Erosion, Mechanical and Microstructural Evolution of Cement Stabilized Coarse Soil for Embankments

Limits to the use of highly compacted bentonite as a deterrent for microbiologically influenced corrosion in a nuclear fuel waste repository

Internal erosion is a phenomenon that occurs in soils constituting hydraulic structures under the influence of internal flow. This erosion occurs because of pipe erosion which becomes widespread, leading in some cases to the rupture of the structure. Soils susceptible to piping, generally have particle size instability. This study aims to provide an empirical understanding of the initiation and development of erosion in coarse soil obtained near Biskra’s dam in Algeria. To assess the soil’s dispersiveness chemical analyses such as SAR and PS were conducted, as well as the particle size criteria were verified. The soil was examined in-depth using a double hydrometer test along with Crumb tests. A Hole Erosion Test (HET) device is developed to investigate the effect of certain parameters, such as the compaction degree and the hole diameter on internal erosion’s onset and progression. The results have shown the instability of the soil toward internal erosion given the considerably eroded particles. furthermore, an inverse relationship between the eroded particles mass and the degree of compaction and the initial hole’s diameter is observed.

Seepage forces due to the flow of water inside embankment hydraulic structures, such as dams or levees, result in internal erosion or piping. This will result in a reduction in soil strength, causing the failure of hydraulic structures. Stabilization of the soil is one of the most effective approaches to avoid such catastrophic failure and prevent significant loss of life and property. The objective of this research is to stabilize sandy soil against internal erosion using fly ash (FA) alone and fly ash mixed with alkali-activated binder (NaOH). Although fly ash is commonly used for clay soil, its reactivity with alkali activators like NaOH makes it a potential candidate for stabilizing non-cohesive sandy soils when combined with alkaline solutions. A well-graded sandy soil was selected and mixed with fly ash alone and fly ash with sodium hydroxide at different percentages. Compaction curves were determined for each percentage, and specimens from the mix were remolded at 98% relative compaction and optimum moisture content corresponding to the compaction curve value. The hole erosion test (HET) was employed to evaluate internal erosion parameters. During the hole erosion test, seepage conditions were simulated by applying a controlled water flow through remolded specimens to replicate erosion caused by internal seepage forces. Additionally, the internal erosion parameters were evaluated at different curing times (2 days, 7 days, and 28 days were selected to capture short-term, intermediate, and long-term effects of chemical reactions on soil stabilization). Parameters such as the friction factor, coefficient of soil erosion, and critical shear stress were obtained, and the erosion rate index (IHET) was determined. It was found that using FA–NaOH significantly reduced internal erosion and increased the erosion rate index and the critical shear of the soil. The addition of 10% fly ash mixed with activated-alkali binder at 7 days curing time stabilized the soil against erosion. At this percentage, the erosion rate index equal to 5.3 and soil was categorized as: “very slow erosion”. However, mixing the sand with fly ash alone has a small or insignificant effect on the internal erosion of the soil, especially at higher percentages of fly ash. The optimum percentage of fly ash alone to improve the soil resistance to internal erosion was found to be 5% at 28 days of curing time where the soil rated as “moderately slow”.

One of the key challenges geotechnical engineers face is the failure of embankments due to internal soil erosion. Therefore, soil stabilization against internal erosion becomes necessary to prevent embankment failure. This paper aims to use lime to stabilize sandy soil against internal erosion. Two types of sandy soil (poorly graded and well-graded) were treated with different percentages of lime (based on the dry weight of the soil) and curing times (1 day, 2 days, and 7 days). For poorly graded soil, the different lime percentages used were from 0.0% to 6.0% with an increment of 1% by dry weight of soil. While for well-graded soil, the lime percentages used were 0.0%, 1.0%, 2.0%, and 3.0% by dry weight of soil. The hole erosion test (HET) was utilized to analyze the erosion parameters of the soil samples. Results proved that lime is an effective soil stabilization agent against the internal erosion of sandy soil. Moreover, for optimum stabilization against internal erosion, poorly graded and well-graded sandy soil required about 5.0% and 3.0% of lime, respectively, with a curing time of 2 days. Significant reduction in erosion rate and improvement in the erosion rate index and critical erosion stress were observed at optimum soil stabilization. In addition, the results demonstrated that the curing time increases the erosion rate index and reduces soil erosion.

In the present experimental investigation, the utilization of euphorbia coagulum as a binder to fabricate euphorbia coagulum modified polyester bamboo fiber composite using a compression molding technique was studied. Composites were fabricated by varying the concentration of pristine bamboo fiber (BF) as well as alkali-treated bamboo fiber from 25% to 50% and also fabricated by the modification of polyester resin (PR) with euphorbia coagulum (EC). Structural and morphological changes of the fiber before and after alkali treatment were analyzed by XRD, SEM, FTIR, and the fabricated composites were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and mechanical properties by universal testing machine (UTM). Alkali treatment removed most of the hemicellulose and lignin content of the fiber which increases the surface roughness of the fiber and the nature of the fiber has been changed from hydrophilic to hydrophobic. It leads to facilitate the interlocking between fiber and matrix resulting in the improvement in mechanical properties of the composites. The maximum improvement in mechanical and thermal properties of composites were observed in case of 40% addition of both the pristine and alkali treated bamboo fiber in the polyester resin matrix. Moreover, it has been observed that with the addition of 30% euphorbia coagulum in the polyester resin further enhanced the mechanical and thermal properties of the composite and decreases the water absorption. The composites developed were found to be eco-friendly and cost effective, can be considered for the multipurpose panel, beam, pedestrian bridge.

Glass fiber/Carbon nanotube/Epoxy hybrid composites: Achieving superior mechanical properties

The mechanical behavior and wear characteristics of nitrided Al-5%Ti-B alloy reinforced with Al2O3 have been investigated in this paper. The integration of Al2O3 reinforcement into the Al-5%Ti-B alloy matrix offers promising opportunities for enhancing the mechanical and wear resistance properties of the composite material. Through a comprehensive experimental approach, various mechanical properties like tensile strength and hardness are evaluated alongside wear behavior under different conditions. The study also investigated how the nitriding treatment influenced both characteristics of microstructures and mechanical properties of the composite material. The results indicate significant improvements in mechanical properties and wear resistance following the incorporation of Al2O3 reinforcement and nitriding treatment. Microstructural analysis using techniques such as scanning electron microscopy and X-ray diffraction provided insights into the structural changes induced by the reinforcement and nitriding processes. The findings of this study contribute to the understanding of the synergistic effects between reinforcement, alloy composition, and surface treatments in enhancing the mechanical and wear properties of metal matrix composites, thereby offering potential applications in various engineering fields.

Construction of earth fill dams offers a cost-effective solution for various purposes. However, their susceptibility to internal soil erosion, known as piping, poses a significant risk of structural failure and resultant loss of life and property. Soil stabilization emerges as a practical technique to fortify these dams against such threats. This study investigated the impact of lime on the internal erosion properties of clay soils, focusing on CH and ML soil types. Specimens of different lime content were prepared and remolded at 95% relative compaction and optimum moisture content. Hole Erosion tests at varying lime concentrations and curing durations were adapted to conduct the investigation. This investigation aims to optimize lime content and curing time for cohesive soil stabilization against internal erosion. Findings revealed that 2% and 5% of quicklime, by dry weight of the soil, effectively stabilized CH and ML soils, respectively, against internal erosion, with a two-day curing period proving optimal. Furthermore, the addition of lime significantly enhanced erosion rate index and critical shear strength in clay soil, underscoring its efficacy in soil stabilization efforts.

Organic–inorganic nanocomposites have attracted great interest due to the remarkable improvement in mechanical properties when compared to neat polymers. The use of a low‐cost nanofiller added to good properties becomes attractive to the industry. Attapulgite (ATP) is a very interesting nanofiller alternative, especially when used with polyolefins, as in the case of high‐density polyethylene (HDPE). However, this system is not simple, as HDPE is a nonpolar polyolefin that can cause low dispersion of ATP. One way to increase the interaction between these phases is the surface modification of ATP. In this work, the surface of ATP was modified using trimethylamine hydrochloride. HDPE/ATP nanocomposites with 1 and 5 wt% of raw ATP (ATPr) or organophilic ATP (ATPo) were prepared by extrusion. The effectiveness of the organophilization process of ATP was evaluated by X‐ray diffraction, mechanical properties (Shore D hardness and tensile test), and thermal properties (thermogravimetric analysis and differential scanning calorimetry), contact angle, and scanning electron microscopy. In the HDPE/ATPo nanocomposites, it was possible to observe an improvement in mechanical and thermal properties when compared to HDPE/ATPr nanocomposites. The organophilization of ATP promoted a greater interaction between the phases, contributing to a better dispersion of ATP in the HDPE matrix.

This study investigates the influence of basalt fiber on the rheological, mechanical, and microstructural properties of sustainable self-compacting concrete (SCC) incorporating fly ash and microsilica as supplementary cementitious materials (SCMs). Various SCC mixes were prepared, incorporating five different volume fractions of basalt fiber (0.05%, 0.1%, 0.5%, 1%, and 1.5%), along with a control mix. The rheological properties of fresh SCC were evaluated using slump flow and V-funnel flow tests. Subsequently, the mechanical properties, including compressive strength, splitting tensile strength, and flexural strength, were measured after 28 days of curing. Additionally, microstructural analysis was conducted using scanning electron microscopy (SEM) on fractured specimen surfaces. The results indicated that the inclusion of basalt fiber adversely affected the flowability of fresh SCC mixes, with increased fiber volume. However, the hardened concrete exhibited significant improvements in mechanical properties with the addition of basalt fibers. The optimal performance was observed in the SCC70-85/0.10 mix specimens, which demonstrated a 69.90% improvement in flexural strength and a 23.47% increase in splitting tensile strength compared with the control specimen. SEM analysis further revealed enhanced microstructural density in the concrete matrix containing basalt fiber. A two-factor analysis of variance (ANOVA) with repetitions was conducted to evaluate the effects of varying basalt fiber concentrations on the compressive, flexural, and tensile strengths of SCC mixes. The ANOVA results indicated significant effects for both SCC grade and basalt fiber concentration, demonstrating that each factor independently affected the compressive, tensile, and flexural strengths of SCC. These findings suggest that the incorporation of basalt fibers holds promise for extending building lifespans and enhancing concrete quality, representing a valuable advancement in structural engineering applications.

Bentonite homogenization with technological voids upon hydration

Laser sintering of screen-printed TiO2 nanoparticles for improvement of mechanical and electrical properties

This paper aims to predict the internal erosion rate index and critical shear of soils based on the initial physical properties of soils. Regression statistical analyses were employed on sixteen types of clayey soils prepared at different initial dry densities and water contents. The Hole Erosion test was conducted to determine the internal erosion parameters: the erosion rate index and the critical shear. Another set of specimens with the same initial dry unit weight and water content was remolded in the direct shear box and tested using the direct shear test to determine the shear strength parameters (i.e., the cohesion and the angle of internal friction). The various physical properties of soil (initial dry unit weight, initial water content, plastic index, liquid limit, optimum water content, maximum dry density, cohesion, and angle of internal friction) were used to develop models that predict both the erosion rate index and the critical shear. The findings show that the initial physical properties can be used to predict the erosion rate index and the critical shear. The coefficient of determination (R2) was found to be between 0.83 and 0.92 to predict the erosion rate index and between 0.85 and 0.9 to predict the critical shear. The high R2 implies that the models can be used to rate the soil erodibility in advance based on simple laboratory testing instead of time-consuming tests. Additionally, the findings give varied options for prediction depending on the availability of the soil initial physical properties.

The hole erosion test (HET) is commonly used to study the occurrence of internal soil erosion when water concentrated leaks occur. This erosion is known as “piping” in soil mechanics. Piping erosion is invisible and occurs randomly within the soil body. Therefore, to gain a better understanding of how piping erosion develops, it would be helpful to utilize a viewable HET design in which the dynamics of the piping hole can be observed directly. In this note, a new HET apparatus is presented that can be used to observe the development of piping erosion and to monitor the dynamic pressure condition during the hole erosion process. A preliminary model test was carried out based on the new viewable HET apparatus and “pressure heads” monitoring technique. The results successfully verified the performance of the proposed apparatus and experimental methods during the process of hole erosion, indicating that the hole shape changes during continuous erosion and is not fully symmetrical because of the initial profile of the hole. The internal hole becomes increasingly curved when subjected to continuous piping flow. Test results agree with the numerical simulation reported in 2015 by Riha and Jandora, who considered the effect of the hole entrance shape.

Internal erosion, among which backward erosion and suffusion, consists of the displacement of soil particles, originating from an embankment or its foundation. In case of flooding, the high head of water can induce piping across a dike, which may finally lead to a breach and inundation of the hinterland. In urban areas structures are often part of the flood defence system and internal erosion phenomena in the interface between dike and structure may occur. The BioGrout process is a biotechnological process in which loose sand is turned into sand stone and this technology can be a new measure for preventing internal erosion. BioGrout may prevent internal erosion by cementing the grains to each other while the permeability is hardly influenced. The main goal of the research described in this paper is to evaluate the suitability of BioGrout as internal erosion prevention technique. Therefore the process and research of BioGrout material is described, the influence of BioGrout on the internal erosion phenomena is studied and the minimum strength improvement, with respect to erosion, has been assessed by hole erosion tests. It was concluded that BioGrout is a feasible measure for retrofitting structures and mitigating (potential) internal erosion problems.