Clayey sand soils require improvement in civil engineering projects due to their low density, high porosity, and inadequate shear behavior. On the other hand, the extensive use of cement in soil stabilization is associated with environmental concerns such as high COQ emissions. In this study, the effect of partial replacement of cement with zeolite (up to 50 %) and the addition of polyvinyl alcohol (PVA) fibers (up to 0.8 wt%) on improving the mechanical, microstructural and environmental properties of clayey sand soil was investigated. Samples were prepared with different cement contents (3 and 6 %) and, after 7 and 28 days of curing, were subjected to compaction, unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV), scanning electron microscope (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and toxicity characteristic leaching procedure (TCLP) tests. The compaction test results showed that maximum dry density (MDD) decreases and optimum moisture content (OMC) increases with increasing zeolite content. The performance of different mixtures showed that the optimum mixture consisted of 6 % cement, 20 % zeolite, and 0.8 % fibers, which increased UCS, ITS, and UPV by 320 %, 194 %, and 35 %, respectively, compared to unstabilized soil. Micro-structural analyses showed the formation of CSH and CAH gels and improved interfacial transition zone bonds. Also, TCLP results showed that zeolite reduced heavy metal leaching. This study, with an innovative approach, investigated the simultaneous effectiveness of zeolite, cement, and fibers and introduced the potential of the UPV method as a non-destructive method for evaluating the mechanical performance of stabilized soil.

Due to the environmental pollution caused by the production and consumption of cement, the demand for new and environmentally friendly methods to improve and strengthen the soil is increasing. In addition, reinforcing the soil with steel fibers improves the mechanical properties, including the formability and bearing capacity of the soil. The purpose of this research is to evaluate the effect of zeolite on the behavior of cemented sand soil reinforced with steel fibers. In the following, the unconfined compressive strength (UCS) test was used to check the compressive strength, and the flexural strength (FT) test was used to check the flexural. It should be mentioned that to improve the soil from cement in the amount of 5% by weight, zeolite in the amount of 0, 25, 50, 75 and 100% was used instead of cement, as well as steel fibers in the amount of 2% and random distribution in the curing of 28-day. In the results of unconfined compressive strength tests, the best replacement percentage of zeolite instead of cement in sandy soil was 25%, which initiated an increase in unconfined compressive strength and an increase in the failure strain of the sample. In the results of flexural strength tests, 25% of zeolite to replace cement in sandy soil affected the greatest increase in flexural strength and increased soft behavior. In addition, with the addition of steel fibers, the samples endured much more displacements than those without fibers. [GRAPHICS]

In this study, the role of zeolite and polyvinyl alcohol (PVA) fibers on the durability of cement-stabilized clayey sand soil under freeze-thaw and wet-dry cycles was investigated. Laboratory tests, including unconfined compressive strength (UCS), scanning electron microscope (SEM), and ultrasonic pulse velocity (UPV), were performed to evaluate the effect of zeolite replacement ratio and fiber content on the durability and mechanical characteristics of the stabilized soil. The results showed that the mechanical properties of cemented samples decreased significantly under wet-dry cycles compared to freeze-thaw cycles. The optimal zeolite replacement ratio to achieve the most appropriate durability behavior of cement-treated clayey sand was 20%. Compared to the unreinforced samples, the samples with 0.8% fibers showed a lower reduction in UCS and mass loss under wet-dry and freeze-thaw cycles. The reduction in UCS was limited to 13% and 15%, respectively. The mass loss was limited to 5.2%, which indicates the positive effect of fibers in improving the durability of soil. Samples containing zeolite and fibers had lower mass loss in wet-dry and freeze-thaw conditions than samples without zeolite and fibers. Finally, the SEM microstructural observations justified the results of the durability tests.

Swelling soils are increasingly recognized as a critical issue in geotechnical engineering, as their presence can lead to substantial damage to built structures. When structures are built on such soils and free swelling is prevented, stresses can develop that may lead to significant damage to the structure. Soil stabilization through the use of additive materials has garnered considerable attention as an effective method for mitigating this problem. The objective of this study was to stabilize the clay soil (CH) with high swelling potential by using sea shell, lime and zeolite additives in two stages. In the initial phase, consistency limits were tested by mixing high plasticity clay soil mixed with 8-10-12-14-16% sea shell 0-3-5-6-8% lime (one of the most used soil stabilizer) and 0-5-10-15-20% zeolite by weight. The three mixtures and the two best percentages determined for each mixture were then combined. Upon completing these steps, five experimental sets were prepared by combining the percentages that yielded the best results. Compaction test, percent swelling test and swelling pressure tests were performed with these datas. According to the test results, adding 14% sea shell, 6% lime and 5% zeolite by weight (SS14L6Z5) gave the smallest swelling value as 1,07% and highes swelling pressure as 23 kPa. This study concludes that the combined use of these additives led to a substantial 96% increase in swelling pressure, along with a marked reduction in swelling potential.

Uranyl ions (UO22+) are the form of uranium usually dissolved in water and are radioactive and can cause serious damage to the environment. Adsorption of uranyl ions is a critical method for removing and safely storing radioactive materials that harm the environment. It is also an important tool for combating water and soil contamination, managing nuclear waste and environmental sustainability. Polymer-based composites were developed for this purpose. Polymer-based composites enable the efficient removal of harmful and radioactive uranium compounds from water and soil. Through the incorporation of polymers and fillers (such as zeolite), materials with specific properties capable of adsorbing uranyl ions with high efficiency can be designed. The ratio of the components constituting the composites can be adjusted to optimize the adsorption capacity, as well as the chemical and thermal behaviors. Two composites were created: P(MA-Z50), consisting of ethylene glycol dimethacrylate (EGDM), methacrylic acid (MA), and zeolite, and P(MA-Z75), which contained a higher amount of zeolite. These composites were synthesized at room temperature and analyzed using various techniques such as Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA), and scanning electron microscopy (SEM). The study investigated the effects of adsorbent quantity, adsorbate concentration, temperature, time, and pH on adsorption efficiency and capacity. The Langmuir adsorption isotherm provided the best fit for uranium (VI) adsorption. The results showed that rapid adsorption occurred within the first 100 min, with the rate slowing down until equilibrium was reached after 360 min. The pseudo-second-order kinetic model best described the adsorption process.

Heavy metal contamination in soil poses significant environmental and geotechnical challenges, requiring effective stabilization to limit contaminant mobility, enhance soil stability, and reduce deformation. This study investigates the dynamic response and microstructural changes in heavy metal-contaminated clayey sand, emphasizing the effects of clay type (kaolin and bentonite) and zeolite stabilization at varying contents (5%, 10%, and 15%). Laboratory tests, including cyclic triaxial, bender element, adsorption, sedimentation, pH measurements, Atterberg limits, and SEM analyses, were performed. Results reveal that contamination significantly reduces liquefaction resistance, with kaolin-based mixtures more susceptible than bentonite-based ones due to differences in plasticity, specific surface area, and swelling capacity. Zeolite stabilization, especially at 10% content, improves resistance by strengthening the soil structure and mitigating pore pressure under cyclic loading. Contamination affects shear modulus and damping ratio differently for kaolin and bentonite mixtures, with zeolite amplifying these impacts at higher contents through enhanced particle dispersion. Heavy metal adsorption increases with bentonite and zeolite addition, with bentonite exhibiting 180% greater lead adsorption than kaolin. Optimal adsorption performance is achieved with 10% zeolite. Microstructural analysis indicates contamination disrupts hydrogen bonding of kaolin, induces flocculation in bentonite, and has minimal effect on the stable structure of zeolite. These findings highlight the importance of clay type, zeolite content, and soil composition in mitigating contamination effects, providing insights into effective soil stabilization strategies.

This paper aims to investigate the effects of zeolite and palm fiber on the strength and durability of cement soil. Based on the findings of previous research, optimal proportions of zeolite, palm fiber, and cement, as well as the appropriate curing age, were determined. Subsequently, unconfined compressive strength tests, dry-wet cycle tests, and freeze-thaw tests were conducted, utilizing NaCl and Na2SO4 solutions over the specified curing period. The strength and durability characteristics of the samples were evaluated by assessing mass and strength loss, taking into account the combined effects of NaCl and Na2SO4 solution erosion. The test data also provide a fitting relationship between strength and the number of cycles under the influence of different solutions, thereby offering a basis for theoretical predictions without the need for additional experiments. Finally, the microscopic mechanisms were analyzed using scanning electron microscopy (SEM). The results indicate that the cement soil composite of zeolite and palm fiber, when combined in optimal proportions, exhibits the best durability and minimal loss of strength and mass, irrespective of whether exposed to clean water or salt erosion, as well as during dry-wet or freeze-thaw cycles.

The low bearing capacity and high erosion potential of calcareous soils are major concerns in marine environments. Lime stabilization is one of the earliest and most widely used methods for improving the mechanical properties of these weak deposits. Nonetheless, the significant amount of air pollution and high energy consumption associated with lime production have led researchers to the exploration of alternative strategies, such as the utilization of supplementary materials to partially replace lime in the stabilization process. In this study, the mechanical behavior of calcareous sand specimens stabilized with 4%, 6%, and 8% of hydrated lime and zeolite-to-lime replacement proportions of 0%, 15%, 30%, 45%, 60%, and 75% was examined through a comprehensive set of unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) tests. The specimens were also subjected to consecutive wetting and drying cycles so that the effects of hydrated lime and zeolite proportions on the durability characteristics of treated calcareous sands were discussed. Results indicated that, in all lime contents, the UCS and constrained modulus (D) of treated samples reached their peak values when lime was substituted with zeolite at an optimum percentage of 60%. Additionally, it was observed that after four and eight wet-dry cycles, the optimum zeolite replacement ratio decreased to 45% and 30%, respectively. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests were also conducted to achieve a better understanding of the microstructural changes in calcareous sands due to the stabilization with hydrated lime and zeolite.

In the current study, the effects of cement or lime content, fibre content, partial cement or lime replacement with zeolite and curing time on the Unconfined Compressive Strength (UCS) of sand have been investigated. The results reveal that increasing cement or lime content increases Maximum Dry Density (MDD) and Optimum Water Content (OMC). However, increasing zeolite replacement percentage decreases MDD and OMC. Increasing the fibre content from 0 to 4% reduces the MDD and increases OMC. The optimum combination of the stabiliser and fibre has been derived from an array of tests. Results comparison shows the 0.5% fibre content and 8% stabiliser results in maximum effect. Also, the optimum percentage of 80% replacement of lime and 30% and 40% replacement of the cement with zeolite leads to the maximum UCS. Observing failure patterns demonstrates the influential performance of fibre content such as controlling the crack length and brittle behaviour. Moreover, SEM analysis was conducted to compare the microscale behaviour.

Although soil stabilization with cement and lime is widely used to overcome the low shear strength of soft clay, which can cause severe damage to the infrastructures founded on such soils, such binders have severe impacts on the environment in terms of increasing emissions of carbon dioxide and the consumption of energy. Therefore, it is necessary to investigate soil improvement using sustainable materials such as byproducts or natural resources as alternatives to conventional binders-cement and lime. In this study, the combination of cement kiln dust as a byproduct and zeolite was used to produce an alkali-activated matrix. The results showed that the strength increased from 124 kPa for the untreated clay to 572 kPa for clay treated with 30% activated stabilizer agent (activated cement kiln dust). Moreover, incorporating zeolite as a partial replacement of the activated cement kiln dust increased the strength drastically to 960 and 2530 kPa for zeolite ratios of 0.1 and 0.6, respectively, which then decreased sharply to 1167 and 800 kPa with further increasing zeolite/pr to 0.8 and 1.0, respectively. The soil that was improved with the activated stabilizer agents was tested under footings subjected to eccentric loading. The results of large-scale loading tests showed clear improvements in terms of increasing the bearing capacity and decreasing the tilt of the footings. Also, a reduction occurred due to the eccentricity decreasing as a result of increasing the thickness of the treated soil layer beneath the footing.