, a significant densification and strengthening of the cement material occurs, while conserving the original color and appearance. ...
... Here we explore the effectiveness and durability of a combined TEOS-nanolime treatment applied on a calcareous substrate (biocalcarenite stone). Concrete/cement composites were not considered here as inherent C-S-H could mask the effect of the treatment, foster the heterogeneous precipitation of consolidant-based C-S-H (i.e., seed effect), or promote pozzolanic reactions between the TEOS-derived silica gel and the portlandite formed upon cement hydration [11]. The textural, physical, hydric, and mechanical properties of treated calcareous stone samples were determined and compared to control samples and samples treated with either ethyl silicate or nanolime. ...
... In the case of cementitious materials, the deterioration rate increases in more permeable materials [2,6,18]. Some ways to improve durability associated with permeability reduction are through matrix densification, self-healing or surface treatment as a physical barrier to the penetration of water, ions and gases [1,12,13,19]. Several studies have been conducted to produce and test new products to decrease permeability as a preventative method [7,11,13,14,20,21] or stop fluid movement in finished structures for repair [1,12,18], which can both contribute to the extension of service life [11]. ...
... This product has a grey powder appearance, with an odour like cement, pH solution between 10 to 13, and density of 1.450 g/cm 3 . Surface treatment is intended to precipitate inside the pores, bonding with the substrate [1,19] to reduce capillary porosity [66]. ...
... In general, silica fume increases durability due to the reduction in permeability and densifications of cementitious matrix [42, 44-50, 52, 53]. The activation mechanism is the same as the pozzolanic reaction because the silica reacts with the hydroxyls present on the pore surface, forming C-S-H [19]. However, part of this material remains unreacted in filler forms and becomes reactive in suitable exposure conditions. ...
The durability assurance in reinforced concrete is necessary during the design conception and mix design as a preventive measure. Permeability in cementitious materials is a crucial durability indicator that can be influenced by many factors, from capillary porosity to cracks. Under those circumstances, it might be helpful to have concrete with the ability to reduce permeability. In this paper, the effectiveness of incorporating a crystalline admixture, both as an admixture and surface treatment, through characterisation tests, durability tests, and self-healing analyses. A concrete with silica fume as an admixture was also produced for comparison to the use of crystalline admixture (CA). The silica fume showed more efficiency in all assessed properties relative to both the reference and CA for condition with limited water availability. Crystalline admixture is also beneficial over reference concrete when used as an admixture, increasing the compressive strength and decreasing the ingress of chloride and carbon dioxide. The concrete with surface treatment had similar behaviour of reference concrete. Additionally, healing products from the use of crystalline admixture take the form of a needle shape in concrete.
... On the other hand, several authors have reported the capacity of alkoxysilanes (e.g. TEOS or its oligomeric forms) to interact with the hydration phases in the cement matrix [18][19][20][21][22], including the reaction with portlandite to yield C-S-H gel, integration of the tetrahedral Si-O units in the C-S-H silica chains, and decomposition of Al-containing phases (ettringite, katoite, carboaluminate) to form amorphous aluminosilicate gels. ...
... De-ionized water was used in order to facilitate interpretation of the chemical interactions with the alkoxysilane, as fluctuations in the Ca content of tap water may affect their reactivity (i.e. different Ca/Si ratios in the pore solution favor either the reaction to form calcium silicate hydrate or auto-condensation to form SiO 2 [18][19][20][21][22]). The mix proportions of the control specimens are presented in Table 1. ...
... As noted in works by several authors [18,19,21,22], TEOS and other alkoxysilanes can undergo different reactions with components of the cementitious matrix (e.g. Portlandite), yielding C-S-H like reaction products in addition the SiO 2 xerogels formed by their auto-condensation. ...
Water and waterborne decay agents (e.g. salts, microorganisms) are commonly associated with undesired alterations and damages on concrete elements. A strategy to mitigate their impact is to decrease water retention in the material either by surface treatments or admixtures. In this work, hydrophobic concretes were developed by the addition of a hydrophobic sol containing TEOS and PDMS oligomers, synthetized by a surfactant-assisted sol-gel route, either as an admixture or as a surface treatment. The hydrophobic performance was similar for both application modes (>70% capillary absorption reduction) and higher than concrete containing a commercial (calcium stearate) admixture or a nanosilica-based hydrophobic coating. Addition as an admixture led to a higher durability in the rain and abrasion tests.
The hydrophobic sol as an admixture promotes an increase of surface roughness and porosity, as well as the formation of C–S–H like reaction products with the cement matrix components, as evidenced by AFM, MIP, SEM and FTIR. Despite the higher porosity, impact resistance and material cohesion were not negatively affected respect to the plain concrete. Application as a surface treatment decreased porosity and led to a higher amorphous SiO2 content. The material cohesion and impact resistance was increased by this application, although penetration was limited to the first 4 mm and the hydrophobic properties were more susceptible to mechanical damages to the surface.
... viscosity, surface tension, density and polymerization time) but also on the characteristics of the substrate: surface energy, porosity, pore size distribution and composition. Nowadays, the most common products used for consolidation generally have an alkoxysilane, such as tetraethyl-orthosilicate (TEOS) [11][12][13][14][15], whose physical properties favour penetration in most porous materials. Furthermore, research on the surface consolidation of natural stone has fully established that alkoxysilanes perform well in siliceous rock characterised by surface silanol groups that chemically bond to the treatment, whereas it is less effective in calcareous rock. ...
... Furthermore, research on the surface consolidation of natural stone has fully established that alkoxysilanes perform well in siliceous rock characterised by surface silanol groups that chemically bond to the treatment, whereas it is less effective in calcareous rock. It is well established [13]that when alcoxysilanes type TEOS, penetrated in a silicon substrate, first undergoes hydrolysis (See Eq. (1)) forming silanol groups (Si-OH) and ethanol , which is easily evaporate without damage in the structure : ...
... After the hydrolysis, condensation takes place inducing the formation and precipitation of an amorphous silica gel that fills the pores in the substrate [13]. In siliceous materials, the hydrolysed silanol groups may interact with the Si-OH groups in the substrate (Supplementary Material), partially restoring the natural binder that fell away during decay and reconnecting loosened mineral grains, with a consolidating effect and an appreciable increase in the material mechanical strength [13]. ...
Surface treatments, especially hydrophobic agents to prevent water ingress and consolidants able to fill decay-induced cracks, are often proposed as a method for preserving stone cultural heritage, however its use to protect concrete heritage is much less common. New products, specifically designed for concrete, have been developed. These products are based on alkoxysilanes that interact directly with the products of portland cement (OPC) hydration (essentially Ca(OH)2 and C-S-H) to generate additional C-S-H gel.
This study assesses the effect of an impregnation treatment, based on alkosysilanes, on artificially decayed cement mortars, in terms of product penetration depth, changes in the porosity of mortars and changes in its mechanical strengths. Reduced porosity and enhanced mechanical strength attested to treatment efficacy. Substrate porosity and pore size distribution were not the only factors found to condition treatment effectiveness, however, mineralogical changes caused by the deterioration processes (such as the presence or absence of portlandite, or the presence of salts) modify the sol gelling time and the substrate surface energy, impacting treatment penetration depth.
... The lower corrosion current density and higher corrosion potential and impedance are the important reasons to explain why the S-concrete coating can protect the inside rebar. Silane based materials could also play a significant role on the surface modification of concrete [10,[55][56] found the addition of TiO 2 led to the higher corrosion resistance compared to the reference steel [59]. Generally, nano-modified coatings could enhance the corrosion resistance of reinforced concrete in the aggressive media. ...
... It can be produced through the reaction between alcohol and tetrachlorosilane. TEOS has been widely used in stone treatment and the refractory[10,[55][56]. It was found[55] that TEOS can effectively enhance the quality of concrete surfaces by either brushing or immersion. ...
... TEOS has been widely used in stone treatment and the refractory[10,[55][56]. It was found[55] that TEOS can effectively enhance the quality of concrete surfaces by either brushing or immersion. TEOS itself does not have binding ability, but it can form a silica gel and fill the pore network through the hydrolyzing process. ...
Concrete is the most widely used construction material in the world due to its versatility and relatively low cost. However, the early deterioration of reinforced concrete constructions due to corrosion of the steel reinforcement has become a major problem. Different corrosion prevention and protection techniques available and recommended including the use of admixtures, change of reinforcement material, steel and concrete coating, and electrochemical techniques. Nowadays, the application of nanomaterials has received numerous attentions to enhance the conventional concrete properties. The introduction of nanomaterials in the concrete could increase its strength and durability. This chapter dealing with the various kinds of nanomaterials incorporating in the reinforced concrete system to provide better corrosion resistance.
... Silanes are being used ever more frequently to improve or modify some of the properties of portland cement mortars and concretes. The silanes most commonly applied to that purpose include tetraethoxysilane (TEOS) [1][2][3], its derivatives [4,5] or mixes of other silanes with TEOS [6]. ...
... Consequently, the Si(OH) 4 resulting from UCA-T hydrolysis could react with those ions to generate calcium aluminosilicates. Several authors [3,7,12,13,46] have shown that Si(OH) 4, resulting from TEOS hydrolysis, can react with calcium ions or with portlandite yielding C-S-H gel, which is the prevalent phase in cement paste. ...
... Silanes are being used ever more frequently to improve or modify some of the properties of portland cement mortars and concretes. The silanes most commonly applied to that purpose include tetraethoxysilane (TEOS) [1][2][3], its derivatives [4,5] or mixes of other silanes with TEOS [6]. ...
... Consequently, the Si(OH) 4 resulting from UCA-T hydrolysis could react with those ions to generate calcium aluminosilicates. Several authors [3,7,12,13,46] have shown that Si(OH) 4, resulting from TEOS hydrolysis, can react with calcium ions or with portlandite yielding C-S-H gel, which is the prevalent phase in cement paste. ...
Silanes added during mortar or concrete preparation, may modify the fresh state properties, hydration kinetics and mechanical strength of the final product. The effects of silanes on cement hydration have been widely studied in the literature, however, there is some controversy about its effect at short ages. The present study was undertaken to determine the effect of a TEOS-based alkoxysilane (UCA-T), produced by ultrasound-assisted pre-hydrolysis of an oligomeric precursor, on early age cement paste hydration. The nature of the processes modifying the various stages of cement hydration kinetics in the presence of the alkoxysilane was ascertained by analysing paste composition at several ages (defined on the grounds of calorimetric curve results) using XRD, TG-DTG, FTIR and Raman spectroscopy. The calorimetric curve of pastes containing UCA-T exhibited a new early age, pre-induction period exothermal peak, indicative of UCA-T hydrolysis, C3A and C3S dissolution and ettringite and C–S–H gel precipitation. Portlandite, however, did not precipitate but reacts with the Si(OH)4 sourced from UCA-T hydrolysis to generate further C–S–H gel. The induction period following on that new exothermal peak was considerably longer than the period observed in the reference cement, an effect that intensified at higher UCA-T content.
... Over recent years, as a commonly used precursor for the synthesis of new materials, it has attracted increasing attention; for example, Pigino et al. [17] used TEOS as a surface protective agent for concrete structures, studied the water blocking and related performance of surfaced concrete, and achieved good technical results. TEOS has good permeability and pozzolanic activity, so it can significantly reduce the capillary suction, chloride ion diffusion coefficient and carbonization depth of concrete, and improve the frost resistance, corrosion resistance and abrasion resistance of concrete, performing well in concrete surfacing [18,19]. Nano-SiO 2 is a new type of surfacing material. ...
... 18 show the XRD, FTIR and TGA test results, respectively. ...
Concrete surface treatment is one of effective methods to increase the durability of concrete. This study chose tetraethyl orthosilicate (TEOS), lithium silicate (Li2SiO3), SiO2 nanoparticles (nano-SiO2) as surface treatment agents, tested their resistance to water penetration, chloride ion penetration, frost, sulfate erosion and abrasion of concrete specimens with different strengths, compared and evaluated the impacts to the durability of concrete by using three surface treatment agents, researched the impact of concrete strength on the surface treatment effects, and analyzed the mechanism of these surface treatment agents in connection with microscopic tests. It was found that all three agents can improve the durability of concrete, of which, the treatment effect from using tetraethyl orthosilicate (TEOS) was the best; however, along with the improvement of concrete strength, its other effects were gradually reinforced except for some small improvement effect in resistance to frost, which means it is an ideal concrete surface treatment agent; for lithium silicate (Li2SiO3), the improvement effect of resistance to frost was the best with little impact on the strength of the concrete, however, the other performance improvement effects were a little bit worse than that of tetraethyl orthosilicate (TEOS), which means it is more suitable for airport pavement with a higher concrete resistance to frost; For SiO2 nanoparticles (Nano-SiO2), the surface treatment effect was extreme limited, not recommended to be solely used for airport pavement with its requirement of high resistance to frost. Upon scanning electron microscope (SEM), X-ray diffraction (XRD), fourier transform infrared radiation (FTIR) and thermo gravimetric analyzer (TGA) tests, the surfaced concrete specimens did not produce any new substances, and the effect of the surface treatment agents was mainly to improve the concrete performance by physical filling, or by filling the cavities with the hydrated calcium silicate gel produced in the chemical reaction. These results may direct the selection of surface treatment agents in airport engineering.
... silane, siloxane, etc.) and the last group forms a physical coating-barrier at the surface of the concrete [11]. A large number of studies have been performed on the application of these treatments and their effect on the performance of concrete [11][12][13][14] and it has widely been reported that the silicate-based solutions have a more moderate impact on the permeability of the concrete compared to the other techniques [11,15]. Baltazar et al. [11] and Franzoni et al. [12] used silicate-based impregnation products for the surface protection of concrete. ...
... The influence of silicates acting as pore-blockers has been reported in Refs. [12,13,15]. Some claim that the efficacy of the silicates in improving the performance of concrete is by the consumption of free Ca or calcium hydroxide at the surface of the concrete and production of C-S-H [15,17,21,50]. ...
Removal of degraded concrete during repair activities might have a detrimental impact on the bond strength between the concrete and the repair mortar. This research aims to improve the bonding strength in case aggressive removal techniques were used, by the singular and combined application of bacterially induced CaCO3 and colloidal nano-silica (CNS) treatments. Water jetting (WJ) and jackhammering (JH) were compared and the treatments were performed on the substrates prepared with the technique causing the lowest bonding. Pull-off test results on crushed stone concrete (CC) substrates showed that JH substrates possessed the lowest bond strength compared to WJ and unprepared substrates. To assure that reported results are reproducible, pull-off tests were also performed on another type of concrete, gravel concrete (GC). The results showed that in both cases JH-substrates achieved a lower bond strength than unprepared- and WJ-substrates. The reduced bond strength by JH was restored by the CNS treatment irrespective of the concrete composition. Regarding the biodeposition treatment, the spraying technique showed to be superior to the pouring technique. Microstructural analysis confirmed the survival of the bacteria and carbonate precipitation. Porosity of the prepared substrate surfaces was studied by capillary absorption, water absorption (including the gravity effect) and vacuum absorption tests. The reduction in the initial water uptake of CNS-treated samples was evidenced by the precipitation of the silica gel at the superficial layer of the substrate. The efficacy of Energy Dispersive X-Ray Analysis (EDX) to recognize the interlayer of layered composites with a monolithic structure was observed.
... It produces silanols or SiOH (Fig. 3e). Silanols react with calcium hydroxide (CH) in the cement to produce the gel calcium silicate hydrate (CSH) (Fig. 3f) (Ji, 2005;Kong et al., 2013;Qing et al., 2007;Sandrolini et al., 2012;Tobón et al., 2012;Vieira et al., 2004). Therefore, the number of calcium hydroxide (CH) crystals decreases at the first step of the hydration. ...
... Therefore, the number of calcium hydroxide (CH) crystals decreases at the first step of the hydration. The gel calcium silicate hydrate (CSH) enhances the solidification by filling the pores in the aggregates and cement particles (Ji, 2005;Kong et al., 2013;Qing et al., 2007;Sandrolini et al., 2012;Tobón et al., 2012;Vieira et al., 2004). Furthermore, the improvement of the cohesion at the lower ages of crystals reduces the water bleeding and the cement materials separation (Koohestani et al., 2016;Senff et al., 2009). ...
A large amount of mine wastes is generated every year through mining and mineral processing operation. The management of mine tailings is an attractive topic for researchers from both environmental and economic aspects. Mine tailings have shown a capacity as a raw material for the construction industry or a substitution for previous materials to produce the cement. It is applied in some specific environments such as offshores or massive projects like large bridges and tunnels. However, the cement industry has caused a variety of environmental issues. The production of Portland cement on an industrial scale increases the greenhouse effects and generates acidic rains. It releases greenhouse gases by the generation of carbon dioxide. In recent years, strict environmental regulations led to more efforts from mining industries to manage their tailings. A new approach to decrease the environmental issues, improve cement technology and obtain economic benefits is the use of mine tailings for cement production. Mine tailings in the cement mixtures decrease the initial hydration, retard the setting time, and lower the product mechanical strength. These problems can be fixed by the use of additives. Additives as chemical compounds are added to a cemented paste to change its properties and improve its performance. Therefore, the additives in cemented paste tailings can increase the pump-ability, reduce the water-to-cement ratio, increase density, or even adjust setting time and hydration according to the desired purposes. However, the amount of additives in the cemented paste tailings changes based on the type of additive. It should be optimized to cause a positive effect on the cement properties. Furthermore, the additives and their adaptation to the physical and chemical characteristics in cement and tailings is an important issue that should be investigated. In this paper, the usage of several chemical additives was studied, which can strengthen the properties of cemented paste tailings during backfilling operation. It can cause a better condition to decrease the environmental problems for the cement industry and mine tailings. A review of previous works is presented with an explanation of the gaps in previous studies.
... In the last few decades, numerous studies have been carried out on liquid surface treatment admixtures which are often preferred because they are usually applied on hard state concrete [23,27]. According to EN 1504-2: 2004 [28] Standard, liquid surface treatment admixtures are divided into 3 different groups in terms of functions: impregnation, hydrophobic impregnation, and coatings. ...
... As it is understood from the literature, various studies have been carried out by the researchers on the use of liquid surface treatment of concrete [27,34,37,38]. However, there is limited research on the effect of using mineral DSHA in road concrete. ...
Durability and dimensional stability problems are emerged in road concrete due to traffic loads and environmental factors. The concrete surface treatment is one of the preferred methods to solve these problems economically. As it is known, surface treatment is applied to the concrete surface as dry-shaking and liquid. It is understood from the literature that there are very limited studies about the use of dry-shake hardener admixture in concrete mixtures. In the present study, the effect of dry-shake surface hardener admixture application on mechanical, durability and dimensional stability properties of concrete mixtures having different w/b ratios were investigated. Totally ten series of concrete mixtures coated with and without dry-shake surface hardener admixture were prepared for this purpose. The slump value of concrete mixtures was determined as 85 ± 5 mm. Vebe, slump and air content tests were performed for each mixture in fresh state and unit weights of mixtures were calculated. Also, compressive strength, modulus of elasticity, transport properties, abrasion resistance, freeze–thaw resistance and drying shrinkage behavior were investigated on the 7, 28 and 90-day specimens. In the light of the experiment results, compressive strength, modulus of elasticity, water sorptivity, abrasion resistance and drying shrinkage behavior of concrete mixtures were positively affected with adding of dry-shake surface hardener admixture. However, it was found that the dry-shake surface hardener admixture application had no significant effect on water absorption, depth of water penetration under pressure and freezing-thawing performances.
... For the first method, the ordinary used silicate-based agents such as sodium silicate, potassium silicate and magnesium fluosilicate could react with portlandite (CH) in the pores to produce calcium silicate hydrates (C-S-H), filling the pores [6][7][8][9][10][11][12][13][14][15]. NanoSiO 2 [16][17][18] and tetraethyl orthosilicate (TEOS) [19][20][21][22][23] also have similar pore filling effect. For the second method, silane-or siloxane-based water-repellent agents could form a dense, continuous and thin film on the surface of the materials [24][25][26][27][28][29][30]. ...
... Similar to sodium silicate and magnesium fluorosilicate, TEOS also can reduce the total porosity, mainly the "M pores" and "L pores", probably due to the same two reasons mentioned above. The hydrolysis of TEOS would produce silicate ions which further react with CH, form C-S-H and fill the capillary pores [20,22,23,33]. However, TEOS is less efficient in reducing the "M pores". ...
In this study, the efficiency of surface treatment in the calcium sulfoaluminate (CSA) cement-based materials were explored. Several frequently used surface treatment agents (sodium silicate (NS), and magnesium fluorosilicate (MFS), tetraethyl orthosilicate (TEOS), poly-methyltriethoxysilane (PMTS)) were applied on hardened CSA mortar and concrete. The penetration depth of these agents and their influence of the treatment on the properties of water sorptivity, carbonation resistivity, mechanical property, and pore structure was investigated. Results showed that the penetration depth of NS and MFS was around 60-85um, and that PMTS, MFS, TEOS, and NS could reduce the water sorptivity by 94.0%, 17.0%, 11.0% and 7.8%, respectively. PMTS and TEOS could reduce the carbonation rate by 38.7% and 14.3%, respectively, but NS and MFS could not reduce it. In addition, PMTS can reduce the pores less than 50 nm (S pores) significantly, whereas has little influence on pores between 50 nm and 1 μm (M pores). NS, MFS and TEOS would reduce M pores, but increase S pores. By the combination of permeability and pore structure test, it was found that volume of S pores was positively correlated to the carbonation rate and the volume of M pores was positively correlated to the water sorptivity. Furthermore, it was found that surface treatment had little influence on the compressive strength, but it could increase flexural strength slightly. This work evidenced the effectiveness of surface treatment on CSA cement-based materials and highlighted the critical role of fine pores (less than 50 nm) in their transport properties.
... When comparing the water absorption reduction extents of samples treated at 1 day and 90 days, a greater effect is in the later age treated sample. It has been reported that the physical pore-refining effect [24] and chemical pozzolanic reactivity [25] of TEOS contribute to a lower water absorption rate. The results shown above also reflect its beneficial effects on cementitious materials at later ages as shown in the compressive strength test. ...
... It can be seen in Fig. 6 that TEOS-and Na 2 SiO 3 -CH systems exhibit comparable IR spectrum, implying the similar reaction products, i.e., the calcium silicate hydrate products as shown by the Si-O stretching band at about 1000 cm À1 . From the immediate occurrence of the Si-O band, as well as the high CH consumption amount at one day reaction as shown in Table 2, it can be deduced that the pozzolanic reactivity of TEOS or the hydrolysis product, the nano-SiO 2 cluster is high, and this is in line with work conducted by NMR [13] and TG [25] studies. ...
... The obtained results are mentioned in Fig. 5. The results show that both samples R17@MC and R171@MC after 300 abrasion cycles, preserved their superhydrophobicity (150 • and 147 • respectively) despite a negligible mass loss, which indicates that the coating penetrates in bulk i.e., into the internal structure of the concrete under capillary forces and reacts with the present oxides (silica, alumina, lime, and so on) closing hence the pores and preventing water and moisture form penetrating, and subsequently preserving the initial properties [57][58][59]. Which was verified by the morphology study in the Section 3.6. ...
In outdoor environment, the exterior walls surface of buildings always suffers from damages caused by ultraviolet radiations, temperature variation, abrasion and erosion phenomenon, dust pollution, and microbial adhesion: Thereby reducing their durability over time. In order to overcome these obstacles, the superhydrophobic coatings can be an advantageous solution to ensure long-term stable use by improving the exterior concrete walls durability. In this line, a fluorine-free water-repellent coating was developed through sol-gel method and successfully applied to concrete substrates by dip-coating technique. The coating was formulated with low surface energy polydimethylsiloxane (PDMS) and polymeric silica (PS) to simultaneously modify the microstructure and chemical properties of concrete substrate surface. The coated concrete substrate showed super-hydrophobicity with high water contact angle (WCA) over than 150°. Besides, the self-cleaning property, mechanical robustness, stability under UV irradiations, resistance to temperature and humidity were investigated. The results indicated that the coated concrete substrate cannot be soiled by dust and can resist over than 300 cycles of abrasion test. It also presents resistance to temperature of 45°C associated with a humidity of 80% during 720 hours and showed excellent resistance to prolonged exposure to UV irradiations during 1440 hours. Natural out-door aging tests have shown that the superhydrophobic coating is weather resistant
... It has been reported that aggressive removal technologies, for example, jackhammers may cause micro-cracking of the old concrete at the interface because of heavy impact (Courard et al., 2014, Yazdi et al., 2020. To study the decreased bond strength between repair mortar and concrete due to aggressive removal techniques, various studies have been performed (Baltazar et al., 2014, Fajardo et al., 2015, Franzoni et al., 2013, Sandrolini et al., 2012. No method is presented so far on recovering the lost bond strength. ...
Patch repair is one of the main techniques for repairing concrete structures. The bond between the repair material and concrete substrate controls the durability and efficiency of a repaired system. The bond strength between the repair mortar and the concrete might have a negative impact due to deteriorated concrete removal during the repair process. This research investigated the bond strength between strain hardening cementitious composites (SHCC) used as patch repair material and concrete in cases that different interface treatments were applied. Strain capacities of SHCC were measured using uniaxial tensile test on the dumbbell specimens that confirmed the post cracking behavior of SHCC. Compressive properties were investigated for concrete substrate and SHCC. For SHCC/concrete combined specimens, slant shear test and pull-off test were performed to assess peak loads and pull-off strength between concrete and SHCC, respectively and the modes of failure were observed. Slant shear and pull-off strength tests showed different trends due to differences in the orientation of interface treatments. The concrete removal operation from old concrete exhibited higher load capacity in the slant shear test because of the interlocking effect due to distorted pit formations on the surface of the concrete. On the other hand, the application of primer seemed to increase the pull-off strength. The surface- polished cases in both slant shear and pull-off test showed the lowest bond strength because of the smooth surface
... Leung et al. [29] found that surface treatment of concrete with nanosilane-clay exhibited impermeable properties and improved resistance against chloride ions ingress, because the treatment is able to modify the microstructure of the concrete surface. At the same time, nano-SiO 2 surface treatments are compatible with the cementitious base [30] and increase concrete performance by blocking capillary pores against chloride ions penetration [11,31,32]. ...
Surface treatments help to protect the built heritage against damage (environmental, accidental, etc.), reducing repair and restitution costs and increasing the useful life of building materials. The use of nanomaterials is currently the most important field of research in surface treatment technology for the preservation of building materials and, more specifically, to improve their durability and prevent their deterioration, extending their useful life. This paper studies the influence of a graphene oxide (GO) suspension as a surface treatment on the properties of concrete. The results indicate that, at best, surface treatment with GO can decrease both the water absorption and capillary absorption of concrete by about 15 %. The increase in the amount of GO deposited as a surface treatment leads to a further reduction in concrete water absorption. It is shown that, at best, GO coating also reduces water penetration at low and high pressures by approximately 20 % and 60 %, respectively. In addition, scanning electron microscopy analysis shows that GO surface treatment facilitates the hydration process and densifies the concrete microstructure. A simple aqueous suspension of GO is revealed as a tool with a high potential to protect concrete surfaces in a fast and cost-effective way, thanks to the easy application by spraying and the small amount of material needed to obtain great results.
... Another silicone-based material is silicone resin that works by coating the inner walls of concrete pores with a film to repel water [40]. When incorporated into concrete, a silicate gel forms and coats the capillary pores of concrete [41,42]. ...
The ingress of water and aggressive substances is the primary reason for the chemical and physical degradation of concrete infrastructure, leading to a reduction in durability and a shortening of life span. In practice, different integral waterproofing admixtures and surface coatings have been widely used to prevent or mitigate this problem. Compared with surface protection, the incorporation of integral waterproofing admixtures (such as densifiers, water repellents, and crystalline admixtures) in concrete has several benefits, such as ease of application, elimination of regular maintenance, and little or no deterioration over time. So far, there is no comprehensive review on integral waterproofing admixtures and their effects on various properties of concrete. This review examines existing literature on integral waterproof concrete containing various commercial and laboratory-made waterproofing admixtures. This comprehensive review highlights that the use of integral waterproofing admixtures has the potential to increase the service life and improve the durability of concrete structures and infrastructure. However, the admixtures may have a negative impact on some concrete properties, such as workability and strength. Whilst many hydrophobic and crystalline admixtures can reduce the water absorption rate of concrete by up to 80%, they often have a negative impact on the concrete compressive strength, causing a strength reduction of about 10% or more. Their influence on some durability properties (e.g., reinforcement corrosion, microbial-induced concrete corrosion) is inconclusive, indicating the need for further research. There is also a need to develop proper guidelines to determine the efficacy of integral waterproofing admixtures. More research is also required to assess the long-term performance of integral waterproof concrete and its benefits based on life cycle assessment.
... quartz sand, C-S-H, aluminosilicates) (Wheeler, 2005). Furthermore, previous studies (Barberena-Fernández et al., 2015;Zarzuela et al., 2020;Sandrolini et al., 2012) have shown the alkoxysilane ability to react directly with portlandite, yielding C-S-H gel, or with C-S-H, incorporating into the structure and increasing the Si-O chain length. ...
... Recently, one of the most promising methods is the use of nanomaterials [8], thanks to their extraordinary potential to penetrate through cracks and pores in concrete [9]. So far, the literature has focused little on the study of surface treatments with nanomaterials [10][11][12][13][14]. ...
Improving the protection of concrete by applying graphene oxide (GO) as a surface treatment has become the objective of the present study. This study focuses on performing a statistical analysis to study different levels of GO application as an exterior coating, thus observing the effectiveness of the coating and the optimization of the treatment material for concrete protection. Four tests were performed to define concrete durability, such as pressurized water penetration, capillary absorption, freeze-thaw resistance and carbonation resistance. The results showed an increase in concrete durability with any level of GO application on the surface, considering that the optimum amount of application for water impermeability and freeze-thaw resistance is 26.2 µg/cm2, since it was possible to reduce pressurized water penetration by 45%, capillary water absorption by 57% and freeze-thaw detachment by 25%. However, the optimum application rate for carbonation resistance is 52.4 µg/cm2, reducing carbonation by almost 60%. In conclusion, if the concrete is going to be exposed to less aggressive environments, the application of a mild surface coating of GO is sufficient for its protection, and if the concrete is going to be exposed to more aggressive environments, it is necessary to increase the amount of GO. The performance of GO as a coating significantly increased the degree of protection of the concrete, increasing its service life and proving to be a promising treatment for concrete surface protection.
... (3) The reaction products of their polymerization are chemically compatible with components from the aggregates and the cementitious matrix. More specifically, the precursors can undergo auto-condensation [21,22], producing an amorphous silica xerogel capable of bonding to siliceous phases (quartz, C-S-H, etc…), or they can react with different phases from the cement matrix [23][24][25][26], yielding products with a similar composition. In a prior work [23], we demonstrated that these reactions include formation of C-S-H gel by reaction with portlandite, lengthening of the silica chains of C-S-H gel. ...
Many of the concrete structures that conform our modern cultural heritage are in need of repair and protective interventions. Silane-based impregnation treatments can be used to repair onset cracks and reinforce the surface due to their ability to produce silica and C-S-H gels, and can be modified by incorporating hydrophobic precursors to create multifunctional treatments that also protect from water ingress.
Since the effectiveness of impregnation treatments is dependent on substrate properties and chemical-physical changes it may have experienced over time, validation using standard materials may not always be representative of on-site application. In this work, the effectiveness of three innovative silane-based impregnation treatments developed by our group (two of them combining superhydrophobic properties) was evaluated on mockup specimens, which simulate the properties of the cementitious materials from six different heritage structures across Europe, artificially aged to simulate weathering by three methods: carbonation, chloride ingress and physical damages (freeze–thaw and thermal cycles).
The characterization of the treatments showed they are compatible in terms of chemical interaction, applicability and minimal aesthetical alterations. Surface resistance and ultrasound pulse measurements have been used to assess the improvement in mechanical properties. The incorporation of hydrophobic components and fumed silica has a relatively low impact over the mechanical properties while it significantly reduces water absorption and grants water repellent properties to the surface, giving rise to a superhydrophobic performance.
... The surface application of colloidal silica nanoparticles has been proposed for improving the resistance of hardened concrete against chloride penetration through the concrete pores [20] and against concrete carbonation [21]. Ethyl-silicate, precursor of nano-SiO 2 , has been reported to have pozzolanic effect when applied as surface treatment on hardened concrete due to the precipitation of silica gel inside the pores [22]. Moreover, nanosilica particles can penetrate through concrete pores promoting the formation of new gels that fill the pores and refine the porous structure of the cementitious matrix [23]. ...
Presence of microcracks in concrete can diminish the service life of a structure. The injection of materials for filling the crack is proposed for facing this problem. The traditional materials used for sealing cracks present some drawbacks, such as the difficulties of inorganic materials for flowing to all the depth of the crack and the lack of compatibility with the cementitious matrix in the case of organic materials. In this work, the injection of colloidal nanosilica dispersed in water is proposed for filling microcracks in mortars. The effect of the injection procedure on the sealing performance of the colloidal nanosilica has been assessed. The ability of colloidal nanosilica for penetrating through the crack and its posterior gelification-solidification inside the crack after a curing period have been confirmed. The microscopic analysis of a cross-section of the crack indicates that the sealing ability of the nanosilica seems to be not only due to the filling of the crack but also to chemical interactions with the cementitious phases of the surrounding crack sides.
... Applying tetraethoxysilane (TEOS) based consolidants to portland cement mortar and concrete has proven to be effective [11][12][13][14]. The originality of such treatments lies in that they interact chemically with the substrate: unlike natural stone mineralogy, concrete composition includes portlandite, a by-product of cement hydration. ...
Cracks sealing in deteriorated concrete often requires the use of repair mortars of compatible composition, good adhesion to the substrate and free of shrinkage. Even where repair mortars properly bond to the substrate, that interface affords a preferred pathway for water ingress. Hydrophobic repair micromortars designed to seal cracks via injection might be one way to solve that problem. This article analyses the effect of adding three hydrophobic products (generic labelled as UCA-TP) comprising silica oligomers, n-octylamine (a surfactant) and polydimethylsiloxane (PDMS) in different proportions (10 wt% of PDMS :UCA-TP10, 28 wt% of PDMS: UCA-TP28 and 56 wt% of PDMS: UCA-TP56) to a fresh repair micromortar. The incorporation of UCA-TP products hastened the early hydration kinetics of repair micromortars, and, at the same time, after 7 days of hydration, declined the total heat released (the higher is the content of UCA-TP product and its proportion of PDMS the lower is the heat of hydration. The inclusion of the hydrophobic products substantially modified the repair micomortar wetting and water transport properties, by inducing a hydrophobic behavior (contact angle >100º) and decreasing water absorption by >60%. Although adding those products to the repair micromortars increased porosity and lowered mechanical performance, 28 d compressive strength was consistently >50 MPa, a value that compared well to the original substrate. Simulated cracks were very effectively sealed by the repair micromortars.
... For example, it is well known that a mixture of TEOS and silane coupling agents can modify the surface properties of inorganic materials. 38,39 Therefore, in this study, we focused on a mixture of TEOS and a saline coupling agent to make homogeneous composites of CaO and calcium silicates to effectively enhance the thermal output rate with small amounts of additives. The novel composite materials, developed after the original sample preparation methods, led to an increase in the reactivity and cyclic stability with additives of no more than 2.0 wt%. ...
The calcium oxide/water/calcium hydroxide system is a promising material system for thermochemical energy storage (TCES). Its high reactivity under various experimental conditions during the cyclic operation of heat storage-and-release is a key challenge for practical applications. In this study, we developed a new type of highly durable TCES medium with hydration reactivity enhancement. The composite materials were prepared by heat treatment of a mixture of calcium carbonate and additives, consisting of tetraethoxysilane (TEOS) and a silane coupling agent, bis(3-triehoxysilylpropyl) pertetrasulfide (SCA). The kinetic performances of the composites and CaO were compared. It was observed that the additives promoted hydration reactivity at 450°C and 70 kPa, and 0.6 wt% composite exhibited the highest thermal output. Furthermore, it was found that the enhancement in hydration reactivity was affected by the experimental conditions as significant enhancements were observed when the experimental conditions were closer to equilibrium, while almost no enhancement was observed when the conditions were far from equilibrium or at a high vapor partial pressure. Sample characterization via X-ray diffractometry and scanning electron microscopy revealed that the agglomeration of CaO particle grains was alleviated by pinning effects, and the component that enhanced the hydration reactivity was identified as Ca2SiO4 nanoparticles.
... These impregnation treatments are highly influenced by the reaction conditions such as concrete type, state of decay, sol composition, Ca/Si ratios, water availability, reaction time/rate etc., which ultimately determine the mechanical properties and the overall effectiveness and durability of the treatment [40]. Predicting the behavior based solely on experimental studies is a challenging task due to the system complexity. ...
The composition and structure of Calcium-Silicate-Hydrate (C-S-H) phases depends on various reaction parameters leading to its formation. Molecular Dynamic simulation studies probing the formation and structure of C-S-H are generally computationally expensive and can reach only very short time scales. Herein, we propose a coarse graining approach to model the formation of C-S-H, using patchy particles and a modified Patchy Brownian Cluster Dynamics algorithm. The simulations show that patchy particle systems can recover the qualitative kinetic evolution of C-S-H formation, and the obtained final structures were comparable to previously reported molecular dynamics studies and experiments. The model was extended to study the effect of water in the polymerization of tetraethoxysilane oligomers, the principal component of an impregnation treatment for deteriorated concrete surfaces. The intermediate system properties predicted by the simulations, such as viscosity and gel time, and structure were found to be well in accordance with the tailored experiments.
... Moreover, NS also has a seeding effect by adsorbing calcium ions and serving as nucleation sites of C−S−H due to the large specific surface area [17]. Furthermore, NS can function as a pozzolana because it can react with CH to form C−S−H [18,19]. ...
To date, reinforcement concrete is the main construction material worldwide. As the concentration of atmospheric CO2 is steadily increasing, carbonation of the reinforcement concrete becomes a pressing concern. In this study, novel surface protective materials (SPMs) modified with hybrid nanoSiO2 (HNS), fly ash, and slag were developed to reduce CO2 emissions and extend the service life of the reinforcement concrete. The carbonation depths were measured by phenolphthalein to reflect the carbonation resistance. X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FTIR), and thermal gravimetric analysis (TGA) were conducted to analyze the chemical components of the samples after carbonation. In addition, MIP was carried out to examine the microstructures of the samples prior to carbonation. Thermodynamic modeling was employed to calculate the changes in the phase assemblages of each blends in an ideal situation. The experimental results showed that the carbonation depth and CaCO3 content of the SPM modified with HNS decreased by 79.0% and 64.6% compared with the reference, respectively. The TGA results showed that after carbonation, the CaCO3 contents were 4.40% and 12.42% in the HNS modified samples and reference samples, respectively. MIP analysis demonstrated that the incorporation of HNS in SPM led to a 48.3% and 58.5% decrease in big pores and capillary pores, respectively. Overall, the SPMs modified with HNS in this study possessed better carbonation resistance and refined pore structures.
... Zhang et al. have demonstrated that both silane gel and silane cream can reduce concrete water absorption, in which surface treatment can reduce concrete carbonation depth, while integral water repellent concrete increased concrete carbonation depth [6] . As a repair material for cultural relic restoration, ethyl silicate can react with calcium hydroxide to enhance the compactness of concrete [7] . Franzoni has studied the application of ethyl silicate in fired-clay bricks. ...
Surface treatment is an effective strategy to reduce concrete water absorption and improve concrete durability in practical engineering application. In this paper, ethyl silicate and anhydrous alcohol mixed solution is chosen as surface treatment for concrete, and water absorption is tested, the test results show that ethyl silicate can effectively reduce the concrete water absorption and water absorption rate. water absorption rate reduction rate is 82.4 for T5 and 84.6% for T7, the initial rate of water absorption is reduced 94.9 for T5 and 94.7% for T7, and the secondary rate of water absorption is reduced 73.2 for T5 and 80.1% for T7.
... For example, it is well known that a mixture of TEOS and silane coupling agents can modify the surface properties of inorganic materials. 38,39 Therefore, in this study, we focused on a mixture of TEOS and a saline coupling agent to make homogeneous composites of CaO and calcium silicates to effectively enhance the thermal output rate with small amounts of additives. The novel composite materials, developed after the original sample preparation methods, led to an increase in the reactivity and cyclic stability with additives of no more than 2.0 wt%. ...
The calcium oxide/water/calcium hydroxide system is a promising material system for thermochemical energy storage (TCES). Its high reactivity under various experimental conditions during the cyclic operation of heat storage‐and‐release is a key challenge for practical applications. In this study, we developed a new type of highly durable TCES medium with hydration reactivity enhancement. The composite materials were prepared by heat treatment of a mixture of calcium carbonate and additives, consisting of tetraethoxysilane (TEOS) and a silane coupling agent, bis(3‐triehoxysilylpropyl) pertetrasulfide (SCA). The kinetic performances of the composites and CaO were compared. It was observed that the additives promote hydration reactivity at 450°C and 70 kPa, and 0.6 wt% composite exhibited the highest thermal output. Furthermore, it was found that the enhancement in hydration reactivity was affected by the experimental conditions as significant enhancements were observed when the experimental conditions were closer to equilibrium, while almost no enhancement was observed when the conditions were far from equilibrium or at a high vapor partial pressure. Sample characterization via X‐ray diffractometry and scanning electron microscopy revealed that the agglomeration of CaO particle grains was alleviated by pinning effects, and the component that enhanced the hydration reactivity was identified as Ca2SiO4 nanoparticles.
... A number of studies have shown that TEOS and their derivatives react with portlandite to produce C-S-H gel [16,[18][19][20][21][22]. The oligomeric alkoxysilane-based product developed by the authors exhibited similar reactivity with portlandite and hydrated cement paste, together not only with portlandite consumption but with a lengthening of the Si-O chains in the C-S-H gel [20]. ...
Chemical compatibility with a wide range of materials is among the features that has driven the use of alkoxysilanes as consolidants in built structures. Such compatibility is particularly important in cementitious materials where the reaction with portlandite may generate C-S-H gel, one of the main hydration phases of OPC. The cementitious matrix is a complex system, however, and the reaction of its many phases with alkoxysilanes, while poorly understood, may determine treatment efficacy. This article describes a detailed study of the individual interactions between an oligomeric alkoxysilane-based impregnation treatment previously shown to interact with the portlandite present in cement paste and the cementitious phases generated in ordinary portland cement hydration.
The findings show that both portlandite and C-S-H gel interact with the silicon oligomers in the hydrolysed impregnation treatment to generate a C-S-H gel (in the case of portlandite) and a rise in C-S-H gel mean chain length (MCL). Ettringite is also altered in the presence of alkoxysilanes, transforming to gypsum and AH3. Its transformation generates a tetrahedral aluminium that is taken up into a high silicon gel sourced from the treatment to form an amorphous aluminosilicate gel. Monocarboaluminate and katoite also partially decompose in the interaction with the product, whereas gibbsite remains unaffected.
... As for opal-CT, the occurrence of the phase could be either related to the accessory mineralogical assemblage of the ochres or to superficial restoration treatments with ethyl silicate-based consolidants. Nevertheless, the second hypothesis is in contrast with published experimental evidence [45], indicating the absence of significant diffraction contributions from these classes of products after polymerization. Furthermore, opal-CT is present also in the materials sampled from the atrium of the domus, where superficial consolidation treatments were not reported. ...
Ochre-based pigments have been employed since the first artistic expressions of mankind, with widespread diffusion during the Roman civilization. Such prominent use influenced their technological development, focused on functional and aesthetic optimization through complex manufacturing procedures. Furthermore, their appearance is also influenced by degradation processes, sometimes driven by natural disasters such as the eruption of Mount Vesuvius in 79 AD, in which yellow ochres of Vesuvian sites were sometimes converted to red by thermal alteration. In this contribution, a multi-analytical approach was adopted based on preliminary non-invasive investigations complemented by laboratory analyses to characterize the painted surfaces of the tablinum of the House of the Bicentenary (Herculaneum) with a particular focus on the ochre-based monochrome backgrounds. The study was aimed at (a) reconstructing the original color scheme of the walls and (b) deciphering the complex decorative techniques adopted by Roman craftsmen. The analytical results allowed testing and defining analytical procedures for the discrimination between the original and converted red pigments. Furthermore, these studies indicated that specific decorative technologies were adopted according to aesthetic, functional, and economic purposes, including the utilization of various qualities of ochre with different compositional and textural properties, and the mixture of ochre pigments with other compounds.
... Multifunctional surface treatments should have at least two functions, for example, ethyl silicate (or tetraethylorthosilicate), an alkoxysilane compound, which itself does not have binding property, and nevertheless it can produce silica gels and block the pores through hydrolysing process. Also, it can prevent the entry of corrosive substances because of its hydrophobic effect [127]. Similarly, Silane-clay nanocomposites are not only show a hydrophobic effect, but also improve the microstructure of concrete cover [128]. ...
The steel reinforced concrete structures perform well in various environmental conditions, but structures may undergo premature damage in aggressive environments such as marine or acidic, primarily due to steel corrosion, and substantial reduction in service life occurs. This also causes huge economical loss and create safety and environmental problems. The repair and maintenance of steel reinforced concrete structures for their safety needs effective monitoring and inspection systems for evaluating the corrosion condition of steel. Since the corrosion of steel reinforcement occurs through electrochemical reactions, electrochemical methods are suitable to study the corrosion processes. In this chapter, some commonly used electrochemical techniques have been comprehensively explained. In addition, there is a critical requirement to develop effective and long-lasting techniques to control the corrosion of steel. Hence, some of the commonly used corrosion control methods have been comprehensively described in this chapter.
... tetraethylorthosilicate) and their derivatives have been commonly used for the conservation of historical buildings [6] due to a series of advantages over other alternatives such as the ability to polymerize in situ by a sol-gel reaction with ambient moisture and formation of reaction products with a Si-O backbone that are stable and compatible with most building materials [31]. In addition to the aforementioned advantages, recent studies [7][8][9], show that alkoxysilanes may have a higher chemical compatibility with cementitious materials due to their reactions with components of their matrix [33]. More specifically, the silanol groups resulting from the hydrolysis stage can react with the portlandite yielding C-S-H gel, the main phase responsible of the cement matrix engineering properties, or get incorporated into the silica chains of the already existing C-S-H. ...
The performance of impregnation treatments used for protection and remediation of porous building materials relies on sufficient penetration depth. The penetration of sol–gel impregnation products into partially saturated porous material is driven by capillary suction and depends on material properties, such as pore size distribution on one hand, and on the other hand on sol physical properties, viscosity, density, surface tension and contact angle, along with the time in which the sol gels. In this work we analyse, by the way of modelling and experiments, the penetration depth of a sol–gel impregnation product as the function of pore size distribution and sol properties. The main goal is to determine the importance of sol’s physical properties for the penetration depth for a specific pore size, which will serve as a basis of the optimization of impregnation products to maximize their penetration depth. The model is first calibrated in terms of penetration depth and sol uptake by the experimental data obtained from mortar samples each with a specific pore-size distribution. The correlation between penetration depth and physical parameters is then established by the use of Monte-Carlo method. The results show that the most important parameters for the optimization are surface tension, whose influence increases for larger pores, and gelation time, which with decreasing importance for larger pores.
... Furthermore, since the silica source is already solubilized, this process can be faster than the pozzolanic reaction with other (solid) silica sources such as nano-SiO 2 . In spite of the significance of this feature, that would allow to repair the concrete buildings and structures by a simple and low cost impregnation treatment, scarce research about that can be found in the literature [17,18]. ...
Impregnation treatments are one of the alternatives to protect concrete-based building and monuments from weathering degradation. However, it is important to consider the chemical compatibility of the reaction products with the building material. The impregnation product studied here consists of a silica oligomer able to poly-merize, by a simple sol-gel process, inside the pore structure of concrete. In this work, we investigate the ability of this impregnation treatment to produce C-S-H gel in contact with cement paste. A complete characterization of the reaction products demonstrated that the silanol groups from silica oligomers react with the portlandite present in the cement paste generating a material with the chemical, structural and morphological features of C-S-H gel. Simultaneously, the 29 Si NMR results indicate that the SieO units are incorporated into the existing C-S-H, increasing its chain length. These results open the way for a simple concrete structures repairing procedure.
... One was the penetrative protective agent based on organic materials, with intention to block the surface pore structure; the other was the inorganic materials, such as mortar or cement paste, to isolate the matrix from erosion ions in outside environment. Silanes [16], ethyl silicate [17,18], and isobutyl-triethoxy-silane [19] were used as typical penetrative protective agents for the resistance of carbonation and erosion, and a silica-based hybrid nanocomposite was reported for surface treatment to reduce the water absorption and gas permeability [20]. One mechanism behind the enhanced impermeability was that the chemicals could go through the capillary and form an inorganic hydrophobic film along the capillary as a result of reacting with hydration products; the other was that these hydrates in the capillary structure would block the transportation of water and gas [21]. ...
Surface protection has been accepted as an effective way to improve the durability of concrete. In this study, nanosilica (NS) was used to improve the impermeability of cement-fly ash system and this kind of material was expected to be applied as surface protection material (SPM) for concrete. Binders composed of 70% cement and 30% fly ash (FA) were designed and nanosilica (NS, 0–4% of the binder) was added. Pore structure of the paste samples was evaluated by MIP and the fractal dimension of the pore structure was also discussed. Hydrates were investigated by XRD, SEM, and TG; the microstructure of hydrates was analyzed with SEM-EDS. The results showed that in the C-FA-NS system, NS accelerated the whole hydration of the cement-FA system. Cement hydration was accelerated by adding NS, and probably, the pozzolanic reaction of FA was slightly hastened because NS not only consumed calcium hydroxide by the pozzolanic reaction to induce the cement hydration but also acted as nucleation seed to induce the formation of C-S-H gel. NS obviously refined the pore structure, increased the complexity of the pore structure, and improved the microstructure, thereby significantly improving the impermeability of the cement-FA system. This kind of materials would be expected to be used as SPM; the interface performance between SPM and matrix, such as shrinkage and bond strength, and how to cast it onto the surface of matrix should be carefully considered.
... In a first stage, the hydrolysis of TEOS takes place to produce Si(OH) 4 groups and ethanol. In a second stage, two competitive processes can take place; (i) Si(OH) 4 can polymerized forming a SiO 2 gel and (ii) Si(OH) 4 groups can interact with the Original Portland Cement (OPC) hydrated phases [such as Ca(OH) 2 ] to produce C-S-H gel, which is the main responsible of the binding properties of concrete (Moropoulou et al., 2004;Sandrolini et al., 2012). ...
Cultural Heritage constructions of twentieth century consist largely of mortar and concrete substrates. These concrete structures have suffered different types of decay processes. One of the most widely used consolidants is the Tetraethoxysilane (TEOS), which forms the basis of most existing commercial strengthening agents to protect porous building materials against deterioration. A novel, non-toxic strengthening and protective agent for mortar and concrete substrates was synthesized in a one-pot sol-gel procedure, incorporating in TEOS, Polydimethyl siloxane (PDMS), and nanoparticles of synthesized calcium oxalate (CaOx). PDMS provided hydrophobicity and reduced surface tension that causes cracks on the surface of produced xerogel. The synthesized nanocomposite both in sol and xerogel form was assessed with a variety of analytical techniques (FTIR, XRF, SEM, Optical Microscopy, Dynamic Light Scattering, Thermogravimetric analysis). The excellent physical properties of the produced colloidal solution of the nanocomposite, such as low viscosity and density, allow a penetration up to 2 cm from the surface in the treated cement mortars. This involved improvement of the mechanical and physical properties, such as the dynamic modulus of elasticity and increased water repellency. The treated cement mortars exhibited well-preserved aesthetic surface parameters and significant maintenance of the treatment. Furthermore, no harmful byproducts were identified indicating the nanocomposite compatibility to the siliceous and carbonate nature of the treated cement mortars.
... Currently, it is one of the most used products in the consolidation of architectural heritage materials, such as bricks, stone, and lime mortars. Also, it can be used as surface treatment on cement-based materials for its pozzolanic effect [17][18][19]. Ethyl silicate reacts with environmental humidity and the free water in the material transforms into silica gel, releasing ethyl alcohol (which evaporates and does not produce any damaging residue on the material surface). Silica gel gives the treated surface new mechanical properties, due to the strong chemical bond that is established with the substrate. ...
Acid attack causes the deterioration of construction material surfaces. The objective of this study was to investigate the degradation of different types of cement mortar in terms of variations in pore size distribution obtained by mercury intrusion porosimetry (MIP), mass loss, and compressive strength. The mortars were manufactured with nanosilica, zinc stearate, and an ethyl silicate coating. After curing (28 days), the samples were subjected to acid exposure for 90 days, immersed ina solution (3% w/w) of sulphuric acid (H2SO4). The results indicate that the mortars showed a more refined microstructure, with a higher proportion of smaller pores (<100 nm) compared to the control mortar. The 28-day and 90-day compressive strength variations of mortars were also determined by observing pronounced reduction due to the appearance of expansive compounds responsible for microcracking.
... Multifunctional surface treatments should have at least two functions, for example, ethyl silicate (or tetraethylorthosilicate), an alkoxysilane compound, which itself does not have binding property, and nevertheless it can produce silica gels and block the pores through hydrolysing process. Also, it can prevent the entry of corrosive substances because of its hydrophobic effect [127]. Similarly, Silane-clay nanocomposites are not only show a hydrophobic effect, but also improve the microstructure of concrete cover [128]. ...
Steel corrosion is the main source of damage and early failure of reinforcement concrete structures that in turns create huge economical loss and creating environmental problems. In the past, several corrosion assessment techniques such as potential measurement, gravimetric weight loss measurement, electrical resistivity measurement, sensors and electrochemical methods for instance potentiodynamic polarization, linear polarization resistance, galvanostatic pulse, and electrochemical impedance have been developed to detect corrosion condition of steel in concrete. Though the potential measurement, resistivity measurement and sensors can only provide the qualitative information about the steel corrosion. The weight loss measurement is an efficient technique for corrosion rate measurement of steel, but it is destructive and requires long exposure times. The electrochemical techniques are non-destructive in nature and are used to determine corrosion rate of steel in laboratory as well as field studies. However each of these methods possesses certain advantages and limitations, therefore a combination of these techniques is recommended to use to obtain the corrosion condition of steel. As far as corrosion control techniques for steel reinforced concrete are concerned, several methods such as cathodic protection, electrochemical chloride extraction, surface treatments of the steel, surface treatment of concrete, utilization of mineral admixtures and chemical corrosion inhibitors have been developed in the past. Each of these methods offers some advantages and disadvantages. Thus, more researches are required to develop such methods of corrosion protection of steel that are economical, durable, environment-friendly and do not cause any adverse effect on the structural performance of concrete and steel.
... In addition, it was shown that TEOS displays pozzolanic behavior. It reacts with calcium hydroxide in concrete substrate, forming calcium silicate hydrate (Pan et al., 2017;Sandrolini et al., 2012). Some researchers applied geopolymer as the coatings on the surface of concrete. ...
... The presence of the material in this state eases its connection to the pores as shown in Fig. 4c (on the right). When applied to concrete, a silicate gel will develop and initiates strengthening points in the internal parts of the pores [12,59]. Hydroxyl groups, formed from the by-products of cement, will possibly react with the silicon in the silicone resin, in the presence of hydrogen bonds, allowing silicone resin to link strongly with the pores all over the drying time. ...
The present paper investigates the performance and efficacy of four protective surface applied materials; sodium acetate, fluoropolymer, silicone resin and silane when applied to marine structures with different moisture contents. Materials were applied to fully dry and fully saturated concrete along with concrete with 2% and 4% moisture contents. The interaction mechanism of the materials with concrete and their microstructural and morphological assessments were conducted by running SEM, EDX and FTIR analyses to evaluate their performance in the presence of moisture. Also, their efficacy in protecting concrete from water ingress and chloride penetration was evaluated by operating the Initial Surface Absorption Test (ISAT) and Unidirectional salt ponding test respectively. Results demonstrated that moisture content imposes a vital effect on the interaction of the materials with concrete and their adhesion inside the pores, and consequently their efficacy in reducing both, water and chloride penetration.
Freeze–thaw cycles, application of deicing salts, and rebar corrosion are becoming main sources of concrete deterioration in bridge decks and pavements. During the past few decades, concrete surface treatments have begun to receive wide acceptance because of their effectiveness in sealing the concrete. Surface treatments achieve this by limiting fluid ingress, thereby reducing damage associated with freeze–thaw cycles, deicing salt application, and rebar corrosion. Soy methyl ester-polystyrene blends (SME-PS) have been shown to be an innovative, promising method of topical sealing. SME-PS, which is a derivative of soybean oil and expanded polystyrene, has been continuously studied since 2008. In this context, a comprehensive literature review compared the performance of SME-PS with that of traditional concrete sealers, including organic, inorganic, hybrid, and biotic sealers. These sealers were reviewed for performance in reducing water absorption and chloride penetration and improving freeze–thaw durability of concrete. The reviewed papers indicate that SME-PS possesses superior performance as a concrete protectant for reducing water absorption, chloride penetration, and freeze–thaw damage. To further enhance the feasibility of SME-PS, future studies may include investigating the physical and chemical protecting mechanisms of SME-PS, understanding the factors that affect the penetration behavior of SME-PS in concrete, and evaluating the short and long-term effectiveness of SME-PS in concrete.
Deep penetrating sealer (DPS) is a general term for a class of waterproofing agents that can fill the internal pores of concrete by mixing an alkali metal silicate solution as the base material with catalysts and additives (Jiang et al. 2015). The objective of this study was to investigate the characteristics and mechanism of the effect of different amounts of DPS sprayed on concrete. The water absorption, hydrophilicity, permeability, microhardness, abrasion erosion resistance, and pore structure of concrete were tested at different water cement ratios and sprayed DPS amounts. The test and analysis results showed that compared with the control concrete, concrete absorbed less water and exhibited less permeability after being sprayed with DPS. Moreover, its hydrophilicity, microhardness, and abrasion erosion resistance improved, while its pore volume significantly decreased. The effect was more evident when the amount of sprayed DPS was higher. This study provides a reference for practical engineering applications by demonstrating the variation in concrete surface properties after spraying different amounts of DPS.
Hybrid nanoSiO2 (HNS) modified cement pastes were explored as a kind of surface protection material (SPM). The carbonation resistance and mechanical properties of SPMs coated samples were tested. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP) were further employed to evaluate the chemical composition and microstructure characteristics of SPM. Besides, thermodynamic modeling was adopted to simulate the changes in the phase assemblages of SPM under the carbonation process. The results showed that SPM with 1 wt% HNS could effectively enhance the carbonation resistance. The incorporation of HNS could densify the microstructure and refine the pore structure. Moreover, the thaumasite can be stable at ambient temperature with the addition of HNS, which is beneficial to maintain alkalinity under the carbonation process.
In this study, the pre-consolidation of the granite used in the north façade of St. Martin’s Cathedral in Ourense, of Romanesque style (S. XII–XIII), and its influence on the effectiveness of a subsequent desalination treatment using poultices of different composition is presented. The need for both treatments lay in the high degree of deterioration of the granite of the façade, which suffers an intense sand disaggregation associated with salt crystallization. The effectiveness and harmful effects of the pre-consolidation using a conventional TEOS (Estel 1000) and a nanoconsolidant based on silicon oligomers (UCAD-2o), initially under laboratory conditions and later on site, were evaluated. In situ desalination was performed applying different types of poultices chosen taking into account the pore distribution of the pre-treated granite. The obtained results, both in the laboratory and on-site, show that the pre-treatment of the deteriorated granite with UCAD-2o restores the necessary cohesion to the rock to be subsequently desalinated, increasing—compared to the other consolidant—the efficiency of desalination through the higher reduction in the granite’s pore volume with capillary access diameter. This research contributes new data to improve the most serious conservation problems that affect granitic monuments affected by soluble salts, when the intense sand disaggregation process complicates the desalination due to the risk of loss of surface material.
While silane-based materials are widely used to improve the impermeability of concrete, the nano-scale interaction mechanismson the interfaces are still unclear. In this study, molecular simulations were employed to explore the inhibiting behaviors of three commonly-used alkoxysilanes(Aminopropyltriethoxysilane (APTES), ethyltriethoxysilane (ETES), and γ-(methylpropyleneoxy)propyltrimethoxysilane (MPS)) on the transport of aggressive ions and water throughout a nano-pore of calcium silicate hydrates (C-S-H). The results show that during the penetration process of silane-doped systems, both water and ions exhibit a low density state and a longitudinal stratification owing to the barrier effect of silanes, where the ranking was APTES < ETES < MPS. The order can be explained by differences in the molecular structure. MPS demonstrates the best inhibiting effect because it possesses maximum hydrophobic groups. For APTES and ETES with similar molecular weights, the drag effect of amino groups, results in water molecules being more likely to penetrate the interface area and escape, causing a weaker inhibiting effect in APTES. The mechanisms interpreted in this work may shed new light on the molecular design of silane-based waterproofing agents.
Deep penetrating sealer (DPS) is water-based permeable crystalline waterproofing coating, and it is widely used to improve the impermeability and durability of cement-based materials. This study investigated the action mechanism of DPS on cement-based materials, especially the microstructure of the newly generated substances and pore evolution in concrete that DPS treated. To explore the action mechanism and permeability of DPS on cement-based materials, experimental specimens were fabricated in this experiment. The specimens included concrete, cement paste, dried DPS, and the product reacted by DPS mixed with saturated calcium hydroxide solution. To test the microstructure, chemical composition, pore structure, and macroscopic permeability of the specimens, scanning electron microscopy, x-ray diffraction, energy dispersive spectrometer, nitrogen absorption, and AutoClam equipment were employed. The experimental and analytical results showed that the calcium silicate hydrate content was increased by the chemical reaction between DPS and cement-based materials. The microstructure of concrete surface then became more densified. The volume of pore with a pore size ranging from 20 to 130 nm inside concrete was decreased, and the water penetration of the concrete was reduced by approximately 75%. This study revealed the action mechanism of DPS and cement-based materials, providing reference for the improvement of DPS and practical engineering application.
Permeability-reducing admixtures (PRAs) are marketed as an option to improve the concrete durability and reduce water ingress in structures. Two categories of PRAs that have become more prominent recently are hydrophobic pore blockers and crystalline waterproofers. A literature review was performed to determine the composition, mechanism of action, test methods to indicate durability, and performance of PRAs in concrete, with focus on their use in infrastructure. The test methods for evaluating the performance of PRAs and their effects have varying degrees of frequency and standardization and there is a lack of consistency in the experimental methods used to evaluate PRAs based on the studies found in the literature; the dosage, water to cementitious ratio (w/cm), testing age, and mixture designs were variable. There remains a need for studies with both field and lab data to establish relationships between lab results and field performance to determine laboratory test method validity for PRAs.
This study experimentally investigates the effects of strontium nitrate (Sr(NO3)2) aqueous solution on hardened concrete composite as a surface hardening method. Density, void content, water sorptivity, and surface abrasion resistance of the concrete mixture treated by Sr(NO3)2 solution were measured under diverse curing and treatment scenarios. The results showed that 30% Sr(NO3)2 aqueous solution increases the density by 1.0% and 2.2% and also decreases the void content by 7.4% and 14.4% with the water-cement ratio (w/c) of 0.5 and 0.4, respectively. Water sorptivity of the treated hardened concrete was decreased by 26.4% and 34.0% from the lithium silicate and sodium silicate treatments, respectively. In addition, the Sr(NO3)2 treatment increases the surface abrasion by 45% from the control specimen and about 25-30% from the two silicate-based treatments. X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive spectrometer (EDS), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were conducted to investigate the micro-morphologies, microstructure, and elemental characteristics. The results illustrate that (1) microstructures of hydrated cement matrix are densified, (2) portlandite (CH) in the matrix decreases as time elapses, (3) multiple types of hydrated aluminosilicate minerals (i.e. zeolites) are formulated, and (4) more subsequent polymerization related to C-S-H/C-A-S-H occurs. Lastly, the densifying and strengthening mechanisms of the hydrated cement by the Sr(NO3)2 treatment process are presented and discussed.
In the present study, silane coupling agents (SCAs) were used as admixture in cement paste. The influence on the cement hydration in different stages as well as the mechanical properties were well investigated. Results demonstrated that silanes play a role of retardant in cement paste at the very early age, the proposed mechanism laid in the attraction force between intermediate hydrolysis products of silanes and cement hydrated products. The intermediate hydrolysis products can form gel-like barrier covering the cement hydrated products and were further proved by the designed pre-hydrolysis effect using calorimeter and Fourier transform infrared spectroscopy (FTIR). However, cement paste modified by silane would have denser structure compared to neat paste as a result of reaction between polycondensated silane and CH after 28 days of curing, leading lower porosity, higher hydration degree and better mechanical performance.
This paper investigated a novel and environmentally-friendly waterproof coating produced by the organic (i.e., styrene-acrylate copolymer) and inorganic (i.e., waterglass and ground granulated blast-furnace slag (GGBS)) compounds. The good cohesion of polymer and sodium silicate-activated GGBS can provide good mechanical properties, and this material also shows a better environmental benefit as no cement was used for coating. In this work, an appropriate proportion of polymer, waterglass and GGBS was given, and the effect of silicate modulus on the macro-performances and microstructures of the waterproof coating was studied. The optimal silicate modulus was 1.75, and the corresponding tensile strength and breaking elongation were 2.20 MPa and 90.48%, respectively. Furthermore, the waterproof coating also exhibited favorable tensile properties, flexibility or water impermeability after subjected to high temperature, alkali, water immersion, low temperature and high water pressure. This new waterproof coating exhibited the favorable tensile properties owing to (i) appropriate reaction rate, (ii) high degree of polymerization of C-S-H gel, (iii) high content of C-S-H gel and CaCO3 crystal, (iv) high reaction degree between emulsion and sodium silicate-activated GGBS, (v) nano-sized CaCO3 crystals and mechanical bond between the CaCO3 particles.
Surface treatment is an effective way to protect existing historic concrete architectures from decay. Silane-based products could be considered as efficient protective materials to improve the concrete durability. However, preservation damages like appearance alteration and expansion stress of surface coatings have been reported. In addition, the long-term effect of silane coating has not been fully studied. In order to evaluate the efficiency of surface treatments and select appropriate materials for protecting historic concrete, three commercial silane-based products were applied on concrete specimens. The properties of the surface treatments on concrete in terms of appearance alterations, contact angles, compressive strengths, penetration depths and pore size distributions were investigated. An accelerated aging test was carried out in order to obtain a comprehensive understanding of the long-term preservation performance of commercial coatings. The results suggested that the three commercial products all showed protective features with little appearance change. However, some materials may lead to the white salt crystallization on the concrete surface, and strong hydrophobicity can easily generate tension and finally accelerate the concrete decay.
Stone consolidation is almost always a very risky intervention. It is a non-reversible intervention and has serious harmful side effects. Due to these shortcomings, a decision to go for a consolidation action is always difficult to take and it is simple only when it is taken as a "last option" when replacement or full destruction are the unique alternatives at sight. Stone consolidation is needed because stones decay and loose cohesion in the exposed surfaces down to a certain depth. This conservation operation should take into account that type, extent and rate of decay largely depend on the intrinsic properties of the stone and on the extrinsic or environment factors. The combination of the intrinsic and extrinsic decay factors can give raise to multiple degradation forms that largely influence the decision on to consolidate and the options on the type of consolidant and on its application forms. The identification and characterisation of decay profiles is also a relevant step in stone conservation, namely when consolidation is concerned. The paper gives a brief introduction to a few topics on stone consolidation exemplifying with some current stone consolidation products. It quotes some cases of stone consolidation in recent Portuguese experience and presents some illustrations on the use of the microdrilling instrument in the detection of past consolidation actions.
This paper discusses synthesis and characterization of (i) rice husk based nanosilica, (ii) nanosilica carbon composite granules and (iii) phosphoric acid activated ash silica. These have been produced by burning husk in air, charring husk in hydrogen and activating husk silica with H3PO4 respectively. X-ray diffraction studies of these products reveal increasing peak width (amorphosity) with decreasing burning temperature. The activated rice husk silica transforms to crystalline product when burnt above 1000 ºC. The variation of surface area and pore volume with burning temperature show different behavior for air fired and hydrogen charred products. Activation energy associated with change in surface area for air fired and hydrogen charred samples have also been studied. Rate of variation in surface area with temperature indicate different trend. The validations of these products have been evaluated by decolorizing capacity of standard molasses and iodine solution. The adsorptive powers of these products have been found to be highest for activated silica and lowest for hydrogenated ash.
Consolidants are sols or solutions that are used to restore the strength of weathered stone. The liquids are drawn into the pores of stone by capillary suction, then they harden by gelation and/or drying. In this chapter, we discuss the requirements that such a material must fulfill, and demonstrate the effectiveness of consolidants based on alkoxysilanes and alkylalkoxysilanes.
Hybrid stone consolidants prepared from tetraethoxysilane (TEOS) and α,ω-hydroxyl-terminated polydimethylsiloxane (PDMS-OH) have been considered as one of the most promising approaches to improve the effectiveness of traditional alkoxysilane-based formulations. They have emerged as response to the negative reports commonly found in the literature: the resulting silica gel phase (SiO2) tends to develop fractures and fissures inside the stone as the gel shrinks during the drying stage. In this work, we employed SEM, solid-state 29Si NMR spectroscopy and compressive tests to characterize SiO2-PDMS hybrid gels. We report the morphological characteristics exhibited by gels prepared in vitro and in situ. It was found an appreciable reduction of gel fracture for hybrids prepared from 5% w/w of PDMS. As TEOS polycondenses, PDMS-OH is chemically incorporated into the gel matrix via Si-O-Si bonds. The inclusion of these elastic chains provides the necessary flexibility to resist the stress imposed by capillary pressure. Additionally, an important hydrophobic character is imparted to the stone.
The enhancement of long-term durability of marine structures is a matter of interest to many researchers. The study presented in this paper examines the effectiveness of a water reducer and chloride barrier surface impregnation of the concrete cover of reinforced concrete (RC) structures, exposed to a marine environment. Specific focuses is on how surface cracks created (1) before impregnation and (2) after impregnation, affect the effectiveness of the surface treatment. The experiments are conducted in an environment which is as close as possible to the real humid subtropical marine environment.
This paper reviews the main physical agents responsible for stone weathering. Particular emphasis is placed on the effects of wind and water. Aeolian erosion occurs in windy regions with sandy terrain, but in urban areas it is extremely rare and is often confused with other forms of deterioration. The problem of condensation on surfaces and in pores is extensively discussed, in relation to pore shape and size. Physical effects dominate in the smallest pores, and solution effects in the largest ones. The Kelvin law and thermodynamic considerations are used to explain condensation-evaporation cycles and adsorption isotherms. Capillary rise, increase in pressure in air pockets, freezing-thawing cycles and micro meteorological conditions favorable for the soaking of monuments are discussed. A final section is devoted to the dissolution of stones and the formation of black crusts as a consequence of the way the stone is washed out or simply wetted by meteoric water. The intensity of rainfall is important in activating or removing the dry pollutant deposits that form on monuments, especially during the dry periods characteristic of the Mediterranean climate. Condensation plays a minor role compared with rainwater. However, the porosity, geometrical shape and exposition of the stone are also important factors which can characterize different local balances and, consequently, the form of weathering.
The characterization of mortar properties can be accomplished by the use of thermal analysis. DTA can be used to identify various component materials and observe the reactions associated with controlled heating of the mortar. This method reveals thermal transformations, which include dehydration, dehydroxylation, oxidation and decomposition. In addition, crystalline transitions can be observed, which are exothermic or endothermic in nature. With TGA, thermogravimetric analysis, the mass of the sample is monitored (weight loss) as a function of temperature. Weight losses at reaction temperatures near 750°C, indicate loss of CO2 not from pure CaCO3, but from recarbonated lime.The dehydroxylated clays acted as a “pozzolan” which imparts early strength to the mortar. However, a more complex phenomenon occurs in crushed brick mortar, since compounds of hydraulic type occur at the brick matrix interface also. The DTA and TG-DTG analyses identify the dehydration of calcium alumino-silicate phases, giving clear evidence of a cementitious mortar rather than one of pure lime.In the present work a spectrum of thermal and XRD analysis results from ancient, Byzantine, post-Byzantine and later historic mortars from Greece is presented and the relevant information concerning the characterization of traditional mortars is validatedGenerally, the CO2 bound to carbonates and the water bound to hydraulic components (in weight loss%) discern two groups of mortars, the typical lime and the hydraulic, respectively. The specific classification of mortars into groups with characteristic transformations indicated by weight loss against temperature, enables discernment of: typical lime, cementitious, with crushed brick, with portlandite, with gypsum, with modern cement or of hot lime technology, mortars. Mineralogical, microstructural, mechanical and technological data could provide further evaluation criteria.
A review of sandstone weathering research, particularly in the past 100 years, reveals a trajectory of enquiry from early description and classification of features, to development of process-based explanations, to decreasing scales of investigation, and a disparity between understanding of process(es) and explanations of the genesis of sandstone weathering features. Developments in expositions on mesoscale weathering features on sandstone surfaces are discussed, demonstrating a range of approaches to weathering phenomena—field-based and laboratory-based—that must be linked to provide an explanation of observed features on a landform scale. Throughout the twentieth century, a thematic chronology highlights certain trends in research: description of forms, often in arid and semi-arid environments; single process–form models; an emphasis on experimentation; difficulties in measuring weathering rates; and a persistent emphasis on physical causes of breakdown. A new research agenda is promoted in which biodeterioration and chemical processes gain parity, a holistic approach based on conceptual modeling of weathering systems gains prominence, and scale issues are addressed more rigorously.
In this study, several aspects of the surface treatment of concrete with ethyl silicate were investigated. After the treatment, two different types of concrete (w/c 0.45 and 0.65) showed a dramatic decrease in capillary suction, chloride diffusion coefficient and carbonation depth. A penetration depth into the concrete of about 3–5 mm was assessed. Microstructural investigations showed evidence of a chemical interaction of the amorphous silica gel within the concrete forming calcium silica gel and a selective distribution of silica gel, which was mainly deposited in the small pores. In addition, the brightness and colour changes of the concrete surfaces after the treatment were analyzed quantitatively, finding limited differences, further decreasing over time. This last aspect is relevant for architectural applications of concrete, for example façades of residential buildings, where the architects may be interested in using the texture of concrete but are concerned by possible colour changes related to surface treatments application.
This paper reports the effects of nanosilica (nS) and silica fume (SF) on rheology, spread on flow table, compressive strength, water absorption, apparent porosity, unrestrained shrinkage and weight loss of mortars up to 28 days. Samples with nS (0–7 wt.%), SF (0–20 wt.%) and water/binder ratio (0.35–0.59), were investigated through factorial design experiments. Nanosilica with 7 wt.% showed a faster formation of structures during the rheological measurements. The structure formation influences more yield stress than plastic viscosity and the yield stress relates well with the spread on table. Compressive strength, water absorption and apparent porosity showed a lack of fit of second order of the model for the range interval studied. In addition, the variation of the unrestrained shrinkage and weight loss of mortars do not follow a linear regression model. The maximum unrestrained shrinkage increased 80% for nS mortars (7 days) and 54% (28 days) when compared to SF mortars in the same periods.
The aim of this study was to evaluate the effectiveness of inorganic compatible treatments, based on nanosized particles of calcium hydroxide (slaked lime) dispersed in alcoholic medium, as consolidants for limestones and painted surfaces affected by different kinds of decay. Both in situ and laboratory tests were carried out on carbonatic, low-porosity stones and on frescoes. The re-aggregating effects of the deposited phase were investigated by superficial area analyses (BET) and SEM-EDX; it was also possible to obtain an estimation of the depth of penetration of the product inside the porous matrix by adopting nanoparticles of magnesium hydroxide as markers. Changes in water-interaction properties were evaluated by water absorption capillarity measurements. The consolidating action of the applied material was also pointed out by observations performed in grazing light on treated areas of painted surfaces. All the results converged in individuating these nanometric particles of slaked lime as an innovative, completely compatible, and efficient material for the consolidation of artistic (lime-based wall paintings) and architectural (limestones) surfaces.
Water and milk of lime are usually adopted for conservative surfaces treatments, thanks to the conversion of lime into calcium carbonate. Calcium carbonate is, as a matter of fact, very compatible with many carbonatic lithotypes and architectonic surfaces, because its characteristics are very similar to those of the materials to be restored. But there are some limiting aspects to treatments effectiveness: the reduced penetration depth, the binder concentration and the incompleteness carbonatation process. In order to improve lime treatments, Ca(OH)2 particles with submicrometric dimensions (nanolimes) are recently introduced in Cultural Heritage conservation. Lime nanoparticles are typically produced by a chemical precipitation process in supersaturated aqueous solutions of the reactants (calcium chloride and sodium hydroxide). The aim of the present work is to analyse the nanolime carbonatation process in relation to some parameters, like time and the relative humidity conditions. For this scope, lime nanoparticles are therefore synthesised and characterised by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM–TEM), electron diffraction measurements (ED) and dark field images (DFI). The possibility to improve the nanolime carbonatation process is investigated using an alcoholic suspension and by adding a baking soda solution in order to disaggregate particles and to increase CO2 content in the suspension respectively. The efficiency of the nanolime carbonatation process is reported too.After that the lime nanoparticles are applied on natural lithotypes (“Estoril” and “Pietra Serena”) and some tests are performed in order to estimate the superficial consolidating and protective effect of the treatment: “Scotch Tape Test”, capillarity and imbibition tests. SEM analyses are performed to evaluate penetration depth and surface adhesion of nanolime treatments.
In this paper, we have performed a systematic characterization of sol and gel properties for particle-modified silica consolidants filled with titania (TiO2-PMC), alumina (Al2O3-PMC), and silica (SiO2-PMC) particles. Viscosity of the sol is not increased much by loading with particles, especially for TiO2-PMC and SiO2-PMC. Composites show a strong reduction of silicate network shrinkage. Also, the incorporation of oxide particles into the matrix increases the elastic modulus while decreasing the thermal expansion. In agreement with the improvement of bulk gel properties, we observed better performance of PMCs against unfilled silicate upon consolidation of Ohio Massilian sandstone. Notably, the sulfate crystallization test has less effect on PMC-treated than on silica-treated samples.
The alteration and weathering of stone is basically determined by natural and anthropogenic impacts influencing various physical, chemical and biological damage factors at the object site. Whether as direct or catalytically enhancing factor, the biodeterioration of stone is coupled with nearly all environmentally induced degradation processes: the presence of the one makes deterioration by the other all the more effective. The bioreceptivity of stone is described by its structure and chemical composition, while the intensity of the microbial contamination is determined by the referring climatic conditions and the anthropogenic euthrophication of the atmosphere. The microflora improves the nutrient and moisture-restricted growth conditions on building stones by the formation of surface-covering biofilms. Besides the aesthetical impairment caused by the coloured biopatina, the biofouling effect promotes even “abiotic” deterioration processes due to the alteration of the material structure as well as their thermo-hygric properties; in addition, mechanical pressure due to the shrinking and swelling of the colloidal biofilms might cause a further weakening of the mineral lattice. Acidolytic and oxido-reductive biocorrosion processes complete the biodeteriorating attack of stone acting as a preliminary precursor for the latter formation of detrimental crusts. Suitable and reliable methods for the detection of biodeterioration processes are available, but only the interdisciplinary diagnosis and evaluation of the entire decay process of stone allows the formulation of adaequate countermeasure strategies. In case the significance of biodeterioration impacts is proven, the possible effects of the microbial contamination on cleaning procedures, protective treatments as well as biocidal applications has to be considered. This paper will give a comprehensive overview to the biodeterioration of stone and stresses the practical relevance for the conservation.
The drying process of wet silica gels obtained from TEOS has been studied by means of FT-IR, DSC and specific surface area measurements. FT-IR spectroscopic results have not given any important information about the drying process of silica gels. However, DSC results have shown a dependence of the DSC peak area on drying time. Three different wateralkoxide ratio were studied, and the DSC peak area was higher when the wateralkoxide ratio increased. A more open xerogel structure was found for the high wateralkoxide ratio showing a high specific surface area and therefore lower drying times. For the silica gels obtained with 2001 and 1001wateralkoxide molar ratio, a complete drying time was observed for 25 and 28 days, respectively. As the drying time increases the gel structure becomes more closed, being necessary higher temperatures for removing water or alcohol from the gel.
Consolidants based on tetraethoxysilane (TEOS) have been widely used for the consolidation of decaying stone heritages. These products polymerize within the porous structure of the decaying stone, significantly increasing the cohesion of the material. However, TEOS-based consolidants suffer from practical drawbacks, such as crack formation of the gel during the drying phase due to the developed capillary force, which is typical for TEOS-based consolidants. We have prepared new consolidants TEOS-based consolidants containing flexible (3-glycidoxypropyl) trimethoxysilane (GPTMS) and silica nanoparticles in order to reduce capillary force development during gel drying, and have characterized them for the application of stone consolidants. Different sizes of silica nanoparticles were used, which were smaller than the pore size of the tested stone. The properties of the TEOS/GPTMS/nanoparticle composite solution were compared with those of the commercial products Wacker OH and Unil sandsteinfestiger OH 1:1. The gelation time was similar to that of commercial consolidants, and the TEOS/GPTMS/nanoparticle solution was stable over a period of up to six months. The contact angle of the surface increased with the addition of the nanoparticle, as well as with the addition the GPTMS, which is higher than that of commercial Wacker OH. The addition of a nanoparticle, as well as GPTMS having flexible segment, provided a crack-free material, while the gels obtained from the commercial consolidants exhibited cracking.
C3S has been hydrated for increasing time and stored for 2.5 years under normal atmosphere, the fresh and aged materials being characterized by X-ray diffraction and infrared spectroscopy. The carbonation occuring during storage gives rise to complete disappearance of CSH gel while portlandite remains in appreciable amount; the siliceous residue is an amorphous silica similar to common silica gels. The carbonates formed are vaterite and aragonite, the latter being relatively more important in samples with a low degree of hydration.RésuméOn a examiné par diffraction de rayons-X et spectroscopie infrarouge les produits d'hydratation du C3S obtenus à différentes échéances et les mêmes produits conservés durant 2 ans et demi dans les conditions du laboratoire. La carbonatation produite durant cette conservation entraîne une disparition complète du gel de CSH tandis que la portlandite reste en quantité appréciable; le résidu siliceux est une silice amorphe similaire aux gels de silice courants. Les carbonates produits sont la vatérite et l'aragonite, laquelle est relativement plus importante dans les échantillons caractérisés par un faible degré d'hydratation.
Nanotechnology seems to hold the key that allows construction and building materials to replicate the features of natural systems improved until perfection during millions of years. This paper reviews current knowledge about nanotechnology and nanomaterials used by the construction industry. It covers the nanoscale analysis of Portland cement hydration products, the use of nanoparticles to increase the strength and durability of cimentitious composites, the photocatalytic capacity of nanomaterials and also nanotoxicity risks.
We studied the synthesis and characterization of Ca(OH)2 colloidal particles and their application to the restoration of wall paintings. Submicrometer Ca(OH)2 crystalline particles have been obtained by mixing equal volumes of NaOH and CaCl2 aqueous solutions with different degrees of supersaturation (from 2 to 10) and in the temperature range 60−90 °C. The Ca(OH)2 particles are crystalline and have the appearance of hexagonal platelets with thicknesses of a few nanometers, as determined by scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, and atomic force microscopy techniques. The kinetic stability of dispersions of Ca(OH)2 particles in water and propan-1-ol has also been studied in view of their possible application in wall painting conservation. A successful example of this application to the restoration of Santi di Tito's wall paintings (16th century) in the Santa Maria del Fiore Cathedral in Florence is also reported.
The present study addresses the effect of different concentrations of Na2O on the structure of a composition of fresh C–S–H gels. The gels were synthesized from laboratory reagents, using calcium nitrate as the source of calcium and a sodium silicate solution for the silicon. A 10-M solution of NaOH was used to maintain a pH of over 13 throughout. The synthesized gels were exposed to different amounts of 8-M NaOH to determine their chemical stability and subsequently characterized with Fourier transform IR spectroscopy. The results showed that the addition of different concentrations of sodium leads to C–S–H gel modification even in the very short term.
Carbonation depth-profiles have been determined by thermogravimetric analysis and by gammadensitometry after accelerated carbonation tests on ordinary Portland cement (OPC) pastes and concretes. These methods support the idea that carbonation does not exhibit a sharp reaction front. From analytical modelling, this feature is explained by the fact that the kinetics of the chemical reactions become the rate-controlling processes, rather than the diffusion of CO2. Furthermore, conclusions are drawn as to the mechanism by which carbonation of Ca(OH)2 and C–S–H takes place. Carbonation gives rise to almost complete disappearance of C–S–H gel, while Ca(OH)2 remains in appreciable amount. This may be associated with the CaCO3 precipitation, forming a dense coating around partially reacted Ca(OH)2 crystals. The way in which CO2 is fixed in carbonated samples is studied. The results indicate that CO2 is chemically bound as CaCO3, which precipitates in various forms, namely: stable, metastable, and amorphous. It seems that the thermal stability of the produced CaCO3 is lower when the carbonation level is high. It is also shown that the poorly crystallized and thermally unstable forms of CaCO3 are preferentially associated with C–S–H carbonation.
We describe a model to determine the relative adsorption rates of aldehydes onto bare and aminopropylsilyl (APS) modified silica gels. The relative adsorption rates of three vapor-phase aldehydes (formaldehyde, acetaldehyde, and acrolein) and 1,3-butadiene were determined for two forms of silica gel and their APS counterparts. The aldehyde gases were mixed individually with nitrogen fill gas and then passed through samples of the granular silica gels or a non-adsorbing control material (usually NaCl) and into a multipass infrared (IR) gas cell. These injections, which were 100 ms in duration, were made through a solenoid valve that could be opened or closed in less than 1 ms. IR absorbance spectra were gathered at intervals of 5 ms with an ultra-rapid-scanning Fourier transform infrared (FT-IR) spectrometer. Differences in the IR absorbance at a particular wavenumber between injections through the adsorbent of interest and injections through NaCl were fit to a polynomial function. The derivative of this polynomial is proportional to the rate of adsorption. Using the ideal gas law and the Bouguer–Beer–Lambert law, a quantitative description of the rate of adsorption for each combination of adsorbate and adsorbent was calculated in units of nmol s−1 g−1.
The facades of the Bank of Greece historic building, mainly consisted of porous stone, gray marble and white pentelic marble, are subjected to an intensive air pollution attack in the center of Athens. A diagnostic study was carried out prior to the cleaning procedures for the weathering evaluation. Weathering appears mainly as black depositions, salt crusts, and oily depositions, due to the heavily polluted urban atmosphere from the nearby traffic. Previous improper cleaning treatment by water spray under high pressure caused detachment of grains and fissuring which were recognized as mechanical abrasion of the surfaces.In this study, a pilot investigation is performed with the intention of evaluating the most appropriate cleaning treatment. Therefore, several cleaning procedures were performed in the laboratory and in situ for the evaluation of methods and products applied on the facades. Both chemical and physical cleaning procedures were applied and they were chosen for their selective action: only water and sepiolite for solvent action, ammonium bicarbonate for exchange action, EDTA for the chemical chelating action and microblasting for physical action were used. In situ non-destructive evaluation was performed by Fiber Optics Microscopy in order to assess the counteractions of each cleaning method to the original surfaces. Digital Image Processing was also used to account for the efficiency of each cleaning method.
In a previous work, the mechanism by which salt crystals grow in porous stone masonries has been studied. It has been shown that the pressure exerted by sodium chloride (NaCl) crystals on the pore walls, when the crystals have entirely filled the coarse pores (10 μm), is the cause of disruption. In the present work, the microstructural parameters controlling the destructive effect of NaCl crystallization in porous stones, and specifically NaCl crystallization in the highly porous biocalcarenite of the historic masonries of the medieval city of Rhodes, which occurs favourable, are studied. Samples from both quarries and monuments have been examined. Porosimetric measurements were performed in order to calculate the NaCl crystallization pressures on the basis of the thermodynamics of crystal growth from a supersaturated solution in a porous material. Comparison of the calculated values of the crystallization pressure and the experimentally measured compressive strength permits one to assess the probability of rock destruction by salt crystallization. Energy balance analysis was performed in order to evaluate whether the successive crystallization of NaCl filling the smaller pores or the disruption of the pore walls is the most probable scenario for the given operating conditions. The release of free energy during the spontaneous crystallization from a supersaturated solution has been compared with the mechanical energy needed for the material's destruction, and the susceptibility of porous stone to salt decay is shown to be a function of the mechanical and structural parameters (compressive strength, modulus of compressibility and pore size distribution).
Traditional pozzolanic mortars such as those from Rhodes, Greece, or Hagia Sophia, Turkey, revealed the presence of a calcium-silicate-hydrate (C-S-H) binding phase. This phase, which is similar to that found in ordinary Portland cement (OPC), is produced under the pozzolanic reaction of slaked lime with fine reactive siliceous sources at temperatures <100 °C. The traditional siliceous sources were replaced by fumed silica or tetraethyl orthosilicate (TEOS). A microstructural analysis revealed an enhanced reaction rate but similar morphologies of the resultant C-S-H phases, confirming that the reaction-limiting factor is the dissolution of the siliceous sources.
In this study some results on the reactivity of silicatic consolidants employed for the conservation of valuable artistic and cultural porous materials are discussed. In particular, a colloidal suspension of silica made by particles with an average diameter of 10–15 nm, a sodium silicate and an ethyl silicate consolidant are studied. The chemical–physical characterization of xerogels achieved from the examined products were carried out determining the superficial area (BET method) and the average dimension of particles (SAXS) while the chemical structure of xerogels were investigated through NMR MAS spectroscopy of the 29Si nucleus. The investigation on reactivity between silica and stone support was executed by mixing consolidants with calcite and quartz powder to simplify as much as possible the system otherwise very complex. On silica produced by the three examined consolidants structural differences are revealed and these diversities can be responsible for the dissimilar reactivity of the silicatic systems towards the stone, in particular with regard to the carbonatic component.
Porous bioclastic limestones of small pore radii and sandy limestones of large pore radii were treated with silicon-based strengthening products, such as tetraethoxysilane, elastified silicic acid ethyl ester (PP), an aqueous colloidal dispersion of silica particles (LD), as well as an oligomeric siloxane water repellent (HP). Changes in color, water vapor permeability, porosity, pore size distribution and tensile strength were evaluated after treatment. Energy Dispersive X-ray Fluorescence (EDXRF) indicated that the products reached a depth from the surface of 30 mm and were evenly distributed inside the stone, except for LD, which accumulated up to the first 10 mm from the surface. Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) showed that linkages created between limestone and gels, due to the hydroxyl groups of the quartz and aluminosilicate minerals included in the limestones. PP and LD reduced the water vapor permeability coefficient to acceptable limits and induced the least chromatic variation. Mercury intrusion porosimetry (MIP) results indicated that the precipitation of the formed gel increased the specific surface area. The porosity and pore size decreased in the treated bioclastic limestones and in the KS and LD treated sandy limestones. In contrast, the PP and PP + HP treated sandy limestones showed an increase in porosity and average pore radius, as a result of the polymer cracking. When polymers were applied to the sandy limestones of large pore radii, the formed gels underwent cracking from drying shrinkage and the mechanical resistance of the stone was reduced. The gels when deposited in the small pore radii of bioclastic limestones behaved as thin films, thereby no cracking was induced by the consolidant from drying shrinkage. This study demonstrated that the performance of a consolidant is greatly dependent on the pore size of the stone. None of the above studied products can be recommended for consolidation of the sandy limestones, while the elastified silicic acid ethyl ester (PP) is only recommended for consolidating the bioclastic limestones.
This paper deals with two experimental methods to determine carbonation profiles in concrete. Gammadensimetry is a non-destructive test method able to measure the total penetrated CO2 and to monitor the carbonation process during laboratory accelerated tests. The second method is thermogravimetric analysis (TGA) supplemented with chemical analysis (CA): as TGA is performed on a small mortar sample not representative of the whole tested concrete, CA is needed to proportion the sample cement content, the sand content and to correct the TGA results becoming thus representative of the concrete mix. Consequently, TGA-CA gives accurate quantitative profiles in carbonated cementitious materials. Results are reported for an ordinary Portland cement paste, and three concrete mixes, containing siliceous or calcareous aggregates. The CO2 mass loss due to carbonation occurs from 530 to 950 °C, which overlaps the temperature range of the calcareous aggregate dissociation. To solve the problem, the origin of CaCO3 is carefully analyzed. Calcium carbonate ensuing from C–S–H carbonation dissociates in a lower temperature range than the more stable one ensuing from portlandite carbonation and from limestone, which enables C–S–H carbonation to be distinguished from calcareous aggregates. Therefore, TGA-CA allows the CaCO3 ensuing from C–S–H carbonation to be measured and to calculate the portlandite degraded by carbonation. Thus, the total calcium carbonates profiles can be deduced even when calcareous aggregates is present in the concrete mix.
Calcium leaching is a degradation process that consists in the progressive dissolution of the cement paste as a consequence of the migration of the calcium ions to the aggressive solution. Although it is a well known phenomenon, a way of reducing it has not been found yet. The aim of this work is to prove how the addition of small amounts of silica nanoparticles to the cement paste can induce such reduction. The experimental results obtained have shown that nanosilica increases the strength of the cement paste about a 30% in cured samples and more than a 100% in the asymptotically leached ones. At the level of the structure of the C–S–H gel, silica nanoparticles increase the average length of the silicate chains and reduce their polymerization as calcium dissolves. An important decrease of the degradation in terms of porosity and amount of calcium lost has also been observed.
The aim of this work is to study the recycling of tile wastes in the manufacture of blended cements. Cracked or broken ceramic bodies are not accepted as commercial products and, therefore, the unsold waste of the ceramic industry becomes an environment problem. The use of powdered roof tile in cement production, as pozzolanic addition, is reported. The wastes were classified as nonglazed, natural and black glazed tiles. The mineralogy of the powders was controlled by SEM-EDX microscopy, XRD analysis and FTIR spectroscopy. Particle size was checked by laser granulometry. Once the materials were fully characterized, pozzolanic lime consumption tests and Fratini tests were carried out. Different formulations of cement-tile blends were prepared by incorporation of up to 30% weight ratios of recycled waste. The compressive strength of the resulting specimens was measured. The evolution of hydration of the cement-tile blends was analyzed by XRD and FTIR techniques. Vibrational spectroscopy presented accurate evidence of pozzolanic activity. The results of the investigation confirmed the potential use of these waste materials to produce pozzolanic cement.
A novel sol-gel synthesis, in which a surfactant acts to make the pore size of the gel network more coarse and uniform, is shown to provide an effective alternative for the consolidation of stone. The new mesoporous silica avoids the main inconvenience of current commercial consolidants, which is their tendency to crack inside the pores of the stone. Since the cracking of xerogels is a well-known drawback of the sol-gel process, the synthesis presented here can be extended to other applications. Finally, preliminary studies of the effectiveness of the novel surfactant-templated sol in consolidating a typical biocalcareous stone are also discussed.
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Method for protecting and consolidating calcareous materials
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