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Using geopolymer in soil stabilization has gained much attention recently due to its efficiency in improving soil properties and being environmentally friendly at the same time. This research aims to investigate the effect of palm oil fuel ash (POFA)-based geopolymer on soft soil stabilization. The mechanical and microstructural performance of two types of clay soil treated with geopolymer produce from POFA material was the focus of this study. In this respect, a series of unconfined compression and direct shear tests were conducted to investigate the mechanical properties of soils treated with POFA-based geopolymer. Furthermore, the microstructural changes in the treated samples were analyzed using field emission electron microscopy (FESEM) and energy dispersive X-ray (EDX). In accordance with the results, it was indicated that the shear strength of both soils soared by increasing the dosage of POFA-based geopolymer. Geopolymer with 40% POFA of the dry weight of soils yielded the highest UCS value at both curing periods, 7 and 28 days. Furthermore, the microstructural analysis revealed material modifications (N-A-S-H gel formation) related to strength enhancement. These results suggest the potentiality of using a POFA-based geopolymer binder to stabilize soft soil. [ABSTRACT FROM AUTHOR]

Copyright of Duzce University Journal of Science & Technology is the property of Duzce University Journal of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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

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

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

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

This paper presents an experimental study, which compares the effect of the sensitivity against the cementation in the recovering of the stress-strain properties in clayey soils from "Sabana de Bogotá". The work methodology included three phases: (i) extraction of samples; (ii) properties assessment of the undisturbed samples; and (ii) stabilization and analysis of the resistance of the stabilized samples with cemented materials. An experimental plan, which included physical and mechanical tests, was developed. The plan had an emphasis on the assessment of the undrained shear strength and the elastic modulus through unconfined compression tests. The samples were compacted and stabilized with the addition of two solid chemical products, calcium carbonate and iron oxide. Results between natural, remoulded and stabilized were compared by means of statistical methods. Therefore, it was found that the use of iron oxide in this kind of soil allows obtaining stress-strain parameters close to the undisturbed state after the compaction process. [ABSTRACT FROM AUTHOR]

This research investigates the microstructural and geotechnical properties, environmental impact, and economic benefit of cement kiln dust (CKD)-treated kaolinite clay with the addition of sodium chloride (NaCl). As a chemical admixture, NaCl is expected to enhance the strength properties of the clay soil stabilized by CKD. To verify this issue, the geotechnical characteristics of CKD-treated soils with different contents of NaCl (2.5, 5, and 10%) were examined. To this end, the Atterberg limits, standard Proctor, unconfined compressive strength and California bearing ratio (CBR) tests were conducted. Besides, scanning electron microscopy (SEM) analysis was used to observe the microstructural changes resulting from using additives. It was found that the addition of NaCl to the CKD-stabilized clay caused the maximum dry density to increase and the optimum moisture content to decrease. 10% NaCl enhanced the unconfined compressive strength of the CKD-treated soil to 18.7% and 8% higher than that of the NaCl-free specimen during 7 and 28 days of curing, respectively. These results were in accordance with the consequences extracted from the CBR behavior diagram. Moreover, cementitious compounds products in the mixtures were presumed to be the significant factor contributing to strength improvements based on the SEM results. The stabilized clayey soil with 15% CKD and 10% NaCl as environment-friendly method could significantly reduce energy consumption, e-CO2 emission, and cost of soil stabilization. [ABSTRACT FROM AUTHOR]

A useful method for the disposal of waste from an incineration plant is to reuse it for geotechnical and civil engineering applications. The primary objective of this study concerns the reuse of local incinerated ash from municipal solid wastes in soil stabilization. Municipal Solid Waste Incinerated Ash (MSWIA) is blended with soil in various combinations and tested for its Atterberg limits, unconfined compressive strength (UCS), California Bearing Ratio (CBR), and Free Swell Index (FSI). A 1-D Consolidation Test was conducted, and changes in the soil during the test were examined by a scanning electron microscopic (SEM) analysis. The test results showed that there are increments in the UCS and CBR values with the reductions in the FSI, swell pressure, and swell potential of the treated soils. [ABSTRACT FROM AUTHOR]

This paper investigates the probable influence of powder from two igneous rocks, namely granite and rhyolite, on the geotechnical properties of lime stabilized clay soil. A clay soil sample was collected from Jhelum, city of the province Punjab in Pakistan, and its major geotechnical properties including particle size distribution, Atterberg limits, Activity, compaction parameters, California Bearing Ratio (CBR) and unconfined compressive strength (UCS) were determined by using standard ASTM procedures. Owing to the presence of clay minerals, the Jhelum soil is classified as CH soil (Fat clays) following the Unified classification system. Lime was added to the soil in the range of 0 – 12 % and the most influential lime percentage, i.e. the one causing the highest possible positive impact on geotechnical properties, was chosen for further stabilization. Following a gradual increase by 8 %, up to 32 % of granite and rhyolite powders were separately mixed with the soil sample showing maximum stabilization with lime, i.e. the sample containing 6 % lime. Each of the resulting samples was tested for all the parameters mentioned above. The results demonstrate that addition of granite and rhyolite powders produces significant improvement in workability and performance of the clay soil previously stabilized with 6 % lime. The improvement is obvious from reduction in Plasticity index, Activity and optimum moisture content, and rapid increase in UCS, maximum dry density and CBR. The principal reason for the observed positive changes is the presence of abundant non-active and denser minerals in granite and rhyolite powders as compared to lime and clay soil. Furthermore, the positive impact of rhyolite on the geotechnical behaviour of soil is relatively higher than granite obviously because of its better petrographic features, physical properties and strength. [ABSTRACT FROM AUTHOR]

Nowadays, there is a storage problem of solid waste materials from the urban transformation projects due to their large volumes. Environmental protection and cost saving are provided when such waste materials are used. Therefore, in recent years the usage of these waste materials has been new trend research topics. In this study, 2% of lime (constant through the experiments) and different percentages of construction concrete wastes (changes between 5% and 35%) were added on a clayey soil taken from field for soil stabilization purposes. First of all, sieve test, hydrometer test and Atterberg test were performed on the soil sample and the soil classified as high plastic clay. Then, the optimum water content and maximum dry density values of the prepared samples has been determined by using proctor compaction test. In order to determine the strength of the samples, 38 mm diameter and 76 mm length cylinders of the samples with the optimum water content has been prepared. Unconfined compression tests were performed on those samples after 3 days, 7 days and 28 days curing time and their strengths have been determined. As a result of these experiments, it was found that the engineering properties of the high plastic clay increases with the different percentages by adding waste material and lime. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

This paper presents a laboratory investigation on the use of construction demolition waste in poor clayey soil to improve its strength and drainage characteristics. Various laboratory tests such as differential free swell, Atterberg's limits, compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), and permeability have been conducted on un-stabilized and Construction Demolition Waste (CDW) stabilized clayey soil. The outcomes revealed that the addition of CDW in poor soil reduced both maximum dry density and optimum moisture content. The UCS, CBR, and permeability got improved on adding optimum content of CDW in poor clayey soil. The secant modulus also increased on addition of the CDW in virgin soil. The regression analysis performed for different tests showed good agreement of laboratory results with predicted values. Thus, it can be revealed that using CDW in stabilization of poor clayey soil will not only solve the problem of its disposal but will also be cost effective and protect the environment. [ABSTRACT FROM AUTHOR]

In this study, an experimental research was conducted on the use of recycled concrete aggregates (RCA) obtained by pulverized of broken concrete samples which were used for determining the strength of concrete. Concrete samples were crushed in the laboratory and reduced to the required dimensions for the experiments. The clayey soil provided in the vicinity was chosen as the sub-base material to be used in road and embankment construction. RCA prepared by sieving 425-micron (No: 40) were mixed with sub-base soil at 5%, 10% and 15% thereby samples were prepared in different mixing ratios. Some geotechnical experiments were performed on the mixtures prepared to determine the effect of RCA on the water-density relationship and mechanical properties of clayey soil such as Proctor, Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR). According to the results of the experimental study, RCA improves the mechanical properties of low plasticity clayey soil. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Ground granulated blast-furnace slag (GGBS), activated with olivine (Mg2SiO4) and sodium hydroxide (NaOH), was used to stabilise a clayey soil. Mechanical and microstructural properties of the stabilised soil were assessed through uniaxial compression strength (UCS) tests, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDS), after curing periods of 7, 18 and 90 days. The UCS of the GGBS-treated soil (without activation with NaOH), even at the highest slag dosage (G20S), after 90 days, showed only a slight increase (142 kPa) relatively to the original soil. When olivine was added to the GGBS-treated mixture (O20G20S), the UCS increased to 444 kPa, after 90 days. However, when NaOH was used as an activator, the UCS of the olivine–GGBS-treated soil (NO20G20S) increased to more than 6000 kPa, after 90 days. This significant strength increase was attributed to the higher reaction degree provided by the NaOH, which enabled a more effective exploitation (dissolution) of the Ca and Mg present in the slag and olivine, respectively, forming a mixture of C–S–H and M–S–H gels. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Loess often has poor engineering properties due to its loose accumulation and strong collapsibility. Therefore, improvement of the soil is necessary to meet the needs of engineering. In the current work, the improvement effect of sodium alginate added in different proportions to loess was studied. Limited water content test and particle size grading test were conducted to study the effect of sodium alginate on the basic physical parameters of soil. In addition, unconfined compressive strength test (UCS) and consolidated undrained test (CU) were used to analyze the changes in the mechanical properties of the soil after improvement. Additionally, permeation and disintegration tests were used to study the change in the soil's water stability. What's more, the microscopic mechanism of sodium alginate improved loess was also proposed based on the results of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that sodium alginate not only can change the liquid-plastic limit and particle size gradation of loess but also improve the strength, shear parameters, and water stability of loess. SEM and XRD studies revealed that sodium alginate changed the microstructure of the loess, formed a colloidal material to encapsulate the soil particles, filled the pores between soil particles, and caused aggregation of the clay material in the soil to form larger particle size via flocculation. These results show that sodium alginate can be used as a more environmental friendly and sustainable additive to replace the traditional soil stabilization additives, such as cement or lime to stabilize loess. [ABSTRACT FROM AUTHOR]

Chemical stabilization is defined as modification of engineering properties of soil with chemical reactions of various additives. Chemical stabilization is applied to the soils which cannot be adequately treated by mechanical stabilization. Chemical stabilization leads to changes in soil properties such as strength, plasticity, compaction and durability, as well as in its permeability. Permeability of soil is important in ground water flow and leakage problems. However, there are few studies about the effect of chemical stabilization on permeability. In this study, the effects of chemical stabilization with lime and perlite combinations on permeability of high plasticity clayey soil were investigated. With the stabilization of high plasticity clayey soils with lime, the permeability of the mixture increases up to 25 times. Moreover, perlite which can be used as a secondary additive in stabilization of such soils causes serious decrease in permeability. [ABSTRACT FROM AUTHOR]

Reactive magnesia (MgO)-activated ground granulated blast furnace slag (GGBS) is a newly developed binder for soil stabilization/solidification. It can be used as an alternative of conventional hydraulic binders for the stabilization/solidification of heavy metal-contaminated soils. Acid rain exposure has been found to weaken the heavy metal immobilization in solidified/stabilized soils in the long term. However, very limited studies have been conducted to investigate the effect of acid rain on the physical and strength properties of GGBS–MgO-stabilized heavy metal-contaminated soils. In this study, GGBS–MgO-stabilized lead (Pb)-contaminated soils are subjected to the semi-dynamic leaching test using the simulated acid rain (SAR) as leachant, which has pH values of 2.0, 3.0, 4.0, and 5.0. Deionized water (pH 7.0) is also used for comparison. Dry density, soil pH, needle penetration depth, and unconfined compressive strength (qu) of the solidified/stabilized soils are measured after the leaching test. The results show that exposure to SAR yields reduction in qu and soil pH, whereas the needle penetration depth increases and dry density changes only marginally. The qu of the solidified/stabilized soils increases noticeably with increased GGBS–MgO content. It is also found that the stabilized Pb-contaminated soil exhibits lower qu than its clean soil counterpart. Furthermore, a quantitative relationship is proposed to correlate the normalized needle penetration resistance with the normalized qu. Finally, a multiple linear regression is performed to statistically reveal the dependence of soil strength on three independent variables, which are SAR pH, Pb concentration and binder content. [ABSTRACT FROM AUTHOR]

Aim of the present note is to contribute to the optimization of the mix-design procedure of lime treated soils with particular reference to compaction characteristics. Seven soils with different plasticity characteristics and clay fractions are included in the experimental program, different amounts of quicklime and hydrated lime were added to the soils by wet mixing and then Standard Proctor compaction was carried out at different water contents in order to study the effect of lime treatment on compaction characteristics. Microstructural investigation was developed by means of scanning electron microscope. A general decrease in the maximum dry unit weight was observed together with a flattening of the Proctor curve. Also optimum water content changes due to lime addition. A factor that takes into account these modifications was defined and compared for several mix designs. Good correlations (confirmed by Fisher's statistical test) between this factor and clay fractions of the soil to be treated were derived for 5% hydrated lime added. In addition, useful directions were retrieved analysing experimental results for soils treated with different types of lime in different proportions. Results contribute to have a preliminary idea of the effective mix design parameters, knowing the soil to be treated, helping, in this way, in possibly reducing the number of tests in the design phase. [ABSTRACT FROM AUTHOR]

The use of waste materials of industries to protect the environment and save the economy has always been significant to humankind. In this research, in order to stabilize and improve soft clay soils, we tried to investigate the possibility of replacing a part of conventional additives in the improvement of soft clay soils (lime) with the waste resulting from the water softening process. In addition, sodium silicate as a facilitating agent of the reactions in soil stabilization process was studied. Firstly, the optimum percentage of lime was obtained by performing the relevant experiments; afterwards, different percentages of waste and sodium silicate were added to this optimum percentage of lime to achieve the best result. Compaction, unconfined compressive strength and consolidation tests were conducted on the specimens, and it was specified that the best function of the stabilized soil will be achieved when there is 6% lime, 6% industrial waste and 1.5% sodium silicate. Then, in order to find the causes of the changes in the results, the specimens were examined using scanning electron microscopy and X-ray diffraction. The pH changes were studied, as well. The results showed that the strength of the treated soil improved with the addition of additives which reduced its porosity by forming the C–S–H gel. [ABSTRACT FROM AUTHOR]

Waste products have recently been used as one of the techniques in soil stabilization. The material is not just environmentally friendly, but also cheap. In this study, two different types of soil stabilizer—lime and alkaline activator (AA) with the inclusion of treated coir fibre as soil reinforcement in marine clay soil—were examined. The inclusion of fibre in the treated soil has had a positive impact in increasing the strength of the soil. Therefore, to assess the effectiveness of the soil treatment, mechanical tests such as indirect tensile strength, flexural test and unconfined compressive strength test were performed at three different curing periods (7, 28 and 90 days) on both untreated and treated soil. From the results, the inclusion of fibre in both lime and alkaline activation indicates an enhancement on post-peak behaviour from brittle to more ductile. Microstructural analyses of Field Emission Scanning Electron Microscope (FESEM) and Energy Dispersive X-ray (EDX) were also conducted after shearing to evaluate the changes of the soil before and after the treatment. Overall, results indicate that the treatment transformed the structure of the soil to become denser where it filled the large pores compared to untreated soil. [ABSTRACT FROM AUTHOR]

Soil stabilization technology based on microbial-induced carbonate precipitation (MICP) has gained widespread interest in geotechnical engineering. MICP has been found to be able to improve soil strength, stiffness, liquefaction resistance, erosion resistance, while maintaining a good permeability simultaneously. MICP processes involves a series of biochemical reactions that are affected by many factors, both intrinsically and externally. This paper reviews various influential factors for MICP process, including bacterial species, concentration of bacteria, temperature, pH, composition and concentration of cementation solution, grouting strategies, and soil properties. Through this comprehensive review, we find that: (1) the species and strains of bacteria, concentration of bacteria solution, temperature, pH value, and the cementation solution properties all affect the characteristics of formed calcium carbonate, such as crystal type, appearance and size, which consequently affect the cementation degree and distribution in geomaterials; (2) the condition with temperature between 20 and 40 °C, pH between 7 and 9.5, the concentration of the cementation solution within 1 mol/L, and high bacteria concentration is optimal for applying MICP in soil. Under the optimal condition, relatively low temperature, high pH value, and low concentration of cementation solution could help retain permeability and vice versa; (3) the effective grain size ranging from 10 to 1000 µm. MICP treatment works most effectively for larger size, well-graded sand; (4) the multi-phase, multi-concentration or electroosmotic grouting method can improve the MICP treatment efficiency. The grouting velocity below 0.042 mol/L/h is beneficial for improving the utilization ratio of cementation solution. The recommended grouting pressure is generally between 0.1 and 0.3 bar for MICP applications in sand and should not exceed 1.1 bar for silty and clayey soils. [ABSTRACT FROM AUTHOR]

Constant rise in price of cement and other binders have caused a constant surge in cost of construction, rehabilitation and maintenance of roads. This study is an attempt to verify the effect of soil stabilization using a chemical stabilizer (lateralite) which is locally produced in Nigeria. Lateralite was used to stabilize two selected soil samples purposely to improve and proffer sustainable subgrade, subbase and base course materials for highway pavement based upon recommended practice of American Association of State Highway and Transportation Officials (AASHTO) classification system. Cement and lime were also used to stabilize the two soil samples, and then the results of the three stabilizers were compared. The first soil sample utilized is a clayey soil material with group classification of A-7-6 whilst the second soil sample was bentonite, a highly plastic swelling clay. Varying percentages of the three stabilizers from 2% to 10% were mixed with the two soil samples. Values obtained before addition of any stabilizer to the A-7-6 lateritic soil and bentonite are MDD of 1.47kN/m3 and 1.15kN/m3; OMC of 19.20% and 38.10%; unsoaked CBR of 8% and 3%; soaked CBR of 6% and 1%; cured unconfined compressive strength of 290 kN/m2 and 46.5 kN/m2 respectively. Values obtained after addition of 10% lateralite to A-7-6 lateritic soil and bentonite resulted in MDD of 1.42kN/m3 and 1.06kN/m3; OMC of 24.00% and 41.50%; soaked CBR of 19.8% and 3.8%; unsoaked CBR of 48.8% and 6.8%; cured unconfined compressive strength of 422 kN/m2 and 64.4 kN/m2 respectively. In all the tests considered for the A-7-6 soil, cement stabilization had the best results and would be most effective in stabilizing this soil. It is followed by the lime stabilization and laterilite was third. However, in the stabilization of the bentonite, there is no significant difference in the results of the three stabilizers; Therefore, laterilite could substitute for cement or lime. Lateralite should be considered for the stabilization of swelling and other very poor soils where cement stabilization would be uneconomical. [ABSTRACT FROM AUTHOR]

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

Subgrades in selected project area may consist of wet, highly plastic clay soil. Weak subgrades can result in fatigue cracking and rutting in asphalt pavement systems. These problems can be prevented by using thick and expensive pavement sections. An alternative to thick pavement sections is to improve the subgrade support quality through soil stabilization. Soils may be improved through the addition of chemical or cementitious additives. These chemical additives range from waste products to manufactured materials and include lime and Portland cement. As a result, this study evolved to find the performance of subgrade formation using lime and cement specific to Jimma subgrade soils. Accordingly, two disturbed samples were collected from different parts of Jimma and the required laboratory tests have been conducted in order to achieve the intended performance. From the tests conducted on Atterberg limits, the addition of cement increased plasticity index for Sample-1 whereas, the addition of cement increased plasticity index initially, while higher percentage of cement led to reduction in plasticity index for Sample-2 and addition of lime increased plasticity index initially and higher percentages of cement led to reduction in plasticity index for both samples. Moreover, addition of cement increases MDD for both samples while OMC increases up to a certain limit for Sample-1 and decreases on further addition whereas the OMC value initially decrease and after that the value increases with further addition for Sample-2. And also in the case of lime stabilization, the MDD decreases up to a certain limit but after that the value increases on further addition for Sample-1 while it was reverse for Sample-2. And the OMC decreases initially for Sample-1 and becomes almost constant while the OMC value first decreases up to a certain limit and after that the value increases with further addition for Sample-2. It was also found that with the addition of stabilizers, cement and lime, the CBR values increased which in turn more applicable for preliminary characterizing the strength of subgrade soils. [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]

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

There has been great interest in biochar application to soil for long‐term carbon (C) sequestration. However, the interactive priming of organic C mineralization, including shifts in microbial community structure and the persistence of biochar in a clayey soil amended with biochar and labile organic matter (LOM) over a relatively long period (i.e. years) remain poorly understood. A 2‐year incubation study was carried out with δ13C‐depleted biochars produced from Eucalyptus saligna Sm. wood biomass at 450 and 550°C. Each of the biochars (at 2%, w/w) in combination with LOM, such as sugarcane residue at input rates of 0, 1, 2 or 4% w/w, were mixed with a C4‐dominated Vertisol. The interactive effect of biochar and LOM on the structure of the microbial community was analysed by terminal restriction fragment length polymorphism (T‐RFLP). Our results showed that at the small LOM rates (0 and 1%), there was a positive priming effect of biochar on organic C in soil (i.e. native soil organic C (SOC) + LOM‐C)), which shifted to being negative when the LOM input was increased to 2 or 4%. Over the 2 years, mineralization of C from the 450°C biochar (1.2–1.7%) was significantly greater than that for 550°C biochar (0.6–1.0%), and the positively primed mineralization of biochar‐C by LOM was enhanced by the increasing rates of LOM input. The negative priming of native SOC + LOM‐C mineralization by biochar was greater at large than small inputs of LOM, which would have been facilitated by greater shifting in fungal communities, while enhancing biochar‐C mineralization and possibly soil aggregation. In conclusion, over the long term, the amount of LOM stabilized by biochar was greater than that of positively primed biochar‐C mineralization by LOM, in particular at the large LOM input. Biochar can persist in soil on a centennial scale and decreases the turnover of native SOC + LOM‐C over the long term, whereas LOM input can shift microbial communities, favouring LOM stabilization in the biochar‐amended Vertisol. Highlights: Do C priming, biochar persistence and microbial response change 2 years after biochar–LOM inputs?Examined interactive C priming (stable‐C isotope), microbial community structure and biochar MRT.Priming of SOC ± LOM‐C by biochar and vice‐versa increased with LOM inputs.Biochar–LOM interaction (2‐year) shifted microorganisms, favouring LOM‐C stabilization in a Vertisol. [ABSTRACT FROM AUTHOR]

• Kaolinitic-illitic, smectitic & allophanic clay fractions were added to a sandy soil. • Wheat residue decomposition was studied in the soil-mineral mixtures. • Clay minerals provided protection to carbon at low residue addition rates. • Carbon decomposition followed: kaolinitic-illitic > smectitic > allophanic minerals. • Carbon stabilisation depended on porous structure and surface area of clay minerals. The interactive effects of the types and contents of soil clay fractions (SCFs) and plant-residue addition rates on soil organic carbon (SOC) stabilisation are largely unknown. We conducted incubation experiments by amending a sandy soil sample with kaolinitic-illitic, smectitic and allophanic SCFs and adding wheat residues to the mineral mixtures to compare their C stabilisation capacity. The rate of carbon (C) decomposition was higher in the kaolinitic-illitic SCF followed by smectitic and allophanic clay minerals. The supply of easily degradable C substrate from decomposing residues markedly influenced the SCFs' abilities to stabilise SOC. The removal of sesquioxides from the SCFs significantly decreased their C stabilisation capacity, which coincided with a decrease in the dehydrogenase activity of the mineral-residue mixture. The allophanic SCF showed the least microbial activity and the greatest C stabilisation due to having a higher proportion of micropores (75%). The high C stabilisation capacity of allophanic SCF could also be explained by its high specific surface area (119 m2 g−1). The results of this study are helpful to understand the role of various SCFs in stabilising added C originating from external wheat residue addition but warrant further validation under field conditions. [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]

In Algeria, inappropriate soils with high plasticity and low bearing capacity are commonly encountered. These soils can be improved using chemical stabilization technique in order to render them acceptable for construction projects. However, various forms of deterioration have been observed in these construction projects due to the presence of sulphates responsible for the formation of new expansive minerals such as mineral ettringite. For this raison, an experimental investigation was undertaken to study the effect of the presence of calcium sulphate (CaSO4·2H2O) on the behavior of the shear strength of two clayey soils stabilized with lime (L; P0L0, P0L4, and P0L8), natural pozzolana (NP; P10L0 and P20L0), and their combination (L-NP; P10L4, P20L4, P10L8, and P20L8). In this study, the mechanical property investigated is the shear strength on samples cured for 7 to 120 days. In addition, X-ray diffraction (XRD) test is also conducted in order to investigate the mineralogical changes of both clayey soils. The results show that both clayey soil samples without CaSO4·2H2O can be successfully stabilized with L or with a combination of lime-natural pozzolana (L-NP), which substantially increases their shear strength and produces high values of shear parameters. In addition, when combining a fraction of CaSO4·2H2O (especially with high content) to samples containing L alone or a combination of L-NP, a further increase in shear strength values is obtained and higher shear parameters values are recorded. The increase in strength values in the presence of CaSO4·2H2O is attributed to the formation of ettringite, which is observed in XRD diagrams. In general, it is shown that the chemical soil stabilization success depends on several factors: the CaSO4·2H2O content, the type of additive and its content, the curing period, and the mineralogical composition of soil. [ABSTRACT FROM AUTHOR]

Geotechnical structures and foundations that are constructed on clay soils normally experience serviceability and structural quandaries due to wetting. Traditional and mechanical binder have been widely used for soil stabilization recently in order to improve clay soil. In this study, a comparison was made between lime and alkaline activation treated tropical marine soil reinforced with modified natural fiber. Treatment of soil with lime and alkaline activation show an excessively brittle behavior that influences the stability of the structure. For this purpose, the inclusion of natural biodegradable material which is coir fiber is needed as it enhanced the tensile strength of the soil matrix. The mechanical properties of unconfined compression test were carried out on tropical marine soil stabilized with lime (5%) and alkali activation with class F fly ash as a precursor (60%) with and without fiber inclusions at different curing times. Based on the test results, the inclusion of modified natural fiber in lime and alkaline activation treated tropical marine clay increased the strength of the soil matrix. [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]

The beneficial role of combining fiber reinforcement with lime stabilization in altering soil behavior has been established in the literature. However, the coupling effect of their combination still remains unclear in terms of its magnitude and microscopic mechanism, especially for natural fibers with special microstructures. The objective of this study was to investigate the coupling effect of wheat straw fiber reinforcement and lime stabilization on the mechanical behavior of Hefei clayey soil. To achieve this, an experimental program including unconsolidated–undrained (UU) triaxial tests and SEM analysis was implemented. Static compaction test samples were prepared on untreated soil, fiber-reinforced soil, lime-stabilized soil, and lime-stabilized/fiber-reinforced soil at optimum moisture content with determining of the maximum dry density of the untreated soil. The lime was added in three different contents of 2%, 4%, and 6%, and 13 mm long wheat straw fiber slices with a cross section one-quarter that of the intact ones were mixed in at 0.2%, 0.4%, and 0.6% by dry weight of soil. Analysis of the derived results indicated that the addition of a small amount of wheat straw fibers into lime-stabilized soil improved the intensity of the strain-softening behavior associated with mere lime stabilization. The observed evidence that the shear strength increase brought by a combination of 0.4% fiber reinforcement and 4% lime stabilization was smaller than the summation of the shear strength increases brought by their presence alone in a sample demonstrated a coupling effect between fiber reinforcement and lime stabilization. This coupling effect was also detected in the comparisons of the secant modulus and failure pattern between the combined treatment and the individual treatments. These manifestations of the coupling effect were explained by a microscopic mechanism wherein the fiber reinforcing effect was made more effective by the ways in which lime chemically stabilized the soil and lime stabilization development was quickened by the water channels passing through the surfaces and honeycomb pores of the wheat straw fibers. [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]

Soil with persistent macroaggregates should maintain its integrity following wetting disturbance. This study determined how wetting-drying cycles affect two pre-sieved macroaggregate size fractions (2–4 mm and 0.6–2 mm) of clay and organic soils pretreated with organic carbon substrates. Soil aggregates were unamended or treated with organic carbon (4 g C from soluble glucose or insoluble wheat straw per kg soil) before being exposed, during three months of incubation, to nine sequential wettings at three wetting intensities (no wetting, slow wetting at the rate of 1 g of water per second or fast wetting with 2 g water per second). The glucose-treated macroaggregates from the clay soil were minimally disturbed by wetting-drying cycles, maintained their shape (shown by high aggregate circularity and low major/minor axis ratio) and were more cohesive, possibly because of a higher microbial activity provided by the glucose treatment. In contrast, the clay soil macroaggregates mixed with wheat straw, which had the same carbon content as glucose, did not persist when exposed to wetting-drying cycles. Macroaggregates from organic soil resisted nine wetting events with or without glucose addition, implying a distinct aggregate binding mechanism in organic soil compared to the clay soil. The persistence of clay soil macroaggregates treated with glucose may be related to microbial processes that promote macroaggregate stability, with glucose physical adhesion expected to substantially improve aggregate stabilization in this mineral soil as well. Glucose-mediated aggregate stabilization can apparently persist for many weeks in an environment with recurring wetting-drying cycles. • Macroaggregates from clay soil disintegrated with 9 repeated wetting events. • Macroaggregates from organic soil resisted 9 wetting events during 3 months. • Glucose improved the persistence of clay soil macroaggregates to repeated wetting. • Glucose maintained aggregate morphology and improved aggregate stabilization. [ABSTRACT FROM AUTHOR]

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

• C:N ratios in soils and particle-size fractions were assessed in tropical highlands. • Sand C:N ratios increase with depth, whereas silt and clay C:N vary little. • C:N ratios decrease with increasing Ca and Mg contents, CEC, and clay activity. • N-enrichment in clays is likely controlled by mineralogy. • R-NH 3 + sorption onto clays can be critical to organic matter stabilization. Factors affecting soil organic carbon (SOC) retention in the tropics are relatively well known, but this is not the case for N retention and thus C:N ratios, a common proxy for organic matter stability. Recent data suggest that SOC and N concentrations vary with climate, whereas soil C:N ratios depend on particle-size fractions contents. However, such knowledge is still incipient for tropical soils, native vegetations and deeper soil layers, which are critical to understand how land use and climate change affect C and N fluxes. We assessed SOC, N and C:N ratios in bulk soils and sand, silt and clay fractions, and their correlations with other soil properties under native tropical forests in the highlands near Lavras, Brazil. Soil samples were collected to 1-m depth in soils of contrasting texture and mineralogy, formed on quartzite, sericite-schist, gabbro, itabirite, ironstone, meta -limestone, gneiss, and phyllite. Mean SOC and N concentrations were generally high, whereas mean soil C:N ratios varied from 9.5 to 18.7 among parent materials, and only in three soils C:N ratios varied considerably with depth. Enrichment factors (EFs) were generally < 1 in the sand and silt fractions for SOC and especially N. Conversely, EFs for clay were mostly > 1 for SOC and even higher (up to 6.58) for N. Such trend indicates that SOC and N are concentrated in clays, and more importantly, that N sorption is favored compared with SOC, and likely dependent on clay mineralogy. Soil C:N ratios decreased with increasing values of exchangeable bases, due to higher N in the most fertile soils, suggesting that a mechanism of R-NH 3 + cationic sorption is likely involved. Our results suggest that soil N is a critical component of the overall stabilization of soil organic matter onto clays of tropical soils, deserving further investigation also under temperate climate and other zones. [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]

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

Lightweight alkali-activated ground granulated blast furnace slag (LAS) is an energy-efficient and environment-friendly cementitious material that can be used as a binder for the fill soil stabilization in subgrade construction. Although physical, hydraulic and mechanical properties of LAS stabilized clayey soils have been previously characterized, their long-term durability under deteriorating environments has not yet been well assessed. This paper reports an experimental study on the sulfate attack resistance of a LAS stabilized clayey soil, which is composed of GGBS, sodium silicate, calcium carbide residue (CCR), air foam, and clayey soil. Stabilized soil specimens are submerged in a sodium sulfate solution for varying periods (3, 7, 14, 28, 60, 90 and 120 days). The mass change percentage, unconfined compressive strength and thermogravimetric characteristics are evaluated at the end of each varying soaking periods. The same virgin soil stabilized by the lightweight Portland cement (LPC) is also tested as a benchmark. The results suggest that the LAS stabilized soil has superior sulfate attack resistance in terms of greater water absorption and higher strength, which is attributed to the presence of larger amount of cementitious hydration products in the LAS stabilized soil, as confirmed via thermogravimetric measurement. [ABSTRACT FROM AUTHOR]

Anchors are mainly employed in foundation systems for resisting uplift forces. A variety of approximate techniques have been proposed to estimate the ultimate pullout capacity of strip anchors in clay. However, little information is available to calculate the pullout capacity of strip anchors installed in a sloping ground. This study presents upper bound analyses of pullout capacities and the corresponding failure surface for strip anchors in a sloping clayey ground. Comparisons of these upper bound solutions with the laboratory test results obtained by Khing et al. & Rao and Prasad are carried out. It is indicated that the laboratory test results tend to underestimate the reduction of pullout capacity of anchors due to the presence of sloping ground, which may introduce safety issues when used for practical designing. The discrepancy between our theoretical results and the laboratory test results is shown, and possible explanations for it are discussed. Simple equations for predicting the pullout capacity of strip anchors are developed to facilitate the use of strip anchors in solving practical problems. [ABSTRACT FROM AUTHOR]