Application of coal fly ash in pavement subgrade stabilisation: A review.

Expansive clays are found in many countries worldwide, and they exhibit inherent volume change during the seasonal moisture variation causing cracks, heaves, and damages to the overlying pavements. Chemical stabilisation is one of the most used approaches to treat the expansive clay subgrades. Cement, Lime and Fly ash are the most commonly used stabilisers, in which fly is cheaper and a by-product obtained from the coal power plant. This paper reviews fly ash stabilisation on various clay types, including low plasticity clays, high plasticity clays, silty clays, organic clays, and peats. The review begins with the properties of fly ash, followed by the characteristics of fly ash stabilised subgrades. The micro-level mechanism, physical, mechanical, and hydraulic characteristics of stabilised pavements are presented graphically for the Class C, and F fly ashes. The micro-level studies reveal that the pozzolanic reaction is stronger than the cation exchange during the fly ash stabilisation. The unconfined compressive strength (UCS), California bearing ratio (CBR) and resilient modulus (Mr) increased with the fly ash addition and curing time for most soft soils except peat clays. Based on the mechanical and hydraulic characteristics, using 15% class C fly ash with 7 days of curing is recommended for optimum performance. Although few research studies confirm that the leachate limit of stabilised soil is within the acceptable limit, further studies are required to investigate the uptake of heavy metals and other certain carcinogenic contaminants. This study will provide key information for researchers and Engineers on the selection of fly ash stabilisation measures for expansive subgrades.

Microstructural and compaction characteristics of tropical black clay soil subgrade modified with lead-zinc mine tailings.

Lead-Zinc Mine tailings (LZMT) are wastes generated after the extraction of lead and zinc from mined mineral ore, whose disposal mechanism is gradually becoming environmentally unfriendly. For effective recycling of LZMT, this present study utilized a combination of LZMT and Portland limestone cement (PLC) to improve the compaction and microstructural characteristics of tropical black clay soil (TBCS) for use in pavement design and construction. The LZMT and PLC were added to the expansive soil in varying proportions with mix ratios generated from Taguchi orthogonal array. The result obtained for the compaction characteristics showed that the maximum dry density (MDD) increased significantly when a combination of 20% LMZT and 4% PLC were blended with the expansive soil. The increase in the MDD was attributed to the formation of cementitious compounds. In addition, the optimum mix ratio obtained from the unconfined compressive strength of the TBCS, was used for the evaluation of the pore structure characteristics which included porosity, tortuosity and permeability. The result obtained from the analysis that was implemented with a combination of fractal geometry and Bradley and Roth adaptive thresholding image segmentation technique, indicates the possibility of a slight reduction in the strength properties of the modified soil due to its high level of porosity. Also, the permeability and tortuosity values obtained from the present study suggest a slight increase in the permeability of the modified soil-additive mixtures which may not be unconnected to the occurrence of pozzolanic reaction that resulted in the agglomeration and flocculation of the LZMT-PLC modified TBCS. Furthermore, microstructural analysis was executed on the modified TBCS and LZMT using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The result from the FTIR analysis indicates the pozzolanic character of LZMT in the presence of Si-O and Al-O tension bond with the bonds around 1000 cm-1 wavenumber, while the SEM analysis reveals the formation of a cementitious compound in the modified expansive soil-LZMT-PLC mixture.

Paper and wood industry waste as a sustainable solution for environmental vulnerabilities of expansive soil: A novel approach.

The traditional disposal methods of paper/wood industry raise serious environmental concerns, thus, requires innovative and productive ideas to manage such waste. This article deals with the appraisal and modification of lignosulphonate, a waste by-product of paper/wood industry, as a soil stabilizer to mitigate the disastrous environmental vulnerabilities of expansive soil related to the wetting-drying cycles. In this context, a novel approach of integrating lignosulphonate with hydrated lime was proposed, based on the short comings of lignosulphonate as a lone soil stabilizer. Periodic variations of wetting-drying cycles were assessed on various engineering properties of untreated and treated expansive soils with the optimum percentage of lignosulphonate, hydrated lime, and proposed binary admixture. Micro-fabric changes were also analyzed to evaluate the stabilization mechanism in mitigating the disastrous environmental aspects of expansive soil. The results showed that both untreated and lignosulphonate treated samples underwent suppression in swelling behavior and gain equilibrium at the third wetting-drying cycle. Whereas, the proposed binary admixture exhibited complete mitigation of the swelling behavior and showed significant hindrance against the wetting-drying cycles in terms of compressibility, hydraulic conductivity, and shear strength of soil. In comparison, lignosulphonate alone showed inferior and hydrated lime showed almost similar amelioration of most of the engineering properties accounting the environmental vulnerabilities of expansive soils. The scanning-electron micro-graphs of all the soil samples showed destructed clay structures with more inter assemblage pore spaces upon wetting-drying cycles. Moreover, the proposed binary admixture exhibited better stabilization mechanism than lignosulphonate alone considering the wetting-drying cycles. Evidently, the proposed binary admixture curtails the environmental vulnerabilities of expansive soil, significantly reduces the lime consumption for expansive soil stabilization, and proposes a sustainable and environment friendly waste management for the paper/wood industry.

Effects of vetiver root on cracking of expansive soils and its mechanistic analysis.

The study investigated the reinforcing effect of vetiver root on soil by conducting outdoor planting tests and indoor root tests. The cracking indexes of soil specimens with varying root contents were analyzed, and a statistical model was established to determine the relationship between the cracking indexes, the number of dry and wet cycles, and the root content. The study revealed the crack evolution law of vetiver-reinforced expansive soil. The study explored the mechanism of the vegetation root in inhibiting the cracking of expansive soil and determined the optimal planting density of vetiver grass through outdoor planting tests. The results indicate that: The surface crack rate (CR), total crack length (CL), and crack number (CN) in the root-soil specimen exhibited exponential growth with an increase in the number of wet and dry cycles. This growth was more pronounced during the first and second cycles. The vetiver root could effectively reduce soil crack formation, and the specimen's cracking resistance is positively correlated with the root content. With the root content increased, the CR, CN, and CL decreased. The logistic model is suited to the CL of added root soil. The logistic model is more suitable for the growth model of the CR of the expansive soil with low root content, while the Boltzmann model is more suitable for the growth model of the CR of the expansive soil with high root content. Width of crack (CW) is better suited to the DoseResp growth model. The Boltzmann model is more applicable to the CN in expansive soils with low reinforcement, while the logistic growth model is more suitable for the development of CN above 0.21% root content. The development of the crack network was influenced by two key factors: the root content and the number of wet and dry cycles. Under the condition of planting roots, the development of crack networks in expansive soil differs from that of expansive soil with added roots, and there is no clear pattern to follow. The inhibitory effect of the vetiver root on cracking of expansive soil is related to the planting density of vetiver.

Compressibility of expansive soil mixed with sand and its correlation to index properties.

Prior research has primarily focused on Atterberg limits, void ratios, and/or water content, often disregarding the impact of coarse material percentage in the soil, which significantly affects compressibility behavior. This paper examines the effects of sand content, initial degree of saturation, and initial dry unit weight on the compressibility behavior of expansive soils. Ninty-six oedometer tests were performed in order to accurately predict the compressibility behavior of expansive soils. The previous studies have attempted to correlate compressibility with different index properties separately, but no single study has taken into consideration all properties influencing compressibility behavior, especially for expansive soils. The findings show that compressibility is greatly influenced by the sand content, initial degree of saturation, and initial dry unit weight. Increasing the initial dry unit weight specifically lowers the compression index and permeability while raising the recompression index for the same percentage of added sand. Moreover, since swelling reduces with increasing initial saturation, raising the saturation degree also lowers the permeability, recompression index, and compression index. The results indicate that a sand content of more than 30 % is recommended for achieving desired properties in expansive clayey soil. This is a result of sand taking the dominant role in the soil mixture, which lowers soil suction and improves soil properties by reducing swelling, permeability, and compressibility. Symbolic regression equations were created to predict the compression and recompression indices, outperforming previous models in accurately predicting the compressibility behavior of expansive soils, considering the percentage of sand. The validation of these equations demonstrates their predictive capabilities.

The infiltration characteristics of expansive soil considering fracture under wet-dry cycle conditions.

Expansive soils exhibit a relatively low permeability coefficient when structurally intact, allowing for their treatment as a homogeneous medium in calculations. However, the susceptibility of the slope's shallow area to numerous primary and secondary cracks under the influence of wetting and drying cycles challenges this approach. Failing to account for the impact of these surface cracks on the soil's permeability can result in a significant discrepancy between calculated and actual conditions. This study initially validated a predictive model for the soil-water characteristic curve that incorporates the effects of wetting and drying cycles. Subsequently, leveraging the fracture volume ratio parameter (pv) and the bimodal distribution characteristics of the dual-pore structure, we proposed a permeability coefficient model for expansive soils that considers fracture effects. This model was integrated with the validated soil-water characteristic curve model to facilitate the analysis of expansive soil's infiltration characteristics under cyclic wetting and drying conditions. The findings indicate that the predictive model accurately captures the hysteresis effect of expansive soil's soil-water characteristics. Moreover, the permeability coefficient model, which accounts for fractures, effectively reflects the infiltration properties of cracked expansive soil and enables the prediction and calculation of its permeability under multiple cycles of wetting and drying. This study introduces a predictive model for the soil-water characteristic curve, leveraging the hysteresis properties of expansive soil. Additionally, it presents a model for calculating the permeability coefficient of expansive soil, utilizing a dual-peak characteristic function. The development of these models establishes a theoretical basis for the computation and analysis of the soil's permeability attributes.

Study on static and dynamic mechanical behavior of expansive soil modified by oyster shell powder.

To investigate the effect of oyster shell powder (OSP) on the static and dynamic properties of expansive soil, the mechanical properties of modified soil were obtained. Taking Ningming expansive soil as the research object, triaxial shear test, dynamic triaxial test and scanning electron microscope test were carried out on plain soil and 9 % expansive soil modified by oyster shell powder (ESMO). The results show that compared with plain soil, the effective cohesion of modified expansive soil with dosp < 1 mm (ESMO (dosp < 1 mm)) and dosp < 0.075 mm (ESMO (dosp < 0.075 mm)) is increased by 15.4 % and 32.8 %, respectively. Under cyclic loading, compared with plain soil, the plastic strain stability value of ESMO (dosp<0.075 mm) is reduced by 40.2 %, the pore water pressure stability value is reduced, and the stiffness is increased. The dynamic mechanical properties of ESMO (dosp<1 mm) showed the opposite trend. Through microscopic experimental analysis, the main reasons for this phenomenon are the particle size distribution, bonding form, and cementation of the two. The results can provide a theoretical basis for the practical application of ESMO and the establishment of constitutive model.

Comparative study on mechanical performance of silty soil and expansive soil below canal structures in cold regions.

Silty soil was widely used as filling soil materials for the replacement of expansive soil in cold regions. This paper presents a straightforward approach for the effects of wetting-drying-freezing-thawing cycles on mechanical behaviors of silty soil and expansive soil by laboratory tests. The results showed that the silty soil and expansive soil after 7th wetting-drying-freezing-thawing cycles presented the decreases of elastic modulus, failure strength, cohesion and angel of internal friction by 8.9 %∼12.0 %, 7.7 %∼9.0 %, 7.9 %, 4.5 % and 17.6 %∼37.0 %, 20.5 %∼29.4 %, 43.2 %, 13.0 %, respectively, indicating that wetting-drying-freezing-thawing cycles had little impact on mechanical property of silty soil and a great influence on that of expansive soil. Among them, the mechanical property attenuation ratio in the first three wetting-drying-freezing-thawing cycles accounted for over 90 % of the total. In the meantime, the micro-structure damage, surface crack characteristics and grain size distribution variations of expansive soil were all more significantly than these of silty soil exposed to wetting-drying-freezing-thawing cycles, which brought insight into the causes of the differences in mechanical properties for silty soil and expansive soil. It is found that the silty soil properties were more stable than expansive soil properties, and the silty soil is very effective for replacing the expansive soil below canal structures in cold regions.

Study on the Water-Sensitivity Passivation Effect and Mechanism of PA-ES Composite Materials.

The water-sensitive effect of expansive soil (ES) poses a serious challenge to the safety and durability of infrastructure. To reduce the effect of water sensitivity on expansive soil, a new powder soil passivator with polyacrylic (PA) as the main component was proposed. In this paper, a series of macroscopic and microscopic tests were conducted to evaluate the water-sensitive passivation effect and mechanism of PA-ES composites. The results showed that PA significantly attenuated the water sensitivity of ES. With the increase in PA content in the PA-ES composites, the water sensitivity of the composites decreased, swelling and shrinkage deformation decreased, and the strength of the composites increased significantly. In addition, when the content of PA in the PA-ES composite is 6%, it can significantly alleviate the deformation of the composite and improve the saturated shear strength of the composite, meeting the requirements of ES engineering disposal. Finally, the results show that the mechanism of PA passivation of ES water-sensitive effect mainly includes adsorption, binding, and filling. The study shows that PA has a broad engineering application prospect as an ES passivator.

Effect of calcined clay on the improvement of compaction, swell and microstructural characteristics of expansive soil.

Expansive soil is problematic soil because its alternate swell shrink behaviour depends on the presence of water. Soil stabilization technique was widely adopted to alter the characteristics of the expansive soil which is suitable for construction. Among the various soil stabilization techniques, chemical stabilization was found to be more suitable method of sustainable stabilizing the soil due to its effective and timely reaction with the chemical compound. Calcined form of clay material is used as an admixture to study the effects on the improvement of soil properties. Calcined Clay (CC) is added into the virgin soil with different percentages of 2%,4%,6%,8% and 10% under varying 1,3,7,14,28 and 60 days of curing by conducting experiments such as standard proctor test, Free Swell test to analyse the compaction characteristics and swelling behaviour of the soil. In addition to that the X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) on virgin and treated soil were studied by varying 2% incremental of CC up to 10% at 28 days of curing. From the test results it shows the variation in the compaction characteristics by rising in Maximum Dry Density (MDD) and reduction in Optimum Moisture Content (OMC) that merges at 8% as an optimum to develop the soil behaviour and from the free swell test, it was found that the Free Swell Index (FSI) of the soil decrease from 210 to 80 at 10% calcined clay added soil and the Mineralogical studies also show the variation in the compounds. Thus, this naturally available calcined clay was used to improve the soil Compaction and swell characteristics that influences the reduction in deformation and increase in shear strength of soil which helped to minimize the environmental problem as well as one of the effective admixtures to improve the expansive soil characteristics.

Evaluation of swelling pressure of an expansive soil stabilized with lime and lignosulphonate as overlay cushion: an experimental and numerical quantification.

Expansive soils are one of the most problematic soils faced by civil engineers in various construction activities. It has the property to swell with the addition of water and shrink on water removal. The volume change behavior of expansive soil occurs vastly during seasonal changes in moisture conditions and can be significantly attenuated by chemically stabilizing the soil. In this study, calcium lignosulphonate (LS), a biopolymer, is added to the soil to curtail the swelling nature of the soil. Lime (L) is also used to treat the soil, and a comparative study is carried out to examine the effectiveness of LS. The expansive soil is treated with several combinations of cushion layers with 1.5% LS, 2% L, 4% L, and combination of 1.5% LS and 2% lime. To counter the swell pressure of the expansive soil, the treated soil and additive composites are placed as a cushion layer over the expansive soil with the replacement ratio of 1:1 and 1:2, represented as configuration "a" and "b." The swelling pressure of the proposed arrangement is evaluated through the constant volume swell apparatus. The soil layers are inundated from the bottom upwards, and the swell pressure is determined for the various configuration adopted. The effectiveness of the stabilized soil cushion over expansive soil is analyzed through the numerical software PLAXIS 2D for further extension to field conditions. As the replacement thickness of stabilized soil increases, the swell pressure decreases. Nevertheless, the lime-treated soil layer depicted lesser swell than the LS-treated soils. Analyzing the conditions for field situations in numerical analysis yielded consistent results with the laboratory inferences.

Integrating wheat straw and silica fume as a balanced mechanical ameliorator for expansive soil: a novel agri-industrial waste solution.

Resource utilization of agricultural and industrial wastes with minimal screening is highly desirable in the context of sustainable development and environmental protection. In this regard, the current study proposes a novel solution of integrating milled wheat straw (WS) with minimal screening and silica fume (SF) in the form of composite binary admixture (CBA) for the stabilization of highly expansive soils. The optimum amount of WS and SF to produce CBA was determined based on a series of Atterberg's limit tests. The mechanical performance of CBA-treated soil was assessed based on the unconfined compression, direct shear, and flexural tests which showed that unconfined compressive strength (qu), cohesion (c), and flexural strength (f) were increased by 94.3%, 65.7%, and 90.7%, respectively, with an addition of 16% of CBA and 28 days of curing. Furthermore, the CBA-treated soil underwent only a 26% reduction in deformability index (ID) with an addition of 24% CBA. Furthermore, volumetric change response was assessed based on ID consolidation and swelling tests which showed that compression index (Cc), recompression index (Cr), swell potential, free swell index (FSI), and swell pressure were reduced by 72.5%, 47.7%, 59%, 35.8%, and 65%, respectively, with an addition of 16% CBA in the soil and 28 days of curing. In addition, wetting-drying (W-D) cycle tests demonstrated that CBA-treated soil was less vulnerable to W-D seasons as compared to untreated soil. Mineralogical and microstructural tests revealed that the balanced Ca:Si and Ca:Al environment created by CBA within the soil matrix produces cementing compounds, i.e., CSH and CAH, imparts strong bonds, and causes aggregation improving the mechanical response of expansive soil.

Dynamic Characteristics of Rubber Reinforced Expansive Soil (ESR) at Positive and Negative Ambient Temperatures.

Using tire waste rubber reinforced expansive soil (ESR) can modify its poor engineering characteristics. The damping properties of ESR at different temperatures may vary dramatically. Two kinds of rubber Ra (large particle size) and Rb (small particle size) are mixed with expansive soil according to gradient ratio. The backbone curves, dynamic shear modulus, and damping ratio of expansive soil in varying temperature fields of 20 °C, -5 °C, and -15 °C are investigated. The Hardin-Drnevich model can well fit the backbone curves of ESR specimens in various temperature fields. Dynamic triaxial results show that 5-10% Ra rubber can withstand higher shear stress in all temperature fields; Rb rubber can increase the dynamic shear modulus of expansive soil and reach the peak value with 10% rubber content. The damping ratio can be significantly improved by using 10% Ra rubber at room temperature, while the ESR damping ratio in a temperature field of -5 °C does not change significantly with increasing shear strain or even decreases; Ra increases the damping ratio of expansive soils in the temperature field of 15 °C while small particle size Rb decreases the damping ratio of expansive soils. The experimental results validate the effectiveness of ESR in the frozen soil area. In an engineering sense, local temperature needs to be considered to use an appropriate ESR, which can provide effective seismic isolation and damping.

Research on the Mechanism and Prevention Methods of the Drying Shrinkage Effect of Earthen Sites.

In view of the fact that it is easy for the ancient city soil site of Cai Kingdom to expand and crack when encountering water, this paper explores the methods to improve the expansion and shrinkage deformation, dry shrinkage cracks and easy water absorption characteristics of the expanded site soil based on a lime and silicone hydrophobic agent. In this paper, the expansive clay in the old city site of Cai Kingdom in Zhumadian was taken as the research object, and the dry-shrinkage fissure test of saturated expansive soil was carried out, to study the influencing factors of the dry-shrinkage cracking of expansive soil in this area. The site soil was modified with lime and glue powder, and the fissure image was quantitatively analyzed by MATLAB. The test shows that the smaller the particle size, the faster the evaporation of water and the smaller the surface fissure rate; the thicker the thickness of the soil sample, the greater the surface fissure rate and the greater the crack width; and with the increase in the number of drying and wetting cycles, the surface fissure rate of the soil sample increases. In this paper, lime and waterproof materials are used to improve the expansive soil. This not only reduces the dry shrinkage crack rate, but also improves the waterproof performance and durability of expansive soil.

Role of Gypsum Content on the Long-Term Performance of Lime-Stabilised Soil.

The role of gypsum level on the long-term strength and expansion of soil stabilised with different lime contents is not well understood. This research, therefore, studied the effect of varying gypsum concentrations of 0, 3, 6, and 9 wt% (equivalent to the sulfate contents of 0, 1.4, 2.8, and 4.2%, respectively) on the performance of sulfate soil stabilised with two lime levels (4 and 6 wt%). This was carried out to establish the threshold level of gypsum/lime (G/L) at which the increase in G/L ratio does not affect the performance of lime-stabilised sulfate soil. Both unconfined compressive strength (UCS) and expansion, along with the derivative thermogravimetric (DTG) analysis, were adopted to accomplish the present objective. Accordingly, the result indicated that the strength and expansion were proportional to the lime and sulfate content, of which a G/L ratio of 1.5 was the optimum case scenario for UCS, and at the same time, the worst-case scenario for expansion. This discovery is vital, as it is anticipated to serve as a benchmark for future research related to the design of effective binders for suppressing the sulfate-induced expansion in lime-stabilised gypseous soil.

Laboratory Study on Improvement of Expansive Soil by Chemically Induced Calcium Carbonate Precipitation.

This paper proposes the use of calcium carbonate (CaCO3) precipitation induced by the addition of calcium chloride (CaCl2) and sodium carbonate (Na2CO3) solutions as a procedure to stabilize and improve expansive soil. A set of laboratory tests, including the free swell test, unloaded swelling ratio test, unconfined compression test, direct shear test, scanning electron microscopy (SEM) test, cyclic wetting-drying test and laboratory-scale precipitation model test, were performed under various curing periods to evaluate the performance of the CaCO3 stabilization. It is concluded from the free swell tests and unloaded swelling ratio tests that the addition of CaCl2 and Na2CO3 can profoundly decrease soil expansion potential. The reduction in expansion parameters is primarily attributed to the strong short-term reactions between clay and stabilizers. In addition, the formed cementation precipitation can decrease the water adsorption capacity of the clay surface and then consequently reduce the expansion potential. The results of unconfined compression tests and direct shear strength tests indicated that the addition of CaCl2 and Na2CO3 has a major effect on geotechnical behavior of expansive soils. Based on the SEM analyses, new cementing crystalline phases formatted by sequentially mixing CaCl2 and Na2CO3 solutions into expansive soil were found to appear in the pore space, which results in a much denser microstructure. A laboratory-scale model test was conducted, and results demonstrate the effectiveness of the CaCO3 precipitation technique in stabilizing the expansive soil procedure. The test results indicated that the concentration of CaCl2 higher than 22.0% and Na2CO3 higher than 21.2% are needed to satisfactorily stabilize expansive soil. It is proposed to implement the precipitation technique in the field by the sequential permeation of CaCl2 and Na2CO3 solutions into soils in situ.

Modification of Mechanical Properties of Expansive Soil from North China by Using Rice Husk Ash.

The construction of buildings on expansive soils poses considerable risk of damage or collapse due to soil shrinkage or swelling made likely by the remarkable degree compressibility and weak shear resistance of such soils. In this research, rice husk ash (RHA) was added to expansive soil samples in different quantities of 0%, 4%, 8%, 12%, and 16% by weight of soil to determine their effects on the plasticity index, compaction parameters, consolidation performance, and California bearing ratio (CBR)of clay soil. The results show that the use of RHA increases the effective stress and decreases the void ratio and coefficient of consolidation. Adding 16% RHA resulted in the greatest reduction in the hydraulic conductivity, void ratio, and coefficient of consolidation. The void ratio decreased from 0.96 to 0.93, consolidation coefficient decreased from 2.52 to 2.33 cm2/s, and hydraulic conductivity decreased from 1.12 to 0.80 cm/s. The addition of RHA improved the soil properties and coefficient of consolidation due to the high density and cohesiveness of RHA. The results of this study can be used to provide a suitable basis for the treatment of expansive soil to provide improved conditions for infrastructure construction.

Experimental study on the effect of plastic waste strips and waste brick powder on strength parameters of expansive soils.

Ethiopia has an abundance of expansive soils. This type of soil is weaker, having low strength and load-resisting characteristics in nature due to its difficulty in volume change when exposed to water. As a result, when saturated with water, the volume of such soils expands and contracts during dry seasons. In civil infrastructure construction, such soil should be removed or improved to be used as foundation soil. However, removing the soil leads to the extra costs of construction. On the other hand, improving requires increasing the stiffness and load-carrying capacity of the road by treating it with stabilizers, which help achieve low cost and good performance. This study aimed at treating such soils with waste-disposed materials to improve the soil's resistance to pressure and to reduce pollution. In this study, locally available expansive soil is treated with brick waste powder (20, 30, and 40 %) and waste plastic strips with (0.25 %, 0.5 %, and 0.75 %) percentages in weight. Disposed plastic water bottles are used. Atterberg limits, compaction, CBR, and unconfined compressive strength were performed to find an optimum percentage of mixes. Many trials were done by varying the percentages of PWS (plastic waste strips) and BP (brick powder). At the addition of 0.75% PWS and 30% BP, a significant change was observed with a considerable improvement in free swell, CBR, and unconfined compressive strength values. The study reveals plastic waste strips and brick waste powder were found to increase the strength qualities of expansive soils. This could pave the way for the use of waste materials in pavement construction while also lowering the environmental pollution.

Study on Crack Development and Micro-Pore Mechanism of Expansive Soil Improved by Coal Gangue under Drying-Wetting Cycles.

Expansive soil is prone to cracks under a drying-wetting cycle environment, which brings many disasters to road engineering. The main purpose of this study is use coal gangue powder to improve expansive soil, in order to reduce its cracks and further explore its micro-pore mechanism. The drying-wetting cycles test is carried out on the soil sample, and the crack parameters of the soil sample are obtained by Matlab and Image J software. The roughness and micro-pore characteristics of the soil samples are revealed by means of the Laser confocal 3D microscope and Mercury intrusion meter. The results show that coal gangue powder reduces the crack area ratio of expansive soil by 48.9%, and the crack initiation time is delayed by at least 60 min. Coal gangue powder can increase the internal roughness of expansive soil. The greater the roughness of the soil, the less cracks in the soil. After six drying-wetting cycles, the porosity and average pore diameter of the improved and expanded soil are reduced by 37% and 30%, respectively, as compared to the plain expansive soil. By analyzing the cumulative pore volume and cumulative pore density parameters of soil samples, it is found that the macro-cracks are caused by the continuous connection and fusion of micro-voids in soil. Coal gangue powder can significantly reduce the proportion of micro-voids, cumulative pore volume, and cumulative pore density in expansive soil, so as to reduce the macro-cracks.

A Novel Application of the Hydrophobic Polyurethane Foam: Expansive Soil Stabilization.

The reversible shrink-swell behavior of expansive soil imposes a serious challenge that threatens the overlying structures' safety and durability. Traditional chemical additives such as lime and cement still exhibit satisfying performance over their counterparts in terms of swelling potential reduction. Nevertheless, significant concerns are associated with these chemicals, in addition to their environmental impact. This paper proposes a novel application of the closed-cell one-component hydrophobic polyurethane foam (HPUF) to stabilize the swelling soil. An extensive experimental study was performed to assess the efficiency of HPUF in mitigating both the swelling and shrinkage response of high montmorillonite content expansive soil. Expansive soil was injected/mixed with different weight ratios of the proposed stabilizer, and the optimum mixing design and injection percentage of the foam resin were identified to be ranged from 10% to 15%. The shrink-swell behaviors of both injected and noninjected samples were compared. Results of this comparison confirmed that HPUF could competently reduce both the swelling potential and the shrinkage cracking of the reactive expansive soil, even after several wet-shrink cycles.