Search Results (4,014)

Collapsible soils present significant geotechnical challenges due to their abrupt volume reduction and strength degradation upon wetting, which can lead to severe structural damage. This study evaluates the effectiveness of sustainable and eco-friendly additives—including rice husk ash, lime, eggshell powder, turmeric, polypropylene fibers, nanosilica, and Sarooj mortar—in stabilizing a naturally collapsible clay soil from Gorgan, Iran. A comprehensive experimental program comprising collapse potential, unconfined compressive strength (UCS), and unconsolidated undrained (UU) triaxial tests was conducted. The untreated soil exhibited a high collapse potential of approximately 11.1%, classifying it as severely collapsible. Upon stabilization, the collapse potential was significantly reduced to 1.35–4.63%, representing a reduction of up to ~88%, and reclassifying the soil into slight to moderate collapsibility. In terms of strength improvement, the UCS increased from 0.71 kg/cm² (untreated soil) to values exceeding 3.5–4.3 kg/cm² after 28 days of curing, corresponding to an increase of more than 4–5 times depending on the mixture composition. Additionally, triaxial test results indicated improvements of over 20% in shear strength parameters, including cohesion and friction angle, particularly after 28 days of curing. The observed improvements are attributed to the combined effects of pozzolanic reactions (lime, rice husk ash, nanosilica), cementitious bonding (Sarooj mortar), and mechanical reinforcement (polypropylene fibers), which collectively enhance soil structure, reduce the void ratio, and increase interparticle bonding. Among the tested mixtures, samples containing higher nanosilica and fiber content demonstrated superior performance in both strength and collapse resistance. Overall, the integration of traditional Sarooj mortar with modern eco-friendly additives provides a sustainable and efficient solution for mitigating collapse potential and enhancing the mechanical behavior of clayey soils. The proposed approach offers a low-carbon alternative to conventional stabilization methods, with significant implications for foundation engineering and infrastructure development in regions with problematic soils. Full article

This study investigates the durability of Class C/Class F fly ash geopolymer mortars with varying ash-to-sand ratios under freeze–thaw cycles, MgSO₄ exposure, and their combined action. The results showed that geopolymer specimens with ash-to-sand ratios of 1:1.4 and 1:1.6 exhibited excellent durability under individual freeze–thaw or MgSO₄ attack. After 60 freeze–thaw cycles, the mass losses ranged from 1.44% to 3.19%, while the residual compressive strength remained between 103.7% and 107.0% of the initial value. After 90 days of MgSO₄ exposure, the mass loss was limited to 0.28–1.40%, and the residual strength increased significantly to 147.5–159.8%. However, the combined effect of freeze–thaw cycles and MgSO₄ corrosion was not simply additive. Under combined degradation, mass loss increased markedly to 7.29–9.28% after 60 cycles, while residual strength declined to 42.6–53.7%. The ash-to-sand ratio significantly influenced the pore size distributions. A direct relationship was observed among reaction products, microstructure, and freeze–thaw resistance. These findings provide insight into the durability mechanisms of fly ash geopolymer mortars and support their application in cold-region infrastructures. Full article

The copper industry generates approximately 24.6 million tons of copper slag (CS) annually, equivalent to about 2.2 tons of CS per ton of copper produced, creating a major waste management challenge. Meanwhile, concrete is one of the most widely used construction materials worldwide, with nearly 11 billion tons produced each year. This high demand requires large volumes of natural aggregates, leading to environmental impacts associated with their processing and transportation. This study evaluates mortar and concrete mixtures incorporating CS to assess the feasibility of valorising this industrial waste as an alternative aggregate in cementitious materials. The experimental programme included in this study tests to determine the workability and mechanical properties for different aggregate replacement ratios. The results show that replacing 40% of the fine aggregate with CS improves mortar performance, increasing compressive and flexural strength by at least 13.9% compared with reference mixtures. For concrete, up to 100% aggregate replacement was feasible, achieving compressive strength gains of up to 11.9%. Given that aggregates represent about 70–80% of the concrete volume, the incorporation of CS offers a promising strategy for large-scale waste valorisation and natural resource conservation. Full article

To promote the resource recovery of phosphate mine tailings and alleviate the pressure caused by the growing scarcity of river sand, this study employs a research methodology combining macroscopic performance analysis with microscopic testing to systematically investigate the effects of three types of recycled sand containing varying proportions of phosphate mine tailings (flint (FS), phosphorite flint (PFS) and dolomitic limestone (DLS)) on the performance of mortar. The study focused on assessing the impact of recycled sand on the workability of mortar, water absorption, mechanical properties, pore structure, cement hydration characteristics, and environmental safety, and conducted a comprehensive evaluation of the project’s feasibility in conjunction with a cost analysis. The effect of DLS was most pronounced in terms of setting time. Water absorption tests show that when the proportions of FS, PFS, and DLS are all 25%, the mortar’s water absorption reaches its minimum value. In terms of mechanical properties, DLS showed a more pronounced increase in early-stage flexural strength, whilst PFS and FS demonstrated a more significant increase in later-stage strength. In terms of compressive strength improvement, PFS outperformed both FS and DLS. XRD and TG-DTA test results show that the three kinds of recycled sand have no adverse effect on cement hydration. SEM and MIP results confirmed that compared with river sand, the porosity of mortar mixed with FS was smaller and the pore structure was denser. Environmental safety assessments have shown that the heavy metal leaching concentrations in the mortar made from the three types of recycled sand are all significantly below the national limits, indicating good environmental compatibility. An economic analysis indicates that the “25% river sand + 75% FS” alternative offers the best economic benefits, resulting in cost savings of 93.27 CNY per cubic metre. In summary, the use of recycled sand derived from phosphate ore tailings as a substitute for river sand in the preparation of mortar is feasible from technical, environmental, and economic perspectives. This approach facilitates the recovery of solid waste resources, conserves natural resources, reduces the environmental burden, and promotes cost optimisation. Full article

This study investigates the effect of polyvinyl alcohol (PVA) on the performance of natural hydraulic lime (NHL)-based repair mortars used in historical building restoration. Mortars were prepared with varying PVA dosages (0.25%, 0.5%, 0.75%, and 1.0%) to evaluate their impact on physical, mechanical, and durability properties, including setting time, strength, water absorption, shrinkage, and resistance to freeze–thaw and sulfate attack. The results demonstrate that PVA significantly enhances bonding strength, reduces water absorption, and improves durability, with optimal performance observed at a 0.5% PVA dosage. Microstructural analysis showed that PVA forms a cohesive film, reinforcing the mortar’s structure. These findings suggest that PVA can enhance the performance of NHL-based mortars, offering significant potential for historical building restoration, particularly under challenging environmental conditions. Full article

This study investigates the effect of metakaolin (MK) as a partial replacement of cement (CEM I) in high-workability mortars, with emphasis on fresh-state behaviour, mechanical properties, microstructural development, and carbon footprint implications. Mortars were produced with MK replacement levels ranging from 0 to 50% by mass of binder, under a constant water-to-binder ratio and fixed superplasticiser amount. Fresh-state results showed that increasing MK content reduced flowability due to its high fineness; however, high workability was maintained for replacement levels up to 20%. At 28 days, MK replacement up to 10% retains approximately 90–95% of the control compressive and flexural strength, whereas higher replacement levels lead to gradual strength reductions (to ~55–60% at 50% MK), despite comparable early-age strength gains across all mixes. Durability-related indicators demonstrated reduced water absorption and capillary uptake at moderate MK contents (approximately 20–30%), indicating refined pore structure and reduced pore connectivity. Microstructural analyses using SEM, TGA, and XRD confirmed effective portlandite consumption and the formation of dense C–A–S–H-type hydration products at moderate MK replacement levels, whereas excessive MK contents resulted in unreacted MK. A comparative carbon footprint assessment showed that MK incorporation leads to proportional reductions in embodied CO₂ emissions, with replacement levels of 10–20% providing the most favourable balance between mechanical performance, durability, and environmental benefit. Therefore, the results demonstrate that MK can be used as a supplementary cementitious material for producing low-carbon, high-workability mortars. Full article

Geopolymer materials represent a novel green cementitious material characterized by excellent mechanical properties and unique microstructural features. This study developed geopolymer mortar using slag as the primary raw material by adjusting alkali content and water glass modulus. Characterization methods, including nanoindentation testing, mercury intrusion porosimetry (MIP), and X-ray diffraction (XRD), were employed to systematically analyze the influence mechanisms of alkali content and water glass modulus on the mechanical properties and microstructure of slag-based geopolymer mortar. Results demonstrated that compressive strength exhibited an initial increase followed by a decline with rising alkali content and water glass modulus, while flowability first increased and then decreased. When the water glass modulus was 1.4, and the alkali content reached 8%, the geopolymer mortar achieved a 28-day compressive strength of 86.5 MPa and flexural strength of 10.2 MPa. At 10% alkali content, flowability reached 240 mm. Compressive strength showed a trend of initial increase followed by a decrease with increasing alkali content, reaching a maximum value of 86.4 MPa at 8% alkali content after 28 days. Nanoindentation analysis revealed that the primary strength-forming phase in geopolymer mortar was C-A-S-H gel. Variations in alkali content and water glass modulus primarily affected the volume fractions of C-A-S-H gel, porous phases, and unreacted slag particles, with limited impact on micromechanical parameters of individual phases. These findings not only provide a theoretical basis for optimizing the mix design of slag-based geopolymer mortar but also offer practical guidance for its application in high-strength and workable construction materials. Full article

Historic structures that possess cultural heritage value are important documents that convey the architectural understanding, material technology, and construction techniques of past civilizations to the present day. However, these structures are exposed over time to physical, chemical, and mechanical deterioration due to environmental effects, climatic conditions, the natural aging processes of materials, and human interventions. The conservation and faithful restoration of historic structures necessitate the scientific determination of the properties of original building materials. In this study, we aimed to determine the physical, chemical, mineralogical, thermal, and mechanical properties of the original building materials used in the Old Armenian Church located in the city of Çanakkale. In order to reveal the chemical and mineralogical compositions of the samples, XRD, SEM, Raman, and FTIR analyses were applied. The thermal behaviors of the materials were examined through TGA. To determine the physical properties, tests for unit volume weight, specific gravity, compactness, porosity, and water absorption capacity were carried out. For the determination of mechanical properties, compressive strength tests—as well as non-destructive testing methods such as the Schmidt hammer and UPV measurements—were employed. The analysis results indicate that the materials used in the structure have a carbonate-based mineralogical composition and that calcite-bonded systems are dominant. While the physical and mechanical data reveal that the materials possess a compact internal structure, they also indicate that microcracks and weathering processes may be effective in certain areas. These findings emphasize the importance of using lime-based mortars and stones compatible with the original materials in restoration works. Full article

From an environmental perspective, the use of clam shells contributes positively to marine waste management and promotes more sustainable construction practices. This study aims to analyze the influence of clam shell-derived filler on the mechanical properties of cementitious mortars, evaluating its effect as a function of dosage and particle fineness, in order to determine its potential as a sustainable additive in construction applications. The shells were ground for 0.5, 1.0, and 1.5 h and incorporated at percentages ranging from 0.5% to 5.0% by mass of cement. Slump (reduced Abram’s cone) was performed in the fresh state for each specimen mixture, while flexural strength, and compressive strength tests were performed at 7, 14, and 28 days of curing. Microstructural characterization was also performed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analysis. In addition, particle size distribution parameters were determined to quantify the effect of grinding time on particle refinement and its relationship with mechanical performance. A multifactor ANOVA was conducted to evaluate the statistical significance of grinding time and filler dosage on compressive strength. The results showed that the combination of 0.5 h of grinding and 1.0% filler provided the best mechanical performance for both flexural and compressive strength, with values of 7.27 MPa and 26.16 MPa, respectively. Dosages higher than 2.0% tended to decrease strength, which is associated with saturation of non-cementing particles. EDX analysis showed adequate calcium distribution without generating chemical segregation. The results showed that the combination of 0.5 h of grinding and 1.0% filler provided the best mechanical performance for both flexural and compressive strength, with values of 7.27 MPa and 26.16 MPa, respectively. Dosages higher than 2.0% tended to decrease strength, which is associated with saturation effects and increased specific surface area. The statistical analysis confirmed that both grinding time and filler dosage significantly influence compressive strength, highlighting the importance of optimizing particle size distribution and filler content to achieve improved mechanical performance. Full article

This study presents two independently optimised Extreme Gradient Boosting (XGBoost) regression models, one for predicting corrosion current density ($i_{corr}$) and one for predicting corrosion potential ($E_{corr}$) parameters of carbon steel rebar embedded in mortar and immersed in simulated pore solution. An experimental dataset consisting of 216 measurements was curated from a systematic potentiodynamic scan study covering six chloride contamination levels, two carbonation states (non-carbonated and carbonated), four moisture conditions for mortar (65%, 85%, 95% relative humidity, and submerged), and three conditioning durations for simulated pore solution (36 h, 72 h and 20 days). Hyperparameters of the XGBoost models were optimised using a Bayesian optimisation framework with the Tree-structured Parzen Estimator (TPE) sampler over 300 trials. Model performance was assessed using 5-fold cross-validation and a random 80:20 train–test split. The optimised models achieved cross-validation $R^2$ scores of 0.936 and 0.953 for $i_{corr}$ and $E_{corr}$, respectively. On the hold-out test set, $R^2$ values of 0.933 and 0.945 were obtained with test RMSE values of 0.2 log₁₀(µA/cm²) and 41.9 mV, respectively. The contribution of each input feature to model predictions was quantified and visualised using the SHapley Additive exPlanations (SHAP) methodology. SHAP analysis reveals that chloride content has the highest impact on $i_{corr}$, followed by carbonation state and the low-humidity condition, while for $E_{corr}$, chloride content and the Submerged condition have the greatest impact. An interactive web application was developed using Streamlit, enabling researchers and practitioners to obtain corrosion parameter predictions. The findings provide data-driven insights into the relative importance of environmental factors governing rebar corrosion, with direct implications for the development of accurate corrosion prediction models for reinforced concrete service life assessment. Full article

The dielectric properties of cement-based composites (CBC) are highly sensitive to environmental humidity, which seriously restricts the quantitative interpretation accuracy of ground-penetrating radar (GPR) in the non-destructive testing of cement concrete pavement. In view of the lack of targeted prediction models due to the unclear mechanism of humidity influence in existing research, the core innovations of this study are: (1) the synergistic mechanism of water vapor dipole polarization and adsorbed water multi-layer polarization is clarified, revealing the intrinsic reason for the accelerated growth of permittivity in the high humidity range; (2) the constructed four-component dielectric model of “cement mortar–aggregate–water vapor–adsorbed water” achieves high-precision prediction within the range of 50~100% RH (R² > 0.94, relative error < 5%), and shows good predictive ability within the test scope of this study; (3) a GPR humidity correction protocol based on the model is proposed, which can effectively improve the accuracy of nondestructive testing of cement concrete structures. In this study, CBC samples with water–cement ratios of 0.4~0.6 were prepared using P.O 32.5/P.O 42.5 cement and limestone aggregate. Under the conditions of 20 ± 0.5 °C, relative humidity (RH) of 50~100%, and 2 GHz (common GPR frequency), the permittivity was measured using an Agilent P5001A network analyzer to verify the model. The results show that the permittivity increases monotonically with humidity, and the growth rate in the high humidity range (70~100%) is 2.2 times that of the low humidity range (50~70%); The higher the water–cement ratio, the shorter the age, and the lower the cement strength grade, the stronger the humidity sensitivity of CBC dielectric properties. This model provides a reliable humidity correction tool for GPR detection, and significantly improves the accuracy of nondestructive evaluation of cement concrete structures. Full article

Karst pile foundation cavity treatment requires grouting materials with suitable flowability, stability, strength, and cost-effectiveness, while large quantities of waste mudstone generated by tunnel excavation in Guangxi, China, also require sustainable valorization. In this study, tunnel-excavated mudstone from a tunnel project in Guangxi, China, was used as the primary raw material to develop a solidified grouting material for karst pile foundation cavity treatment. Uniform experimental design, stepwise nonlinear regression, response surface analysis, and multi-objective optimization were employed to evaluate the effects of key mix parameters and determine the optimal formulation. The results showed that the optimal slurry was obtained at a cementitious material-to-mudstone ratio of 0.16, an admixture-to-cementitious material ratio of 0.06, a water-to-solid ratio of 0.63, and the slag powder content-to-cementitious materials ratio of 0.34. In addition, the anti-dispersion performance improved by 87.78%, and compared with conventional cement-soil, C25 concrete, and C30 concrete, the CO₂ emissions were reduced by 37%, 67.4%, and 68.6%, respectively, with the material cost being 73.8% lower than that of traditional cement mortar. These results indicate that the proposed material has promising engineering applicability and demonstrates significant economic and environmental benefits, as well as the valorization potential of tunnel-excavated mudstone. Full article

Masonry buildings have shaped construction history since about 6500 BCE. They offer durability, strength, and cost effectiveness, especially in developing countries. Yet assessing compressive strength during construction remains challenging due to the constituent materials soil, cement, and stone, complicating standardization worldwide. In the present study, an innovative model based on a machine learning algorithm is put forth to predict the compressive strengths of prisms. Some important factors considered as input to the algorithm based on traditional methods are the brick and mortar strengths, prism geometry, mortar bed thickness, and empirically derived height-to-thickness (t) (h/t) ratios. Three different ANN algorithms are coded and trained on the input data, and they are based on the Levenberg–Marquardt algorithm, the resilient backpropagation algorithm, and the conjugate gradient algorithm. The optimal ANN model trained using the conjugate gradient Polak–Ribière algorithm (traincgp) achieves superior performance, with R² = 0.9881, R² = 0.9927, RMSE = 0.9914 MPa, MAE = 0.6039 MPa, MAPE = 20.9141%, VAF = 0.9881, and WI = 0.9970. Sensitivity analysis shows the height-to-thickness (h/t) ratio is the dominant influence on compressive strength, consistent with structural mechanics. The primary contributions are the systematically curated, richly parameterized dataset and its use to produce robust, physically interpretable predictions with established ANN methods. Full article

To enhance the utilization rate and mechanical performance of recycled sand (RS) in extrusion-based 3D printing, this study investigates the influence of varying incorporation ratios of RS across two particle size fractions: 0.075–1.18 mm (RS01) and 1.18–2.36 mm (RS12). The RS utilization rate was determined via the material balance method, while microstructural mechanisms were analyzed using scanning electron microscopy and Vickers microhardness testing. The results indicate that: a combination of 75% RS01 and 25% RS12 achieves the maximum RS utilization rate of 84.3%. At an RS12/RS01 ratio of 1:3, the printed specimens exhibit the smallest tilt angles in bidirectional buildability tests, measuring 7.6° and 7.2°, with corresponding tan θ values of 0.066 and 0.063. Compared to mortar with 100% RS01, this optimized mixture yields average increases of 36.5% in compressive strength, 40.7% in flexural strength, and 6.8% in interlayer splitting strength. Analysis of variance indicates that different particle size combinations have a significant effect on the mechanical properties. Microhardness analysis reveals that the combination of 75% RS01 and 25% RS12 achieves a minimum interfacial transition zone width of 46 µm. Utilizing larger-particle-size RS in 3D printing effectively enhances its utilization rate while maintaining satisfactory printability and mechanical properties. Full article