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.

An experimental study was conducted to evaluate the effects of crumb rubber (CR) on mechanical properties of roller compacted concrete (RCC) for use in pavements. In the experiment, proportions of 0%, 10%, 20% and 30% by volume (vol) CR, were incorporated into RCC as sand replacement material. Mixtures were made at cement contents of 275 kg/m3 (11%) and 201 kg/m3 (8.6%). The water content quantities used to prepare RCC mixtures, were determined from the moisture-dry density relationship obtained based on the soil compaction approach. Various mechanical properties were measured comprising compressive strength, splitting tensile strength, ultrasonic pulse velocity, static and dynamic moduli of elasticity. Also measured were pore-related physical tests consisting of water absorption and volume of permeable pores. It was found that cement content has significant influence on the amount of CR that can be suitably utilized in RCC mixtures. The RCCs prepared at the adequate cement content of 275 kg/m3, exhibited suitable performance for all mixtures containing up to 20% vol CR content. Results showed that the standard relationships between compressive strength, static and elastic moduli as established for normal concretes, are also applicable to RCCs.

Stabilizing problematic soils with new materials can reduce environmental problems and improve mechanical properties. This research uses the results of various tests, such as unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV), direct shear test, and standard Proctor compaction, to evaluate the effect of curing time and the nano aluminum oxide contents on the mechanical and shear characteristics of clay soil stabilized with cement and nano aluminum oxide. This research showed that the optimal content of replacing cement with nano aluminum oxide to stabilize clay soil is 0.9% by weight of cement. Adding the optimal content of nano aluminum oxide to cement-stabilized clay soil increased UCS and ITS by 28% and 51%, respectively. Also, the drained internal friction angle and cohesion increased by 17 and 25%, respectively. The results of UPV non-destructive testing can also be used to predict the mechanical characteristics of stabilized clay. By reducing cement consumption and enhancing soil stabilization, this research contributes to Sustainable Development Goals (SDGs) by promoting resource efficiency, lowering environmental impact, and supporting durable infrastructure development.

The increasing demand for sustainable civil engineering solutions requires balancing present-day infrastructure needs with environmental preservation for future generations. This study explores the potential of xanthan gum, an eco-friendly biopolymer, for stabilizing clayey sand as an alternative to traditional soil stabilizers. Various concentrations of xanthan gum (0.25 % to 1.5 %) and curing durations (7, 14, and 28 days) were evaluated using standard geotechnical testing methods, including compaction, unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV), and scanning electron microscopy (SEM) analysis. The soil samples comprised 80 % poorly graded sand and 20 % high-plasticity clay. Results showed a significant improvement in soil properties, with just 0.25 % xanthan gum after a 7-day curing period leading to notable increases in UCS and tensile strength. However, further increases in xanthan gum concentration yielded diminishing returns in strength enhancement. Extending the curing time from 7 to 28 days improved compressive strength and stiffness. Additionally, xanthan gum-enhanced samples exhibited increased energy absorption, stiffness, and brittle behavior, forming a denser soil matrix and improving the particle bonding, supported by UPV results and SEM imagery. Also, the relationship between the stiffness from UCS tests and the ultrasonic pulse velocity was obtained. The findings underscore xanthan gum's potential as a sustainable and effective soil stabilizer for geotechnical applications.

Microbially Induced Calcite Precipitation (MICP) is an eco-friendly method for improving sandy soils, relying on micro-organisms that require nitrogen and essential nutrients to induce carbonate mineral precipitation. Given the substantial annual generation of chicken manure (CM) and the associated challenges in its disposal resulting in environmental pollution, the nutrient-rich composted form of this waste material is proposed in this study as a supplementary additive (along with more costly industrial reagents, e.g., urea) to provide the necessary carbon and nitrogen for the MICP process. To this end, different CM contents (5 %, 10 %, and 15 %) along with various concentrations of cementation solution (1 M, 1.5 M, and 2 M) are employed in multiple improvement cycles to augment the efficiency of the MICP technique. Unconfined Compressive Strength (UCS), Ultrasonic Pulse Velocity (UPV), and Water Absorption (WA) tests are performed to assess the mechanical properties of the samples before and after exposure to freeze-thaw (F-T) cycles, while SEM, XRD, and FTIR analyses are carried out to delineate the formation of calcite within the porous structure of MICP-CM-treated sands. The findings suggest that an optimum percentage of CM (10 %) in the MICP process not only contributes to environmental conservation but also significantly enhances all the mechanical properties of bio-cemented sandy soils due to markedly improved bonding within their porous fabric. The results also show that although prolonged exposure to consecutive F-T cycles causes a reduction in strength and stiffness of enhanced MICP-treated soils, the mechanical properties of such geo-composites still remain within an acceptable range for optimal CM-enhanced biocemented mixtures, significantly superior to those of MICP-treated sands.

Silty sandy soils usually have low shear strength due to their non-cohesive structure, weak internal bonds, and high porosity. Environmental challenges, such as freeze-thaw (F-T) cycles, also reduce the mechanical characteristics and instability of infrastructures and structures built on these soils. Biopolymers and fibers offer a sustainable solution to improve soil strength and F-T strength. However, while much research focuses on stabilizing silty sand, fewer studies examine the combined effects of biopolymers and fibers on soil properties under F-T cycles. Additionally, the correlation between ultrasonic pulse velocity (UPV) and unconfined compressive strength (UCS) in biopolymer-stabilized and fiber-reinforced soils still needs to be explored. This study examines the stabilization of silty sand using Persian gum (PG) (0.5-3%) and kenaf fibers (KF) (0-1.5%) with lengths of 6, 12, and 18 mm at the curing times of 7, 28, and 90 days. The samples were subjected to F-T cycles (0, 1, 2, 3, 6, and 12). The results showed that the highest UCS was achieved with 2.5% PG and 1% KF (12 mm) after 28 days. After 12 F-T cycles, the UCS reductions were 41% for sample with 2.5% PG and 34% for sample 2.5% PG and 1%KF. The swelling after freezing for the 2.5% PG and 1% KF sample and the 2.5% PG sample was 4.8% and 3.45%, respectively. A correlation between UPV and UCS after various F-T cycles was suggested. The scanning electron microscopy (SEM) analysis revealed increased voids, weakened polymer bonds, and cracks after 12 F-T cycles.

Coal waste (CW) could be used for soil stabilization due to the pozzolanic elements it contains. There hasn't been much investigation into how different fibers affect the mechanical qualities of stabilized sand, although adding fibers of any kind to soils may improve the soil because of fiber characteristics like rigidity. For this reason, several tests were carried out on sand that contained 6% cement (by dry weight of used sand), 5 wt% CW, 0, 0.25 wt%, and 0.50 wt% fiber, as well as the unconfined compressive strength (UCS) test, indirect tensile strength (ITS) test, unconsolidated undrained triaxial test (UU), scanning electron microscope (SEM) test and ultrasonic pulse velocity (UPV) test. The results showed that in comparison to other fiber reinforced mix designs, the specimen reinforced with 0.5% fibers and the mix design of 0.25 wt% glass and 0.25 wt% polypropylene (PP) fibers exhibited the maximum strength. Examining the impact of fiber type found that glass fibers influence PP strength more favorably than other fiber types. The use of PP fibers is an excellent solution for the problem of large strains in design processes, while adding glass fibers is considered a suitable treatment for issues related to small strains.

The ultrasonic pulse velocity (UPV) correlates significantly with the density and pore size of subgrade filling materials. This research conducts numerous Proctor and UPV tests to examine how moisture and rock content affect compaction quality. The study measures the changes in UPV across dry density and compaction characteristics. The compacted specimens exhibit distinct microstructures and mechanical properties along the dry and wet sides of the compaction curve, primarily influenced by internal water molecules. The maximum dry density exhibits a positive correlation with the rock content, while the optimal moisture content demonstrates an inverse relationship. As the rock content increases, the relative error of UPV measurement rises. The UPV follows a hump-shaped pattern with the initial moisture content. Three intelligent models are established to forecast dry density. The measure of UPV and PSO-BP-NN model quickly assesses compaction quality. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Bricks are manufactured using clays, which are fired at temperatures ranging from 1000 to 1200 degrees C. Due to the lack of quality clay, it is necessary to find alternate soils and waste materials for manufacturing bricks. The use of agricultural, aqua-cultural, and industrial wastes in the manufacturing of construction bricks leads to low-carbon material. This addresses the problem of agro-aqua-industrial waste disposal. The present study focuses on the utilization of biomass (BM) and slaked seashell powder (SSP) in compressed soil bricks made with locally available lithomargic soil (LS). The proposed soil bricks are prepared with 85% processed lithomargic soil, 12.5% biomass and 2.5% seashell powder. The reaction of multi-binder materials has been activated by one-part activation. The cast soil blocks are temperature cured at 100 degrees C, 250 degrees C, 500 degrees C & 750 degrees C to understand the effect of temperature on the hydration process of binder material. The compressed soil bricks are tested for compressive strength, initial rate of absorption, water absorption test, chloride content, sulphate content, microstructure analysis and thermal conductivity. The strength of soil bricks in bonding and in masonry, 3 prism and 4 prism tests were also conducted. Overall results indicate that bio-based alkali-activated brick masonry is superior for real-time adaptation because it reaches 10 MPa to 11.2 MPa compressive strength and 0.98 MPa to 1.2 MPa shear strength with curing at 500 degrees C.

Soil-cement mixtures have practical applications in geotechnical engineering. Peculiarities associated with the stiffness and strength gains over the curing time provided by cementation need to be investigated, especially for tropical soils. Few studies investigated mixtures of tropical soils and high early strength Portland cement, in order to understand the changes in physical and mechanical properties associated with mineralogical and microstructural alterations caused by artificial cementation. This work aimed to study the effects of cementation on a tropical clay soil using ultrasonic method and to correlate the results with those of other tests. The ultrasonic pulse velocity (UPV) was evaluated for the natural soil and mixtures of soil with different cement contents (1%, 2%, 3%, 5%, 7%), after different curing times, based on propagation of longitudinal ultrasonic waves. Mineralogical and microstructural analyses, geotechnical characterization, resilient modulus (RM) and unconfined compressive strength (UCS) tests, and physical-chemical investigation through volumetric variation were also developed. The ultrasonic response revealed direct effects of cementation on micromorphology, plasticity and granulometry. A microstructure with larger pores was transformed into a dense structure with particles bonded by cementitious compounds. This change provided new paths for the propagation of ultrasonic waves (UPV increases exceeded fourfold for a cement content of 7%) and greater mechanical resistance to the application of cyclic and static loads. Nearly linear increases in UPV, UCS and RM were observed with the addition of cement. A good linear relationship was observed between the values of UPV and RM (R-2 > 0.8968) or UCS (R-2 > 0.8925).