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Enhancing the dynamic properties of expansive soils using cementitious materials has attracted the attention of many researchers over the past few decades. Supplementary cementitious materials (SCMs) can be used as partial substitutes for cement owing to their pozzolanic activity that further improves the mechanical performance of cement-stabilized soils upon curing. In this study, the effect of cement and zeolite incorporation on the mechanical behavior of expansive clay was quantified using the pressure wave velocity (Vp) indicator obtained from ultrasonic pulse velocity tests performed at different curing times. Furthermore, a polynomial model was developed to establish the relationship between Vp and zeolite replacement levels at specific curing times and cement contents. The results show that a polynomial function captured the decreasing trend of Vp upon the increase in zeolite at curing times below 14 days. Additionally, the developed equation explained the upward trend of Vp owing to the pozzolanic activity of zeolite at later curing times with an accuracy of over 92%. The coefficients of the polynomial model also increased with the increment of the cement percentage which conformed to the consecutive rise in Vp. Ultimately, the polynomial coefficients were expressed in terms of cement content and curing time using the Volterra series. Using this model, the optimum percentage of cement replaced with zeolite (Zopt), the efficiency of using Zopt instead of cement, and the percentage of zeolite replacement to achieve equivalent Vp of cemented clay samples (ZC) were estimated. The findings of this study contribute to promoting geotechnical sustainability by replacing cement with zeolite that has a considerably lower environmental footprint. Clay is a type of soil that can be found in many construction projects. For instance, many roads and buildings' foundations are constructed on clay soils. To ensure the necessary strength of the clay under the main structure, the soil should often be stabilized using adhesive construction materials such as cement. Interestingly, a portion of the cement could be replaced with other minerals not only to improve engineering performance but also to promote sustainability by lowering cement consumption. In this study, the effect of zeolite as a partial replacement for cement on the strength of clay soils was experimentally evaluated. The effect of various design parameters, such as cement replacement level and curing time, on the stability of clays was investigated using an advanced technique called the ultrasonic pulse velocity (UPV) test. Furthermore, a simple mathematical model was proposed based on the experimental results to help engineers design the stabilization plan and timely decide about the next steps of the construction process. [ABSTRACT FROM AUTHOR]

New ways to apply sustainable materials, such as biomass components, are essential for reducing dependence on fossil fuels. This work investigated the engineering properties of unsaturated expansive subgrade soils stabilized by bio-based energy coproducts containing lignin. Lignin is a waste by-product of the paper and pulp industry that is frequently burned. Highway subgrade could consume lignin as an environmentally benign, low-cost, and energy-efficient chemical substance for soil stabilization. Swell and shrink behavior of expansive subgrade soils complicates highway construction and causes damage to existing highways. However, research on the hydromechanical properties and volume change behavior of lignin-stabilized expansive soil is limited, and better insight is required into its unsaturated behavior for safe and economical pavement design practices. In this research, a series of geotechnical laboratory tests were conducted to characterize expansive subgrade soils treated with lignin by determining the Atterberg limits, compaction and consolidation behaviors, swelling characteristics, and water retention properties. The mechanisms influencing the changes in engineering properties of lignin-treated expansive soils were further investigated using soil pH, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analysis. The study shows that the optimal lignin content contributed to an acceptable degree of soil stabilization. The lignin-based cementing material effectively bonds soil particles together and fills pores, thereby preventing water infiltration into the soil and reducing the swell–shrink potential of stabilized soils. [ABSTRACT FROM AUTHOR]

The low bearing capacity of expansive soils often results in serviceability issues and premature failures of infrastructure built upon them. Various studies have demonstrated the use of different soil treatment methods using mechanical or chemical approaches to stabilize the weak ground as a precaution. Most of the reported studies are limited to either lab-based investigations or field monitoring works without the scientific connection between theory and translation. This study aims to verify the field application of a novel soil stabilization method by conducting laboratory-controlled experiments and field performance testing as verification. Enzyme–based soil stabilization was adopted for in-situ clay soil in combination with ordinary portland cement as a sustainable stabilization approach. Soil samples were collected at different regions from the field to evaluate the effectiveness and the mechanism of soil stabilization in the field by the means of replicating stabilization at the laboratory scale using identical mixing proportions of the additives. The mechanical behavior of stabilized soil was assessed through the unconfined compression strength and California bearing ratio test methods. In addition, the changes in the chemical composition of the soil due to the additives were evaluated through the X-ray diffraction testing technique and microporosity test using 2D images translated to 3D profiles from X-ray micro CT tomography. The efficacy of field stabilization was evaluated by conducting the falling weight deflectometer test in the stabilized site. Results from the study are useful to understand the efficacy of field soil stabilization and enhance the reliability of enzyme–based stabilization in practice. [ABSTRACT FROM AUTHOR]

The present work aims to evaluate expansive soil stabilization using different additives. Twenty soil mixtures consisting of 10%, 20%, 25%, and 30% zeolitic tuff (ZT) with 2%, 4%, and 6% lime in various combinations were used to stabilize the soil for pavement subbase application. A comprehensive test program, including Atterberg's limits, compaction, unconfined compression strength (UCS), California Bearing Ratio (CBR), resilient modulus, and permanent deformation, was performed on natural and stabilized soil specimens. Scanning electron microscopy (SEM) supplied with energy-dispersive X-ray spectroscopy (SEM/EDX) was used to confirm the study findings. Adding ZT increases the availability of the silica and alumina needed for the pozzolanic reaction; test results revealed that adding ZT increases the maximum dry unit weight, CBR, UCS, resilient modulus, decreases plasticity, and permanent deformation. As such, ZT can improve the physical and mechanical properties of lime-stabilized soil as a pavement's subgrade and subbase layers. [ABSTRACT FROM AUTHOR]

This study investigated the different geotechnical characteristics of soil stabilization with the addition of lime and rice husk ash (RHA) in varying amounts (3%, 5%, 7%, and 9% lime, and 4%, 8%, 12%, and 16% RHA). A series of compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), pH, and X-ray diffraction (XRD) tests were performed in the laboratory to assess the impact of the considered admixtures on the stabilized soil parameters. This study also proposes the successful integration of an artificial neural network (ANN) and a Gaussian process regression (GPR) with the experimental UCS observations. The lime concentration, RHA concentration, and curing period were considered as the input parameters, and UCS was considered as the response. The proposed framework was extended to analyze the compressive behavior of treated soil on the minuscule level. Such coupled machine learning-based experimental investigation can provide deep insight into the soil behavior which otherwise would have remained unexplored due to the prohibitive nature of performing laboratory experiments on a large scale. The findings demonstrated the effectiveness of RHA in addition to lime in stabilizing the considered expansive soil. With the addition of lime and RHA mix, the UCS and CBR values of the treated soil increased significantly. [ABSTRACT FROM AUTHOR]

Efficient utilization of problematic soils such as soft clay by imparting additional strength using various stabilization techniques is done to improve soil properties. The application of nanomaterials in the area of soil stabilization has great potential to create a stiff skeleton, especially when blended with cementitious materials. Using the response surface method, this study focused on studying the effects of single and blended cementitious systems, comprising cement (0% to 20%), slag (0% to 20%), and nanosilica (0% to 2.4%), on the properties of soft clay in wet conditions [water-to-soil ratio (w/s) of 53% to 87%]. The mechanical [California bearing ratio (CBR), unconfined compressive strength up to 91 days] and durability (freezing-thawing durability factor) properties of stabilized clay were investigated, and the bulk trends were corroborated by thermogravimetry and microscopy analyses. Based on statistical analysis, incremental addition of cement, slag, and nanosilica led to the systematic increase in the properties of soft clay, albeit to different extents and with different mechanisms. At the low w/s (53%), superior mechanical and durability properties were obtained for soft clay stabilized with the ternary binder comprising cement, slag, and nanosilica. Numerical optimization showed that stabilizing this weak type of soft/expansive clay is possible, but the results (proportions, performance, cost) varied based on the target design criteria and application. [ABSTRACT FROM AUTHOR]

Plastic clays in subgrade may cause major engineering defects such as excessive heave or settlement during the wet season that contribute to the formation of uneven geometry at the pavement surface. Soil stabilization is often a requisite to ameliorate the engineering properties of soft soils or reactive clays. This study investigates the application of nano-silica and nano-alumina to improve the California bearing ratio (CBR) of a local clay. The clay was treated with cement (2%–8%), with nano-additive (0.1%–1.5%) and with cement and nano-additive (3% cement + 0.1%–1.5% nano-additive). The compacted sample was cured for 7 days and subjected to soaked and unsoaked CBR tests. The soaked CBR of the nontreated clay increased by 49% and 27% for 1% nano-silica and 1% nano-alumina treated clay, respectively. Although 3% cement addition improved the CBR of the soaked clay by 28%, the combination of 3% cement with 1% nano-silica and nano-alumina resulted in 196% and 164% increase in the soaked CBR of the nontreated clay, respectively. The combination of nano-additives and cement yielded the same soaked CBR as if 6%–7% cement would have been used. Clay treated with 1% nano-silica and 3% cement achieved the highest CBR value within the tested samples and the sample treated with 1% nano-alumina and 3% cement achieved the lowest free swell potential. The scanning electron microscopy (SEM) micrographs of the treated clay showed the formation of uniform fabric with fewer pore spaces and calcium silicate hydrate (CSH)/calcium aluminate hydrate (CAH) products within the fabric of nano-additive treated clay. [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]

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]

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]

This study presents the characteristics of municipal solid waste (MSW) incineration ash obtained from an electric energy generation plant and evaluates the MSW ash applicability in base road pavement layers through the mixture of ash with a nonlateritic regional clay soil. Chemical, physical, and mechanical tests and the mechanistic-empirical design for a typical pavement structure were carried out on the pure soil and also in the soil mixture with the addition of different ash content (20 and 40%). Fly ash reduced the expansion of the material, showing an increase in the California bearing ratio (CBR) and resilient modulus value. The results are satisfactory, depending on the content and type of ash used, highlighting the positive work of MSW fly ash for its use in base road pavement layers. [ABSTRACT FROM AUTHOR]

Calcium carbide residue (CCR) is a waste product from acetylene gas factories, which is rich in calcium hydroxide []. Because clayey soils contain high amount of natural pozzolanic materials (silica and alumina), CCR can be used as a soil stabilizer. This article presents the engineering properties of CCR-stabilized silty clay to ascertain its performance in pavement base and subbase applications. The input of CCR, which reduces the plasticity index of the clay, increases the optimum water content (OWC) and decreases the maximum dry unit weight () of the stabilized clay. The CCR fixation point, simply obtained from the index test, is proved as a practical indicator for determining the CCR content to obtain the required engineering properties at a particular molding water content. The state of water content controls the densification, chemical reaction, and water absorption capacity. The soaked engineering properties are thus dependent upon the state of water content. For a particular CCR content, the optimum water content is the most appropriate in terms of strength, swelling and collapse behaviors, and bearing capacity. The lower water content is not sufficient for the chemical reaction, while the higher water content yields a higher water/binder ratio. The water absorption is smallest for the CCR-stabilized samples compacted at the OWC. To conclude, the optimal mix proportion is the CCR fixation point at OWC. CCR stabilization is more effective than lime stabilization in terms of engineering, economic, and environmental viewpoints. [ABSTRACT FROM AUTHOR]

The present study examined the potential of pumice waste of the Isparta-Gelincik region, which has been categorized under the lightweight aggregate class as a stabilizing additive to problematic clayey subgrade of pavements. The physical properties of lightweight aggregate material were analyzed. In earlier research, few experiments have been carried out by using experimental samples to test for properties such as stability when frozen, solidity, strength, Atterberg limits, California bearing ratio (CBR), and dynamic repeated load triaxial (RLT) tests. The utilization of Gelincik pumice waste as a stabilizer was determined for the clayey subgrade. Pumice waste of the Isparta-Gelincik region and high plasticity clay were mixed in varying proportions to improve the engineering properties of the clayey soil. The CBR experiment was also performed to observe the change of strength through the use of waste material. In addition, RLT testing was performed by using mixed materials to observe the changes in the resilient moduli values of the mixtures. The results of the experimental research showed that Gelincik pumice waste can be used as a stabilizer for problematic clayey subgrades when constructing roads. This research is the first example of a stabilization approach for problematic clayey subgrade of pavements by using pumice waste. [ABSTRACT FROM AUTHOR]

The potential of woodash to stabilize clay soil was evaluated. The evaluation involved the determination of the geotechnical properties of clay soil in its natural state as well as when mixed with varying proportions of woodash. The parameters tested included the particle size distribution, specific gravity, Atterberg limits, compaction characteristics, California bearing ratio (CBR) and the compressive strength. The CBR and strength tests were repeated after 28-day curing of the treated samples. Results showed that the geotechnical parameters of clay soil are improved substantially by the addition of woodash; plasticity was reduced by 35% and CBR and strength increased by 23–50% and 49–67%, respectively, depending on the compactive energy used. The highest CBR and strength values were achieved at 10% woodash. Results also showed that curing improved the strength of the woodash-treated clay. However, the strength gain was short lived as the strength quickly decreased after 7–14 days of curing. These results imply that although woodash provides some of the beneficial effects of lime in soil stabilization, such as plasticity and swell reduction, improved workability, and strength increase, it is unlikely to be a substitute for lime as strength gain is short lived. [ABSTRACT FROM AUTHOR]

This paper presents, by way of comparison, the effect of fly ash on the volume change of two different types of clay, one a highly plastic expansive clay and the other a nonexpansive clay, also of high plasticity. Expansive clays swell on absorbing water and shrink on drying. Nonexpansive clays undergo large compression at high water contents. The effect of fly ash content on free swell index, swell potential, and swelling pressure of expansive clays was studied. Compression index and secondary consolidation characteristics of both expansive and nonexpansive clays were also determined. Swell potential and swelling pressure, when determined at constant dry unit weight of the sample (mixture), decreased by nearly 50% and, when determined at constant weight of clay, increased by nearly 60% at 20% fly ash content. Compression index and coefficient of secondary consolidation of both the clays decreased by 40% at 20% fly ash content. [ABSTRACT FROM AUTHOR]

Physicochemical interactions between polymer molecules and clay particles affect the swelling rate and magnitude of expansive clay soils. The effectiveness of aqueous solutions of three polymers: Sodium carboxymethyl cellulose (CMC), polyacrylamide (PAM), polyethylene oxide (PEO) ranging in concentration from 0.5 to 10 g/L, as soil stabilization agents against Na-montmorillonite swelling was analyzed. Rates of volumetric swelling of Na-montmorillonite upon hydration were recorded over durations ranging from 120 to 200 h, and data were used to compute the volumetric swelling ratio (VSR), an expression of the clay volume at any time relative to the initial volume of clay in the immersion tube. The results show that PAM, the cationic polymer reduces the VSR by as much as 40% relative to distilled water. PAM molecular weight and concentration have minimal effects on VSR although sorption of PAM of higher molecular weight (PAM B) is favored at aqueous concentration below 2 g/L. Data from x-ray diffraction and batch sorption tests on dried Na-montmorillonite samples indicate that postsorption/swelling interlayer spacings of 0.74 and 0.78 nm for PAM A (molecular weight=4×106) and PAM B (molecular weight=7×106) respectively, are attained through fixation of PAM molecules in clay interlayer space during sorption at an aqueous concentration of 4 g/L. Test results for CMC (the anionic polymer) and PEO (the neutral polymer) show that swelling is not significantly reduced relative to that of distilled water. PAM can be used at aqueous concentrations between 0.5 and 4 g/L as an effective stabilization agent for expansive soils. [ABSTRACT FROM AUTHOR]

This paper aims to show that the addition of lime and lime/cement can significantly improve both the stiffness and the resistance to permanent deformation of clay soils even under adverse, though realistic, curing conditions. The AASHTO Guide for Design of Pavement Structures incorporates a method of calculating subgrade resilient modulus (MR), using repeated load triaxial testing, with respect to seasonal variations of the soil’s moisture content and temperature, while the equivalent British specifications adopt a “soaked California bearing ratio” approach. In practice 8°C is a realistic worst case curing temperature in situ and a (necessarily) wetter underlying clay will allow water to be drawn into the chemically treated layer during curing as a result of suctions, while the material will experience a small degree of confinement after compaction. These conditions have been replicated in a series of repeated load triaxial tests on lime and lime/cement stabilized, predominantly kaolinitic clay and the results compared with those from sealed samples, which were also cured at 8°C. All samples were subjected to 100 cycles of stresses representing 20, 40, 60, and 80% of the relevant undrained shear strength. This paper concludes that allowing the samples access to water is necessary if field performance is to be replicated. [ABSTRACT FROM AUTHOR]

Laboratory tests have been carried out in order to evaluate the improvement in engineering properties relevant to highway design and construction obtained when clayey subgrade soils are stabilized with lime or fly ash. The experimental program included California bearing ratio (CBR) tests to evaluate the bearing strength of stabilized soils used as working platforms during highway construction. The admixture of lime or fly ash caused an increase in the plasticity limit, while both the liquid limit and the plasticity index of the soils have been reduced. Substantial increases in the California bearing ratio value, higher than those of the soil-fly ash mixtures, have been obtained when the soil samples were mixed with lime. The swelling after a 4-day soaking period has been reduced with the addition of both additive materials. The increase in optimum moisture content acts subsidiarily to the increased CBR value, particularly at high lime or fly ash percentages. An analogous effect has been found for the maximum dry density reduction. [ABSTRACT FROM AUTHOR]