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Contaminant soil remediation has potential engineering applications with various stabilization techniques addressing heavy metal contamination. Conventional soil stabilizers, however, have an environmental impact, promoting international research into environmentally friendly alternatives. Using waste byproducts to produce geopolymer binders as new green cementitious materials can provide an environmentally friendly and effective option for soil improvement. Silica-rich wastes have been advanced as a sustainable option for soil stabilization. The effectiveness of alkaline-activated silica-rich wastes in stabilizing cadmium-contaminated soil and its potential engineering utilization remain of profound significance, demanding sustained and rigorous research investigation. Cadmium was immobilized in silty clay soil by rich silica waste products—fly ash, silica fume, and rice husk ash—at various percentages with 4.5 and 6.5-molar alkaline activators. Unconfined compressive strength tests assessed soil behavior, while Toxicity Characteristic Leaching Procedure (TCLP), pH tests, X-ray diffraction, and scanning electron microscope analyses explained cadmium immobilization mechanisms. The experimental results revealed that alkali-activated silica-rich wastes enhanced strength and cementitious properties and reduced cadmium leaching in the contaminated silty clay. The Finite Element Method was also employed to analyze the bearing capacity of the stabilized contaminated soil. The numerical results support the experimental results and confirm increased soil strength and reduced compressibility, endorsing the efficacy of the stabilization techniques and environmental benefits. [ABSTRACT FROM AUTHOR]

Stabilization of cohesive soils has been practiced for some time by mixing additives, such as cement, lime, and fly ash, into the soil to increase its mechanical strength. However, there is a lack of investigation on the use of natural pozzolana (NP) alone or combined with lime for soil stabilization applications. This work is a part of a research project focused on the evaluation of the effects of adding natural pozzolana as an additive to improve the lime treatment results of local clayey soils. The main purpose of this paper is to present the results of using lime, natural pozzolana, and their combination on shear strength, shear parameters, and failure mode variations of the local clayey soil, classified as fat clay (CH). CH, selected from Tlemcen city in Algeria, is known for its high plasticity and importance in cohesion and compressibility. To achieve this goal, several physicomechanical tests (pH, compaction, undrained unconsolidated triaxial compression test) and microstructural analysis, scanning electron microscope (SEM) have been carried out for the different studied combinations. Natural pozzolana and lime were added to the studied soils at ranges of 0–20% and 0–6%, respectively. The treated samples were cured for 1, 7, and 28 days. The results indicated that the studied properties of clay soil can be considerably improved when treated with lime. The combination of lime and natural pozzolana appears to produce higher shear strength parameters, than when lime or natural pozzolana is used alone. Adding natural pozzolana to clay soil treated with lime produces an additional chemical reaction, especially in the long term, resulting in better flocculation and additional formation of cementing materials. Therefore, the deviatoric stress of the treated soil, with 6% lime and 20% NP, increased up to 200% within 28 days of curing. The treated soil became more brittle, with a significant increase in shear strength, cohesion, and a higher friction angle. [ABSTRACT FROM AUTHOR]

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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]

This paper addresses a soil bio-stabilization technique using bacterial enzyme-induced calcium carbonate precipitation (BEICP) as an alternative to previous conventional methods including microbial-induced carbonate precipitation and plant-derived enzyme-induced carbonate precipitation. The extracted urease enzyme of viable S. pasteurii was used as a biological source along with calcium chloride and urea to solidify sandy soil and silty sand soil. The bio-treated soil columns were subjected to freeze and thaw (F–T) cycling for a durability evaluation. Engineering properties of bio-cemented soil including unconfined compressive strength, calcium carbonate contents, moisture contents, porosity, permeability, and microstructure were examined before and after the F–T durations. It was found that although bio-stabilizer was able to increase a frost duration of soil, the F–T cycling significantly impacted on the compressive strength of bio-treated soil, due to a formation of microcracks. This investigation has revealed that the BEICP method provided a similar capacity in F–T resistance of soil as using the traditional Portland cement stabilizer, whereas the class F fly ash did not improve F–T durability of medium dense soil. [ABSTRACT FROM AUTHOR]

The practice of pre-compression with sand drains is a widely accepted soil stabilization method for improving soft soil deposits. The scarcity of quality sand contributed to the substitution of a more cost-effective material. An effort was made in the present investigation to utilize waste products like quarry dust (QD), coir pith (CP), fly ash (FA), and rice husk ash (RHA) as the vertical drain in clayey soils. A sand drain (SD) has been used for comparison purposes. Kuttand Clay (KC) and Cochin marine clay (CMC) was selected for the study. Tests were conducted on conventional oedometer cells with a diameter of 6 cm and a height of 2 cm using vertical and radial consolidation models. In addition, this paper demonstrated the effect of the density of drain on radial consolidation characteristics. From the analysis, it was observed that the rate of consolidation increases with the inclusion of any drain material. The radial coefficient of consolidation using sand, quarry dust, and coir pith drain shows a higher value when comparing with the other drain material, which can be owing to their high permeability. The present study can recommend that the quarry dust and coir pith drain, or maybe the combination can be a better alternative for the sand drain. [ABSTRACT FROM AUTHOR]

In construction, the foundation is an integral part of a structure and its function is to transfer the building loads safely into the ground and to keep the settlement within permissible limits. Here, soil is an essential component of the earth's surface that transfers building load through the foundation. Generally, different foundations are adopted depending on the different soil conditions and number of floor loads to be transferred to the deeper strata. Therefore, improving the bearing capacity of soil by experimental stabilization achieves better strength at required shallow depth. This paper develops an improved bearing capacity for shallow foundations on clays considering actual soil constitutive behavior. The geopolymer-stabilized soil specimens were synthesized and characterized with compressive strength testing and effective soil stabilizer for clay soils. [ABSTRACT FROM AUTHOR]

Soil stabilization is an in situ soil treatment in which soils are mixed with cementitious or other chemical stabilizing agents. Determining the unconfined compressive strength (UCS) of stabilized soil is a principal task in the design and construction of the ground improvement. Hence, this study aims to develop a reliable predictive model for the UCS of clay stabilization with common cementitious binders using the gene-expression programming (GEP) technique. Eleven parameters, including the soil characteristics, the binder types, the binder contents, the mixing method, and the curing period, were considered as the independent variables in the model. The research results show that the selected optimal GEP-based model performs well with an acceptable correlation coefficient (R = 0.951) and low errors (e.g., RMSE and MAE). Besides, parametric analyses indicate that the plastic index, the percentage of clay, and the total water content have a negative effect on the UCS of stabilized soil. In contrast, the percentage of silt and sand, the binder types, the binder contents, and the curing time show a positive effect on the strength of stabilized soil. In addition, the strength of stabilized clay could be significantly enhanced by combining cement with slag, lime, or fly ash with a reasonable ratio, or by reducing the natural water content in the soil. The research findings could help engineers choose suitable binder types and cost-effective methods to optimize the UCS of stabilized clay. [ABSTRACT FROM AUTHOR]

Clays generally have a low strength and capacity, and additives are usually used to stabilize them. In recent years, using fly ash to stabilize soil has decreased environmental pollution while also having an economic benefit. The objective of this study is to perform a comparative investigation on the effect of class C and class F fly ashes on geotechnical properties of high-plasticity clay using the Atterberg's limit, compaction, California Bearing Ratio (CBR), and unconfined compressive strength tests. The results showed that with an increase in the amount of fly ash, there was a decrease in the maximum dry density and an increase in the optimum moisture content. Moreover, an addition of fly ashes of up to 25% caused a reduction of the liquid limit and plasticity index, and an increase in the maximum unconfined compressive strength and CBR. Lengthening the curing time had a positive impact on the unconfined compressive strength of the soil. The soil samples with class C fly ash were seen to possess more efficient geotechnical properties as compared to class F fly ash. [ABSTRACT FROM AUTHOR]

Carbide lime is a by-product obtained during the manufacturing of acetylene from the reaction of calcium carbide and water. A major portion of carbide lime is dumped in waste deposition areas, creating an environmental problem. Carbide lime and fly ash have possible applications in slope stabilization, subgrade improvement of roads, and soil treatments under shallow foundations. A series of Atterberg limits tests, compaction tests, unconfined compressive strength tests, ultrasonic pulse velocity tests, and wetting–drying tests were performed on carbide lime and fly ash treated clay soils to evaluate the effects of additive content, curing time, strength development, and the effects of wetting and drying. A total of 8% of carbide lime constituted the fixation point, and peak strength was achieved at 12% carbide lime content. A total amount of 25% additive was found as a threshold changing the Atterberg limits. Test results indicated that the strength of the treated soil improved by the existence of carbide lime and fly ash; best performance was observed in 28-day specimens with 10% carbide lime and 20% fly ash content reaching to 8 times larger strength than untreated soil. The failure patterns of the specimens reflected the curing time and wetting–drying effects. Although, the application of wetting–drying cycles deteriorated the treated soil, the presence of carbide lime partially prevented the strength loss. New relationships between normalized strength and curing time depending on carbide lime content were proposed. Furthermore, a linear relationship between the unconfined compressive strength and the ultrasonic pulse velocity of the treated soils was established. [ABSTRACT FROM AUTHOR]

As quality soils become scarce and their location is more difficult and expensive, it becomes increasingly necessary to improve soil quality through soil stabilization. The benefits of energy saving and resource conservation, effective recycling of all solid wastes (fly ash, slag, lime, marble dust, etc.) has become a global concern that requires research and development. This article presents the results of a laboratory tests to investigate the effects of marble powder and lime on compaction characteristics, Atterberg limits, shear strength parameters, and unconfined compression test of two Algerian soils. Marble powder and lime are added in varying percentages (2%, 4%, and 6% by weight) to the soil samples. Test results reveal that the liquid limit and plasticity index decrease, whereas the plastic limit increases with the addition of lime and marble powder for soil A and soil B, in which the decrease is more significant with soil A than soil B. The unconfined compressive strength increased with increasing curing time and percentages of lime and marble powder for the two soils. The highest unconfined compressive strength was achieved at 6% marble powder for soil B after 28 days. The addition of marble powder for both soils decreased the optimum moisture content and increased the corresponding maximum dry unit weight. However with lime addition, both soils show decrease in the optimum moisture content and in the corresponding maximum dry unit weight. The shear strength parameters increased for both soils with increase of lime percentages. Whereas for the addition of marble powder, there is an increase of friction angle and decrease of cohesion for soil A. There is considerable change for soil B with marble powder, a decrease in friction angle and an increase in cohesion. The results show that marble powder could be used as a stabilizer for soils with high clay content and known mineralogy composition. In addition, it is very important to get rid of its negative effect on environment and to obtain economical benefit from it. [ABSTRACT FROM AUTHOR]

The geotechnical properties of subgrade soils may need to be enhanced for appropriateness in pavement construction using mineral additives such as cement, lime (L) and fly ash. An experimental investigation was undertaken to study the effects of sodium (Na2SO4) and calcium (CaSO4·2H2O) sulphates on pH and pozzolanic reactions of soil–lime–natural pozzolana (soil–L–NP) mixtures in order to choose an adequate mixture for pavement subgrade soil stabilisation. The pH was measured for different curing periods with and without sulphates. The results showed that increases and decreases in pH values depend on the type of additive and its amount, type of sulphate and its content, mineralogical composition of stabilised soil and curing period. In addition, the pH parameter can be used as an indicator to track the pozzolanic reactions process. On the other hand, clayey subgrade soils can be stabilised with Lime–Natural Pozzolana (L–NP) mixtures containing any amounts of CaSO4·2H2O which is highly recommended. However, Na2SO4 with a low content has a better effect on the behaviour of these soils but become deleterious when its content is greater than 2%. In general, the addition of sulphates accelerates both the pozzolanic reactions and NP dissolution. [ABSTRACT FROM AUTHOR]

Highlights • Study of binder for soil stabilization based on fly ash (FA) alkaline activation. • Different proportion of kaolin are progressively added as model soil. • Calcium-rich phase of FA governs the system reactivity. • The thenardite formation raises the question of durability of such stabilised material. Abstract This study addresses the use of alkali activated high-calcium fly ash-based binder to improve engineering characteristics of soft clay-rich soils as an alternative to common stabilisers. The physico-chemical reaction sequence has been investigated by considering the binder alone and the binder mixed with kaolin. An insight into the reactivity evidenced that calcium-containing phases derived from high-calcium fly ash represent the reactive phases and, hence, pozzolanic activity is the dominant process. New compounds are formed, thenardite Na 2 SO 4 and an amorphous silicate consisting of chains combined with calcium probably incorporating three-dimensional four-fold aluminium environments. [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]

Damages and economical losses due to problematic soils have caused researchers to conduct many studies for the stabilization of these soils within years. Especially, the use of fly ashes in soil stabilization provides great benefits in contributing to the economy, as well as decreasing the environmental pollution. In the present study, the stabilization characteristics of soil-fly ash mixtures were evaluated in terms of Atterberg limits, compaction characteristics, swell potential and unconfined compressive strength with curing effect. To determine these effects, Catalagzi and Soma fly ashes obtained from Turkey were used in different proportions by weight for stabilization of clay soil samples. It was found that the plasticity index of the soils decreased considerably with the addition of fly ashes, while the strength improved and swell potential decreased. The decreasing trend in the swell percentage and swell pressure values decelerated especially after 25% fly ash additive content and negligible changes occurred. Similar behavior was observed in strength tests. Experimental results show that swelling and strength properties of the soils could be improved by using fly ash and Soma fly ash is far more effective than Catalagzi fly ash. [ABSTRACT FROM AUTHOR]

Clayey soils are usually stiff when they are dry and give up their stiffness as they become saturated. Soft clays are associated with low compressive strength and excessive settlement. This reduction in strength due to moisture leads to severe damages to buildings and foundations. The soil behavior can be a challenge to the designer build infrastructure plans to on clay deposits. The damage due to the expansive soils every year is expected to be $1 billion in the USA, £150 million in the UK, and many billions of pounds worldwide. The damages associated with expansive soils are not because of the lack of inadequate engineering solutions but to the failure to identify the existence and magnitude of expansion of these soils in the early stage of project planning. One of the methods for soil improvement is that the problematic soil is replaced by suitable soil. The high cost involved in this method has led researchers to identify alternative methods, and soil stabilization with different additives is one of those methods. Recently, modern scientific techniques of soil stabilization are on offer for this purpose. Stabilized soil is a composite material that is obtained from the combination and optimization of properties of constituent materials. Adding cementing agents such as lime, cement and industrial byproducts like fly ash and slag, with soil results in improved geotechnical properties. However, during the past few decades, a number of cases have been reported where sulfate-rich soils stabilized by cement or lime underwent a significant amount of heave leading to pavement failure. This research paper addressed the some fundamental and success soil improvement that used in civil engineering field. [ABSTRACT FROM AUTHOR]

Clayey subgrade soil requires treatment in order to make the subgrade stable for pavement structures. Treatment of clayey soil i.e. stabilization of clayey soil by cement, lime, and fly ash are established techniques used in geotechnical and highway engineering. Stabilization by alkali activation of fly ash is reported recently but literatures are limited. Present study investigates the stress strain behavior, peak stress and ultimate strain of clayey soil stabilized by slag and slag-fly ash blending by alkali activation. The peak stress as high as 25.0 N/mm may be obtained at 50% slags content when 12 molar sodium hydroxide solutions were used. Peak stress, ultimate strain and slope of stress-strain curve of stabilized clay are controlled by Na/Al and Si/Al ratios. Stress-strain response and peak stress of slag and fly ash blended specimen are not governed by Na/Al and Si/Al ratios; rather the behavior is dependent predominantly on slag content. [ABSTRACT FROM AUTHOR]

Viability of Artificial Neural Network (ANN) in predicting unconfined compressive strength (UCS) of geopolymer stabilized clayey soil has been investigated in this paper. Factors affecting UCS of geopolymer stabilized clayey soil have also been reported. Ground granulated blast furnace slag (GGBS), fly ash (FA) and blend of GGBS and FA (GGBS + FA) were chosen as source materials for geo-polymerization. 28 day UCS of 283 stabilized samples were generated with different combinations of the experimental variables. Based on experimental results ANN based UCS predictive model was devised. The prediction performance of ANN model was compared to that of multi-variable regression (MVR) analysis. Sensitivity analysis employing different methods to quantify the importance of different input parameters were discussed. Finally neural interpretation diagram (NID) to visualize the effect of input parameters on UCS is also presented. [ABSTRACT FROM AUTHOR]

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]

A large amount of coal fly ash produced in thermal power plants is disposed of in landfills which causes many environmental problems. The utilization of fly ash can be encouraged in geotechnical engineering projects. In this paper, the effects of class C and class F fly ash on the mechanical and microstructural behavior and stabilization of clay soil were evaluated through a program of laboratory experiments. The experiments included compaction, unconfined compressive strength, consolidated-undrained triaxial, one-dimensional consolidation tests, and scanning electron microscopy analysis on samples of fly ash-stabilized clay soil after 1, 7, and 28 days of curing. The tests were conducted on mixtures of clay with class C or class F fly ash, ranging from 0% to 30% of the soil. Experimental results showed that the strength parameters and permeability of the stabilized soil improved while the compression and swelling indices decreased by the addition of fly ash and by the increase of curing days. The results obtained from the mechanical tests agreed with the results from the SEM analysis. Based on the results, the soil could be successfully stabilized by using class C fly ash. The improvements in strength, swelling, and permeability parameters of the stabilized soil were higher with the class C fly ash compared with class F fly ash. [ABSTRACT FROM AUTHOR]

Geopolymers, or also known as alkali-activated binders, have recently emerged as a viable alternative to conventional binders (cement) for soil stabilization. Geopolymers employ alkaline activation of industrial waste to create cementitious products inside treated soils, increasing the clayey soils' mechanical and physical qualities. This paper aims to review the utilization of fly ash and ground granulated blast furnace slag (GGBFS)-based geopolymers for soil stabilization by enhancing strength. Previous research only used one type of precursor: fly ash or GGBFS, but the strength value obtained did not meet the ASTM D 4609 (<0.8 Mpa) standard required for soil-stabilizing criteria of road construction applications. This current research focused on the combination of two types of precursors, which are fly ash and GGBFS. The findings of an unconfined compressive strength (UCS) test on stabilized soil samples were discussed. Finally, the paper concludes that GGBFS and fly-ash-based geo-polymers for soil stabilization techniques can be successfully used as a binder for soil stabilization. However, additional research is required to meet the requirement of ASTM D 4609 standard in road construction applications, particularly in subgrade layers. [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]

Pavement structures on poor soil sub grades show early distresses causing the premature failure of the pavement. Clayey soils usually have the potential to demonstrate undesirable engineering behavior, such as low bearing capacity, high shrinkage and swell characteristics and high moisture susceptibility. Stabilization of these soils is a usual practice for improving the strength. This study reports the improvement in the strength of a locally available cohesive soil by addition of both fly ash and lime. Analysis using X-ray diffraction, scanning electron microscopy, coupled with energy dispersive spectroscopy, thermal gravimetric analysis, zeta potential and pH value test was carried out in order to elucidate the stabilization mechanism. The micro level analysis confirmed the breaking of montmorrillonite structure present in the untreated clay after stabilization. In the analysis, it was also confirmed that in the stabilization process, pozzolanic reaction dominated over the cation exchange capacity. [ABSTRACT FROM AUTHOR]

This study evaluated the constituent make up of simulated rainwater runoff from Class C fly ash–stabilized and nonstabilized clay soil using laboratory test pads to assess the potential for impacts to surface water from the use of uncovered fly ash–stabilized soils as potential roadbed material. Recirculated runoff from test pads was sampled and tested during three simulated rainfall events over an 84-day trial period. All samples were analyzed for trace metals. Analytical results from the simulated runoff were screened to identify five indicator parameters in the runoff that were used as the basis for assessing potential environmental effects to surface waters. Runoff water results from fly ash–stabilized test pads for these indicator parameters were compared to water quality benchmarks. Based on the low concentrations measured in runoff relative to applicable criteria, and on the conservative nature of the experimental methods relative to typical field conditions, we concluded that surface runoff from fly ash–stabilized soil would not present significant adverse effects to surface water if used uncovered on low traffic exposed surfaces. [ABSTRACT FROM AUTHOR]

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]

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]

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]

• Blocks were manufactured from soils (A-4, A7-5) and alkali-activated binder. • Fly ash with high content of unburned carbon (up to 39%) was used as precursor. • Paving blocks using soil type A-4 reported compressive strength of 17 MPa at 28 days. • The global warming potential was reduced up to 75% compared to commercial pavers. In this study, blocks were manufactured from clay soil and alkali-activated binders. The soils used were classified as A-4 and A7-5 according to ASTM D3282. The binder was produced from fly ash with a high content of unburned material (carbon). Blast furnace slag and lime were used as calcium sources. The physical–mechanical results of the blocks showed that the texture of the soil is a very important parameter for manufacturing this type of compacted soil masonry element, because the soil with the highest sand content (soil A-4) showed a higher dry density, indicating that this property corresponded to a lower percentage of permeable pores, a lower water absorption and an average compressive strength of 17 MPa at an age of 28 days. A life cycle analysis of the blocks was carried out and the results compared to that of the concrete paving blocks and fired clay blocks, which showed that the Global Warming Potential (GWP) can be reduced from 38 to 75%. Of the materials used to prepare the activated blocks, lime and silicate generate the greatest impact. In general, the results show the technical feasibility of manufacturing alternative blocks to traditional pavers with alkaline activation processes by using natural soils as the basic raw material and a low-quality fly ash as precursor. [ABSTRACT FROM AUTHOR]