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Enhancing the dynamic properties of expansive soils using cementitious materials has attracted the attention of many researchers over the past few decades. Supplementary cementitious materials (SCMs) can be used as partial substitutes for cement owing to their pozzolanic activity that further improves the mechanical performance of cement-stabilized soils upon curing. In this study, the effect of cement and zeolite incorporation on the mechanical behavior of expansive clay was quantified using the pressure wave velocity (Vp) indicator obtained from ultrasonic pulse velocity tests performed at different curing times. Furthermore, a polynomial model was developed to establish the relationship between Vp and zeolite replacement levels at specific curing times and cement contents. The results show that a polynomial function captured the decreasing trend of Vp upon the increase in zeolite at curing times below 14 days. Additionally, the developed equation explained the upward trend of Vp owing to the pozzolanic activity of zeolite at later curing times with an accuracy of over 92%. The coefficients of the polynomial model also increased with the increment of the cement percentage which conformed to the consecutive rise in Vp. Ultimately, the polynomial coefficients were expressed in terms of cement content and curing time using the Volterra series. Using this model, the optimum percentage of cement replaced with zeolite (Zopt), the efficiency of using Zopt instead of cement, and the percentage of zeolite replacement to achieve equivalent Vp of cemented clay samples (ZC) were estimated. The findings of this study contribute to promoting geotechnical sustainability by replacing cement with zeolite that has a considerably lower environmental footprint. Clay is a type of soil that can be found in many construction projects. For instance, many roads and buildings' foundations are constructed on clay soils. To ensure the necessary strength of the clay under the main structure, the soil should often be stabilized using adhesive construction materials such as cement. Interestingly, a portion of the cement could be replaced with other minerals not only to improve engineering performance but also to promote sustainability by lowering cement consumption. In this study, the effect of zeolite as a partial replacement for cement on the strength of clay soils was experimentally evaluated. The effect of various design parameters, such as cement replacement level and curing time, on the stability of clays was investigated using an advanced technique called the ultrasonic pulse velocity (UPV) test. Furthermore, a simple mathematical model was proposed based on the experimental results to help engineers design the stabilization plan and timely decide about the next steps of the construction process. [ABSTRACT FROM AUTHOR]

Foam lightweight soil (FLS) has been widely used in geotechnical engineering because of their high strength, low density, and thermal insulation. However, few scholars have researched its application to subgrade engineering, especially roadbed widening. In this case, this special artificial soil can significantly reduce the differential settlement of subgrades due to its lightweight and high strength. In the research background, a series of laboratory experiments were conducted to investigate the effects of mixing ratio and fibers on the physical, mechanical, and microporous structural properties of clay-based foamed lightweight soils (CFLS), with clay and cement as the main raw materials. The experimental results indicate that preparing CFLS for road widening using clay soils from around highways as raw materials is an alternative treatment method. During the application process, one should select the optimal mixing ratio and fiber content considering the fluidity, stability, and mechanical strength of CFLS. In addition, the dynamic modulus of elasticity and cumulative plastic strain of CFLS samples also indicate that CFLS has superior dynamic properties compared with cohesive soils and can meet the criteria for road construction. [ABSTRACT FROM AUTHOR]

This document discusses a research paper that explores the use of alternative binders to ordinary portland cement (OPC) in soil stabilization. The authors conducted a study using a binder composed of ground-granulated blast furnace slag (GGBS) and carbide sludge (CS) to stabilize clayey slurries. They found that the GGBS-CS binder performed better than OPC and proposed a pH-based approach to predict the optimum CS content. The document provides information on the unit weight of different materials, calculation of soil mass, and determination of GGBS and CS masses. It also presents data on the unconfined compressive strength (UCS) of different types of soil and suggests using a normalization procedure to fit the data to a single equation. The authors' experimental procedures are also questioned. [Extracted from the article]

The use of bacteria-based self-healing concrete for substructures in ground conditions is an area of increasing interest for enhancing the durability and longevity of infrastructure. In line with this objective, the present study investigates the bio-self-healing performance of a cementitious material embedded in clay soil with varying chemical exposures and water saturation regimes. Laboratory experiments were conducted on pre-cracked mortar specimens with Bacillus subtilis encapsulated in perlite. The specimens were incubated in the soil with different pH and sulphate levels, representing three exposure classes (based on Eurocodes). The crack healing ratio was evaluated through visual inspection and capillary-water absorption—before and after soil incubation. Findings showed that all inoculated specimens exhibited healing ratios noticeably larger than those of the control specimens, which mainly experienced small autogenous healing. Of note, the best healing performance was observed when the soil was fully saturated and pH-neutral. From the design perspective of bio-concrete, this study emphasizes the consideration of groundwater regime as well as acidity and sulphate of the soil. [ABSTRACT FROM AUTHOR]

This document serves as a follow-up to a previous paper on the use of lime and rice husk ash (RHA) to stabilize clayey soil. The original paper found that the addition of lime and RHA increased the strength of the soil, with the highest strength observed in samples containing 7% lime and 12% RHA. The document also includes additional research studies that support the use of RHA to improve soil strength. These studies found that the inclusion of RHA increased the California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) values of the soil, with the maximum strength achieved at an optimal RHA content. The increase in strength was attributed to the formation of cementitious products and agglomeration of soil particles. The degree of strength development varied depending on the type of soil and RHA used. The article also suggests future research directions, such as considering the effect of dry density and evaluating the suction effect. [Extracted from the article]

This document is a discussion of a research paper titled "Probing the Stochastic Unconfined Compressive Strength of Lime–RHA Mix Treated Clayey Soil." The paper explores the use of lime and rice husk ash as binders to stabilize clayey soil. The authors conducted tests to measure the unconfined compressive strength of soil-binder specimens with varying amounts of rice husk ash and lime. They used artificial neural networks and Gaussian process regression to analyze and predict the data. The discussers raise questions about the influence of suction on the strength of the blends and the effect of dry density, suggesting further evaluation of these factors. [Extracted from the article]

New ways to apply sustainable materials, such as biomass components, are essential for reducing dependence on fossil fuels. This work investigated the engineering properties of unsaturated expansive subgrade soils stabilized by bio-based energy coproducts containing lignin. Lignin is a waste by-product of the paper and pulp industry that is frequently burned. Highway subgrade could consume lignin as an environmentally benign, low-cost, and energy-efficient chemical substance for soil stabilization. Swell and shrink behavior of expansive subgrade soils complicates highway construction and causes damage to existing highways. However, research on the hydromechanical properties and volume change behavior of lignin-stabilized expansive soil is limited, and better insight is required into its unsaturated behavior for safe and economical pavement design practices. In this research, a series of geotechnical laboratory tests were conducted to characterize expansive subgrade soils treated with lignin by determining the Atterberg limits, compaction and consolidation behaviors, swelling characteristics, and water retention properties. The mechanisms influencing the changes in engineering properties of lignin-treated expansive soils were further investigated using soil pH, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analysis. The study shows that the optimal lignin content contributed to an acceptable degree of soil stabilization. The lignin-based cementing material effectively bonds soil particles together and fills pores, thereby preventing water infiltration into the soil and reducing the swell–shrink potential of stabilized soils. [ABSTRACT FROM AUTHOR]

Freeze–thaw cycles can deteriorate the expansive soil performance. Phase change materials (PCMs) absorb and store heavy latent heat from the environment, which can be utilized to mitigate freeze–thaw deteriorations in expansive soil. In this study, an environmentally friendly paraffin-based PCM was selected, which included two different forms: liquid (pPCM) and microcapsules (mPCM). The volume change, mechanical properties, thermal properties, and microstructure of the improved soil were studied. These results showed that PCMs can release considerable thermal energy during phase transitions, which improves the thermal stability of the soil. The pPCM enhanced the plasticity of soil and prevented brittle failure; mPCM reduced the damage to the soil microstructure caused by freeze–thaw cycles. Macroscopically, it weakened the swell–shrink behavior and limited the degradation of the resilient modulus, unconfined compressive strength, and failure strain of expansive soil. The optimal PCM content was determined based on the mechanical and thermal properties of the improved soil. This study provides a new idea for the engineering treatment of expansive soil in cold regions. [ABSTRACT FROM AUTHOR]

The low bearing capacity of expansive soils often results in serviceability issues and premature failures of infrastructure built upon them. Various studies have demonstrated the use of different soil treatment methods using mechanical or chemical approaches to stabilize the weak ground as a precaution. Most of the reported studies are limited to either lab-based investigations or field monitoring works without the scientific connection between theory and translation. This study aims to verify the field application of a novel soil stabilization method by conducting laboratory-controlled experiments and field performance testing as verification. Enzyme–based soil stabilization was adopted for in-situ clay soil in combination with ordinary portland cement as a sustainable stabilization approach. Soil samples were collected at different regions from the field to evaluate the effectiveness and the mechanism of soil stabilization in the field by the means of replicating stabilization at the laboratory scale using identical mixing proportions of the additives. The mechanical behavior of stabilized soil was assessed through the unconfined compression strength and California bearing ratio test methods. In addition, the changes in the chemical composition of the soil due to the additives were evaluated through the X-ray diffraction testing technique and microporosity test using 2D images translated to 3D profiles from X-ray micro CT tomography. The efficacy of field stabilization was evaluated by conducting the falling weight deflectometer test in the stabilized site. Results from the study are useful to understand the efficacy of field soil stabilization and enhance the reliability of enzyme–based stabilization in practice. [ABSTRACT FROM AUTHOR]

The present work aims to evaluate expansive soil stabilization using different additives. Twenty soil mixtures consisting of 10%, 20%, 25%, and 30% zeolitic tuff (ZT) with 2%, 4%, and 6% lime in various combinations were used to stabilize the soil for pavement subbase application. A comprehensive test program, including Atterberg's limits, compaction, unconfined compression strength (UCS), California Bearing Ratio (CBR), resilient modulus, and permanent deformation, was performed on natural and stabilized soil specimens. Scanning electron microscopy (SEM) supplied with energy-dispersive X-ray spectroscopy (SEM/EDX) was used to confirm the study findings. Adding ZT increases the availability of the silica and alumina needed for the pozzolanic reaction; test results revealed that adding ZT increases the maximum dry unit weight, CBR, UCS, resilient modulus, decreases plasticity, and permanent deformation. As such, ZT can improve the physical and mechanical properties of lime-stabilized soil as a pavement's subgrade and subbase layers. [ABSTRACT FROM AUTHOR]

This study investigated the different geotechnical characteristics of soil stabilization with the addition of lime and rice husk ash (RHA) in varying amounts (3%, 5%, 7%, and 9% lime, and 4%, 8%, 12%, and 16% RHA). A series of compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), pH, and X-ray diffraction (XRD) tests were performed in the laboratory to assess the impact of the considered admixtures on the stabilized soil parameters. This study also proposes the successful integration of an artificial neural network (ANN) and a Gaussian process regression (GPR) with the experimental UCS observations. The lime concentration, RHA concentration, and curing period were considered as the input parameters, and UCS was considered as the response. The proposed framework was extended to analyze the compressive behavior of treated soil on the minuscule level. Such coupled machine learning-based experimental investigation can provide deep insight into the soil behavior which otherwise would have remained unexplored due to the prohibitive nature of performing laboratory experiments on a large scale. The findings demonstrated the effectiveness of RHA in addition to lime in stabilizing the considered expansive soil. With the addition of lime and RHA mix, the UCS and CBR values of the treated soil increased significantly. [ABSTRACT FROM AUTHOR]

Curing temperature and curing mode could affect the mechanical properties of cement-stabilized soil, which is of both scientific and practical importance for cement mixing performance. This paper aims to present the strength development of cemented soil cured in a water and 95% relative humidity (RH) environment with a series of curing temperatures (T) based on laboratory tests and model characterization. The base soil was low-liquid-limit organic clay (OL) classified by the Unified Soil Classification System (USCS). Unconfined compression (UC) testing was conducted in this study, and a combination of Fourier transform infrared spectroscopy (FTIR), scanning electronic microscopy (SEM), and energy-dispersive spectroscopy (EDS) was used to further investigate the microcharacteristics of the stabilized specimens. Results showed that the unconfined compressive strength (UCS or qu) of cemented soil increased with the increment of temperatures T both at early (7 days) and long-term (90 days) curing periods. Nevertheless, the cemented soil cured in 95% RH mode constantly achieved higher strength compared with that cured in water. The qu of 28 and 90 days gained in 95% RH mode can be taken as 1.2–1.5 times and 1.4–2.0 times of that in the water bath. In addition, the crossover effect was observed in samples cured in water when T reached 80°C, which was verified by the decalcification of calcium silicate hydrates (C-S-H) formed inside cemented soil through microtests. Based on the observations, a modified hyperbolic model characterizing the strength development of samples was proposed, in which the effects of curing temperature and curing time could both be considered regardless of the crossover effect. Moreover, the failure pattern of samples under different curing conditions was also analyzed. The findings presented in the current study are expected to provide insights and references for cement mixing engineering design. [ABSTRACT FROM AUTHOR]

Efficient utilization of problematic soils such as soft clay by imparting additional strength using various stabilization techniques is done to improve soil properties. The application of nanomaterials in the area of soil stabilization has great potential to create a stiff skeleton, especially when blended with cementitious materials. Using the response surface method, this study focused on studying the effects of single and blended cementitious systems, comprising cement (0% to 20%), slag (0% to 20%), and nanosilica (0% to 2.4%), on the properties of soft clay in wet conditions [water-to-soil ratio (w/s) of 53% to 87%]. The mechanical [California bearing ratio (CBR), unconfined compressive strength up to 91 days] and durability (freezing-thawing durability factor) properties of stabilized clay were investigated, and the bulk trends were corroborated by thermogravimetry and microscopy analyses. Based on statistical analysis, incremental addition of cement, slag, and nanosilica led to the systematic increase in the properties of soft clay, albeit to different extents and with different mechanisms. At the low w/s (53%), superior mechanical and durability properties were obtained for soft clay stabilized with the ternary binder comprising cement, slag, and nanosilica. Numerical optimization showed that stabilizing this weak type of soft/expansive clay is possible, but the results (proportions, performance, cost) varied based on the target design criteria and application. [ABSTRACT FROM AUTHOR]

The unconfined compressive strength (UCS) of soils is essential for both researchers and practitioner geotechnical engineers. UCS is well-understood and standardized for laboratory and field tests. Nevertheless, the large number of environmental and physical governing factors makes the reasonable prediction of UCS complicated. In this paper, a deep learning approach using the multilayer perceptron regressor (MLP) method along with the genetic expression programming (GEP) are used to assess nine variables that contribute to form a reflective multivariate formulation of the UCS. These variables include clay mineral percent (CF), specific gravity (Gs), dry unit weight (γd), saturated unit weight (γsat), natural unit weight (γt), moisture content (MC), void ratio (e), degree of saturation (S), and porosity (n). MLP and GEP are implemented to classify, correlate, rank, and reduce the number of variables that govern the UCS through the application of classification algorithms, importance analysis, interrelations and interdependency analysis of the variables, and functional indicators that shape the UCS. The changes of UCS in line with the variations of void ratio are analytically formulated according to both the critical state soil mechanics and the inverse proportionality between the voided area and soil strength. Moreover, the validity of the UCS principle is examined as opposed to the variation of the clay percent in the soil. Findings show that there shall be a breakpoint (clay percentage) after which the concept of UCS is radically changed due to the presence of a significant amount of frictional and drainable materials in the soil. The breakpoint appears to be centralized between 40% and 55%. The study is concluded by identifying the fundamental soil parameters, providing practical models to evaluate UCS, developing fundamental relationships between UCS and void ratio, and defining the breakpoint of clay content. [ABSTRACT FROM AUTHOR]

Plastic clays in subgrade may cause major engineering defects such as excessive heave or settlement during the wet season that contribute to the formation of uneven geometry at the pavement surface. Soil stabilization is often a requisite to ameliorate the engineering properties of soft soils or reactive clays. This study investigates the application of nano-silica and nano-alumina to improve the California bearing ratio (CBR) of a local clay. The clay was treated with cement (2%–8%), with nano-additive (0.1%–1.5%) and with cement and nano-additive (3% cement + 0.1%–1.5% nano-additive). The compacted sample was cured for 7 days and subjected to soaked and unsoaked CBR tests. The soaked CBR of the nontreated clay increased by 49% and 27% for 1% nano-silica and 1% nano-alumina treated clay, respectively. Although 3% cement addition improved the CBR of the soaked clay by 28%, the combination of 3% cement with 1% nano-silica and nano-alumina resulted in 196% and 164% increase in the soaked CBR of the nontreated clay, respectively. The combination of nano-additives and cement yielded the same soaked CBR as if 6%–7% cement would have been used. Clay treated with 1% nano-silica and 3% cement achieved the highest CBR value within the tested samples and the sample treated with 1% nano-alumina and 3% cement achieved the lowest free swell potential. The scanning electron microscopy (SEM) micrographs of the treated clay showed the formation of uniform fabric with fewer pore spaces and calcium silicate hydrate (CSH)/calcium aluminate hydrate (CAH) products within the fabric of nano-additive treated clay. [ABSTRACT FROM AUTHOR]

Dispersive clays are one of the common problematic soils owing to their unstable structure, which causes numerous geotechnical problems in construction projects. One of the main strategies to ameliorate these weak soils is to modify their mechanical properties with additives. Because little research about the influence of nanomaterials on the problematic soils' characteristics is available, this study aims to evaluate the effect of nanosilica on the mechanical, mineralogical, and microstructural behavior of dispersive clay. A series of experimental tests, including the pinhole, double-hydrometer, and crumb tests, is conducted to determine the dispersivity potential of the soil treated with nanosilica. The Atterberg limits, standard compaction, unconfined compression (UCS), and direct shear tests are also carried out. Additionally, mineralogy and the microstructure of the base soil and treated specimens were analyzed through X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The results indicate that adding the optimum amount of 1% nanosilica to the dispersive clay altered the soil characteristic into nondispersive. The liquid limit (LL), plastic limit (PL), and optimum moisture content (OMC) of the treated soil specimens increased; nevertheless, the plasticity index (PI) and maximum dry density (MDD) decreased with the application of nanosilica. Remarkable improvement in UCS, absorbed energy, secant elastic modulus (E50), and the direct shear strength was achieved in the specimens treated with 1% nanosilica content after 7 and 28 days curing. The formation of calcium–silicate–hydrate (C─ S─ H) gel and substantial reduction of the porous structure were observed through the XRD results and SEM micrograph after 28 days of curing. [ABSTRACT FROM AUTHOR]

A novel statistical framework was developed to quantify the variability of the fitting parameters of the soil–water characteristic curve (SWCC). Reliable estimation of the mean, standard deviation, and associated probability density function (PDF) of the fitting parameters of SWCC is an important tool for addressing reliability-based designs in unsaturated soil mechanics. The assumption of either Gaussian or lognormal distributions may not be valid for representing a high degree of variability associated with fitting parameters. This study aimed to provide the most appropriate continuous PDFs by optimizing the mean and standard deviation such that errors associated with quantile, percentile, and cumulative distribution function (CDF) were as low as possible. A total of 261 and 111 sample points were collected from the most comprehensive experimental works on the fitting parameters of SWCC for clayey and silty soils, respectively. Optimum distributions suitable to the model fitting parameters of SWCC are highly dependent on the type of soil. The most appropriate PDFs for representing the fitting parameters af , nf , and mf of Fredlund and Xing's model were gamma, Weibull, and inverse Gaussian distributions, respectively. Similarly, fitting parameters af , nf , and mf for silty soils were represented by inverse Gaussian, Gumbel maximum, and Gumbel maximum distributions, respectively. This study found that the selection of inappropriate PDFs overestimated the probability of failure of unsaturated infinite slopes considerably, by 99.49% and 99.76%, respectively, for clayey and silty soils. Recommended mean, coefficient of variation (COV), and PDF are useful in the reliability-based design of unsaturated soil slopes and in judging the performance of existing infinite and finite slopes. [ABSTRACT FROM AUTHOR]

The physical and mechanical behavior of soil polymer composites tightly depends on the properties and structures of both soil and polymer. This study aims to investigate the effect of glass transition temperature as one of the most important characteristics of adhesive resins of acrylic polymers on the geotechnical behavior of soils that have not been fully covered by previous studies. To achieve that, three similar copolymers of methyl methacrylate-co-butyl acrylate with different glass-transition temperatures of 1°C, 33°C, and 51°C were synthesized, and two representative specimens of cohesive (kaolinite clay) and noncohesive (sand) soils were chosen to perform a full investigation of the consequential changes in the physical and mechanical behavior. A series of laboratory tests, including the Atterberg limits tests, the unconfined compressive strength tests, direct shear tests in soaked and unsoaked conditions, swelling tests, and odometer tests, were conducted on untreated and treated soils with synthesized polymers. The results showed a salient enhancement in the cohesion and the unconfined compressive strength value of both soils. However, the polymer with a glass-transition temperature near to ambient temperature led to a greater increase in the compressive and shear strength of stabilized soil among its peers. Samples treated with the polymer having the lowest glass transition temperature revealed a more compression index (i.e., obtained from odometer tests) and lower unconfined compressive strength. It is also observed that the swelling index and swelling pressure decreased marginally with increasing the glass transition temperature. [ABSTRACT FROM AUTHOR]

Many techniques, most notably soil stabilization, have been developed to enhance soil characteristics due to the growing trend of constructing structures on clayey soils. Therefore, it is imperative that researchers address clay-related issues utilizing geotechnical engineering achievements. This study evaluated the effect of volcanic ash (tuff) as a natural pozzolan on the improvement of cement performance in the clay stabilization. Various compositions of cement (0%–6% by dry mass) and tuff (0%–20% by dry mass) were added to clay and cured for 7 and 28 days. Then a set of tests, including modified Proctor, Atterberg limits, electrical conductivity (EC), pH, unconstrained compressive strength (UCS), California bearing ratio (CBR), wet-dry durability, and scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses, were performed on the untreated and treated samples. The secant modulus (E50) was measured to evaluate the stiffness of the specimens. The data showed that the incorporation of tuff into the studied cement-stabilized clay considerably enhanced the mixture mechanical properties and substantially reduced the plasticity index of the samples. After a 28-day period, the samples containing 6% cement and 15% tuff, as the optimum mixture, had increases of the UCS and CBR values of approximately twice those containing 6% cement. Moreover, the inclusion of tuff into the cement–soil blends increased the durability of the samples. According to the SEM and XRD analysis, the addition of tuff to the samples containing cement caused the formation of more cementitious compounds and fully changed the soil structure. The findings indicate that the use of tuff can lead to improved cement performance in the stabilization process. [ABSTRACT FROM AUTHOR]

The results of the unconfined compressive strength tests provided in the paper under discussion show the highest shear strength obtained with the geotextile layer placed at a similar depth. On the other hand, from the results shown in the figure, it appears that the direct shear test consisted of only one layer of geotextile located at midheight in the shear box mainly to determine the resistance it afforded. Apart from tests reported as having been done thrice in relation to the direct shear box test, no mention is made whether the same scheme was used for the swelling and unconfined compressive strength tests. Is it to be interpreted as the result for the unreinforced sample added to the result for the geotextile layer, or is it to be interpreted as the result for only the geotextile layer?. [Extracted from the article]

3 represents the application of Eq. (4) with HT ht . For this, they established as criteria HT ht for the subbase and 2,100 kPa for the bases. Notation I The following symbols are used in this paper: i HT ht unconfined compressive strength; HT ht coefficient of determination; and HT ht porosity-to-volumetric cement index. [Extracted from the article]

This paper compares experimental results on the stabilization of clayey dredged material (DM) using quicklime (QL), hydrated lime (HL), portland cement (PC), and Class F fly ash (FA). The DM was a clay, high-plasticity soil, dredged from the US Army Corps of Engineers Port Arthur (USACEPA) facility along the Neches River located in Orange and Jefferson Counties, Texas. The soil consists of a large proportion of clay (66%), has high moisture limits (plasticity index: PI = 52 and liquid limit: LL = 80), and is characterized as a fat clay with silt. Physical properties of the untreated DM, such as unconfined compressive strength (UCS), consistency limits, and compaction behavior, were determined. Stabilizing reagents were mixed in various percentages by dry weight of DM. Results indicate that 12% QL, 6% HL, 6% PC, and 7.5% Class F FA by dry soil weight must be used to meet a minimum benchmark criterion of a PI value below 35, which was established based on Texas Department of Transportation (TxDOT) specifications. Standard compaction tests were carried out in accordance common standards with ASTM D698 to determine the optimum moisture content (OMC) for all mixtures. Stabilized mixtures were prepared at the corresponding OMC, and unconfined compressive tests were run according to common standards. Tests results were compared with the relevant literature, and a linear regression model was developed to predict the PI reduction as a function of initial PI, LL, and stabilizer type and content with good accuracy (R2 = 0.86). Overall, tests showed that stabilization of clayey DM using lime products, PC, or FA significantly improved the DM physical properties, which could then potentially be used as a local fill construction material that is cost-effective and environmentally friendly and reduces the overall use of cement products. [ABSTRACT FROM AUTHOR]

The original paper explicitly reports that large direct shear tests were performed to quantify the shear strength of geotextile-reinforced expansive soil subgrade. The writers agree with the discusser about the critical soil mechanics of geotextile-reinforced and unreinforced expansive soil; however, in the original scope of work was limited to and focused on assessing the interface efficiency of geotextile-reinforced expansive soil. 6(b-d), which compared different configurations of the geotextile layer test sections with the unreinforced expansive soil test section. [Extracted from the article]

Exchangeable sodium ions are widely reported to be the principal reason for the dispersivity of soils. From fundamental theoretical considerations, several other factors such as pH, cation exchange capacity, mineralogy, electrolyte concentration, and dissolved salts can affect the attractive/repulsive forces in soils and hence are considered to have a significant role in assessing the dispersivity of soils. To assess the influence of these parameters, a known dispersive soil was treated with sodium hydroxide and lithium hydroxide and the dispersivity was assessed. It was confirmed that the effects of these factors on dispersivity are manifested through the amount of hydration of the adsorbed monovalent cations. Because the inner hydration shell of adsorbed monovalent cations is larger than those of higher-valency ions, dispersivity is related to the presence of monovalent cations alone. It was also established that within the monovalent cations, the size of hydrated ions can vary and can influence the dispersivity of the soil. The dispersivity of soils increased with a reduction in the size of the ions. The increase in repulsive force (causing dispersion) due to the reduction in the size of the cation is explained through diffuse double layer theory. A complete philosophy of dispersion is proposed in light of the current experimental results. [ABSTRACT FROM AUTHOR]

To study effect of plasticity on shear behavior of low-plasticity fine-grained soil, a Mississippi River Valley (MRV) silt with a plasticity index (PI) of 5.8 was treated with different dosages of sodium bentonite to modify its plasticity up to a PI of 13.5. The naturally occurring material originated from the MRV exhibited dilative behavior under normally consolidated conditions. The silt-bentonite mixtures tend to lose quasi-steady-state strength and dilative characteristics as the plasticity increased. At a PI of 13.5, the silt-bentonite mixture had plastic stress-strain clay-like behavior. Overconsolidation did not influence the friction angle of the natural silt, but for silt-bentonite mixtures with Pis of 6.2 and 9.4 the influence of prestress was evident. The normalized shear strength was significantly reduced with an increase in PI from 5.8 (natural MRV silt) to 6.0 (natural MRV silt with 2.5% bentonite added). Compared to the predictive relationships proposed by other researchers, the normalized shear strength of the natural silt was clearly higher. The critical PI was about 6 to differentiate clay-like soil and intermediate soil for the subject silt. The PI was found not to be an ideal parameter to identify the transformation of the shear behavior of the MRV silt, because the shear behavior had a big change with a slight change of PI. [ABSTRACT FROM AUTHOR]

Lime stabilization of clay soils is becoming, if not already, one of the most used construction techniques for road embankments and for subbase stabilization. In warm countries, lime stabilization is used without any problems; but in cold countries, some concerns are still present in relation to behavior of lime-stabilized soils at low temperatures, particularly in conditions of freezing and thawing. The research in this paper presents the results of an experimental campaign made on a typical Italian clay soil stabilized with lime. The research studies the evolution of mechanical performances of lime-stabilized soil under the effect of freeze and thaw cycles and after a series of several freezes and thaws. The results of the research clearly show that lime-stabilized soils can have proper mechanical performances after freeze and thaw cycles. In particular, the test campaign shows that lime-stabilized soils have decreased resistance after freeze and thaw cycles and that they almost fully recover their resistance if the temperature comes back constantly to 20°C. [ABSTRACT FROM AUTHOR]

An investigation into the behavior of a contaminated clay soil and its treatment was carried out through a program of experimental tests. The contaminated soil samples were prepared with different percentages (3, 6, and 9%) of a glycerol solution with 40% concentration. The samples were prepared as mixtures of clean or glycerol-contaminated soil with different cement contents (3, 6, and 9%). Atterberg limits and unconfined compressive strength (UCS) tests were conducted on the samples. The results showed that Atterberg limits are reduced by adding glycerol or cement or adding glycerol to soil-cement. Both the strength and stiffness of the contaminated soil are reduced by increasing the degree of contamination. The results of treated soil showed that adding cement to contaminated soil increases the strength and the amount of increase in strength is dependent on the percent of cement, curing time and degree of contamination. Based on scanning electron micros- copy analysis, it was found that the presence of glycerol prevents the interaction between soil and cement. [ABSTRACT FROM AUTHOR]

Soft clays are widely distributed in Missouri, United States. Due to their relatively low strength and high compressibility, subgrade construction in soft clays has encountered many difficulties. In recent practice, the use of fly ash (FA) along with lime to tackle soft subgrade problems has shown promising results. The effectiveness of Class C FA and lime kiln dust (LKD) in clay subgrade stabilization is examined in this research. Scanning electron microscopic (SEM) analysis, proctor compaction tests, unconfined compression tests, and resilient modulus tests were carried out on the FA and LKD modified soil mixtures. Test specimens were prepared at optimum water content and tested at various curing periods. The test specimens were reconstituted by static compression. Test results revealed that the addition of Class C FA could increase the dry unit weight of the FA treated soil, enhance the unconfined compressive strength, and improve the resilient modulus. Regression equations were developed to correlate the resilient modulus with curing time. The mechanism of FA stabilization was discussed based on the SEM results and the measurement of the electrical conductivity of the FA-soil-water system. Correlations between the unconfined compressive strength and resilient modulus were developed. It is concluded that subgrade stabilization with Class C FA and LKD are cost-effective for road-base construction. [ABSTRACT FROM AUTHOR]

The discussers would like to point out the observed value of HT ht is 2.0 [Eqs. The factor HT ht (or HT ht ) is also affected by the exponent HT ht , which is controlled by the soil matrix properties. (7)-(12) of the original paper] for the studied sedimentary soil-cement mixtures, leading to a theoretical HT ht of 0.50, which is very similar to the value of 0.45 found experimentally by the authors. [Extracted from the article]

The writers would like to thank the discussers for their acknowledgment of the research presented in the original paper, for the interesting model to predict soil-cement strength they presented, and for their question about kambara reactor (KR) slag properties. It is quite interesting to see the excellent correlation among the normalized soil strength with adjusted porosity/cement index for S1 and S2 soils and curing periods (7 and 28 days) considered in the original paper, demonstrating the efficiency of the model to predict the soil-cement strength as a function of soil characteristics and percentage of cement addition. For low percentages of cement addition, the soil-stabilized mixtures are treated under the category of "soil improved by cement". [Extracted from the article]

Eq. (2) is similar to the unconfined compressive strength empirical correlation found by Consoli et al. ([2]) [Eq. (3)] HT ht (3) where HT ht , HT ht , and HT ht = scalars; and HT ht = volumetric cement content in relation to the total specimen volume. The value of HT ht was chosen to normalize the results. [Extracted from the article]

This study presents the characteristics of municipal solid waste (MSW) incineration ash obtained from an electric energy generation plant and evaluates the MSW ash applicability in base road pavement layers through the mixture of ash with a nonlateritic regional clay soil. Chemical, physical, and mechanical tests and the mechanistic-empirical design for a typical pavement structure were carried out on the pure soil and also in the soil mixture with the addition of different ash content (20 and 40%). Fly ash reduced the expansion of the material, showing an increase in the California bearing ratio (CBR) and resilient modulus value. The results are satisfactory, depending on the content and type of ash used, highlighting the positive work of MSW fly ash for its use in base road pavement layers. [ABSTRACT FROM AUTHOR]

Calcium carbide residue (CCR) is a waste product from acetylene gas factories, which is rich in calcium hydroxide []. Because clayey soils contain high amount of natural pozzolanic materials (silica and alumina), CCR can be used as a soil stabilizer. This article presents the engineering properties of CCR-stabilized silty clay to ascertain its performance in pavement base and subbase applications. The input of CCR, which reduces the plasticity index of the clay, increases the optimum water content (OWC) and decreases the maximum dry unit weight () of the stabilized clay. The CCR fixation point, simply obtained from the index test, is proved as a practical indicator for determining the CCR content to obtain the required engineering properties at a particular molding water content. The state of water content controls the densification, chemical reaction, and water absorption capacity. The soaked engineering properties are thus dependent upon the state of water content. For a particular CCR content, the optimum water content is the most appropriate in terms of strength, swelling and collapse behaviors, and bearing capacity. The lower water content is not sufficient for the chemical reaction, while the higher water content yields a higher water/binder ratio. The water absorption is smallest for the CCR-stabilized samples compacted at the OWC. To conclude, the optimal mix proportion is the CCR fixation point at OWC. CCR stabilization is more effective than lime stabilization in terms of engineering, economic, and environmental viewpoints. [ABSTRACT FROM AUTHOR]

The present study examined the potential of pumice waste of the Isparta-Gelincik region, which has been categorized under the lightweight aggregate class as a stabilizing additive to problematic clayey subgrade of pavements. The physical properties of lightweight aggregate material were analyzed. In earlier research, few experiments have been carried out by using experimental samples to test for properties such as stability when frozen, solidity, strength, Atterberg limits, California bearing ratio (CBR), and dynamic repeated load triaxial (RLT) tests. The utilization of Gelincik pumice waste as a stabilizer was determined for the clayey subgrade. Pumice waste of the Isparta-Gelincik region and high plasticity clay were mixed in varying proportions to improve the engineering properties of the clayey soil. The CBR experiment was also performed to observe the change of strength through the use of waste material. In addition, RLT testing was performed by using mixed materials to observe the changes in the resilient moduli values of the mixtures. The results of the experimental research showed that Gelincik pumice waste can be used as a stabilizer for problematic clayey subgrades when constructing roads. This research is the first example of a stabilization approach for problematic clayey subgrade of pavements by using pumice waste. [ABSTRACT FROM AUTHOR]

Cement kiln dust, rice husk ash, and their combinations are used variously as stabilizers in different percentages (maximum up to 20%) to develop and evaluate stabilized clayey soils. The influence of stabilizer types and dosages on fresh and mechanical properties is evaluated through Atterberg limits, standard Proctor compaction, unconfined compressive strength, splitting tensile strength, modulus of elasticity, and California bearing ratio (CBR) tests. The durability characteristics of 19 developed stabilized soil mixtures are also investigated by studying the influence of water immersion on strength, water sorptivity, and drying shrinkage. Correlations between strength, modulus of elasticity, and CBR are also established. Developed stabilized soil mixtures have shown satisfactory strength and durability characteristics and can be used for low-cost construction to build houses and road infrastructures. The use of locally available soils, rice husk ash, and cement kiln dust (waste from the cement industry) in the production of stabilized soils for such applications can provide sustainability for the local construction industry. [ABSTRACT FROM AUTHOR]

There exists an effort to develop dosage methodologies for cement improved soils based on a rational criterion, as in concrete technology, in which the water to cement ratio plays an essential role in strength determination. This study aims to assess the strength controlling parameters of two clays with distinct coarse grained materials (silty clay and sandy clay) treated with cement and to show that the porosity/cement ratio plays a fundamental role in target strength assessment of clayey materials. The controlling parameters evaluated were the cement content, porosity, and porosity/cement ratio. A number of unconfined compression tests and suction measurements were performed for the present work. The results show that a linear function better fits the unconfined compressive strength-cement relationship. The strength increased exponentially with the reduction in porosity for the studied soil-cement mixtures. Finally, the porosity/cement ratio is shown to be a key parameter in an evaluation of the unconfined compressive strength of the clayey soils studied. [ABSTRACT FROM AUTHOR]

The potential of woodash to stabilize clay soil was evaluated. The evaluation involved the determination of the geotechnical properties of clay soil in its natural state as well as when mixed with varying proportions of woodash. The parameters tested included the particle size distribution, specific gravity, Atterberg limits, compaction characteristics, California bearing ratio (CBR) and the compressive strength. The CBR and strength tests were repeated after 28-day curing of the treated samples. Results showed that the geotechnical parameters of clay soil are improved substantially by the addition of woodash; plasticity was reduced by 35% and CBR and strength increased by 23–50% and 49–67%, respectively, depending on the compactive energy used. The highest CBR and strength values were achieved at 10% woodash. Results also showed that curing improved the strength of the woodash-treated clay. However, the strength gain was short lived as the strength quickly decreased after 7–14 days of curing. These results imply that although woodash provides some of the beneficial effects of lime in soil stabilization, such as plasticity and swell reduction, improved workability, and strength increase, it is unlikely to be a substitute for lime as strength gain is short lived. [ABSTRACT FROM AUTHOR]

This paper presents, by way of comparison, the effect of fly ash on the volume change of two different types of clay, one a highly plastic expansive clay and the other a nonexpansive clay, also of high plasticity. Expansive clays swell on absorbing water and shrink on drying. Nonexpansive clays undergo large compression at high water contents. The effect of fly ash content on free swell index, swell potential, and swelling pressure of expansive clays was studied. Compression index and secondary consolidation characteristics of both expansive and nonexpansive clays were also determined. Swell potential and swelling pressure, when determined at constant dry unit weight of the sample (mixture), decreased by nearly 50% and, when determined at constant weight of clay, increased by nearly 60% at 20% fly ash content. Compression index and coefficient of secondary consolidation of both the clays decreased by 40% at 20% fly ash content. [ABSTRACT FROM AUTHOR]

Lime continues to be one of the most popular chemical admixtures used to modify expansive clays despite the associated mixing and pulverization problems. In the present investigation, the efficacy of CaCl2 in place of conventionally used lime is studied by conducting laboratory and field tests. These investigations were carried out on the slopes of a trapezoidal trench made in expansive clay bed. Heave measurements were taken on the lime and CaCl2 treated slopes and also on untreated slopes for four consecutive cycles of wetting and drying. The field cyclic seasonal movements and the subsequent laboratory tests on undisturbed and disturbed soil samples revealed that the CaCl2 could be a promising chemical modifier instead of conventionally used lime, not only due to its multifold influence on heave control, plasticity reduction, and swell properties but also its easy application in the form of solution without any need for pulverization and mixing. Though an apparent reduction in unconfined compressive strength of treated samples is observed, the drained triaxial tests on treated and untreated samples revealed that there is an increase in the angle of internal friction of treated samples. [ABSTRACT FROM AUTHOR]

Physicochemical interactions between polymer molecules and clay particles affect the swelling rate and magnitude of expansive clay soils. The effectiveness of aqueous solutions of three polymers: Sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), polyethylene oxide (PEO) ranging in concentration from 0.5 to 10 g/L, as soil stabilization agents against Na-montmorillonite swelling was analyzed. Rates of volumetric swelling of Na-montmorillonite upon hydration were recorded over durations ranging from 120 to 200 h, and data were used to compute the volumetric swelling ratio (VSR), an expression of the clay volume at any time relative to the initial volume of clay in the immersion tube. The results show that PAM, the cationic polymer reduces the VSR by as much as 40% relative to distilled water. PAM molecular weight and concentration have minimal effects on VSR although sorption of PAM of higher molecular weight (PAM B) is favored at aqueous concentration below 2 g/L. Data from x-ray diffraction and batch sorption tests on dried Na-montmorillonite samples indicate that postsorption/swelling interlayer spacings of 0.74 and 0.78 nm for PAM A (molecular weight=4×106) and PAM B (molecular weight=7×106) respectively, are attained through fixation of PAM molecules in clay interlayer space during sorption at an aqueous concentration of 4 g/L. Test results for CMC (the anionic polymer) and PEO (the neutral polymer) show that swelling is not significantly reduced relative to that of distilled water. PAM can be used at aqueous concentrations between 0.5 and 4 g/L as an effective stabilization agent for expansive soils. [ABSTRACT FROM AUTHOR]

This paper aims to show that the addition of lime and lime/cement can significantly improve both the stiffness and the resistance to permanent deformation of clay soils even under adverse, though realistic, curing conditions. The AASHTO Guide for Design of Pavement Structures incorporates a method of calculating subgrade resilient modulus (MR), using repeated load triaxial testing, with respect to seasonal variations of the soil’s moisture content and temperature, while the equivalent British specifications adopt a “soaked California bearing ratio” approach. In practice 8°C is a realistic worst case curing temperature in situ and a (necessarily) wetter underlying clay will allow water to be drawn into the chemically treated layer during curing as a result of suctions, while the material will experience a small degree of confinement after compaction. These conditions have been replicated in a series of repeated load triaxial tests on lime and lime/cement stabilized, predominantly kaolinitic clay and the results compared with those from sealed samples, which were also cured at 8°C. All samples were subjected to 100 cycles of stresses representing 20, 40, 60, and 80% of the relevant undrained shear strength. This paper concludes that allowing the samples access to water is necessary if field performance is to be replicated. [ABSTRACT FROM AUTHOR]

Laboratory tests have been carried out in order to evaluate the improvement in engineering properties relevant to highway design and construction obtained when clayey subgrade soils are stabilized with lime or fly ash. The experimental program included California bearing ratio (CBR) tests to evaluate the bearing strength of stabilized soils used as working platforms during highway construction. The admixture of lime or fly ash caused an increase in the plasticity limit, while both the liquid limit and the plasticity index of the soils have been reduced. Substantial increases in the California bearing ratio value, higher than those of the soil-fly ash mixtures, have been obtained when the soil samples were mixed with lime. The swelling after a 4-day soaking period has been reduced with the addition of both additive materials. The increase in optimum moisture content acts subsidiarily to the increased CBR value, particularly at high lime or fly ash percentages. An analogous effect has been found for the maximum dry density reduction. [ABSTRACT FROM AUTHOR]

Proper understanding of the field performance of lime-treated expansive soils requires the evaluation of their unsaturated properties under stress conditions similar to that in the field. This paper studied the influence of net vertical stress on the soil-water characteristic curves (SWCC) of lime-treated expansive clay. The first phase of this study investigated the influence of lime content and curing period under low net vertical stress (7 kPa) using axis translation and filter paper techniques with simultaneous measurements of sample volume change. The second phase evaluated the SWCCs of untreated and lime-treated clays under vertical stresses of 100 and 600 kPa. Different representations of SWCCs were considered in the interpretation of test results. Test results indicated that lime content had a significant effect on the shape and air entry value of SWCCs because of changes in soil microstructure, whereas curing period had a far less significant effect. Furthermore, the application of net vertical stress delayed the desaturation of samples causing increase in air entry value. On the basis of plots for the variation of void ratio versus suction, the increase in air entry value was attributed to considerable reduction in volume (void ratio) associated with the application of the net vertical stress causing samples to remain saturated up to high suctions levels. [ABSTRACT FROM AUTHOR]