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In this study, the mechanical and durability performance of clay soils reinforced with different proportions of Cherry Marble Powder (CMP) and non-woven geotextile configurations, both independently and in combination, is investigated in detail at both the macro and micro levels. The effectiveness of reinforcement in the stabilization of clay soils in cold climates has been evaluated by means of Gray Correlation Analysis (GCA). The results show that as the CMP ratio and the number of geotextiles increase, the peak strength of the soil increases, with higher CMP levels showing perfect plastic behavior and more geotextiles showing linear strain hardening, particularly in combination. Substantial strength reductions post-7th cycle ranged between 91.09 % and 103.38 % for 12 % CMP and 219.83 % and 270.42 % for three-layered geotextile groups. Cohesion increased by 59.76 % and 179.41 %, while the internal friction angles remained stable and decreased after F-T cycles, except with additives. Failure modes shifted with CMP content, F-T cycles and confining pressure. The transition was from strain hardening to strain softening, with increased shear fracture planes and brittleness. The energy absorption capacity (EAC) increased with the CMP ratio, with the geosynthetic reinforcement increasing the EAC by a factor of 1.5 before and after the F-T cycles. The combined use of CMP and geotextiles in soil stabilization improved the engineering properties in areas of frost, with the optimum gradation being three layers of geotextile and a CMP ratio of 12 %, which effectively mitigated the effects of the maximum F-T cycle. • CMP and geotextile increase soil strength pre and post F-T. • 7 cycles cause significant strength reduction: up to 103.38 % for 12 % CMP, 270.42 % for 3 layers. • Cohesion rises: 59.76 % in 1st stage, 286.96 % in 2nd, 83.99 % in 3rd, and 179.41 % in 4th. • EAC increased with CMP ratio, and geosynthetic boosted CMP's EAC by 1.5 times. • Failure modes shift from strain-hardening to strain-softening with CMP, F-T cycles, and pressure. [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]

[Display omitted] • The incorporation of nanoclay and rice plant fibers improves the mechanical properties of clay soils. • As a reinforcement, rice fibers increase the interlocking and binding of soil particles, while nanoclay's viscous gel increases cohesion. • Rice plant fiber is a highly renewable and eco-friendly material that can be an alternative to traditional stabilizers when combined with nanoclay as a natural material. Conventional stabilizers such as cement and lime are extensively used to improve the mechanical properties of soils. However, these materials suffer from geo-environmental concerns, especially greenhouse gas emissions. In this respect, incorporating sustainable and renewable materials into the soil is an effective technique to enhance its mechanical properties. This study investigated the effect of rice fibers (as a low-cost and eco-friendly material) and nanoclay on soil's mechanism and mechanical performance. In this study, pure soil samples and three nanoclay dosages (0.4, 0.8, and 1%) and three rice fiber ratios (0.3, 0.6, and 0.9%) in three lengths of 5, 10, and 15 mm in random distribution were tested. The prepared samples were characterized through compaction, unconfined compressive strength (UCS), direct shear strength, tensile strength, California bearing ratio (CBR), and scanning electron microscopy (SEM) examinations. First, the optimum amount of nanoclay was determined based on the compressive strength test. Then, the effect of optimum nanoclay and randomly distributed rice fibers was investigated on the mechanical properties of stabilized soil. The results showed that the shear and compressive strengths of the reinforced soil were higher than those of the control samples. An increase in the dosage of rice fibers improved the failure strain, soil ductility, and shear strength. The optimum amount of fibers was 0.9%, exceeding which led to fiber twisting and agglomeration. However, increasing the nanoclay content decreased the failure strain. According to the microscopic examination, when fibers were combined with nanoclay, the interaction between soil particles and fibers increased due to the filling property and the formation of a viscous gel. Overall, fiber added with nanoclay improved the mechanical properties of clay soil and could be used as a low-cost and sustainable option for soil improvement. [ABSTRACT FROM AUTHOR]

Highlights • Analysis of soil-slag mix interactions with expansion and leaching tests. • Magnesium oxide content a predictor of long-term slag expansion. • Mathematical modeling accurately predicts potential ladle furnace slag expansion. • Expansion of soil-slag mixes less than in each individual material. Abstract Volumetric expansion tests are performed on both ladle furnace slag and mixtures with natural soils, with a view to their use in civil engineering projects such as embankment construction and related earth works. The study provides an analysis of the effects of magnesium oxide and proposes an analytical model to predict LFS expansion within shorter time frames than the potential expansion tests specified in the ASTM D 4792 standard. It was found that major chemical reactions between the mixture of clayey soils and the slag occurred in the first 40 h of the potential expansion test. An acceptable relationship was also established between the values of the potential expansion test and the CBR swelling test described in ASTM D 1883. [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]

Highlights • Mechanical properties of geopolymer and OPC treated clayey soil increases overtime. • Geopolymer treated clayey soil is more efficient in dry curing conditions. • OPC treated clayey soil is more efficient in wet curing conditions. • The increase in molarity and content of alkali activator improve the compressive strength. • The geopolymer specimens show a higher ductility compared with OPC. Abstract This study compares the mechanical performance of clayey soil stabilization using volcanic ash (VA) based geopolymer and ordinary Portland cement (OPC). The effects of curing conditions and time, alkali activator/clay and alkali activator molarity, and VA/clay ratio are determined. The compressive strength of the untreated clayey soil specimens could be increased from 0.2 to 4 MPa and 2 to 12 MPa at the OC and DC conditions, respectively, when the soil partially replaced by 15 wt% of the binders. It is observed that geopolymer treatment is more efficient at the dry conditions (DC) while the Portland cement is superb at the wet environments (OC). This difference is associated with the role of water and pH in the kinetics of geopolymerization and the Portland cement hydration. Moreover, increasing the molarity of alkali activator and alkali activator/clay improve the compressive strength of the geopolymer treated soil. Besides, the higher energy absorption in all geopolymer specimens shows the superior ductility of this material in comparison with OPC. [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]

• The use of a residual alkaline solution to enhance the clay properties is examined. • UCS , ITS , UPV and microstructural (SEM , XRD) tests are conducted. • High- and low- calcium fly ash are introduced into the alkaline activation process. • A microstructural analysis showed the formation of binding gels. • An environmental assessment is performed to compare the CO 2 emission. This study aims to evaluate the usability of a recycled alkaline solution, a residue from cleaning iron plates in the car manufacturing industry, to enhance the strength and stiffness of clayey soil by carrying out unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV) and microstructural (SEM , XRD) tests. High- and low- calcium fly ashes with percentages of 10% to 40% and 10% to 30%, respectively, were independently introduced into the alkaline activation process to determine the proper type and content of precursors at room temperature. Two mixtures of the residual cleaning solution blended with 2 M and 4 M NaOH solutions at a weight ratio of one were also utilized to determine how efficiently binary solutions could improve the performance of the parent clay soil. These experiments revealed that all mixtures of the residual alkaline solution work better to activate high-calcium fly ash as compared to the low-calcium fly ash in terms of both mechanical strength and stiffness. The sample of high-calcium fly ash with fly ash/solid and Na/ash ratios equal to 30% and 0.037, respectively, experienced the highest improvement. A microstructural analysis showed the formation of C-(A)-S-H and N–(C)–A–S–H gels in the corresponding sample, thus providing a considerably dense structure, which in turn significantly contributed to the enhancement of the maximum strength and stiffness of the treated soil. In fact, the high-calcium precursor proved to be the best candidate for a low-range alkaline activator because it contributes more calcium to a low-alkaline environment. An environmental impact assessment was also carried out to compare the CO 2 emissions of clays treated with the 4 M NaOH binary solutions tested in this study with those conventionally stabilized by cement and lime and also those treated traditionally with commercial 2, 4, and 8 M NaOH. The samples in this study treated with environmentally friendly binary solutions (residual cleaning solution blended with 2 M and 4 M NaOH solutions at a weight ratio of one) performed better in terms of both CO 2 emissions and strength gain compared to the samples stabilized with conventional materials. [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]

Clay soils are widely distributed throughout the world and are the source of multiple technical problems in their application for the construction of sub-grade and sub-road bases. These types of soils are found in areas where civilian infrastructure such as roads and rural roads must be built. Therefore, in many situations it is necessary to use stabilized expansive soils, in the formation of the foundation and structural layers of linear infrastructures. Soil stabilization is used to increase the load capacity of the soil, and mixtures of lime and cement are generally used as binders. In recent years, interest in the recycling of industrial products and by-products has increased. One example of this is the use of biomass combustion in power plants. The management of significant amounts of waste (biomass bottom ash) from biomass power plants remains a problem. This paper presents the results of an experimental study for stabilizing expansive soil to determine its bearing capacity and mechanical properties via a triaxial test of the addition of biomass bottom ash. A double objective was targeted: reduction of the problems in using this type of soil and provision of a use for this type of waste. The results showed significant improvements in the mechanical. Therefore, herein is proposed the use of biomass bottom ash as a stabilizing agent for expansive soils, to improve the efficiency of the construction process by incorporating this product into a second life cycle as road bases. [ABSTRACT FROM AUTHOR]

Potential of support vector machine regression (SVR) technique for strength estimation of geopolymer stabilized clayey soil has been investigated in the present paper. A comprehensive experimental database of 213 soil samples stabilized with ground granulated blast furnace slag (GGBS) based geopolymer binder were used to develop the SVR model. The database contains 28 day unconfined compressive strength (UCS) results of soil samples generated with different combinations of experimental parameters. A comparative study of different kernel function on SVR model performance is discussed. The study showed that SVR is an effective tool for strength prediction of geopolymer stabilized clayey soil. Subsequently, a parametric study with SVR model was conducted to evaluate the effect of input parameters on UCS. Trends of the result obtained from parametric study were found to be in good agreement with previous research findings. Finally, using the SVR model, an empirical approach for strength prediction of GGBS based geopolymer stabilized clayey soil is proposed for practical application purpose. [ABSTRACT FROM AUTHOR]

• Mechanical and microstructural behavior of a clayey soil stabilized by an alkali-activated binder composed of two residues. • Experimental design to analyze the mechanical behavior of soil-alkali activated binder, and soil-Portland cement mixtures. • Porosity/binder content index as a reliable parameter when evaluating soil stabilization. This paper evaluated the mechanical and microstructural behavior of a clayey soil stabilized by an alkali-activated binder composed of two residues (sugarcane bagasse ash and hydrated eggshell lime) and sodium hydroxide. The sugarcane bagasse ash, an agro-industrial waste, contains high aluminosilicates content (64.74 % silica and 13.25 % alumina), needed for alkali-activation processes; calcium additions from the lime (72.90 % calcium oxide) allow curing at room temperatures. An experimental design analyzed the mechanical behavior of soil-alkali activated binder, and soil-Portland cement mixtures. Unconfined compressive strength (UCS), tensile strength (STS), stiffness (G 0), durability (accumulated loss of mass, ALM), and matric suction tests, and XRD and SEM-EDS investigations were performed. Statistical analysis showed a higher influence of the dry unit weight over the binders' mechanical results. In addition, binders presented similar mechanical results for mixtures cured in room temperature (23 °C) (e.g., UCS around 5 MPa for high density-high binder content samples with 30 % moisture content, and STS around 0.6 MPa for high density-high binder content samples with 28 % moisture content). For both binders, the lowest ALM was 1.63 % for high density-high binder content samples. The porosity/binder content index was a reliable parameter when evaluating soil stabilization. XRD and SEM analysis of alkali-activated samples showed, respectively, an amorphous hump attributed to disordered structures (C S H and (C,N)-A S H) and soil particles embedded in a cementitious matrix. Higher temperature (40 °C) and curing period (28 days) resulted in a denser structure. [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: Clayey soils are stabilized with various dosages of cement kiln dust, volcanic ash and their combinations. The influence of stabilizers is evaluated through Atterberg limits, standard Proctor compaction, unconfined compressive strength, splitting tensile strength, modulus of elasticity and California bearing ratio (CBR) tests. The durability properties of 14 stabilized soil mixtures are also investigated by studying the influence of water immersion on strength, water sorptivity and drying shrinkage. Correlations between strength, modulus of elasticity and CBR are also established. Developed stabilized soil mixtures have shown satisfactory strength and durability characteristics and can be used for low-cost construction to build houses and road infrastructures. The use of stabilized soils with locally available soils, volcanic ash and cement kiln dust can provide sustainability to the local construction industry. [Copyright &y& Elsevier]

• In this study, different types of green cement-free soil stabilizers are proposed. • CKD outperforms cement based on enhancing kaolinite clay soil strength properties. • Silica fume and nano-silica are considered stabilization's activators. • Replacing cement with CKD significantly reduces environmental pollutions. • Nano-silica should not be applied more than 1% in clayey soil stabilization. This investigation aims to assess the nano-silica and silica fume effectiveness on engineering clay soils' characteristics stabilized with cement kiln dust. Laboratory tests, including Atterberg limits, standard Proctor compaction, unconfined compressive strength, and California bearing ratio, were performed. The manufactured specimens were tested 7 and 28 days after preparation to analyze the curing time impacts on soil's strength characteristics. Meanwhile, changes in the chemical and microstructures of soil were observed using scanning electron microscope examination and X-ray diffraction analysis. Subsequently, the mixtures were compared based on eight environmental parameters. To this end, a new environmental index was developed to consider all environmental criteria simultaneously. Afterward, three criteria, including 28-day unconfined compressive strength, environmental index, and unit price, were taken into account as sustainability criteria. Moreover, the gray relational analysis was employed to examine the mixtures' sustainability. The results demonstrated that the amount of 1% nano-silica and 15% silica fume by dry soil weight was an optimum addition content of employed activators for enhancing the CKD-treated soil's geotechnical properties, respectively. Furthermore, the sustainability evaluation revealed that CKD-treated soil was the most sustainable mixture. Given the sustainability effects, nano-silica addition less than 2% and silica fume to the CKD-stabilized soil can lead to propose treated soil with considerably more sustainability than cement. It is essential to highlight that the sustainability of CKD-treated soils containing silica fume was considerably more than that of stabilized soils comprising nano-silica. [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]

• Recycled concrete aggregates are a sustainable replacement for cement in stabilization of clay soils. • Recycled concrete aggregate inclusion in clay soil leads to higher compressive and shear strength. • Recycled concrete aggregate addition to clay soil reduces deformability and settlements. • Clay soil modified with 15% recycled concrete aggregate is strong enough to be used as subbase of rigid pavements. Due to the abundance of urban building constructions and renewals in developing and developed countries, there is a continuous increase in the amount of construction and demolition (C&D) wastes that is landfilled. Recycling and reuse of construction and demolition materials, in applications such as in pavement constructions and non-structural building elements, results in preserving natural resources and reducing environmental pollution. This experimental study evaluates the viability of using recycled concrete aggregates (RCA) for improving the shear/compressive strengths and deformation properties of clay soils. A comprehensive series of compaction, uniaxial compression and direct shear tests were performed on carefully proportioned mixtures of RCA and a clay soil. Test results and observations indicate that the introduction of RCA to clay soils results in lower dry density and higher unconfined compressive strength (UCS) which increases with moist curing. Clay soils mixed with RCA have higher tendencies for dilative behavior (during shear) and enhanced shear strengths compared to the parent clay soil. Mixing RCA with clay soils results in stronger, stiffer and less compressible blends that are particularly suitable for construction purposes such as sub-base/subgrade of road pavements. [ABSTRACT FROM AUTHOR]