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Use of Nondestructive Impedance Spectroscopy for the Assessment of Clay–Lime Reaction Kinetics: Influence of Clay Mineralogy, Lime Content, and Curing Conditions
Abstract
This study describes the nondestructive testing and evaluation of different clay–lime composites by real-time impedance spectroscopy (IS) monitoring of lime hydration and cementation mechanisms. The experimental investigations were carried out on two different clays, white clay (with predominantly kaolinite mineralogy) and brown clay (with predominantly montmorillonite mineralogy), to determine the influence of clay mineralogy on the fate of lime stabilization processes in different soils. Additionally, the effects of key influencing parameters such as lime content, curing period, and curing temperature were assessed. The time-dependent electrical impedance behavior of different clay–lime systems was determined in terms of bulk resistance and interfacial capacitance, obtained by equivalent circuit modeling of the impedance spectra. The variations in the electrical impedance properties showed a strong correlation with unconfined compressive strength (UCS) of different clay–lime composites. Further, the microstructural improvement of various clay–lime composites was determined with the aid of scanning electron microscopy, mercury intrusion porosimetry, and thermogravimetric analysis to get an auxiliary interpretation of the electrical impedance spectroscopy (EIS) results. The time-dependent variations of the soil impedance evidently manifested the continuous chemical and morphological evolution of the different clay–lime systems during the curing process at different thermal conditions by the formation and deposition of cementitious calcium-silicate-hydrates (C-S-H) and calcium-aluminate-silicate-hydrates (C-A-S-H) compounds. Overall, the nondestructive impedance spectroscopy technique has been proven effective in describing the microstructural changes and related mechanical improvement of lime-treated soils. Although the use of this technique seems to be inefficient for a field quality control assessment, the analysis of the electrical parameters calculated from the impedance spectra measured gives a comprehensive idea of the evolution in the chemically stabilized soil material.
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Granular lateritic soil is commonly used for road construction in humid tropical and subtropical regions. However, the high plastic clay content and poor particle distribution of some laterite materials make them unsuitable for bases and subbases. Lime treatment is a widely used method for improving problematic lateritic soil, and liquid ionic stabilizers are considered an environmentally friendly solution for reinforcing such soils. However, using only lime or only stabilizers may not be optimal. This study investigated the effect of treating granular lateritic soil with hydrated lime and a new liquid stabilizer, Zhonglu-2A (ZL-2A). A series of indoor tests, including compaction, California bearing ratio, and unconfined compressive strength tests, were conducted to evaluate the effects of hydrated lime content and stabilizer content on the mechanical properties, mineralogical composition, and microstructure of the soil. The results show that an increase in hydrated lime dosage increases the optimal moisture content and decreases the maximum dry density. The CBR of lime-stabilizer-treated laterite was at least 2–3 times higher than that of the only-lime-treated soil. The highest CBR was observed in samples treated with 0.2‰ ZL-2A stabilizer. The sample with 6% lime and 0.2‰ ZL-2A stabilizer exhibited the highest unconfined compressive strength, and a nearly linear increase was observed between the unconfined compressive strength and CBR. Further investigation of the stabilization mechanism using X-ray diffraction mineralogy analysis and scanning electron microscopy revealed that the inorganic substances of the ZL-2A stabilizer and the hydrated lime provided the basic conditions for the reaction and generated cementitious hydrates on the clay particles. The mixture of granular lateritic soil and hydrated lime was wrapped by the ZL-2A stabilizer, forming a complex spatial structure and improving the strength of the soil. To improve the bearing capacity of subgrades in actual subgrade engineering, a combination of a liquid ionic stabilizer and lime should be used to treat laterite.
The electrochemical parameters of cement-based materials with different water–cement ratios in carbon curing and water curing were measured with electrochemical impedance spectroscopy (EIS). The optimized circuit model and corresponding electrical parameters were obtained to illustrate the variation of the microstructure of cementitious materials after carbon capturing. The results show that, to a large extent, the semicircle diameter in the high frequency area gradually increased along with carbon curing and water curing. However, carbon curing showed a difference that the semicircle diameter in the high frequency appeared at the minimal value at 3 days, which was higher than that at 1 day and 7 days. This should be the result of the joint influence of water content and porosity in the cement matrix. It was also found that the mass increase rates of carbonation with water–cement ratios of 0.4, 0.5, and 0.6 were basically stable at 3.4%, 5.0%, and 5.5%, respectively. The electrochemical parameters ρct2 of cement mortar corresponding to carbon curing were around three times that of water curing specimens, mainly due to the reduction of soluble materials and refinement of connecting pores in the microstructure of cementitious materials. A quadratic function correlation between the mass increase rate and ρct2 in the carbonation process of cement mortar was built, which proved that EIS analysis could be applied to monitor the carbon capturing of cement-based materials, either for newly mixed concrete or for recycled concrete aggregates.
The impedance spectroscopy technique has been used to study the microstructure of the binder resulting from the alkaline activation of SiMn slag. Two alkaline activators were used: waterglass and NaOH. Three different concentrations were analysed for both activators: 3.0, 3.5 and 4.0% Na2O for NaOH; and 4.0, 4.5 and 5.0% Na2O for waterglass with a constant SiO2/Na2O ratio of 1.0. The time evolution of the microstructure has been followed up using the non-destructive technique of impedance spectroscopy. This technique has been proved to be effective describing the microstructural changes in alkali activated pastes, and also can help predicting the mechanical behavior of mortars. The use of the resistivity itself seems to be deficient, but the analysis of the electrical parameters calculated from the impedance spectra measured gives a complete idea of the evolution in the material.
This paper explores the stabilisation of dredged lakebed sediments with ordinary portland cement and fly ash to repurpose the sediment as road pavement construction material. Data are obtained from previous studies on sediments collected from Phayao Lake and Huai Mae Phong Reservoir in Phayao province, and Mae Sab Reservoir in Chiang Mai province in Thailand. Empirical correlations are established between strength and stiffness parameters of the chemically stabilised dredged sediments intended for transportation and geotechnical applications. The strength and stiffness parameters considered in this study include unconfined compressive strength, the California bearing ratio, and the resilient modulus. The influence of curing period on strength development is determined. New strength and stiffness correlations are proposed and presented to describe stabilised soils based on the extensive experimental data. Optimised sediment/cement/fly ash mixtures which proved to be most effective in generating appropriated material strengths for road construction are reported.
The carbonation of lime-treated soils that occurs during the short-term and long-term curing is not sufficiently explored in the domain of lime stabilization. The present study investigates the carbonation mechanism in lime-treated silty clay treated with two lime contents (4%, 8%) subjected to different curing periods (7, 90, 180, and 365 days). The cured samples were exposed to accelerated carbonation, and subsequent change in the unconfined compressive strength was compared with that of control samples tested under a nitrogen environment. The extent of carbonation was measured using phenolphthalein solution. X-ray diffraction technique and thermogravimetric analysis were used to analyze the reaction products resulted from carbonation. The morphology of carbonates and effects of carbonation on the pore structure were assessed using a scanning electron microscope and mercury intrusion porosimeter, respectively. Results show that carbonation has a deleterious effect on the performance of lime-treated clay. The strength of lime-treated soils upon carbonation decreased by 30% on average. The fabric structure of treated clay was found to vary with lime content and curing period, which determined the extent of carbonation. Decalcification of reaction products and cracking induced by the carbonation of residual lime contributed to the reduction in compressive strength of treated clay. The observed strength behavior of the carbonated samples is substantiated by quantifying the variation in pore structure characteristics.
PurposeThis research presents experimental results of dredged lakebed sediment-stabilised with ordinary Portland cement (OPC) and fly ash (FA) for use as pavement materials in road infrastructure. The work also proposed empirical correlations for the strength and stiffness parameters of chemically stabilised dredged sediments intended for pavement engineering.Materials and methodsThe dredged sediment was collected from the drop-off area around Phayao Lake in Thailand. The sediment’s optimal moisture content was determined by a Proctor compaction test. The OPC and FA content ranged from 3 to 10% and 5 to 20% per dry weight of sediment. The shear strength of treated sediments at different curing time was measured using the unconfined compression (UC) test.Results and discussionThe optimum FA content proved to be most effective in generating the highest material strengths and stiffnesses from the stabilised sediments, regardless of OPC contents and curing duration. A suitable replacement ratio of cement with fly ash was 15%. The results were compared with data on other types of chemically stabilised sediments available in literature. Correlations between engineering properties and design parameters such as UCS, E50, {\upvarepsilon }_{f}, and eot can be suggested based on the comprehensive experimental results.Conclusions
Using OPC and FA as admixes together provided the greatest improvement in the strength characteristic of dredged sediment. In addition, the study presented an empirical correlation between the strength and stiffness of adding fly ash on cement-stabilised lakebed sediment for using in geotechnical and pavement works.
Purpose
The process of removing sediments from the bottom of dams generates large amounts of dredged sediments, which are considered waste. The purpose of this research was to present the results of testing conducted on dredged sediment stabilized with ordinary Portland cement (OPC) and fly ash (FA) for reuse as pavement materials.
Materials and methods
The base sediment was high plasticity silt (MH) based on the Unified Soil Classification System (USCS). The experiments in this study consisted of unconfined compression (UC), California bearing ratio (CBR), and resilient modulus (Mr) tests on stabilized dredged sediment. A combination of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) was used to investigate the microstructures of the stabilized specimens. Finally, a simple comparative cost analysis between roads using conventional earthen materials and stabilized dredged sediment was performed.
Results and discussion
The results showed that the unconfined compressive strength (qu), CBR, and Mr improved the pavement materials from unsuitable to suitable, and a 10% FA content provided the optimal strength enhancement. The SEM images showed that the calcium silicate hydrate (CSH) product, which was formed by hydration and pozzolanic reactions, attached to the clay clusters and filled the pore spaces between clay particles, resulting in a denser sediment structure. The EDX analyses showed that the calcium weight proportion and the silica-aluminum ratio were important factors in improving the strength of the dredged sediment treated with OPC and FA. These EDX results agreed with the qu, CBR, and Mr results. For the studied situation, roads using stabilized sediment were 1.5 times more economical than roads using conventional earthen pavement materials.
Conclusions
Dredged sediments treated with OPC and FA can be sustainably reused as pavement materials based on the Department of Highways of Thailand standard, as well as the recommendations of Austroads (2017). Thus, for suitable sediments, reuse in road and pavement construction may be considered with appropriate treatment and conditioning.
The characterization of ultra-soft clayey soil exhibits extreme challenges due to low shear strength of such material. Hence, inspecting the non-destructive electrical impedance behavior of untreated and treated ultra-soft clayey soils gains more attention. Both shear strength and electrical impedance were measured experimentally for both untreated and treated ultra-soft clayey soils. The shear strength of untreated ultra-soft clayey soil reached 0.17 kPa for 10% bentonite content, while the shear strengths increased to 0.27 kPa and 6.7 kPa for 10% bentonite content treated with 2% lime and 10% polymer, respectively. The electrical impedance of the ultra-soft clayey soil has shown a significant decrease from 1.6 kΩ to 0.607 kΩ when the bentonite content increased from 2% to 10% at a frequency of 300 kHz. The 10% lime and 10% polymer treatments have decreased the electrical impedances of ultra-soft clayey soil with 10% bentonite from 0.607 kΩ to 0.12 kΩ and 0.176 kΩ, respectively, at a frequency of 300 kHz. A new mathematical model has been accordingly proposed to model the non-destructive electrical impedance-frequency relationship for both untreated and treated ultra-soft clayey soils. The new model has shown a good agreement with experimental data with coefficient of determination (R²) up to 0.99 and root mean square error (RMSE) of 0.007 kΩ.
Lime generally improves the performance of soils. However, some cases reported an adverse effect. To develop an understanding of the underlying mechanisms, a systematic study covering a wide range of plasticity and mineralogy of soils was carried out. Six different soil samples were reconstituted using two extreme types of soils, in other words, a montmorillonite rich expansive soil and a silica-rich non-expansive soil. The influence of lime stabilization on these soils was evaluated through determination of geotechnical properties such as liquid limit, plastic limit, swell, compressive strength, mineralogy, and microstructure. An optimum lime content beyond which the strength improvement decreased was found. This phenomenon is more prominently observed with silica-rich soils that form silica gel. As the silica gel is highly porous, when formed in large scale the strength gain from cementation is substantially countered by the strength loss from gel pores, giving rise to a visible reduction in overall strength. Additionally, the gel materials hold a large amount of water, leading to increased plasticity and swelling. Therefore, excessive lime treatment should be avoided for silica-rich soils. DOI: 10.1061/(ASCE)MT.1943-5533.0000431. (C) 2012 American Society of Civil Engineers.
The permeability (k) of lime- and cement-treated clayey soils was investigated in the laboratory by flexible-wall permeability tests and oedometer tests. Test results indicate that for the cement-treated soils (with up to 8% cement content by dry weight), the value of k is almost equal to that of untreated soils under identical void ratio (e) conditions, and the k value decreases significantly when the cement content is higher than 8%. For lime-treated soils, the threshold lime content is about 4%. Investigation of the soil microstructure using the mercury intrusion porosimetry (MIP) test and scanning electron microscope (SEM) imaging indicates that when the cementation products formed by the pozzolanic reaction fill mainly the intra-aggregate pores, the value of k is comparable for the treated and untreated samples. When the cementation products begin to fill the interaggregate pores, the value of k of the treated sample becomes smaller than that of the untreated soil sample under the identical e value condition. An indication that the cementation products have filled the interaggregate pores is the rapid increase in strength of the treated soil.
The stabilization of problematic fine-grained soils using lime as an admixture is a widely accepted practice, owing to its simplicity and cost-effectiveness. The optimal quantity of lime required for soil stabilization primarily depends upon the reactive nature of soil as well as the degree of improvement desired. The term ‘optimum lime content’ (OLC) defines the amount of lime required for satisfying the immediate/short-term soil-lime interaction, and still providing sufficient amount of free calcium and high residual pH necessary to initiate long-term pozzolanic reaction. Previous researchers proposed various empirical correlations and experimental methodologies for determining OLC, in terms of clay-size fraction and plasticity characteristics of virgin soil. However, the limiting lime content obtained using various conventional methods does not account for the most influencing inherent clay mineralogy of the soil; and hence, the results of these methodologies are observed to be quite disagreeing with each other. In view of these discrepancies, the present study attempts to validate the existing conventional methodologies for OLC determination at an elementary level, by comprehending the fundamental chemistry following soil-lime interactions. Based on the theoretical and experimental observations, it is quite evident that the accuracy of conventional tests is limited by combined influence of chemical and mineralogical properties of soils. Hence, it is proposed to develop a precise methodology to ascertain the required optimal lime dosage based on scientific criteria, by incorporating the influence of soil properties such as clay mineralogy, specific surface area, soil pH, cation exchange capacity, soil acidity, base saturation capacity, and buffer capacity.
A new electrochemical model has been carefully established to explain the carbonation behavior of cement mortar, and the model has been validated by the experimental results. In fact, it is shown by this study that the electrochemical impedance behavior of mortars varies in the process of carbonation. With the cement/sand ratio reduced, the carbonation rate reveals more remarkable. The carbonation process can be quantitatively accessed by a parameter, which can be obtained by means of the electrochemical impedance spectroscopy (EIS)-based electrochemical model. It has been found that the parameter is a function of carbonation depth and of carbonation time. Thereby, prediction of carbonation depth can be achieved.
One common concern limiting the proliferation of high-volume fly ash (HVFA) concrete mixtures is the significant delay in setting that is sometimes encountered in field concrete mixtures. While several methods to mitigate the delayed setting times of HVFA mixtures have been demonstrated, a related issue is the prediction of setting times in field mixtures, so that construction operations including finishing and curing can be anticipated and properly scheduled. This paper presents a feasibility study evaluating the employment of simple electrical measurements to predict the setting time of paste mixtures on which concurrent Vicat needle penetration testing was performed. Electrical, setting, and accompanying calorimetry tests are conducted at three different temperatures, each under quasi-isothermal conditions to minimize the confounding influence of temperature variation on the obtained results. Electrical resistance (or heat flow) measurements can be used to adequately predict a mixture’s initial setting time for a wide variety of binary and ternary powder blends, prepared at a constant water volume fraction. However, a simple parametric study in 100 % ordinary portland cement pastes in which water content (water-to-cement ratio) is varied indicates that the relation between resistance trends and subsequent setting times is strongly dependent on the water content, as is also the case for the thermal measurements. This suggests that employment of this approach for field mixtures may require pre-determination of the resistance-setting time relationship for each mixture of interest (e.g., calibration) or at least that the on-site water content of the concrete mixture be assessed and verified by a separate measurement.
This paper describes a study of the hydraulic reactions between metakaolin (MK) and air lime using Electrochemical Impedance Spectroscopy (EIS) and Nuclear Magnetic Resonance Spectroscopy (NMR). Tests were carried out at 20, 25 and 30°C on lime-MK pastes with 10:1 w/w ratio. Tests over 28 days allowed identification of relevant changes in the EIS signals and characterization of pastes using Thermal Analyses (TGA/DSC), Scanning Electron Microscopy (SEM), Mercury Intrusion Porosimetry (MIP) and uni-axial compressive tests. Tests over shorter periods of time (up to 42 hours) allowed more detailed studies of the hydraulic phases formed at the very beginning of the reactions.
Results of thermal analyses demonstrate formation of hydraulic compounds such as CSH, C4AH13 and C3ASH6 and show their evolution over the time. MIP analysis demonstrate changes in pore size distribution related to the formation and trasformation of hydraulic phases. Changes of impedance response with time are shown to be associated with reaction kinetics. Changes in the NMR signal within the firsts 42 hours reaction are shown to be associated to the dissolution of calcium hydroxide in the pore solution. Overall, this paper demonstrates the importance of NMR in the study of hydraulic reactions in lime based materials and the ability of EIS to detect the formation of hydraulic compounds and the end of the calcium hydroxide dissolution process.
This paper describes a test procedure for determining the total surface area of fine-grained soils using the Ethylene Glycol Monoethyl Ether (EGME). The test involves saturating a soil sample with EGME and then removing the excess EGME in a vacuum desiccator, until the EGME forms a monomolecular layer on the soil surface. The results of the test are expressed as Specific Surface Area (SSA), which describes the surface area/unit mass of dry soil with units of m2/g. Test results are presented demonstrating the effect of various test parameters on the results. Results for a number of different fine-grained soils are presented. A detailed recommended test procedure is given. The proposed method uses simple and inexpensive laboratory equipment, is relatively simple to perform, and allows for rapid determination of SSA.
Computer simulation of impedance spectroscopy (IS) of hydrating cement paste, using a three-dimensional, four-phase model, is described. Two puzzling features of experimental IS results, the possible offset resistance in the Nyquist plot and the sharp decrease in normalized conductivity within the first 50 h of reaction, have been studied using the computer simulation model. Insight is provided into these features using the ability of the model to compare quantitatively microstructure and properties. It is concluded that the offset resistance is an experimental artefact, and does not directly relate to microstructure. The drop in conductivity during the first 50 h is shown to be a consequence of a gradual shift from parallel-dominated to series-dominated behaviour of the electrical conductivity, as microstructural modifications take place during hydration, causing the capillary pore structure to become more tortuous. This tortuousity can also explain the high-frequency impedance behaviour in terms of a two-arc response.
A non-nuclear, non-invasive instrument capable of measuring density and moisture content of soil using electromagnetic impedance spectroscopy (EIS) is currently being developed. During the development of the empirical soil model, it was found that the model was sensitive to the specific surface area of the material being measured. With the material's specific surface area being accounted for, in six test compactions a 119% increase in accuracy was seen by the soil density gauge's (SDG) wet density calculation when compared to the Nuclear Density Gauge's wet density calculation.
With the advent of modern microstructural testing techniques and microstructure based constitutive models the microstructural
characterisation of soils is gaining prominence. This paper reviews the history of microstructure investigation in unsaturated
soils and discusses the engineering significance of this research to date. After a brief overview of the main microstructural
techniques, the paper focuses on the evaluation of the current state of use and the development of two widely used techniques
to study the microstructure of partially saturated soils, namely mercury intrusion porosimetry and the environmental scanning
electron microscopy. The details of these techniques, their advantages and limitations, are first covered, followed by the
presentation of selected test results. These results highlight the use of these techniques for understanding different hydro-mechanical
behavioural features observed at macroscopic scale. Specifically, the paper shows the use of these techniques to explore the
fundamental properties of water retention characteristics, water permeability, and micro and macrostructural interactions
along different hydro-mechanical paths.
Electrode effects on impedance spectra of cement pastes were investigated by two-, three-, and four-point measurements without a potentiostat over the frequency range 0.01 Hz–10 MHz. Electrode immittance effects arising from highly resistive/capacitive contacts cannot be fully corrected by nulling procedures. Two-point measurements are much more susceptible to such effects than three- or four-point measurements. The three- and four-point results on pastes suggest that there is negligible high-frequency offset resistance, and that bulk paste arcs are not significantly depressed below the real axis in Nyquist plots. The important impedance-derived equivalent circuit parameters are bulk resistance and capacitance; offset resistance and arc depression angle may not be physically meaningful parameters. Whereas all electrode configurations give reliable values of bulk paste resistance, only the three-point configuration provides the total paste/electrode dual arc spectrum involving a single electrode. Multielectrode (three- or four-point) measurements may be necessary to establish the true bulk paste dielectric constant.
Carbonation is an inevitable reaction during the construction and curing stages of lime-stabilized earthworks. Both bench-scale and field studies on lime stabilization recognize carbonation as a deleterious reaction due to the consumption of lime, which otherwise participates in pozzolanic reactions. Besides lime paucity, exposure of stabilized clays to carbon dioxide initiates the carbonation of cementitious phases. The stability of these phases is compromised and affects the cohesion among soil aggregates and the overall shear strength of stabilized clays. The mechanism of carbonation has been extensively investigated in the context of cement and concrete. However, limited efforts have been made to understand a similar phenomenon in lime- or cement-treated soils. Given this, a novel attempt is made to comprehend the carbonation reaction in lime-stabilized clays concerning the primary sources, fundamental mechanisms, significant factors, and deleterious effects. The historical developments in carbonation of lime-treated soils, microanalytical characterization, state-of-the-art, and prospects of future research opportunities in this field are also emphasized.
Due to the growing expansion of cities and industries, housing and infrastructure works are essential to meet the demands of development in all countries. However, the increasing concern for environmental and sustainability aspects requires not only the search for alternative materials but also the search for techniques for characterizing civil construction materials that are more economical, less aggressive to the environment, and meet the technical requirements of construction. In this sense, electrical impedance measurements can provide information about the microstructure of the cementitious composite and, consequently, offer additional details about its physical and mechanical properties. This article sought to investigate the influence of the dimensions of the specimens and the electrical contacts necessary to obtain the electrical impedance. Mortars of different sizes were molded, and electrodes were made with different amounts of electrical contacts. The experimental results showed a dependence on the behavior of the impedance module and the phase concerning the physical dimensions of the specimens and the number of electrical contacts. The results of this article can be helpful in the characterization and interpretation of electrical impedance measurements of cementitious composites.
Deep soil mixing is a ground improvement method that enhances the characteristics of soft soils by mechanically mixing the soil with cementitious binders such as cement and fly ash (FA). The objective of this paper is to investigation the post-treatment mechanical properties and shrinkage cracking characteristics of soft Bangkok clays treated with ordinary Portland cement (OPC) and FA. Unconfined compressive strength, modulus of elasticity, and shrinkage cracking after 7 and 28 days of mixture curing were measured. The effects of wet/dry cycling on the durability of mixtures were examined. Microstructures of treated soft clays were examined using scanning electron microscopy with energy dispersive x-ray analysis (SEM/EDX) techniques. Test results showed that strength and stiffness improvements of stabilised soft clays increased with OPC content but decreased with FA content, while the extent of sample shrinkage decreased with increasing FA content. Based on these results, we propose the preliminary guideline of applying 15% replacement of OPC with FA to obtain the optimal mixture ratios that allows FA to act as a shrinkage-reducing agent for deep soil mixing purposes. By adding OPC and 15% FA at a binder-per-water ratio (B/w c) of 0.4, the stabilised soft clay satisfied both strength and shrinkage cracking criteria for deep soil mixing purposes. SEM/EDX analyses further supported these experiment results. In addition, correlations between the mechanical properties and the chemical compositions of stabilised soft clay were derived and presented.
Sustainable rammed earth (RE) material was formulated using pulp mill fly ash (PFA), an industrial waste product, as an alternative low carbon cementing material. The alkali-silicate activation of PFA in RE showed substantial strength improvement. However, combinations of calcium bentonite clay and raw PFA without activation imparted significantly better frost resilience properties. The recommended RE formulation with 5% PFA, 5% Portland cement and 15% bentonite showed 3.56 MPa compressive strength at 28 days curing and retained 92% strength after 12 freeze–thaw cycles. Further, the leachate analysis revealed that the cementitious reaction products immobilized toxic elements within the stabilized RE matrix.
This study investigated the performance of alkali-activated, cement-based controlled low-strength materials (CLSMs). The CLSM was produced by mixing fly ash, steel slag, sodium hydroxide, and water with bottom ash (BA) aggregate. Properties of fresh and hardened composites were measured, and tests were conducted to determine their microstructure characteristics. Highlighted properties including slump flow, bleeding, unit weight, unconfined compressive strength, and resilience modulus were reported. The results indicated that the inclusion of 10%-30% slag resulted in a stronger CLSM with a higher Ca/Si ratio in the cementitious matrix of its microstructure. Higher slag content in the CLSM also shortened setting time and led to a lower bleeding rate. A mixture containing slag up to 20% of fly ash was recommended for pavement applications. Finally, the economic and environmental impacts were also preliminarily studied.
Expansive soil is the most predominant geologic hazard which shows a large amount of shrinkage and swelling with
changes in their moisture content. This study investigates the macro-mechanical and micro-structural behaviours of dredged
natural expansive clay from coal mining treated with ordinary Portland cement or hydrated lime addition. The stabilised
expansive soil aims for possible reuse as pavement materials. Mechanical testing determined geotechnical engineering
properties, including free swelling potential, California bearing ratio, unconfined compressive strength, resilient modulus, and
shear wave velocity. The microstructures of treated soils are observed by scanning electron microscopy, x-ray diffraction, and
energy dispersive spectroscopy to understand the behaviour of the expansive clay blended with cement and lime. Test results
confirmed that cement and lime are effective agents for improving the swelling behaviour and other engineering properties of
natural expansive clay. In general, chemical treatments reduce the swelling and increase the strength and modulus of expansive
clay, subjected to chemical content and curing time. Scanning electron microscopy analysis can observe the increase in
formation of particle clusters with curing period, and x-ray diffraction patterns display hydration and pozzolanic products from
chemical particles. The correlations of mechanical properties and microstructures for chemical stabilised expansive clay are
recommended.
Dredged river or lake sediments are ideal for repurposing in engineering applications. Unfortunately, the low strength of these materials makes it necessary to amend them with chemical stabilisers before utilisation. This research attempted to improve the shrinkage and swelling potentials of cement-stabilised dredged sediments by addition of fly ash (FA). Material mixtures were created from combinations of sedimentary soil from Phayao Lake in Northern Thailand, Ordinary Portland cement (OPC) type I, and FA. Mechanical tests determined that the unconfined compressive strength of cement-stabilised sediments with 7% and 10% OPC increased with the addition of 25% FA. Digital imaging technology and free swell tests determined that the 3D volumetric shrinkage and swelling of OPC-stabilised sediment reduced by 40% and 2.8%, respectively, when 20% FA was added. With this additional OPC and FA, the treated sediment satisfied both strength and durability criteria for reuse as road material as set by the Thailand Department of Highways.
In this study, electrical impedance spectroscopy (EIS) is applied to investigate the effect of alkali dosage on the microstructural evolution of the alkali-activated slag (AAS) system during the curing process. Pore solution chemistry and pore structure of the paste samples were also determined to get auxiliary interpretation of the EIS results. It is shown by equivalent circuit analysis that the resistance attributed to continuous (R1) and discontinuous pores (R2) increases with curing age due to pore structure development. The value of R1 is more affected by pore solution chemistry while the value of R2 is mainly affected by pore structure. With the increase of alkali dosage, the value of R1 decreases while R2 gradually increases. The exponent n of the constant phase element (CPE), which relates to the capillary pores (n1), decreases with the increase of alkali dosage while the exponent relating to gel pores (n2) is independent of the alkali dosage of AAS paste. The bulk conductivity of AAS paste obtained from the bulk resistance gradually increases with the alkali dosage, partially because of the enhanced conductivity of pore solution. The improvement of microstructure at early age is mainly attributed to the decreased porosity, which is more affected by the pore connectivity with the increase of curing age. These results confirm that EIS is an effective technique to determine the hydration properties and pore structure features of AAS paste.
Deep cement mixing (DCM) columns are used to support embankments built on soft clay, but these columns have limitations in terms of their engineering properties such as low column strength and low column permeability. Therefore, the use of cement fly ash gravel (CFG) instead of DCM columns has been introduced. The objective of this paper is to present an experimental investigation of the properties of CFG. Gravels with sizes of 4.76 to 12.70 mm were mixed with ordinary Portland cement (OPC) Type 1 and fly ash (FA) to create CFG materials. OPC was partially replaced by FA at levels of 0 to 25% by weight of OPC. The engineering properties of the CFG materials were studied through the porosity, compressive strength, flexural strength, modulus of elasticity, and permeability coefficient after curing for 28, 50, and 90 days. The microstructures of the OPC-FA pastes were examined by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Finally, preliminary guidelines for selecting a suitable porosity of CFG columns were proposed. Test results show that the porosity of the CFG materials ranged from 25.8 to 31.1% and affected the strength and permeability. The strength of CFG was 6 to 13 times greater than that of a DCM column, and the permeability of CFG was 9 to 17 mm/s, which was much higher than that of a DCM column, indicating that the use of a CFG column-supported embankment built on soft clay was more effective than the use of a DCM column in terms of the column bearing capacity and acceleration of consolidation settlement. The replacement of 15% of the OPC with FA exhibited the highest strength and smallest porosity because it provided the greatest amount of calcium silicate hydrate. Preliminary guidelines show that small-sized gravel with medium porosity is proper for generating column-supported embankments on soft clay to carry medium loads and to accelerate the consolidation process.
Carbonation of cementitious materials can greatly shorten the length of lifetime for steel-reinforced concrete structures constructed in atmospheric environment, due to steel corrosion issue. Notwithstanding the physical and chemical reactions of carbonation in cementitious materials are well known, the carbonation process is still not comprehensively understood since it is affected by many complicated factors including curing treatment, material composition and environmental exposure. On the other hand, it is generally recognized that a deeper scientific understanding of carbonation process relies on the development of advanced techniques for material characterization. From current literatures on cementitious carbonation, the present article shows the state-of-the-art research findings on (1) fundamental of carbonation reaction, (2) factors of influencing and modelling the carbonation process, and (3) development of techniques for carbonation characterization. This review also provides the future research perspectives to enhance the understanding of concrete carbonation and to improve the application of techniques for carbonation characterization.
Lime is often used to increase strength, reduce compressibility, and reduce moisture sensitivity in soils with moderate to high plasticity. In the case of road construction, state agencies typically have specifications that prevent lime stabilization of subgrade soils during low temperatures (e.g., <4°C). Part of the rationale for these specifications is that lower curing temperatures reduce the kinetics of pozzolanic reactions, which in turn may prevent the design strength from being reached. The objective of this research was to investigate the effect of temperature and time on reactivity and strength for lime-soil mixtures. The pH, electrical conductivity, and unconfined compressive strength of soils mixed with varying lime contents were respectively measured at various curing temperatures at multiple curing periods. Results indicate that increased curing duration leads to decreases in pore fluid pH and conductivity. However, this reduction in pH is less at temperatures below 10°C, which indicates lower levels of reactivity. Increased lime is recommended for situations in which stabilization will proceed at cooler temperatures. Unconfined compressive strength does not significantly increase with curing duration until after 7 days, after which the effect of pozzolanic reactions is evident. The trend of increasing unconfined compressive strength with increasing temperature was observed for both short-and long-term curing durations. The 7-day cured sample strengths at 2°C increased by 10% when allowed to cure for 56 days, while the samples cured at 21°C increased by 100% with the same curing duration. Exposure to either freeze-thaw cycles or low curing temperatures (2°C) resulted in significant reductions in strength gain for a given curing duration. However, once the freeze-thaw cycles or temperature reduction was removed, strength gain resumed at approximately the same rate. Overall, these results suggest that current specifications may be modified to allow lime stabilization to proceed in lower temperatures, if a corresponding increase in curing time and/or thermal protection is provided.
A new type of material, magnesium oxysulfate cement (MOSC), has attracted widespread attention as an environmentally friendly and low-energy inorganic green cementitious material due to its outstanding performance. In this study, electrochemical impedance spec-troscopy (EIS) and in situ X-ray diffraction (XRD) were used to characterize the hydration behavior and process of MOSC. EIS was also used to investigate the effect of fly ash (FA) on the hydration behavior of MOSC. Mercury intrusion porosimetry (MIP), backscattered scanning electron microscopy (BSE), and scanning electron microscopy (SEM) were used to study the evolution of the pore structure and micro-morphology of MOSC incorporated with FA. The results show that the resistance values (R 1) in the equivalent circuit for MOSC increase with increasing curing time. The incorporation of FA can affect the resistance values for each element in the equivalent circuit. In the early stages of hydration (1 day and 2 days), high-volume FA can reduce the degree of hydration of MOSC paste. At the later stages of hydration, the resistance values (R 1) increase with increasing FA content. The MIP, BSE, and SEM results also show that the porosity of MOSC decreases with increasing FA content; the incorporation of FA can significantly improve the morphology of MOSC, resulting in a denser microstructure. This study shows that the electrochemical impedance spectroscopy is a powerful technique to investigate the hydration behavior and process of MOSC, and the results also indicate that FA is a good mineral admixture used as a partial substitute for MOSC cementitious materials.
Phayao Lake, the largest lake in the north of Thailand, supplies water for consumption and irrigation in the region. Currently, the lake is faced with serious problems as it is becoming shallow with a consequent decrease in the volume of water. Every year the local government invests a lot of resources to dredge and pump the lake bed of sediments. However, it is difficult to find suitable landfill areas to dump such large quantities of sedimentary soil. The purpose of this study was to improve the engineering properties of sedimentary soil using Portland cement for possible use in road construction. The sedimentary soils were mixed with cement in a 3–10% proportion by weight. The strength and durability of the improved soil were examined using unconfined compression and durability tests, respectively. A long-term strength improvement was observed and well-fitted to a power function. Soil−cement losses due to multiple wet−dry cycles were examined by means of durability tests. Finally, suitable cement percentages for sediment improvement are suggested to achieve the requirements for road base and subbase materials.
The quantification of the kinetics of short-term clay–lime interactions is a key step for optimizing the parameters during lime stabilization of fine-grained soils, and also for predicting the long-term performance of lime treated soil matrix. The existing scientific literatures often believed that monitoring of consistency limits as well as compaction characteristics of lime treated soils yield significant amount of information regarding their physico-mechanical behaviour. However, apparently limited extent of works has been carried out to assess the role of clay mineralogy and pore fluid chemistry on inherent variations in plasticity and compaction characteristics. Further, no definite single conclusion could be drawn from the previous studies conducted to comprehend the plausible mechanisms of stabilization occurring in the lime treated soils during short-term and long-term interaction periods.In order to enhance the current understanding, this study primarily focused on the critical evaluation of plasticity properties and compaction characteristics variations of lime treated soils with respect to change in pore fluid chemistry (such as pH and concentration of lime). The study employed soils with quite diverse physico-chemical and mineralogical compositions so as to highlight the role played by the clay mineralogy in governing the extent of short-term improvement that can be mobilized by lime treatment. Based on the significant observations gathered from experimental works, attempts have been made to elucidate the possible short-term mechanisms of lime stabilization which also contribute to long-term strength and durability of lime treated soil.
The recent research infers that the detailed characterization of lime-treated soils using analytical techniques enables better understanding of the complex soil–lime interaction mechanisms as well as the pivotal factors influencing the efficacy of lime treatment. In view of this, the present study focuses on evaluating the effects of lime treatment on the strength properties of sodium bentonite clay in terms of the variations in thermal characteristics derived by employing analytical thermogravimetric analysis. This technique is effectively used to monitor the consumption of free lime and evolution of new cementitious hydration products (viz., calcium silicate hydrate and calcium aluminate hydrate), as well as detrimental lime carbonation phenomenon occurring in the sodium bentonite-lime composite during short-term curing. Based on the comparative evaluation of untreated and lime-treated sodium bentonite, variations in the weight loss corresponding to thermal decomposition of different chemical phases are estimated. The additional inferences from X-ray diffraction and Fourier transform infrared spectroscopy analyses substantiated the interpretations of thermogravimetric results regarding the lime stabilization mechanisms and consequent strength evolution in sodium bentonite-lime composites. Thus, the present study demonstrates that the comprehensive analysis of thermogravimetric results enables reliable interpretation of the soil–lime interaction mechanisms and the evolution of strength during curing.
Premature failures in chemically stabilized expansive soils cost millions of dollars in maintenance and repair. One reason for these failures is the inability of existing stabilization design guidelines to take into account the complex interactions between the clay minerals and the stabilizers. It is vital to understand these complex interactions, as they are responsible for the improved strength and reduction of swelling/shrinking in these soils, which in turn affects the overall health of the infrastructure. This research study examined the longevity of chemically stabilized expansive soils subjected to wetting/drying conditions, with a major focus on clay mineralogy. Eight different natural soils with varying clay mineralogy were subjected towetting/drying durability studies after theywere stabilizedwith chemical additives including quicklime and cement. Performance indicators such as volumetric strain and unconfined compressive strength trends were monitored at regular intervals during the wetting/drying process. It was observed that clayey soils dominant in the mineral montmorillonite were susceptible to premature failures. It was also noted that soils dominant in other clay minerals exhibited early failures at lower additive contents. For the first time, an attempt was made to address the field implications of the laboratory studies by developing a correlation that predicts service life in the field based on clay mineralogy and stabilizer dosage.
The fundamental behaviour of fine-grained geomaterials compacted over a range of moisture content is
strongly influenced by the resulting porosity and pore size distribution (PSD) characteristics. The majority
of pertinent studies have employed mercury intrusion porosimetry (MIP) for determining these properties.
Since the PSD analysis using MIP technique demands moisture free specimen, it is necessary to select an
appropriate sample drying technique that minimises the alteration of soil fabric during sample preparation.
In view of this, the present study evaluated the influence of various drying techniques, such as oven-drying,
solvent-replacement and freeze-drying, up on the soil fabric in terms of its PSD characteristics. Further,
the study investigated the role of placement moisture content on the modifications of soil fabric when
soil specimens are compacted over a range of compaction states, using scanning electron microscopy.
Based on the obtained results, it is demonstrated that the sample drying using lyophilisation technique
is efficacious.
Based on three different kinds of conductive paths in microstructure of soil and theory of electrochemical impedance spectroscopy (EIS), an integrated equivalent circuit model and impedance formula for soils were proposed, which contain 6 meaningful resistance and reactance parameters. Considering the conductive properties of soils and dispersion effects, mathematical equations for impedance under various circuit models were deduced and studied. The mathematical expression presents two semicircles for theoretical EIS Nyquist spectrum, in which the center of one semicircle is degraded to simply the equivalent model. Based on the measured parameters of EIS Nyquist spectrum, meaningful soil parameters can easily be determined. Additionally, EIS was used to investigate the soil properties with different water contents along with the mathematical relationships and mechanism between the physical parameters and water content. Magnitude of the impedance decreases with the increase of testing frequency and water content for Bode graphs. The proposed model would help us to better understand the soil microstructure and properties and offer more reasonable explanations for EIS spectra. © 2015, Central South University Press and Springer-Verlag Berlin Heidelberg.
The microstructures of cement pastes at the 5 to 100 mu m level are conveniently studied by electron probe microanalysis. In a recent study, X-ray images of a 23-year old portland cement paste showed that the shapes of the original, largely polymineralic cement grains, and also those of the clinker phases within them, are largely preserved in the hydrated material, and gave much information on both the compositions of the hydrated phases and their distributions in space. The results also gave some indications of the hydration mechanism.
Quantitative phase analysis of a number of multicomponent standard and natural mineral mixtures has been done using an adaptation of the Rietveld method. Quantitative information was extracted from refined individual scale factors and unit-cell volumes (derived from refined unit-cell parameters), obtained with a Rietveld refinement program modified to analyze up to ten phases. The quantitative results for standard mixtures were within 2.5% (absolute) of the true values, with the exception of the hematite, ilmenite, and magnetite mixtures. Quantitative mineralogical analysis by the Rietveld method has several significant advantages over conventional methods of quantitative analysis. The method should find a wide application in geology, including in modal analysis and compositional determinations of individual mineral components using unit-cell parameter systematics. -from Authors
Conflicting recommendations and opinions can be found in literature concerning the effects of a delayed compaction of lime-stabilized soils. This study was carried out to evaluate such effects on a clayey soil (CH) with 5% of quicklime and hydrated lime. One-dimensional consolidation and hydraulic conductivity tests were carried out on samples compacted soon after lime addition and after 48 h. Analysis of results, helped by scanning electron microscopy and mercury intrusion porosimetry, shows that, for the tested soil, delayed compaction causes a reduction of the dry unit weight up to 11% with hydrated lime and to 18% with quicklime and a greater compressibility of the mixtures at high pressures (at 800 kPa the compression index of samples compacted with delay is doubled relative to that of the immediately compacted ones). However, pozzolanic reaction was found to progress with curing time, even in the case of delayed compaction. The hydraulic conductivity is not significantly modified by a delayed compaction; it is strongly affected by the wetting conditions of curing in the case of hydrated lime. In general, a prompt compaction is always recommendable after addition of hydrated lime whereas the use of quicklime mitigates the influence of a delayed compaction.
The relations among soil structure, soil mechanical impedance, and moisture retention and movement were investigated on undisturbed soil cores from soil horizons exhibiting six distinct kinds of soil structure (prismatic, columnar, blocky, granular, platy, massive) over a broad range of soil texture. Mechanical impedance was characterized by measurements of bulk density and soil strength. Moisture retention and movement were characterized by measurements of -atm moisture content and saturated hydraulic conductivity. The columnar structures from Solonetzic soils were singled out as having a higher mechanical impedance and lower hydraulic conductivity than the other structures, most of which were sampled from Chernozemic soils. Total porosity (P) and bulk density (Db) were highly correlated; however, the regression coefficient for P vs. Db for columnar structures was significantly higher than that found for the other five structural types. Regression equations predicted that the hydraulic conductivity of platy structures could be zero for samples having as much as 15% air-filled pore space at -atm suction as compared with 6–8% for the other structures.
Mineralogical analysis of Devonian Red Marl using XRD, TEM, SEM and EDAX showed that it consisted of illite, quartz, and feldspar with minor amounts of chlorite and hematite. Physico-chemical changes in the soil minerals on reaction with lime (calcium hydroxide) from one day up to two years were investigated by these techniques to gain information on the soil-lime reaction mechanism. Significant reaction of the soil minerals and lime was found to occur only at elevated temperatures (50–75°C) in a moist environment. At these temperatures, formation, growth and development of fibrous and foil-like cementitious material was observed. XRD analysis provided no strong evidence for the formation of new phases. TEM analysis and EDAX, however, showed that the newly-formed fibrous and foil-like material consisted of an amorphous calcium silicate aluminate hydrate gel, similar to the gels formed during hydrothermal treatment of lime-silica, but with lower calcium to silicon ratios than previously reported for such gels. The morphological development of the gel suggested that it formed as a result of the progressive breakdown of the clay component in the soil by reaction with the calcium ions from the lime.
Impedance spectroscopy (I.S.) measurements were carried out on ordinary Portland cement paste, cured in 100% relative humidity environment, at different temperatures. The results collected during 28 d show that the electrical conductivity decreases to an almost constant value. The higher the curing temperature the shorter is the time necessary to obtain the quasi-steady-state conditions. A thermally activated conduction mechanism in cement paste was observed. The possibility of using I.S. (a non-destructive and in-situ technique) to follow the evolution of the cement paste hydration process was validated by traditional techniques (X-ray diffraction and thermogravimetry). Very good agreement was obtained.
A.C. impedance spectroscopy is now gaining favour as an investigative technique for monitoring the development of cement microstructure. This paper extents the range of application of the method by showing the compositional dependence of the complex impedance of cement-aggregate-water systems (ie. concrete and mortar), with attention being directed towards this material while still in the plastic state. In the work presented, the composition of such systems was varied over a wide range and a number of features of the complex response were identified which can be linked to cement-paste content, cement type and aggregate content. Measurements were, in the main, taken over the frequency range 1Hz–15MHz.
Laboratory measurements have been made of the impedance of saturated samples of Berea Sandstone and Spirit River Formation sandstone throughout the frequency range of 5Hz to 13MHz. When the data from a saturated sample are presented as a complex impedance plot the frequency dispersion produces a “non-ideal” distribution of points in the form of a depressed and slightly distorted semicircle and an inclined straight line. It is possible to separate the low frequency electrode response from the bulk sample response, thereby isolating the effect of polarization at the sample/electrode interface. The frequency response of the sample can be modelled by an equivalent circuit proposed by RAISTRICK et al. (1976) which includes a frequency dependent admittance term. Different samples and varying levels of water saturation cause changes in the complex impedance plots which can be related to this admittance term. The form of this term and its significance with respect to rock properties needs further investigation.
A structure refinement method is described which does not use integrated neutron powder intensities, single or overlapping, but employs directly the profile intensities obtained from step-scanning measurements of the powder diagram. Nuclear as well as magnetic structures can be refined, the latter only when their magnetic unit cell is equal to, or a multiple of, the nuclear cell. The least-squares refinement procedure allows, with a simple code, the introduction of linear or quadratic constraints between the parameters.
Penetration of Liquids into Cylindrical Capillaries.—The rate of penetration into a small capillary of radius r is shown to be: dldt=P(r2+4εr)8ηl, where P is the driving pressure, ε the coefficient of slip and η the viscosity. By integrating this expression, the distance penetrated by a liquid flowing under capillary pressure alone into a horizontal capillary or one with small internal surface is found to be the square root of (γrt·cosθ2η), where γ is the surface tension and θ the angle of contact. The quantity (γcosθ2η) is called the coefficient of penetrance or the penetrativity of the liquid.
The paper presents a series of laboratory tests and evaluates the effect of lime and fly ash on the compressibility and hydraulic characteristics of an expansive soil in Cyprus. The tests were performed at different percentages of lime (07%) and fly ash (15 and 25%) by dry weight of soil, and additional tests were also performed on soils treated with 15% fly ash plus 3% lime. Previously published research reveals that few data are available concerning the compressibility and hydraulic conductivity of lime-treated soils. The results of this study indicate an increase in the vertical effective yield stress (apparent preconsolidation pressure) and a decrease in the compressibility characteristics of the treated soils. Moreover, unlike some of the findings in the literature, higher hydraulic conductivity values were obtained with time. This finding has been substantiated by the reduced cation exchange capacity (CEC) values, which indicate that the pozzolanic reaction causes the soils to become more granular in nature, resulting in higher hydraulic conductivity.Key words: cementation, compressibility, fly ash, hydraulic conductivity, lime.