Reduction In Compressive Strength Research Articles

Trade-Off Between Wear/Corrosion Performance and Mechanical Properties in D-AlNiCo Poly-Quasicrystals Through CNT Addition to the Microstructure

An ultrafine-grained Al71Ni14.5Co14.5/CNT poly-quasicrystal (QC/CNT) composite was synthesized using spark plasma sintering of powder components developed through electroless Ni-P/CNT plating of Co particles and mechanical alloying. The performance of the synthesized samples was studied using various testing methods, such as room temperature/hot compression, wear, and corrosion tests. The results were compared to the properties of alloy samples fabricated from raw and coated powders (without CNTs). The wear rate and friction coefficient of the quasicrystalline samples improved significantly due to the contribution of the CNTs. The wear rate of the CNT-containing specimens was 0.992 × 10−4 mm3/N/m, which is 47.1% lower than that of the QC sample. The positive impact of the CNTs on the corrosion potential and current density was further validated by the potentiodynamic polarization tests in a saline solution. However, these improvements in surface properties came at the cost of a 21.5% reduction in compressive strength, although the compressive strength still remained above 1.1 GPa at 600 °C. The results highlight an interesting trade-off between surface properties and mechanical strength, pointing toward the development of materials suitable for extreme conditions.

Optimizing sustainable concrete mixes with recycled aggregate and Portland slag cement for reducing environmental impact

Concrete is the world’s most extensively manufactured material, with the integration of recycled materials becoming crucial for sustainable construction. This study investigates the mechanical properties of concrete mixes containing Recycled Aggregates (RA) and Portland Slag Cement (PSC) to understand their suitability for sustainable construction applications. Utilizing normal-strength concrete with a compressive strength of 35 MPa and a 0.45 water-to-cement ratio, fifteen mix designs were tested, varying RA and PSC replacement levels from 0 to 100% and 0% to 50%, respectively. Comprehensive mechanical testing, including compressive and tensile strength assessments at 7 and 28 days, alongside modulus of elasticity and stress–strain curve evaluations, was conducted. The results reveal that full replacement of Natural Aggregate (NA) with RA decreased compressive strength by 10% and modulus of elasticity by 20%. However, a partial replacement of 25% of Ordinary Portland Cement (OPC) with PSC, in the presence of RA, moderated the reduction of compressive strength to 0.92% and increased the modulus of elasticity by 3.7%. The optimum mix, consisting of 75% OPC, 25% PSC, and 50% RA, significantly enhances concrete’s mechanical properties, recommending it for reinforced concrete applications due to its potential environmental and structural benefits.

Expansion in low calcium fly ash-based geopolymer concrete: chemical factors influenced by silica fume and NaOH concentration

Geopolymer technology offers a sustainable alternative to energy-intensive cement production, potentially reducing dependence on natural resources and mitigating environmental impact. Silica fumes (SF) are mostly used to enhance the fresh, hardened, and durable performance of geopolymers. However, their influence on geopolymerization may result in the expansion of the geopolymer mortar (GPM) due to reaction with alkaline liquid. In this study, the effect of NaOH concentration, particle size and dosage of SF, alkaline liquid-to-binder ratio, Na2SiO3-to-NaOH ratio, and sand-to-binder ratio on the expansion behavior of a low calcium fly ash (FA)-based GPM was investigated. FA-based GPMs were tested using two distinct SFs with varying particle sizes (SF1 = 9.5 µm and SF2 = 16.2 µm) and two varying dosages of SF (2.5% and 5%). Physical observations of GPMs revealed that NaOH concentration, particle size and dosage of SF are crucial factors that significantly impact the expansion which is concomitant with a reduction in compressive strength. Analytical techniques such as X-ray diffraction (XRD), Rietveld analysis, Fourier transform infrared spectroscopy (FTIR), and Thermo Gravimetric Analysis (TGA) were employed to comprehensively investigate reaction product(s) that led to the expansion of such GPMs. The chemical analysis confirmed the presence of excess analcime in the mortars fabricated by blending SF1 and FA at 12 M NaOH concentration. This study is the first to report the expansion of low calcium FA-based GPMs blended with a SF of particle size 9.5 µm. These findings emphasize the significance of selecting the appropriate SF particle size to prevent expansion and ensure optimal compressive strength in geopolymer applications.

Optimization of Hybrid Microwave Curing Approach Based On the Performance of Metakaolin-Based Geopolymer Mortars

Geopolymer binders have been highlighted due to their low carbon emission during production and processing. While metakaolin and F-type fly ash are commonly used as raw materials for aluminosilicate-based geopolymers, the long heat-curing requirements for hardening and strength development still pose challenges. This paper investigates the possible use of a hybrid microwave curing technique to design a set-on-demand approach to reduce the duration of heat curing in metakaolin-based geopolymer. The experimental design was established for samples with three different molar ratios (MR; 1.3,1.5, and 1.7) containing metakaolin, fly ash, and silica fume. Samples were subjected to 3 different curing regimes: oven curing, microwave (MW) curing, and hybrid curing (a combination of optimized microwave and oven curing). The performance evaluation was based on compressive strength, dimensional stability, and alkali leaching (efflorescence). Implementing only MW curing resulted in a significant decrease in compressive strength compared to their counterpart oven-cured samples. The reduction of compressive strength was more pronounced at lower molar ratios. The design of a hybrid curing approach where a portion of oven curing was replaced by MW resulted in a higher strength development than those only cured with MW. Similarly, the efficiency of hybrid curing was more pronounced in samples having MR of 1.5 and 1.7. Using MW curing in the geopolymer binders did not affect the alkali leaching; however, it increased the material’s drying shrinkage. Results showed that replacing a portion of oven curing with microwave curing in a hybrid approach can increase the operation speed and the hardening rate without significantly decreasing compressive strength.

A test on fire-induced damage of concrete with multiple parameters analysis—Based on tunnel linings of China

Fires in highway tunnels will have a significant impact on the structural performance of lining materials. A ablation test was conducted on 288 concrete specimens (1500 ×1500 ×1500 mm) with four commonly used grades of C20, C25, C30, and C35 at temperature levels of 300 ℃, 600 ℃, 750 ℃, and 900 ℃ for constant periods of 1 h, 2 h, and 4 h. The experiment revealed that: (1) From low to high temperatures, the specimens experienced cracking, spalling, explosion and eventually complete collapse; all grades of concrete remained intact or mostly intact at 600 ℃ but suffered varying degrees of damage above 750 ℃. (2) At the same fire temperature, the damage rate increased linearly with longer ablation time; while at the same ablation time, the damage rate increased quadratically with higher fire temperature. (3) The ultrasonic wave velocity ratio decreased exponentially as the ablation time increased; higher fire temperatures resulted in lower wave velocity ratios within the same ablation time period and there was a turning point at a two-hour ablation time where specimen integrity was lost. (4) For concrete specimens of the same grade and under identical exposure times to fire, as the fire temperature increased,the rate of compressive strength reduction accelerated significantly; sudden drops in compressive strength occurred at temperatures of 600 °C，750 °C，and900°C,and there was a turning point for compressive strength reduction loss after one hour's ablation to fire.(5) When subjected to high ablation temperatures,the decrease rate in concrete strength exceeded that in wave velocity,and changes in strength were more sensitive than changes in wave velocity.

Effect of Waste Glass Powder Replacement of Hydraulic Lime on Properties of Natural Hydraulic Lime Mortars.

This paper investigates the effects of the partial replacement of natural hydraulic lime (NHL) with waste glass powder (GP) on the physical, mechanical, and microstructural properties of NHL mortars. In the experimental study, five mixtures containing up to 50% GP were prepared to evaluate its effect on the flow, carbonation, unit weight, water absorption, porosity, ultrasonic pulse velocity, capillary water absorption, compressive strength, and microstructure of NHL mortars. The experimental results suggest that the partial replacement of NHL with GP significantly affects the properties of NHL mortars. A reduction in compressive strength was observed with increasing GP content in mortars at both early and later stages. Nevertheless, the compressive strength difference between samples containing 50% GP and the reference was found to be relatively minor at 91 days, implying an enhanced pozzolanic reaction over time. The incorporation of GP improved the consistency and capillary water absorption of mortars, while the opposite was observed for ultrasonic pulse velocity, porosity, and water absorption. The microstructural analysis revealed distinct changes in the structure of samples incorporating GP. The partial substitution of hydraulic lime with GP could be beneficial in reducing the CO2 emissions of NHL mortars.

Sustainable and mechanical properties of Engineered Cementitious Composites with biochar: Integrating micro- and macro-mechanical insight

Engineered Cementitious Composites (ECC) are ductile, strain-hardening cementitious composites with a tightly controlled crack opening profile. A significant concern in the development and application of ECC is its high carbon emissions associated with high cement content consumption. As an emerging green additive, biochar can significantly cut down on the carbon emission of concrete products. However, research that integrates micro- and macro-mechanical insights with biochar incorporation is limited. In this study, micro-mechanical tools indicated that a certain amount of substitution biochar could enhance the tensile properties of ECC. The study assessed various properties including compressive strength, porosity, density, tensile performance, crack pattern, sustainability and cost of ECC with different biochar proportions. The findings showed that incorporating 10 %–20 % biochar effectively increased the tensile strain capacity and decreased the crack opening width in ECC materials. This improvement can be attributed to the introduction of finer biochar particles (≤75 μm) at the fiber/matrix interfacial transition zone, which alters the fiber-bridging force by reducing the chemical and frictional bond strength between the fiber and matrix, as revealed by micro-mechanical tests and microstructural inspection. Moreover, the utilization of biochar contributes to reducing the carbon emission of ECC, enhancing sustainability while maintaining a ∼10 % minimal reduction in compressive strength. Overall, this study introduces a novel approach for reusing low-carbon biomass waste in the production of building materials, offering potential advantages in micro- and macro-mechanical performance, cost-effectiveness, and environmental sustainability.

Ensemble machine learning models for compressive strength and elastic modulus of recycled brick aggregate concrete

This study delivers an in-depth analysis of predicting the compressive strength and elastic modulus of recycled brick aggregate concrete (RBAC). It assembles an extensive database of 633 compression test results and develops five ensemble learning models—random forest (RF), gradient boosting regression trees (GBRT), extreme gradient boosting (XGB), light gradient boosting machine (LGBM) and stacking (St). These models are evaluated against existing empirical formulas with respect to their effectiveness. The findings reveal that machine learning (ML) models outperform existing formulas: for compressive strength prediction, traditional models achieve a maximum determination coefficient R² of 0.38, whereas ML models attain an R² range of 0.91–0.94. For elastic modulus, the highest R² values are 0.44 for traditional models and 0.97 for ML models. Notably, the LGBM and St models excel in predicting compressive strength and elastic modulus, respectively. The study also identifies critical parameters influencing RBAC’s compressive behavior and highlights their impact trends. Remarkably, while the mass-weighted water absorption of coarse aggregates and the replacement ratio of recycled brick aggregates (RBAs) have less impact on compressive strength compared to the effective water-to-cement ratio, they become more influential for elastic modulus. Additionally, the decrease in elastic modulus due to higher RBA replacement ratios or increased mass-weighted water absorption of coarse aggregates exceeds the corresponding reduction in compressive strength. This research not only deepens the understanding of RBAC’s mechanical properties but also provides valuable predictive tools for civil engineering applications.

Chemical interference between graphene oxide and polycarboxylate superplasticizer, and the resulting impact on the concrete strength, workability, and microstructure

Graphene oxide (GO) nanoreinforcement is shown to significantly improve the strength and durability of concrete at the expense of mix workability. While polycarboxylate superplasticizers (PCSP) addition has improved GO-cement/mortar strength and workability in existing literature, this article examines if this improvement is translated to concrete with lower cement and water contents. PCSP and GO showed colloidal instability and particulate aggregation through surface charge measurements, presumably caused by divalent Ca 2 + ion interbridging between the GO and PCSP. This chemical interference results in a 26% reduction in 28-day compressive strength and a 20% decrease in the workability of PCSP-treated GO-concrete. Microstructural examination reveals significantly larger pores in PCSP+GO cement than in GO-cement or PCSP-only cement due to the chemical interference induced by PCSP-GO interactions in cement and concrete. Hence, PCSP and GO interactions must be further researched for practical use in concrete structures.

Experimental Study on Damage Constitutive Model of Rock under Thermo-Confining Pressure Coupling

Underground engineering frequently encounters the challenges of high temperatures and high confining pressures. The combined effects of temperature and confining pressure can significantly alter the mechanical properties of rock. Evaluating the impact of these factors on rock is a crucial aspect of engineering. This study investigates the mechanical properties of rocks under various temperature and stress conditions, focusing on the deformation and failure characteristics of four typical rock types: granite, red sandstone, gray sandstone, and shale under temperature-confining pressure coupling. The results indicate that high temperatures cause internal structural damage and crack propagation in rocks, leading to a reduction in compressive strength and elastic modulus. Conversely, high confining pressures can inhibit crack propagation and enhance rock deformation capacity. Additionally, significant differences were observed in the mechanical responses of different rocks; red sandstone and shale predominantly exhibited shear failure under the coupled effects of temperature and confining pressure, whereas granite and gray sandstone exhibited bulging failure. Based on the experimental results, an elastic modulus fitting model considering the temperature-confining pressure coupling effect was proposed, and the parameters of the Drucker–Prager criterion were modified. A constitutive model was constructed to accurately reflect the stress–strain state of rocks under the coupled effects of temperature and confining pressure. The constitutive model results show good agreement with the experimental findings.

Impact Tendency Characteristics of Borehole Coal Samples under Real-Time and Uniaxial Loading Conditions: Insights from Physical Experiments

Real-time drilling depressurization technology is widely used in the prevention and control of dynamic disasters, such as deep-seated rock burst. However, current coal- and rock-loading tests under drilling conditions seldom account for real-time issues associated with drilling, thus failing to fully reflect the actual stress state of the surrounding rock during the implementation of drilling depressurization technology. Therefore, this study designed and implemented a uniaxial loading scheme for coal samples incorporating real-time-drilling characteristics. The results indicate a significant reduction in the uniaxial compressive strength (RC), elastic energy index (WET), and impact energy index (KE) of the samples post-drilling. These parameters show a clear decreasing trend with increasing axial stress during real-time drilling. The weakening effect of impact tendency following real-time drilling depressurization is significant, and the depressurization effect is pronounced. The RC, WET, and KE of each real-time-drilled sample exhibit a notable decrease with increasing drilling stress, with the reduction rate significantly diminishing after the drilling stress reaches 20% of the peak strength.

Study on Dynamic Mechanical Properties and Failure Pattern of Thin-Layered Schist

This paper studies the effect of schistosity on the dynamic mechanical properties and failure pattern of thin-layered schist. Wudang Group schist with thin layers is selected as the research object, and the influence of the dynamic mechanical properties and failure pattern of schist under different angles and spacing is studied by combining an SHPB test and numerical simulation. The results indicate that under dynamic loading, the stress–strain curve demonstrates elastic compression, plastic deformation, and strain softening stages. Moreover, it is observed that the dynamic critical failure strength of schist exhibits typical “U”-type strength anisotropy. Specimens with a schistosity angle of 0° or 90° exhibit higher dynamic compressive strength under dynamic loading, with axial splitting and schistosity splitting as predominant failure modes. Conversely, when the schistosity angles are 30°, 45° or 60°, there is a noticeable decrease in compressive strength accompanied predominantly by shear failure along with local compressive shear failure. We additionally noted that as the spacing between schists decreases from 22 mm to 7 mm, there is a gradual reduction in dynamic compressive strength by approximately 20.3%.

Carbonation and chloride penetration performance of self-compacting concrete with masonry and concrete wastes

In this research, masonry and concrete construction and demolition wastes (CDWs) were used as supplementary cementitious material (25% vol. residue of masonry, RM) and recycled coarse aggregate (RCA) in increasing levels (0%, 50% and 100% vol. residue of concrete), respectively, in the development of self-compacting concrete (SCC). The performance of SCC mixtures was evaluated in terms of fresh properties, compressive strength, resistance to both accelerated (1% CO2, 65% R.H. and 23 °C temperature) and natural carbonation as well as chloride penetration. Experimental results showed a monotonic workability reduction associated to the incorporation of increasing levels of RCA. In compressive strength, the SCC with RCA showed the greatest increase in this mechanical property after 28 days of accelerated exposure in the carbonation chamber, when compared to its water-cured counterpart. Yet, at 360 days of accelerated carbonation exposure, all SCCs showed compressive strength reductions compared to their water-cured counterparts. On the other hand, the chloride permeability resistance of the SCCs was low and very low at the ages evaluated. Thus, the findings of this study indicate that the use of CDW can generate SCCs with adequate fresh properties, compressive strength and carbonation and chloride penetration performance, which offers benefits for the environment.

Axial compression stress-strain relationship of lithium slag rubber concrete

Replacing cement with lithium slag and fine aggregate with rubber in concrete solves waste disposal, reduces material consumption, boosts sustainability, and enhances concrete performance. A set of prismatic concrete specimens with varying proportions were designed and experimentally tested in order to study the compressive stress-strain behavior of lithium slag rubber concrete (LSRC). The main factors affecting the specimens were lithium slag substitution ratio (SL=0%, 10%, 20%, 30%) and rubber substitution ratio (SR=0%, 5%, 10%, 15%). The results demonstrated that the LSRC exhibited good integrity during the damage. Furthermore, the incorporation of lithium slag (LS) was found to effectively compensate for the reduction in compressive strength due to the incorporation of rubber. When 10% of the fine aggregate was replaced with rubber and 20% of the cement was substituted with lithium slag, the axial compressive strength, elastic modulus, and peak strain of the tested specimens increased by 21.57%, 6.92%, and 17.26%, respectively. Compared with ordinary concrete, LSRC has good toughness, impact resistance and durability with minimal loss of strength, and has broad application prospects in engineering fields (such as airports, highways, housing expansion joints, concrete floors and railway concrete sleepers, etc.). Based on the experimental data, simplified modified equations to predict the compressive strength, elastic modulus, peak strain and axial stress-strain constitutive model of LSRC were proposed, so as to promote the development of LSRC.

Enhancing compressive behaviour of seawater sea sand concrete filled hybrid carbon-glass FRP tubes exposed to seawater: Effect of thickness

This study presents a novel investigation into the impact of tube thickness on the residual compressive strength of sea water sea sand concrete (SWSSC) filled filament wound hybrid fibre-reinforced polymer (HFRP) tubes, positioning them as innovative alternatives to traditional concrete-filled steel tubes in corrosive marine environments. The research explores tube thicknesses of 2 mm, 3 mm, and 4 mm, employing a unique hybrid configuration of 50 % carbon fibre reinforced polymer (CFRP) internal layers and 50 % glass fibre reinforced polymer (GFRP) external layers. This study examines the effect of these configurations on compressive mechanical properties, microstructural characteristics, and damage progression under alkaline and seawater conditions. Additionally, the research evaluates cross-ply and hoop orientations as variables in filament winding fibre orientation. A comprehensive set of 108 hybrid tubes were filled with an alkaline solution to simulate the SWSSC environment and exposed to seawater at varying temperatures and durations. Accelerated aging experiments were conducted in the laboratory to assess the long-term compressive performance of SWSSC-filled HFRP tubes exposed to seawater. Long-term compressive strength predictions were made using the Arrhenius theory, based on short-term accelerated aging data. The accelerated test data revealed maximum compressive strength reductions of 33 %, 15 %, and 17 % for 2 mm, 3 mm, and 4 mm cross-ply HFRP tubes, respectively, after 150 days of exposure at 60 °C. For hoop HFRP tubes, the corresponding reductions were 19 %, 18 %, and 17 %. Thicker tubes (3 mm and 4 mm) with sufficient internal CFRP layers protect external GFRP layers from alkaline damage, akin to pure CFRP tubes. Thinner tubes (2 mm) exhibit similar performance to GFRP tubes as alkaline damage spreads from their less substantial internal CFRP layers to the outer GFRP layers. For cross-ply tubes, the recommended strength reduction factors are 0.6 for 2 mm, 0.8 for 3 mm, and 0.8 for 4 mm thicknesses. For hoop tubes, the suggested factors are 0.7 for 2 mm, 0.7 for 3 mm, and 0.8 for 4 mm thicknesses. This study shows the innovative potential of tailored hybrid HFRP tubes in enhancing the durability and performance of marine infrastructure.

Physical and mechanical properties of concrete containing plastic tube fibers

Plastic tube fibers (PTFs) are one form of plastic waste resulting from the production of plastic mats that end up in the landfill. Until today, no attempt has been made to explore the applicability of PTFs as a construction material for a circular economy. This paper investigates the applicability of PTFs as fibers in fiber-reinforced concrete (FRC) production. A series of tests are carried out to investigate the effects of volume fractions (VFs) and the length of the fibers on the physical and mechanical properties of FRC-containing PTFs. The effects of the length and VFs on the unit weight, compressive strength, flexural strength, tensile strength, pulse velocity, thermal conductivity, and microstructure of FRC are examined. Three different lengths of fibers of 20 mm, 30 mm, and 50 mm, and VFs of PTFs of 0 %, 0.5 %, 1 %, and 1.5 % are studied. Results show that although the mechanical properties of concrete decrease as the VFs increase from 0 % to 1.5 %, the rate of reduction becomes smaller as the length of the fiber becomes larger. The maximum reduction of compressive, tensile, and flexural strength was found to be as high as 35 %, 25 %, and 35 % compared to the control sample obtained for 20 mm fiber length having 1.5 % VFs. Formulas to predict the tensile and flexural strengths of concrete containing PTFs as a function of the compressive strength are proposed and found to be providing satisfactory results. From a microscopic view, it is seen that the sample containing higher VFs shows less density and homogeneity of concrete which leads to an increase in the micropores of the concrete. Furthermore, the ultrasonic pulse velocity and attenuation coefficient decrease as the VFs of PTFs increase.

A novel method for through-thickness reinforcement of laminated composites using discrete micro-polarization-induced fiber injection (DMFI) approach

Conventional through-thickness reinforcement methods for laminated composites, such as Z-pin, encounter issues with in-plane property degradation and complex fabrication processes. To achieve rapid and low-damage reinforcement, a novel approach using short-chopped carbon fibers (SCFs) to form a micron-diameter interlaminate structure has been proposed. This method employs a discrete micro-polarization-induced fiber injection (DMFI) technique, where polarized SCFs are electrostatically oriented and injected at high speeds into pre-formed holes in the laminates. The insertion process of SCFs was thoroughly investigated, with optimal interlaminate conditions determined using high-speed cameras and other equipment. The toughening mechanism of SCFs was explored through various characterization methods, including metallurgical microscopy. This innovative method offers several advantages over the traditional Z-pin reinforced method. Notably, present method eliminates the need for prefabrication of Z-pins and fully leverages the excellent mechanical properties of individual carbon fiber in short length. It provides superior interlaminar mechanical properties, achieving a 392% improvement compared to the control group and a 15% improvement compared to 0.1 mm Z-pin reinforcement at the same insertion volume fraction. Additionally, it has minimal impact on the in-plane properties of the laminates, with only a 3.6% reduction in tensile strength and a 4.1% reduction in compression strength. Furthermore, it is environmentally friendly, allowing for the recycling and reuse of waste SCFs.

Properties of foam glass produced with the use of soot from a cement factory as a foaming agent: A Study Based on Taguchi Design of Experiments

Cellular glass is a lightweight, porous medium with excellent heat transfer resistance that can be used in a variety of industries. This study investigated the use of soot from cement plants as a new foaming agent for producing foam glass. The experiments were designed using the Taguchi Design of Experiments (DOE) method. By applying this approach, instead of creating and testing 27 different groups of samples, only 9 groups were produced. The properties of the remaining 18 sample groups were then predicted based on Taguchi analysis. Soot and silicon carbide were used simultaneously (at weight ratios of 2% and 3%) as foaming agents in the samples. Alumina was also used as a modifier with weight ratios of 4%, and 8%. Mechanical strength, water absorption, density, and thermal resistance were evaluated. The findings indicated a direct correlation between elevated soot content and increased water absorption (open porosity), coupled with a reduction in compressive strength and overall density of the foam glass. Electron microscopy observations revealed a wide range of crystallite morphologies in the resulting foam glass, which results in diverse properties in the material. The developed glass foams exhibit a density spanning from 125 to 700 kg/m3, with compressive strength varying between 1.2 and 6.7 MPa, and thermal conductivity in the range of 0.08–0.5 W/m·K. The samples with 3% soot, 0% alumina, and 3% SiC exhibited exceptional thermal insulation properties. In contrast, the samples containing 1% soot, 8% alumina, and 1% SiC demonstrated the highest compressive strength. Overall, this study found that soot from cement plants is a viable foaming agent for producing foam glass with desirable properties. The use of soot from cement plants can not only reduce the dispersion of pollution in the environment but also produce a wide range of foam glass with different properties at a lower cost.

Freeze-thaw durability of clayey soils stabilized by alkaline-activated kaolin and recycled cement kiln dust

Weak soils pose significant challenges for civil engineering projects, particularly in cold regions. Stabilizing such soils with additives is a common practice to enhance their geotechnical properties. This research aimed to evaluate the durability of clayey soils stabilized by alkaline-activated kaolin at 10, 25, and 50%, along with 10% recycled cement kiln dust (CKD). The stabilization process involved curing the soils at different temperatures (40, 60, and 80°C) for varying durations (1, 7, 14, and 28 days). The stabilized soils underwent 5, 10, and 20 freeze-thaw (F-T) cycles to evaluate their durability. The results indicated F-T cycling led to a reduction in the unconfined compressive strength (UCS) of unstabilized soils, with a more pronounced impact as the number of cycles increased. However, this adverse effect was mitigated by additive stabilization. The improvement in UCS in stabilized soils was directly linked to the additive content, curing duration, and temperature. Both additives demonstrated superior resistance to F-T cycles, with CKD outperforming kaolin. These findings provide guidelines for utilizing kaolin and CKD for earthwork applications in cold regions with economic and sustainability advantages.

Assessment of structural concrete made by sustainable sand at high temperatures: An experimental research

This study assesses the mechanical properties of sustainable sand concrete mixes of DM1*, DM2, DM3, and DM4 by absolute volume method when exposed to elevated temperatures. The concrete specimens were placed in a muffle furnace for two hours at (150–600 °C). Experimental investigations show that the mix strength increases (up to 300 °C), a sudden fall in strength at 450 °C, and a sharp decline at 600 °C was seen. At 600 °C, the highest reduction in compressive and flexural strength of the mixes was reported (21.2, 11.2, 16.6, and 20.4 MPa) and (2.87, 1.41, 2.42, 1.95 MPa), respectively. The concrete mix DM2 with (100 % recycled crushed sand) shows a more significant loss than other mixes. The concrete mix DM4 (50 % recycled crushed sand + 50 % desert sand + 12.5 % silica fume) performs significantly better than other mixes at elevated temperatures. Hence, 100 % recycled crushed sand in structural concrete is not recommended for engineering work.