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Calcium carbide residue (CCR) has been identified as an effective replacement for traditional lime for the stabilization of expansive soils. The shrinkage of expansive clay severely threatens the foundation layers’ long-term stability. The efficacy of CCR stabilization in reducing compressibility and enhancing the strength and stiffness of clay has been widely reported; however, the calcium-based additive stabilized soil tends to lose its engineered integrity under field-exposed seasonal moisture variation, specifically, shrinkage induced by prolonged drying. In this study, the shrinkage characteristic of CCR-treated clay (6%, 9%, and 12%) slurry was investigated by digital image analysis and mercury displacement method to quantify volumetric shrinkage strain. The results were compared with those of 4% and 6% lime-treated clay, which revealed the higher efficacy of CCR in reducing shrinkage strain by 47–57%. A characteristic shrinkage curve that depicted the significant variation of shrinkage phases in CCR-treated clay samples is developed. The dominance of the proportional shrinkage phase is observed in both untreated and treated clay samples. The shrinkage caused by evaporation, hydration, and decalcification is postulated in treated clays. This study is expected to contribute to the understanding of shrinkage mechanisms of CCR-treated clay and assist in the future design of stabilized embankment sections or subgrade for unpaved roads. [ABSTRACT FROM AUTHOR]

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]

Purpose. To study the effect of hardened cement waste and compare it to the effect of fresh cement in the treatment of expansive soil. Methodology. To show the performance of hardened cement waste compared to that of fresh cement, an experimental study is conducted concerning a swelling clay soil in the Mila region of eastern Algeria. The study involves a series of soil treatment tests with fresh cement and hardened cement waste (with reasonable proportion) for each type of cement. Finally, a comparison of the influence of the addition of hardened cement waste and the addition of fresh cement on the physical and mechanical behavior of the soil. Findings. Treatment with fresh cement provides a good improvement in certain properties, and in this work we show that the use of hardened cement waste could also improve the physical and mechanical characteristics of the treated soil. Originality. The originality of this work is to replace fresh cement with the waste of hardened cement in the treatment of clay soils in general and swelling soils in exceptional cases to minimize the cost of treatment with fresh cement and protect the environment from waste of the cement. Practical value. This study shows that the results obtained by adding 6 % of fresh cement and 6 % of hardened cement waste changed the physical and mechanical properties of the soil (plasticity, bearing capacity, swelling and settlement). Comparison of the results obtained shows that the performance of hardened cement waste represents 90 to 98 % of the performance of fresh cement. The convergence of the treatment results indicates the possibility of replacing fresh cement with hardened waste cement in soil stabilization. [ABSTRACT FROM AUTHOR]

This study on the effectiveness of lime as a stabilizing additive in clayey soils addressed the uncertainty regarding its specific efficacy, taking into account the degree of soil expansion and application percentages. The research focused on three geotechnical sectors in the Manabí region, where the presence of expansive soils impacts the stability of civil engineering structures. Significant geotechnical issues were identified in expansive soils, including their high plasticity and volumetric changes associated with moisture. The limited bearing capacity of the subgrade is a recurring challenge in pavements. Intervening to improve these soils was deemed essential, and the study focused on evaluating the effectiveness of lime under different degrees of expansion. A mixed approach, predominantly quantitative, was adopted, conducting laboratory tests to establish the efficacy of lime. The results contributed to a robust understanding of soil stabilization, suggesting that adjusting lime percentages is crucial to optimizing stabilization without compromising soil compaction. These findings were valuable for informing future construction projects in areas with expansive soils, emphasizing the importance of considering geotechnical variability for effective technical and economic solutions. [ABSTRACT FROM AUTHOR]

Expansive clayey soils (CSs) expand and become softer as moisture content increases, but they get harder and stronger as they dry out. The earth's swelling and shrinkage characteristics under varying moisture conditions make roads built on expansive CS, in particular, vulnerable to early degradation. In this investigation, coffee husk ash (CHA), gypsum, and a blend of the two additives (G-CHA) were used in experimental tests to treat expansive CS. This study aims to evaluate experimentally the potential of expansive soil stabilization using different additives: CHA, gypsum, and a combination of gypsum and CHA. Five different percentages of CHA (5%, 10%, 15%, 20%, and 25%), three percentages of gypsum (3%, 6%, and 9%), and variable percentages of their combinations were used to stabilize the soil for pavement subgrade application. Atterberg limits, compaction, linear shrinkage (LS), swelling, unconfined compressive strength (UCS), and California bearing ratio (CBR) tests were performed on treated and virgin soil specimens at 3, 7, 14, 28, and 56-day curing times. Results showed that CHA additives effectively reduced the plasticity, LS, and swell potential in addition to increasing the maximum dry unit weight, UCS, and CBR. It was determined that the UCS and CBR values for the 6% stabilized gypsum soil increased by 28.95% and 19.54%, respectively, and reduced by 41% of the plastic index parameter after the addition of 15% CHA. Based on the evaluation of the results, an optimum mixture of 6% gypsum and 15% CHA (SG6C15) stabilized soil can be used in pavement subgrade applications as it achieved the minimum strength target. The performance of CHA-treated samples as subgrade material is superior to that of untreated virgin soil. Because of the stronger subgrade, smaller pavement layers result in a thinner pavement structure. [ABSTRACT FROM AUTHOR]

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]

Expansive soils contain water-absorbing clay minerals, including smectite and montmorillonite. So expansive soil undergoes a process of expanding and shrinking. Changes in expanding and contracting can weaken structures built on expansive soils. One effort to overcome the problem of expansive soils is a chemical stabilization process using lapindo deposits. The purpose of this study was to determine the effect of stabilizing expansive soils using lapindo sediment materials. Using physical and mechanical testing before and after the expansive soil stabilization process. Using a mixture of 0%, 5%, 10%, 15% & 20% between expansive soil and stabilizing agent. The results showed that the plasticity index decreased from 37.8% to 15.3%, and the compressive strength increased from 0.30 kg/cm² to 0.90 kg/cm² with the addition of 20% sediment material lapindo. The physical and mechanical properties of expansive soils can be increased by stabilizing them with lapindo sediments. These modifications can reduce the soil's expanding potential, increase its weight, and give it clay-like qualities. [ABSTRACT FROM AUTHOR]

Expansive soils are extremely susceptible to swelling and shrinkage associated with seasonal changes in their moisture content. This can cause serious damage to structures constructed on expansive soils. Stabilization using additives is widely used to mitigate the concerns of expansive soils by controlling the changes in volume, thereby increasing the strength and durability of the soils. Multistabilizers, including a low percentage of conventional additives with nonconventional additives, can reduce the costs of stabilization. The performance of the stabilized soil can be enhanced by admixture optimization to ascertain that the agent's ratios are quite adequate to meet the optimal levels of modification. Unfortunately, despite the development of advanced techniques for investigating the stabilization of expansive soil, limited studies are devoted to the optimization of admixture to soils. Hence, in this research, an approach based on rough set theory, a mathematical data mining approach, is presented for multiagent optimization for efficient treatment of expansive soils. The multiadditives used in this study are almond shell ash (ASA), volcanic rock dust (VRD), and portland cement (PC). The differential free swell test, the California bearing ratio test, and the unconfined compressive strength test were applied for assessing the characteristics of the stabilized soil specimens. The obtained results and the confirmatory tests demonstrated that a combination of 20% ASA and 20% VRD with 8% PC provides the optimum results in the properties of expansive soil. The microstructural analysis denoted an enhanced modification of the soil engineering properties. The outcomes of this research confirm that the rough set optimization procedure is highly suitable for application in multiagent optimization for the efficient treatment of expansive soils. [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]

The utilization of fly ash (FA) and powdered granulated steel slag (PGSS) as additives in soil stabilization plays a crucial role in environmental, economic, and weak soil property improving advantages. In this study, the combined effect of FA and PGSS in improving expansive subgrade soil was investigated. The materials used for this study were expansive soils, FA, and PGSS. The study has applied an experimental research method. For this investigation, the index properties, Free Swell Index (FSI), unconfined compressive strength (UCS), optimum moisture content (OMC), California bearing ratio (CBR), and scanning electron microscope (SEM) tests were done for treated and untreated expansive soils. The findings indicated that as the mixture of FA (0 to 12.5% at 5% increment) and PGSS (0 to 25% at 5% at 2.5% increment) is added to the untreated expansive soils, the index properties, FSI, and OMC of the soils were significantly declined. The CBR values of expansive soils containing 20% FA and 10% PGSS mixture were 13.8% and 16.21%, respectively, which improved the quality of the soils by 85.43% and 84.82%, respectively. While the untreated expansive soils have a UCS value of 0.34 kg/cm2, the treated soil comprising 20% FA and 10% PGSS mixture has a UCS value of 13.42 kg/cm2, indicating that the soil strength is enhanced by 97.47%. The results of the studies demonstrate that adding FA and PGSS to expansive soil improves its stability and strength. The study concluded that disposals such as FA and PGSS might be effectively used in enhancing the characteristics of construction materials and used for the construction. [ABSTRACT FROM AUTHOR]

Featured Application: This study attempts to identify optimal dosage ranges of lime and PG for maximizing the strength performance of stabilized expansive soils. The study involved the utilization of an industrial waste product, Phosphogypsum (PG) as an additive to lime for the stabilization of soil. Three lime dosages, viz. initial consumption of lime (ICL), optimum lime content (OLC) and less than ICL (LICL) were adopted for stabilizing the soil. The study investigated the stress-strain characteristics of soil composites stabilized with these three lime contents modified with optimum dosages of PG. Mineralogical studies were performed on the spent samples used for a series of determinations of unconfined compression strength tests with various combinations of lime and optimum PG content. The addition of an optimum dosage of PG resulted in an early strength gain of 8.8%, 14.1% and 13.9% and a delayed strength gain of 9.9%, 19% and 19.7% for 3%, 5.5% and 7% for the lime-stabilized soil, respectively. It was found that the addition of PG to the lime resulted in enhanced stiffness, residual strength and reduced brittleness due to the PG amendment of the stabilization reactions. However, in terms of the overall improvement of soil properties, the most favorable benefit was obtained by optimal PG modification of ICL rather than OLC. Microanalysis of the X-ray diffraction scatter also supported the results revealed through stress-strain characteristics. ICL with its optimal PG dosage showed a better progression of pozzolanic reactions when compared to the other two in terms of reduction of peaks of soil minerals and increase in peaks of CSH. [ABSTRACT FROM AUTHOR]

Volume change of expansive soils is a challenging issue, which affects various engineering structures all over the world. Consequently, we need environmentally-friendly and cost-effective soil stabilizers to address the challenges related to expansive soils. The utilization of natural fibers allows for the reduction in environmental impact since they are renewable and biodegradable raw materials. Moreover, the current article presents an experimental approach to study the effect of natural fibers on the mechanical behavior of expansive soils. Various experimental tests—such as Atterberg limits, standard compaction, direct shear, swelling potential, and swelling pressure—were conducted on control and treated soil samples using different percentages of fibers. The results of measurements of the physico-mechanical properties after reinforcement of the soil with 1%, 5%, and 10% of natural fibers indicate that the mechanical behavior of expansive soils is greatly influenced by the addition of natural fibers. To conclude, 86% reduction was observed in the swelling coefficient of treated soil. Future research can be done to check the durability of the current practice in detail. [ABSTRACT FROM AUTHOR]

Weak subgrade is the main problem facing most highway projects. Therefore, this study focuses on trying to improve the properties and increase the strength of weak, clayey, swelling soil for use as a subgrade for pavement structural sections. This trial was developed using a mix of granular and chemical stabilization for the soil. Granular stabilization was applied firstly by mixing natural sand at different percentages of 20%, 35%, and 50% of the total weight of clayey, swelling soil samples to find the minimum percentage that could be added to improve it to sandy, clayey soil, which is acceptable as a subgrade according to the Egyptian highway specification code. Secondly, chemical stabilization was applied to enhanced sandy, clayey soil to increase its strength properties. This was performed by adding chemical additives (lime, cement kiln dust (CKD), fiberglass, Addicrete 11, and gypsum) at different ratios of 2%, 4%, and 6% of the total weight of the samples of enhanced sandy, clayey soil. An experimental program was conducted consisting of characteristics and consistency tests, the California bearing ratio (CBR) test, a proctor test, and a consolidated-drained (C-D) tri-axial shear test. The results showed that 50% sand was the minimum percentage that could be mixed with swelling, clayey soil for granular stabilization to be enhanced and become sandy, clayey soil, which is accepted as a subgrade layer according to the Egyptian highway specification code. In addition, using a mix of granular and chemical stabilization increased the compressive strength of this enhanced subgrade by adding 6% lime or cement kiln dust (CKD) of the total sample weight. They enhanced the strength of the soil and reduced its plasticity. Adding 6% fiberglass and polymers could slightly enhance the desired properties; however, it is not recommended to use them due to their slight effect and economic cost. In addition, it is not recommended to use gypsum at more than 4% due to its negative effect on CBR. [ABSTRACT FROM AUTHOR]

Sugarcane Press Mud (SPM) is a waste generated from the sugar industry. India generates about 12 million tonnes of SPM annually and hence, needs effective management. The present study delves into the use of SPM as a ternary blend in cement-lime stabilization of an expansive soil. An expansive soil was stabilized using a combination of 4.5% lime (determined from the Eades and Grim pH test) and a fixed cement content of 1%. The effect of the stabilization was studied by casting cylindrical specimens of dimensions 38 mm x 76 mm and curing them for periods of 7, 14 and 28 days. This process was modified by blending it with SPM as a ternary additive up to 5% in increments of 1%. The optimal dosage of SPM was evaluated for enhanced strength gain which was then subjected to a wet-dry cycle to understand the effect of variation in moisture content. The results of the investigation revealed that cement-lime stabilization of the soil was significantly better than lime stabilization alone. 1% SPM was found to be the optimal dosage required for maximum strength gain. Based on the results, it was concluded that ternary blending of SPM can potentially be beneficial in soil stabilization. [ABSTRACT FROM AUTHOR]

Construction and demolition waste (CDW) are the largest waste products in the world today and competes as a viable recycled additive material in place of natural aggregates. Due to the increase in compressive strength of different mix proportions of CDW, it is also considered for reuse in concrete and subbase construction. This study shows the effect of CDW in expansive soil stabilization. The chemical and mechanical properties of these materials have shown that they are capable of developing compressive strength properties for replacement of cement with significant reduction in carbon emission. The inherent compositional properties of recycled CDW compared in this review suggests that CDW have good filler properties in highly expansive soils. Mixtures of crushed brick and recycled aggregates characterised based on chemical properties of different replacement ratios suggests that CDW of good-quality aggregates reduces swell potential of expansive soils and increased mechanical strength in pavement construction. [ABSTRACT FROM AUTHOR]

In recent years, there has been an increasing interest in investigating the use of non-traditional additives for stabilizing problematic soils. As the demand for eco-friendly alternatives to cement rises, magnesium chloride, a widely used deicer and dust suppressor, has emerged as a potential choice. This study aims to provide a comprehensive understanding of the microstructural changes that occur and affect the macro behavior of treated bentonite (B) and yellow marl (YM). To achieve this, MgCl 2 solution was added to the soils at 3, 6, 9, and 12 percent by dry weight of the soil, and samples were cured for 7, 14, and 28 days at 5° C , 25° C , and 35° C. The mechanical properties of the treated soils were then evaluated using the unconfined compression test, direct shear test, and pressure chamber test (SWCC), while microstructural analysis techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDAX), and Fourier transform infrared spectroscopy (FTIR) were employed to examine the mechanism of MgCl 2 stabilization. The results indicate that adding MgCl 2 and extending the curing period significantly increased both soils' unconfined compressive strength (UCS). However, the UCS value decreased for treated samples cured at temperatures higher than 25°C due to an incomplete cation exchange process and the reduction of apparent cohesion. A part of the gained strength from apparent cohesion and matric suction in the unsaturated samples was lost when the samples reached full saturation during the direct shear test. Changes in the particle size, pore size, and pore void distribution due to the MgCl 2 stabilization affected the SWCCs of the treated soils. Microstructural analyses revealed the formation of magnesium hydration products, such as magnesium silicate hydrate (M-S-H) and magnesium aluminate hydrate (M-A-H), which contributed to the strength increase by increasing grain size, filling the pores, binding fine particles within coarse grains, and forming a flocculated structure through recrystallization of MgCl 2 and the formation of cementitious gel. Additionally, for B, adding MgCl 2 led to soil flocculation through ion exchange, while for YM, the same process occurred due to the greater surface tension of the saline solution encircling the particles. • Microstructural analyses indicated the production of cementitious hydration products M-S-H and M-A-H. • Increasing curing temperature reduced the strength by decreasing the apparent cohesion. • The treatment of the B and YM with MgCl 2 decreased the LL and PI. • Stabilized soil structure changed to a flocculated, interlocked, and denser one. • UCS of both soils improved up to 110 % due to recrystallization and cementation of MgCl 2. [ABSTRACT FROM AUTHOR]

Building on expansive soil is risky due to its high compressibility, low shear strength, and differential settlement. This study evaluates the potential of the use of sodium hydroxide (NaOH) as an additive to improve the stability of clay. For this research, the compaction properties namely Dry Density, Optimum Moisture Content, Atterberg Limits, and Unconfined Compressive Strength were performed on soil samples prepared with different percentages of NaOH (0%, 5%, 10%, 15%, and 20%). In this work, the clay sample was obtained from a highway project site near the Haspolat village in the eastern suburb of North Nicosia, Cyprus. No works of such have been done in the area. The results indicated that NaOH can be added to improve the engineering properties of the soil. Moreover, this paper presents a comparative study between an empirical equation (Quadratic model (QM)), Multilayer Feed-Forward Neural Network (MFFNN), Cascade Feed-forward Neural Network (CFNN), Radial Basis Neural Network (RBNN), and Elman neural network (ENN)) and multiple linear regression (MLR) for modeling the stress–strain behavior of CS15 (contains 85% of soil and 15% of NaOH). The coefficient of determination, root mean squared error, mean absolute error, Nash–Sutcliffe efficiency, and Willmott's index of the agreement were used to select the best predictive model. The results indicate that all the developed models are expedient in predicting the stress–strain behavior of treated soil. Furthermore, the findings demonstrated that the QM model performed well and presented high accuracy in modeling the stress–strain behavior. [ABSTRACT FROM AUTHOR]

Expansive clay is one of the problems in construction work. The soil has the characteristics of being easy to expand when exposed to water, causing a decrease in the strength value of the soil. The can be overcome by stabilizing the soil. The soil is formed from weathering and contains the mineral montmorillonite. The soil is very sensitive to moisture content, has a high shrinkage rate, thus interfering in construction work. Therefore, additional materials are needed to overcome the problem, one of which is soil stabilization. The study aimed to stabilize the expansive clay soil. This is done by analyzing the physical and mechanical properties of expansive clay with a shell ash mixture. Expansive clay is taken directly (undisturbed) or disturbed. Undisturbed soil is taken using a tube, so that the soil is not disturbed by outside air, while disturbed soil is taken using a shovel and then put into a sack container. Expansive clay stabilization method lies in adding the percentage of shell ash mixture (5 %, 10 %, 15 %, and 20 %). The soil, the initial moisture content (γd) of which has been determined, is mixed, then molded into a cylindrical shape. The mold was stored in a desiccator, then watered with 5 % water every day until the soil became saturated. Then, using a Proctor test, chemical tests (soil chemical test, soil mineral test), physical tests (soil moisture, Atterberg limit), and mechanical tests (unconfined compression test, compaction test, swelling test) were carried out. The results showed that the addition of an oyster shell ash stabilizing agent to expansive clay affected the physical and mechanical properties of the soil. The addition of shell ash can reduce soil moisture with various plasticity indexes. While the soil stress value decreased, the swelling of the soil increased significantly above the original soil. [ABSTRACT FROM AUTHOR]

The mineralogy of fine soils such as clays has always posed problems and remains an uncontrollable phenomenon in the presence of water and causes destructible damage throughout the world. In order to minimize the cost of implementation, it is necessary to find practical and less expensive solutions to ensure the stabilization of these soils by the valorisation of local waste available in nature. This article concerns an experimental study on the treatment of reconstituted soil by the addition of paper ash of different proportions on a set of standardized tests, the preliminary results show that the paper ash to the clay soil improves its swelling potential, its plasticity, its compaction characteristics, and its shear strength parameters. [ABSTRACT FROM AUTHOR]

The treatment and stabilization of soils make it possible to recycle materials on construction sites in preparation for the installation of a final covering or the construction of a road network. In road geotechnics, various materials such as lime, cement, and pozzolans were used as additions to stabilize clay soils. In recent years, bio-polymers and bacteria are of increasing interest to researchers in the field of stabilization and improvement of the physico-mechanical and chemical characteristics of clay soils. Currently, in place of traditional clay treatment techniques and to minimize environmental problems, natural fibrous waste is being used increasingly and spectacularly. Several studies on biotechnological engineering applications already exist, such as the use of vegetation, algae, bacteria, enzymes, and biopolymers. The northern Algerian region where the urban tissue does not stop expanding contains significant potential in terms of wheat straw, which represents a very present agricultural waste. So, there is a local interest in the sustainable development of several regions known to produce wheat. This study is interested in investigating the effect of wheat straw on the stabilization of swelling clay soil. In order to improve the physico-mechanical characteristics of clay soils, a series of laboratory tests (Atterberg limit, Proctor test, direct shear test, Oedometer test, and unconfident compressive strength test) were carried out on reconstituted clay soil with defined initial properties through numerous analyses (e.g., XRD and XRF) and then treated with different vegetable fiber content. The results indicate that there is an improvement in the compressibility characteristics of the treated soil, a remarkable decrease in the swelling index and the compressibility index respectively with increasing percentages of wheat straw. [ABSTRACT FROM AUTHOR]

The marble process industry from Shaq Al-Thouban region, which is located in East Cairo, Egypt, produces a huge amount of marble wastes every day during the cutting and processing stages. Up to now, most of these wastes are dumping on open land which creates serious environmental problems. The amount of waste marble from the processing stage is about 20 to 25% of the total processed stone. Egypt also suffers from the problem of expansive soil that occupies a large area of its lands, especially in the new cities that are built on these lands. The primary purpose of this study is to use this waste material in the soil stabilization in point of view utilization of this waste as local low-cost materials and elimination of their negative environmental impacts. The waste marble dust was mixed with expansive soil samples with various percentages of 5%, 10%, 15%, 20%, and 25% by dry weight of soil. Different tests including Atterberg's limits, standard Proctor compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), swelling percentage, linear shrinkage (LS) tests, and XRF and XRD analyses were conducted for natural and marble dust stabilized soils. The soil mixtures used for UCS, CBR, and swell tests were compacted at the optimum moisture content (OMC) and maximum dry density (MDD) using the standard Proctor compaction method and cured for 7 days. The results of the tests showed that there are significant effects in enhancing the properties of expansive soils. Also, the results showed that as the percentage of the marble dust increases the plasticity index, the swelling potential of the expansive clayey soil decreases. Furthermore, the optimum moisture content decreases, and the maximum dry density increases. Also, UCS, CBR, and the calcite content of the soil mixtures increase with the increase in marble dust content. [ABSTRACT FROM AUTHOR]

The swelling potential analytics and the ion exchange reaction of highly expansive soils in a soil stabilization process have been reviewed. The importance of these factors in deciding suitable construction materials and chemical additives utilized as alternative or supplementary binders in clayey soil stabilization has been discussed also. The outcome of this study has shown that Al3+, Si4+, and Ca2+ are the most suitable exchangeable cations with OH- as the suitable exchangeable anion leading to the formation of C-A-S-H, which is the compound responsible for strengthening. The swelling potential analytics also proposed the expression wsT = 0.00216 × (Σi=1 i=n Ip1 2.44) (Σi=Dn i=D1 Di) as the total swelling potential with respect to the depth of a foundation material constructed with clayey soil. This study revealed that during the wet season, hydraulically bound foundation materials experience undesirable volume changes with the highest swelling potential expected at the surface within the active (unstable) zone of the foundation. Generally, the treatment of highly expansive soil with very high swelling potential should be concentrated at the surface and reduced along the depth of the foundation matrix. With this proposed guide, the utilization of alternative or supplementary cementing materials as construction materials in the stabilization of clayey soil to improve swelling can be conducted with a more sustainable approach. [ABSTRACT FROM AUTHOR]

The expansive clay soils, which cover most of the new urbanized areas in Egypt, create major damages in most of the engineering structures and infrastructures such as buildings, roads, bridges, pipelines and others due to bad human activities, e.g. lack of maintenance for sewage and drinking lines, and flood irrigation of golf areas which causes fluctuation of water content through the foundation clay layers associated with shrink-swell behavior. These geotechnical challenges and their treatment solutions consume most of the urbanized project budget and delay the development plan. Therefore, in this study the high plasticity and soft to firm clay soils were stabilized using various dosages of fresh cement kiln dust (CKD) as an economical alternative to the other expensive stabilizing agents (stabilizers or binders) such as lime, cement and other chemical stabilizers. The effectiveness of this type of CKD as a stabilizing agent, soil stabilization mechanism, and changes in mineralogical and microstructural characteristics of stabilized soils due to this stabilization process were evaluated through Atterberg limits, unconfined compressive strength (UCS), stiffness (stress–strain behavior, Es), pH, electrical conductivity (EC), total dissolved solids (TDS), X-Ray diffraction (XRD) and scanning electron microscope (SEM) investigations. The present study revealed that by adding CKD, the workability of the treated clays was increased by decreasing the liquid limit and plasticity index as well as increasing the bearing capacity and decreasing the settlement by increasing UCS and Es. This study also showed that by adding CKD, the initial pH, EC, and TDS of CKD-clay system increased, creating favorable conditions for dissolution of edges and surfaces of clay flakes. The active montmorillonite clay flakes adsorbed the soluble calcium cation and sulfate anion on their surfaces that are rich in soluble silica and alumina and then the cation exchange and flocculation–agglomeration processes began. With curing, the pozzolanic products grew on the surfaces and edges of clay flakes and extended into the voids of the agglomerated inter-clay particles resulting in the filling of these micro-voids. The present investigation also found that, the progressive decreasing in pH, EC, and TDS values of CKD-clay systems through different curing periods is a good indicator for pozzolanic activity. [ABSTRACT FROM AUTHOR]

Problematic soil stabilization processes involve the application of binders to improve the engineering properties of the soil. This is done to change the undesirable properties of these soils to meet basic design standards. However, very little attention has been given to the reactive phase of soil stabilization. This phase is the most important in every stabilization protocol because it embodies the reactions that lead to the bonding of the dispersed particles of clayey soil. Hence, this reactive phase is reviewed. When clayey soils which make up the greatest fraction of expansive soil come in contact with moisture, they experience volume changes due to adsorbed moisture that forms films of double diffused layer on the particles. When this happens, the clayey particles disperse and float, increasing the pore spaces or voids that exist in the soil mass. Stabilizations of these soils are conducted to close the gaps between the dispersed clayey soil particles. This is achieved by mixing additives that will release calcium, aluminum, silicon, etc., in the presence of adsorbed moisture, and a hydration reaction occurs. This is followed by the displacement reaction based on the metallic order in the electrochemical series. This causes a calcination reaction, a process whereby calcium displaces the hydrogen ions of the dipole adsorbed moisture and displaces the sodium ion responsible for the swelling potential of clayey soils. These whole processes lead to a pozzolanic reaction, which finally forms calcium alumina-silica hydrate. This formation is responsible for soil stabilization. [ABSTRACT FROM AUTHOR]

Volume change in expansive soils is a problem encountered in earth work around the world. This is prominent with hydraulically bound structures or foundations subjected to prolonged moisture exposure. This behavior of clayey used as subgrade, foundation, landfill, or backfill materials causes undesirable structural functionality and failures. To prevent this happening, clayey soils are studied for possible volume change potential and degree of expansion. Consequently, the problematic soils are stabilized. In this work, the stabilization of clayey highly expansive soil classified as A-7-6 soil and highly plastic with high clay content was conducted under laboratory conditions. The treatment exercise was experimented using quicklime-activated rice husk ash (QARHA), hydrated lime-activated rice husk ash (HARHA), and calcite-activated rice husk ash (CARHA) at the rates of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10%. Upon treatment with the three calcium compounds to produce three sets of treated experimental specimens, the plasticity index was observed and recorded and swelling potentials were evaluated using the plasticity index method (PIM). The results showed a consistent improvement on the properties of the treated soil with the addition of the different activated admixtures. While the utilization of CARHA and HARHA improved the clayey soil to medium expansive soil, the treated clayey soil substantially improved from highly expansive soil with a potential of 23.35% to less expansive with a final potential of 0.59% upon the addition of 10% QARHA. Finally, QARHA was adjudged as the best binding composite due to the highest rate of reduction recorded with its utilization. [ABSTRACT FROM AUTHOR]

The main purpose of this study is to investigate the effects of swelling clay mineral content on ion migration and column performance during stabilization of expansive soils by lime column technique. For the purpose of the study, soil samples which contain Na-bentonite in different percent amounts were prepared and laboratory scale models were built for each sample. Na-bentonite proportions of samples were chosen to be 0%, 20%, 40%, 60%, 80% and 100%. At the end of the curing time, migration of Ca2+ and OH− ions were determined by chemical analysis and the relations between bentonite proportion and migration distances of ions were revealed. Moreover, the changes on swelling behaviour of soil samples were determined by using experimental methods. The results of this study reveals that migration distances of Ca2+ and OH− ions reduced with increasing bentonite content. However, migration distances of ions followed a steady course after 60% of bentonite content. Ca2+ ion migrated to larger distances than OH− ions in the soils with 0%, 20%, 40% of bentonite while migration distance of the ions in soils with 60%, 80% and 100% of bentonite were the same. Additionally, the highest stabilization was detected in the soil with 100% of bentonite although the biggest migration distance was detected in the soil with 0% of bentonite. The results of this study show that the effects of swelling clay proportion in the soil on ion migration and column performance during stabilization of swelling soils with lime column technique are quite important. [ABSTRACT FROM AUTHOR]

• Waste materials from different sources have been utilized in chemical stabilization of expansive pavement subgrade soils. • Engineering properties of expansive pavement subgrade soils can be improved with waste material stabilization. • The issue needs further investigation, since durability properties of expansive soils are affected by many parameters. • Microstructural characteristics of materials are a key factor that need more attention in expansive soils stabilization. • Waste materials-based stabilization can be sustainable, economic and eco-friendly alternative to traditional ones. Expansive soils, also known as swell-shrink soils, are one of the most problematic soils in highway construction and exhibit significant volume changes by swelling and shrinking while wet and dry, respectively. These changes in soil cause cracks, heaves, differential settlements, and damages to the overlying pavements leading to high maintenance costs. The annual average maintenance cost of structures built on expansive soils ranges from $9 to $15 billion, with 50% of the expenses associated with highways and streets. Chemical stabilization techniques such as cement and lime stabilization are one of the most efficient ways to treat expansive soils. However, there is a need to develop environmentally friendly approaches to stabilize expansive soils due to worldwide growing interest in sustainable developments and concerns about greenhouse gas emissions and climate change. In this context, using waste materials in soil stabilization has been considered an important issue for sustainability concerns. The aim of the current study is to review the relevant studies performed to improve the geotechnical and engineering properties of expansive subgrade soils of pavements by using waste materials arising from industrial, agricultural, and other activities in the last decade. In the organization of this study, characteristics of expansive soils including plasticity, compaction, strength & stiffness, microstructural characteristics, shrink-swell properties, and durability were focused to point out the effect of the waste materials. The overall results obtained throughout the scope of the current study indicated that the use of waste materials in soil stabilization improves the engineering properties of expansive soils, significantly. This paper also provides key information and creates awareness for researchers and sector representatives about sustainable soil stabilization. [ABSTRACT FROM AUTHOR]

Expansive soils have been inevitable during road constructions due to its widespread availability. Conventional stabilizers; cement and lime have not been quite reliable in terms of economic, environmental, and durability perspectives. Thus, geopolymer has come into limelight as a sustainable alternative. However, the complexity of geopolymer-soil behaviour makes it challenging to predict their strength development patterns and it requires a large number of trial and error tests in laboratory scale due to the soil specific nature of such mixes. To date, no research has been attempted to develop design charts for geopolymer-expansive soil stabilization field applications. This study proposes design charts using Artificial neural networks (ANN) to predict the 28-day unconfined compressive strength (UCS) of Class F fly ash (FA) based geopolymer stabilized expansive soil (PI = 32% – 46%) to support field implementation of this novel geopolymer based soil stabilization. The model was developed based on a robust collection of literature data; FA/Soil, Activator/FA, Na 2 SiO 3 /NaOH, alkaline molarity, and their respective 28-day UCS values. Three contour plots for mix design: FA/soil vs. NaOH molarity, activator/FA vs. Na 2 SiO 3 /NaOH, and Na 2 SiO 3 /NaOH vs. NaOH molarity were proposed based on the model predictions. The proposed mix design charts were validated through the in-house tests which showed reasonable match in comparison with the predicted 28-day UCS using the contour plots. The proposed mix design charts can be employed for in-situ geopolymer-expansive subgrade stabilization to achieve strengths between 0.6 and 2.1 MPa. [ABSTRACT FROM AUTHOR]

[Display omitted] • High performance paradigm for predicting UCS of stabilized expansive soil. • Waste glass powder (WGP) and Fly Ash (FA) were used for stabilization of expansive soil. • Effect of the WGP, FA, and Clay content on microstructural behavior of expansive soil. • The MEP predicted the UCS of stabilized expansive soil more robustly. Expansive soils (ES) are unsuitable for construction because of their low shear strength, bearing capacity, unconfined compression strength (UCS), and high shrink-swell potential. The traditional experimental techniques for obtaining the optimized mixes of stabilized ES using a variety of waste additives are laborious, time-consuming and uneconomical. Therefore, this study determines the optimized mixes by evaluating the UCS of waste glass powder (WGP) and Fly Ash (FA) modified ES by deploying a robust computational technique, i.e., multi-expression programming (MEP). The ES was modified using WGP at 0, 5, 10, 15, 20, 25, and 30%, in order to determine the optimum dosage of WGP. Furthermore, FA was incorporated at 0, 5, 8, 11, 14, and 17% in the ES at the optimum WGP content, and their synergistic effect was determined. An experimental dataset was compiled with 180 test results on the untreated ES to develop the MEP model. The proposed optimal MEP model relates the UCS at 28 days (UCS 28d) to its plasticity index, specific gravity, swell potential, UCS 3d , and UCS 7d. It was also evaluated using different statistical indices, such as correlation coefficient (R = 0.995), Nash-Sutcliffe efficiency (NSE = 0.989), coefficient of determination (R2 = 0.989), and error analysis indices (MAE = 6.87 kPa, RMSE = 11.42 kPa, and performance index ρ = 0.016) for the test dataset. These values suggest the robust predictive capability of the MEP model, thus enabling the designers and practitioners to readily use these equations where cost-effectiveness and time are to be considered in engineering projects. In addition, the inclusion of these industrial waste-based additives would lead to sustainability in the field of geoenvironmental engineering. [ABSTRACT FROM AUTHOR]

Abstract: For soil stabilization, lime, fly ash, and different chemicals additives were used to improve the swelling characteristics of the clayey soil. In the present study, the hay of wheat is added to a type of clayey swelling soil to improve and stabilize its characteristics. Old houses in Egyptian villages were built with clay mixed with hay as a cementious agent between clay particles. The hay ratio used in the present study was 0.5%, 1% and 1.5% by weight of the clayey soil. The soil used in the study represents a type of swelling clayey soil. Index, strength and swelling properties tests are carried out on the clay–hay mixture. The results showed that the shear strength increases with the increase of hay ratio till approximately 1% hay addition. The indirect tensile strength for air dried samples increased as well. The deformation due to the swelling potential also decreased to about 20%. [Copyright &y& Elsevier]

Abstract: An experimental study was conducted to investigate the long-term performance of fly ash stabilized two fine-grained soil subbases. One low plasticity clay soil and one high plasticity expansive clay soil were stabilized with a Class C fly ash with fly ash contents of 0%, 5%, 10%, and 20%, and compacted statically at the maximum dry density (standard Proctor) and at the optimum moisture content of the corresponding soil to prepare ten sets of replicates from each of the combinations. After curing all specimens for 7 days, the first set was subjected to plasticity index tests, unconfined compression tests, and vertical swell tests to estimate the improvement due to stabilization. Similar tests were also conducted on another nine sets of replicates in which six sets were subjected to 12 wet–dry cycles (three sets with tap water and the other three sets with saline water), and the other three sets were subjected to 12 freeze–thaw cycles in a laboratory controlled environment to simulate the weathering action. The effect of wet–dry cycles on stabilized soils was essentially insignificant; however, the fly ash stabilized soils lost up to 40% of the strength due to freeze–thaw cycles. Even after losing the strength significantly, the strength of stabilized soils was at least three times higher than that of the unstabilized soils. The swell potential of stabilized expansive soils also increased due to freeze–thaw cycles. The vertical swell increases rapidly for first four to five cycles and then increases very slowly. [Copyright &y& Elsevier]

Abstract: Low rise buildings are particularly vulnerable to ground movements sourced from swelling and shrinking of the expansive clay soils. Geotechnical engineers have long recognized that swelling of expansive clays caused by moisture variation may result in considerable damage to the overlying structures, and engineers should take them into the consideration. The literature contains a vast number of stabilizing techniques such as lime, cement, and fly-ash for treatment of expansive clay soils. However the use of gypsum as a stabilizing agent is currently not clear. This paper deals with the performance of the gypsum as an additive for treatment of the expansive clay soils by means of swell potential and strength. Optimum water content for the best compaction of the bentonite was first determined by standard compaction tests. Different quantities of gypsum such as 2.5%, 5%, 7.5%, and 10% by mass were added to bentonite and compacted in optimum water content obtained. Atterberg limits, free swell and unconfined compressive strength tests were performed on treated and untreated samples, after a curing period of 7 days. Obtained changes in the plasticity, swell percent and strength parameters of treated and untreated samples indicated that gypsum can be used as a stabilizing agent for expansive clay soils, effectively. [Copyright &y& Elsevier]

Abstract: Failures in soil stabilization have been reported previously as being due to the formation of ettringite, an expansive mineral which develops in the presence of sulfate, calcium, and aluminum compounds of clay fraction in high pH levels between 10.36 and 14. By comparing the pattern of formation of ettringite, formed from different possible sources and specifically in stabilized soil, it is expected that a clearer picture of the kinetics of ettringite formation from different sources will be obtained. In this paper, a set of physico-chemical experiments and XRD tests were performed to investigate the process of ettringite formation and to explore its possible performance in clayey soils. The growth of the ettringite XRD peaks was used as a measure of the rate and its formation pattern. It is shown that the rate of ettringite formation in soil stabilization is much slower than that of artificial ettringite. Furthermore, it is shown that ettringite swells to the order of 50% and its fluid retention is significantly higher (by as much as 400%) than that of the soil sample studied in this research. [Copyright &y& Elsevier]

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]

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]

Expansive soil shows dual swell–shrink which is not suitable for construction. Several mitigating techniques exist to counteract the problem promulgated by expansive clayey soils. This paper explored the potential mecho-chemical reinforcement of expansive clayey soil to mitigate the effect of upward swelling pressure and heave. The polypropylene fiber is randomly distributed in the soil for mechanical stabilization, and the industrial residual silica fume is used as a chemical stabilizer. The experimental analysis was made in three phases which involved tests on mechanically-reinforced expansive soil, using randomly distributed polypropylene fibers with different percentages (0.25%, 0.50%, and 1.00%), and which were 12 mm length. The second phase of experiments was carried out on chemical stabilized expansive soil with different percentages (2%, 4%, and 8%) of silica, and the next phase of the experiment focused on the combination of mecho-chemical stabilization of the expansive soil with different combinations of silica (i.e., 2%, 4%, and 8%) and polypropylene fibers (i.e., 0.25%, 0.50%, and 1.00%). Maximum dry density (MDD), optimum moisture content (OMC), liquid limit (LL), plastic limit (PL), plastic index (PI), grain size, and constant volume swelling pressure tests were performed on unreinforced and reinforced expansive soil, to investigate the effects of polypropylene fiber and silica fume on the engineering properties of expansive clayey soil. The experimental results illustrate that the inclusion of polypropylene fiber has a significant effect on the upward swelling pressure and expansion property of expansive soil. The reduction in the upward swelling pressure and expansion is a function of fiber content. These results also indicated that the use of silica fume caused a reduction in upward swelling potential, and its effect was considerably more than the influence of fiber. [ABSTRACT FROM AUTHOR]