Search Results (1,004)

Repair mortars containing recycled concrete powder (RCP) and ground granulated blast-furnace slag (GGBFS) are promising low-carbon materials for the rapid repair of concrete structures and pavements. However, their practical use is often limited by slow early hydration, insufficient early strength, and weak bonding with existing concrete substrates. In this study, four early-strength admixtures, namely calcium formate, anhydrous sodium sulfate, calcium acetate, and triethanolamine, were incorporated into a P·I 42.5 cement-based repair mortar containing RCP and a low dosage of GGBFS. Their effects on fluidity, flexural and compressive strength, tensile bond strength, drying shrinkage, and hydration characteristics were investigated. The results showed that the suitable dosages of calcium formate, anhydrous sodium sulfate, calcium acetate, and triethanolamine were 1.5%, 1.0%, 0.8%, and 0.05% by mass of total cementitious materials, respectively. Among the four admixtures, calcium formate provided the best balance among strength enhancement, bond performance, workability retention, and dosage tolerance. Compared with the control group, the 3 d and 28 d flexural strengths of the 1.5% calcium formate group increased by 37.0% and 20.3%, respectively. Anhydrous sodium sulfate gave the highest tensile bond strength, with the 14 d value increasing by 33.15% to 1.052 MPa, but its effective dosage range was relatively narrow. Calcium acetate was more effective in reducing drying shrinkage, with a 28 d shrinkage value of 695.14 × 10⁻⁶. SEM and XRD results suggested that the admixtures mainly accelerated early hydration, while no new major crystalline phases were detected. Excessive dosages caused strength loss, bond deterioration, or increased drying shrinkage. These findings are applicable to the specific RCP–GGBFS repair mortar formulation and dosage ranges investigated here. They provide a practical basis for selecting early-strength admixtures for RCP-containing repair mortars used in concrete structure and pavement repair. Full article

The mechanical properties of soil–concrete interfaces directly impact the bearing capacity and structural stability of underground projects. Characterizing mechanical responses and quantifying multi-factor influence mechanisms are fundamental to geotechnical design, numerical simulation, and safety assessment. To reveal the mechanical properties of the unsaturated loess–structure interface, this study conducted a series of direct shear tests on loess–concrete interfaces under varying moisture contents. The effects of interface roughness, soil dry density, normal stress, and soil moisture content on the interfacial shear strength were quantitatively evaluated. The results show 20–35% shear stress variation with dry density, up to 35% shear strength reduction upon wetting, less than 10% shear stress difference due to interface roughness, and normal stress controls, shear stress magnitude, and initial failure sliding displacement. Based on the test results, moisture content was introduced as an additional variable to establish a modified hyperbolic model for unsaturated soil-structure interfaces. This model contains six parameters, all of which can be determined through interface direct shear tests at different moisture contents. These findings advance the quantitative understanding of unsaturated loess–concrete interface mechanics and provide a critical theoretical foundation for the design, numerical analysis, and stability assessment of unsaturated loess–structure interfaces under multi-factor coupled conditions in practical geotechnical engineering. Full article

Sulfate attack is a major cause of deterioration in tunnel lining concrete under aggressive underground conditions. This study investigates the sulfate resistance of fiber-reinforced ferroaluminate cement concrete incorporating steel slag powder through combined experimental and numerical approaches. Specimens with different fiber contents (0, 0.2%, and 0.4%) were subjected to dry–wet cycles in a 5% sodium sulfate solution. The results show that fiber incorporation significantly enhances sulfate resistance, with the optimal performance achieved at 0.2% fiber content. Compared with ordinary Portland cement concrete, ferroaluminate cement-based concrete exhibits improved durability, including lower mass variation, reduced strength degradation, and more stable dynamic elastic modulus. Microstructural analyses indicate that hydration products refine the pore structure, while fibers effectively inhibit crack propagation and expansion damage. Numerical simulation of tunnel lining structures further demonstrates that the optimized material reduces stress concentration, displacement, and crack development. Overall, the proposed material shows superior performance and promising application potential for tunnel linings in sulfate-rich environments. Full article

This study proposes a novel analytical model to predict one-dimensional moisture transport in concrete under cyclic drying and wetting conditions. The framework distinguishes between two physical mechanisms: diffusion-driven evaporation during drying and capillary-driven suction during wetting. Governing equations for weight loss and gain are derived for each respective phase. During the drying phase, weight loss follows a linear relationship with the square root of time, allowing the diffusion coefficient to be determined via evaporation tests. For the wetting phase, a modified sorptivity approach is employed, incorporating an error-function baseline to account for residual moisture. A calibration coefficient of ε is utilized to correct for varying conditions between standard water suction tests and environmental wetting, particularly for air-entrained concrete characterized by larger capillary volumes and complex tortuosity. Experimental validation was conducted on concrete with varying water-to-cement ratios. The model demonstrated excellent agreement with experimental data, maintaining relative errors below 10% for standard mixes. While higher-porosity samples exhibited greater scatter due to “water traps” and complex pore structures, the model effectively captured cumulative moisture trends over multiple cycles. This framework provides a robust tool for assessing the durability of concrete structures in unsheltered environments. Full article

The escalating depletion of river sand resources poses a critical sustainability challenge for the production of foam concrete, while the reinforcement mechanism of locally abundant aeolian sand in cementitious matrices remains insufficiently quantified. To address this gap, the present study investigates the feasibility of partially substituting river sand with Taklamakan desert sand at replacement ratios of 0%, 20%, and 40%, under varying water-to-binder (W/B) ratios (0.3, 0.4, 0.5) and sand-to-binder (S/B) ratios (0, 0.3, 0.6). To correlate macroscopic performance with microstructural features, compressive strength was tested, and pore structure evolution was characterized using deep learning-based image segmentation, supplemented by XRD and SEM analyses. Results indicate that increasing the W/B ratio from 0.3 to 0.5 elevates porosity by up to 111.7%, resulting in a 47.4% reduction in compressive strength. Similarly, raising the S/B ratio from 0 to 0.6 introduces additional interfacial transition zones (ITZs) and dilutes the cementitious phase, which consequently weakens the matrix and leads to a strength reduction of up to 66.5%. However, the contribution of desert sand replacement exhibits a pronounced “S/B ratio dependence”. Notably, at an S/B ratio of 0.6 and a 40% desert sand replacement rate, the compressive strength experiences a significant increase of 51.4% compared to the control group. Quantitative analysis further reveals that the compressive strength follows positive and negative power-law relationships with dry density and porosity, respectively. Ecological assessment shows that desert sand foam concrete (DSFC) with high S/B and high desert sand replacement ratio reduces embodied CO₂ by 36.4% and cost by 26.9% compared to conventional foam concrete. These findings demonstrate that partial replacement of river sand by desert sand offers a low-carbon, cost-effective solution for foam concrete. Full article

This study investigates the prediction of carbon emissions from fly ash and ground granulated blast furnace slag-based geopolymer concrete (GPC) using advanced ensemble machine learning (ML) techniques. Although ML has been extensively utilized to model GPC’s mechanical performance, its application in estimating environmental impacts, specifically carbon emissions, is limited. The research employs six ensemble ML models, such as random forest, gradient boosting, extreme gradient boosting (XGB), CatBoost, and light gradient boosting machine (LGBM), including versions optimized using ant colony optimization (ACO). Among them, the ACO-enhanced XGB model demonstrated the highest predictive accuracy with a coefficient of determination (R²) of 0.97, with low prediction errors (MAE = 3.92, RMSE = 6.17). However, cross-validation and uncertainty analyses indicate that the performance differences among top models are relatively small. Conversely, LGBM exhibited the least predictive reliability. Feature importance analysis revealed that curing parameters, specifically initial curing time, curing temperature, and the dosage of dry sodium hydroxide, had the most influence on carbon emissions. To evaluate model robustness and interpretability, Monte Carlo simulation and Gaussian white noise analyses were conducted. Results confirmed that CatBoost and ACO–gradient boosting (ACO-GB) demonstrated greater stability under varying and noisy conditions, whereas XGB-based models, although highly accurate, were comparatively more sensitive to input variability. Overall, the research establishes a data-driven, efficient framework for quantifying carbon emissions in GPC, highlighting the importance of evaluating both predictive accuracy and model robustness, advancing sustainable material design through intelligent modelling. Full article

The effective utilization of recycled concrete powder remains a key challenge for sustainable construction. In this study, carbonated recycled concrete powder (CRCP) was applied to replace cement at levels of 4–16% in Portland cement–fly ash (OPC-FA) systems, and its effects on fresh properties, hydration behavior, shrinkage, pore structure, and mechanical performance were systematically investigated. The incorporation of CRCP reduced flowability and accelerated setting, while slightly advancing and enhancing the main hydration peak at 4–8% replacement, accompanied by higher CH at early ages and increased C–S–H formation at later stages. More significantly, the addition of CRCP substantially decreased both autogenous and drying shrinkage, achieving reductions in the ranges of 6.0–21.4% and 3.2–24.1%, respectively. This improvement is primarily attributed to the elevated internal relative humidity and the lowered capillary pressure within the system. In addition, the mechanical properties exhibited a clear optimum with the addition of 8% CRCP, where the 28 d compressive strength and flexural strengths increased by 16.3% and 4.0%, respectively. Further analysis indicates that this improvement is associated with a higher fraction of high-modulus regions and an increase in average elastic modulus from 23.89 GPa to 27.42 GPa, reflecting a denser microstructure. These results demonstrate that CRCP can effectively regulate hydration and microstructure, providing a feasible approach for improving dimensional stability and mechanical performance while enabling the value-added utilization of recycled concrete powder. Full article

Promoting construction waste utilization, this study explores using 30% mass fraction recycled micro powder (brick/concrete/hybrid) to replace cement in A03 foam concrete, as well as microbial foaming agents for insulation boards. The results show that hybrid micro powder foam concrete achieved higher compressive strength (0.7 MPa, 0.65 MPa) than pure brick (0.54 MPa) and concrete powder (0.61 MPa). For 30% hybrid micro powder insulation boards (brick:concrete ratios 2:8–8:2), when the ratio is 4:6, their performance meets JC/T 2200-2013 standards. At this point, the compressive strength is 0.43 MPa, the drying shrinkage is 0.29 mm, and the thermal conductivity 0.062 is W/(m·K). As the proportion of recycled brick powder increases, the material properties first improve and then decline, indicating that the proportion of recycled brick powder has a significant impact on the material’s overall performance; within an appropriate range, optimal performance can be achieved. Full article

In this study, the two-dimensional aligned steel fiber-reinforced micro-expansive concrete (2D) was prepared, aiming to address the inherent vulnerabilities of concrete, such as early-age shrinkage cracking and low tensile ductility. For this purpose, the steel fibers and expansive agent were utilized. Furthermore, the planar rotating magnetic field was used to randomly distribute the steel fibers in a two-dimensional plane. In order to verify its superior mechanical and shrinkage properties, the compressive, fracture and drying shrinkage tests were carried out. The results demonstrate that the 2D alignment method enhances the fiber utilization efficiency. Compared with fiber-free groups, the compressive strength and fracture parameters of specimens incorporating steel fibers were improved. Furthermore, compared with randomly distributed steel fiber-reinforced micro-expansive concrete (RD), the 2D alignment method made the cubic compressive strength and fracture energy improve 8–14.2% and 19.4–110%, respectively. Additionally, the advantage of the fiber 2D alignment method was also reflected in the inhibition of drying shrinkage. Compared with normal concrete, the 180-day shrinkage strain of the 2D1.2 group was reduced to 200 με (only 19.5% of that of normal concrete, or 30.6% of that of micro-expansive concrete). Mechanistically, these superior performances are fundamentally governed by a coupling effect: chemical shrinkage compensation and physical alignment constraint. Full article

Drying shrinkage is a critical durability issue in concrete structures, particularly in high-strength concrete (HSC), which is more susceptible to early-age cracking due to its low water–cement ratio and dense microstructure. This study experimentally evaluates the restrained drying shrinkage behavior of fiber-reinforced concretes with compressive strengths ranging from 23 to 84 MPa, employing a total of 84 ASTM C1581 ring specimens exposed to three exposure conditions: outdoor climate, indoor laboratory conditions (25 °C, 50% RH), and a controlled chamber (50 °C, 30% RH). Plain concretes exhibited increasing shrinkage with both strength and environmental severity. Under indoor exposure, 90-day shrinkage reached approximately 660 × 10⁻⁶ (23 MPa), 291 × 10⁻⁶ (40 MPa), 753 × 10⁻⁶ (60 MPa), and 338 × 10⁻⁶ (84 MPa), with high-strength mixes showing greater cracking susceptibility. Fiber incorporation significantly mitigated both strain and cracking in a dosage-dependent manner. Steel fibers at 1.0–1.5% reduced shrinkage by up to 75% in 40–60 MPa concretes, while polypropylene fibers at 0.25–0.5% achieved reductions up to 66% and eliminated cracking in several cases. Results demonstrate that concrete strength, exposure condition, fiber type, and dosage collectively govern shrinkage and cracking resistance. Full article

During the decommissioning of the BN-350 reactor, the spent nuclear fuel (SNF) was transferred to long-term dry storage in TUK-123 transport and storage cask systems designed for transportation and long-term storage with a design service life of approximately 50 years. The TUK-123 system consists of a UKKh-123 storage package, which is a sealed metal-concrete cask (MCC), and a protective-damping cover (PDC) used only during transportation. Radiation characteristics are a key quantitative criterion for assessing the safety of long-term storage in the absence of direct access to fuel and cask components. This paper presents the results of a computational study of the radiation characteristics of BN-350 SNF under dry storage conditions as of 1 January 2025. Spatial distributions of the ambient dose equivalent rate were determined for normal storage conditions and for accident scenarios involving partial failure of fuel assembly (FA) canisters and fuel redistribution. It was established that in the near-field region, the dose fields are formed predominantly by long-lived fission products and activation nuclides, whereas the neutron contribution is determined mainly by the spontaneous fission of actinides and (α, n) reactions. The results obtained provide a quantitative basis for assessing the radiation safety of long-term BN-350 SNF dry storage. Full article

This study addresses the critical challenge of low reactivity and environmental leaching associated with high-volume phosphogypsum by implementing an ettringite seed induction strategy to optimize foam concrete performance. These issues may lead to insufficient mechanical reliability, weak structural integrity, and environmental safety concerns in engineering applications. The results demonstrate that an optimal 2% seed dosage increases the 28-day compressive strength to 4.7 MPa, which represents a 150% improvement over the control while maintaining mass loss below 3.0% after 15 wet–dry cycles. Microstructural analysis reveals that the seeds serve as heterogeneous nucleation sites that help mitigate the inhibitory effects of phosphogypsum impurities to facilitate the growth of a dense 3D interlocking ettringite framework within the pore walls. This densification significantly reinforces the mechanical skeleton and reduces phosphorus leaching by 64.2%. However, excessive seed dosages at or above 5% may promote local AFt accumulation and rheological slurry-bubble mismatch which could contribute to microstructural defects and strength regression. The findings are expected to provide a scientific basis for the engineering application of high-volume phosphogypsum in foam concrete, particularly as lightweight fillers and non-load-bearing construction materials for sustainable construction. Full article

Steel reinforcement corrosion induced by chloride ingress in coastal environments is the dominant factor leading to the durability degradation of concrete structures. In this study, Ordinary Portland Cement (OPC) concrete beams and Portland Pozzolana Cement (PPC) concrete beams were used as test specimens, subjected to sustained loads to induce cracks, and exposed to accelerated reinforcement corrosion through 10 wet–dry cycles using a 3% NaCl solution. Testing methods including half-cell potential, corrosion current, and acoustic emission signals were employed to quantify the likelihood and progression of reinforcement corrosion. The results show that the half-cell potential of the loaded PPC beams remained below −350 mV, with a corrosion current density exceeding 0.5 μA/cm², indicating a significantly higher corrosion risk than that of the OPC beams; under unloaded conditions, the half-cell potential of the PPC beams remained consistently above −200 mV, with a corrosion current density below 0.2 μA/cm², exhibiting superior corrosion resistance. The event counts in the acoustic emission tests additionally revealed the progression of chloride ions gradually penetrating and corroding the steel reinforcement. Although PPC beams exhibit lower early-stage crack resistance under loading conditions and are prone to forming more cracks, their advantage in resisting chloride ingress becomes significant after appropriate mitigation measures are implemented to reduce early crack formation, making them remain a preferred material for reinforced concrete members in coastal environments. Full article

In architecture and construction, it is common practice to use acrylic products with a high flammable content, ranging from lacquers designed to improve the curing of concrete and mortar to resins that provide protection, sealing, flexibility, and elasticity. The drying process of the treated surface involves the formation of vapours of volatile organic compounds (VOCs); to prevent these from creating a potentially hazardous flammable atmosphere, a procedure is presented that establishes the maximum application rate for solvent-based products, providing equations that relate the maximum application area and the minimum drying time to the available air velocity in the work area. The results are provided for both indoor and outdoor applications. A maximum application rate is established to prevent the creation of areas classified as fire or explosion hazards: 1.5 m²/h indoors and 1 m²/h outdoors. When this is carried out at an ambient temperature of 20 °C, and from 40 °C upwards, it is not possible to apply the varnishes in practice without creating a flammable atmosphere. Full article

The safe service of tunnel inverted arch structures in high-altitude cold regions is heavily restricted by the performance of backfilling materials, which need to simultaneously adapt to low-temperature, low-pressure extreme environments and meet the long-term mechanical requirements of underground building structures. However, the strength development and preliminary mechanical applicability of foam concrete for tunnel inverted arch backfilling under reduced atmospheric pressure remain insufficiently understood. To this end, this paper carries out mix proportion optimization and mechanical performance testing of foam concrete, focusing on the strength behavior under different dry densities and simulated high-altitude low-pressure conditions. The test results show that the compressive strength of foam concrete is positively correlated with dry density, and the growth rate accelerates when the dry density is above 1000 kg·m⁻³. Specifically, the developed high-performance foam concrete with a dry density of 1200 kg·m⁻³ achieves a 28-day compressive strength of 27.1 ± 1.2 MPa under 60 kPa atmospheric pressure, indicating stable mechanical performance with low variability. The results indicate that, within the tested dry-density range and under the adopted curing and pressure conditions, the developed foam concrete can meet the basic compressive-strength requirement for tunnel inverted arch backfilling. This study provides a reference for material selection and structural design in high-altitude cold-region tunnel engineering and highlights the potential applicability of lightweight foam concrete in underground structures. Full article