Search Results (800)

Epoxy resins often require toughening to broaden their engineering applications, such as in durable concrete repair. This study addresses this need by developing high-performance polyurethane/epoxy (PU/EP) interpenetrating polymer networks (IPNs). The composites were synthesized via prepolymer and stepwise methods using polyether polyol (PPG-1000), isocyanate (MDI-50), and E51 epoxy. At an optimal PU prepolymer content of 15 wt%, the polyether-based IPNs achieved a balanced mechanical profile (tensile strength: 59.90 MPa; elongation at break: 6.46%; compressive strength: 69.99 MPa). Further tuning of the soft segment by introducing polyester polyol (PS-2412) yielded superior performance at a PS-2412/PPG-1000 ratio of 30/70. This formulation increased tensile and compressive strengths by 11.4% and 6.07% (to 66.74 MPa and 74.24 MPa), and dry and wet bond strengths by 12.1% and 36.3% (to 5.68 MPa and 4.62 MPa), respectively. The enhancement is attributed to the increased crosslinking density and more uniform network structure imparted by PS-2412, which improves stress distribution and interfacial adhesion. This work provides an effective soft-segment design strategy for fabricating toughened epoxy composites with robust mechanical and adhesive properties. Full article

Metakaolin (MK) obtained from calcined kaolinitic clay is a highly reactive pozzolanic ingredient for use as an emerging supplementary cementitious material (SCM) in modern sustainable binder productions. It provides elevated alumina to promote formations of Alumina Ferrite Monosulfate (AFm) and Calcium-Aluminium-Silicate-Hydrate (C-A-S-H) phases, enhancing the chloride binding capacity. However, due to inherent material uncertainty and lack of approach in quantifying hydration kinetics and chloride binding capacity across varied mixes, robustly assessing the chloride resistance of metakaolin-blended concrete remains challenging. In light of this, a machine learning-aided framework that encompasses physics-based material characterisation and ageing modelling is developed to bridge the knowledge gap. Through applying to laboratory experiments, the impacts of uncertainty on the phase assemblage of hydrated system and chloride penetration are quantified. Moreover, the novel Extended Support Vector Regression (XSVR) method is incorporated and verified against a crude Monte Carlo Simulation (MCS) to demonstrate the capability of achieving effective and efficient uncertainty-aware chloride resistance analyses. With the surrogate model established using XSVR, quality control of metakaolin towards durable design optimisation against chloride-laden environments is discussed. It is found that the fineness and purity of adopted metakaolin play important roles. Full article

Coal gangue, as a predominant solid byproduct of the global coal industry, poses severe environmental challenges because of its massive accumulation and low utilization rate. This review systematically synthesizes and analyzes published experimental and analytical studies on the dual-pathway utilization of coal gangue in concrete, including Pathway 1 (aggregate substitution) and Pathway 2 (cementitious activity activation). While the application of coal gangue aggregates is traditionally limited by their inherent high porosity and lower mechanical strength than those of natural aggregates, this review demonstrates that performance barriers can be effectively overcome. Through multiscale modification strategies—including surface densification, biological mineralization (MICP), and matrix synergy—the interfacial defects are significantly mitigated, allowing for feasible substitution in structural concrete. Conversely, for the mineral admixture pathway, controlled thermal activation is identified as a key process to optimize the phase transformation of kaolinite, thereby significantly enhancing pozzolanic reactivity and long-term durability. According to reported studies, the partial replacement of natural aggregates or cement with coal gangue can reduce CO₂ emissions by approximately tens to several hundreds of kilograms per ton of coal gangue utilized, depending on the substitution level and activation strategy, highlighting its considerable potential for carbon reduction in the construction sector. Nevertheless, challenges related to energy-intensive activation processes and variability in raw gangue composition remain. These limitations indicate the need for future research focusing on low-carbon activation technologies, standardized classification of coal gangue resources, and long-term performance validation under realistic service environments. Based on the synthesized literature, this review discusses hierarchical utilization concepts and low-carbon activation approaches as promising directions for promoting the sustainable transformation of coal gangue from an environmental liability into a carbon-reduction asset in the construction industry. Full article

The deterioration of concrete hydraulic structures caused by chemical factors, seepage, and environmental stress necessitates advanced protective coatings that enhance durability, flexibility, and environmental sustainability. Conventional protective systems often exhibit limited durability under combined hydraulic, thermal, and chemical stress. In this study, a novel polyfluorosilicone-based coating system is presented, which integrates a deep-penetrating nano-primer for substrate reinforcement, a crack-bridging polymer intermediate layer for impermeability, and a polyfluorosilicone topcoat providing UV and weather resistance. The multilayer architecture addresses the inherent trade-offs between adhesion, flexibility, and durability observed in conventional waterproofing systems. Informed by a mechanistic study of interfacial adhesion and failure modes, the coating exhibits outstanding high mechanical and performance characteristics, including a mean pull-off bond strength of 4.56 ± 0.14 MPa for the fully cured triple-layer coating system, with cohesive failure occurring within the concrete substrate, signifying a bond stronger than the material it protects. The system withstood 2.2 MPa water pressure and 200 freeze–thaw cycles with 87.2% modulus retention, demonstrating stable mechanical and environmental durability. The coating demonstrated excellent resilience, showing no evidence of degradation after 1000 h of UV aging, 200 freeze–thaw cycles, and exposure to alkaline solutions. This water-based formulation meets green-material standards, with low volatile organic compound (VOC) levels and minimal harmful chemicals. The results validate that a multi-scale, layered design strategy effectively decouples and addresses the distinct failure mechanisms in hydraulic environments, providing a robust and sustainable solution. Full article

Since the number of existing steel-reinforced concrete buildings affected by carbonation-induced corrosion is steadily increasing, there is a high demand for durable repair methods. Chemical re-alkalization (CRA) represents one such approach, relying on the transport of alkaline pore solution from a repair mortar into carbonated concrete. With the introduction of clinker-reduced binder systems such as hybrid alkali-activated binders (HAABs), their suitability for CRA and governing material parameters require further clarification. In this study, material-related chemical and structural influences on CRA were investigated using an adapted form of Fick’s second law of diffusion, incorporating a time-dependent attenuation factor, β(t). The CRA progression was evaluated over 28 days, distinguishing between an initial suction phase and a subsequent diffusion phase. The results show that a high initial alkalinity of the mortar pore solution (pH > 14) significantly enhances re-alkalization during the suction phase, reflected by suction factors a > 1. In contrast, progression during the diffusion phase is primarily governed by the potassium concentration gradient at the mortar–concrete interface, while structural parameters such as capillary porosity show no systematic correlation with the deceleration factor b (−0.46 ≤ b ≤ −0.26). The findings indicate that, within the investigated range, mortar pore solution chemistry has a stronger influence on CRA than structural properties, providing guidance for the targeted design of alkaline repair mortars. Full article

Coral aggregate concrete (CAC) serves as a critical material for sustainable development in marine engineering, effectively addressing the shortage of aggregate resources in the construction of offshore islands and reefs. In this paper, the aggregate characteristics, static and dynamic mechanical properties and modification technology of CAC are systematically reviewed. Research indicates that the coral aggregates (CAs), due to its high porosity (approximately 50%), low bulk density (900–1100 kg/m³), and rough, porous surface, results in relatively low static compressive strength (20–40 MPa), insufficient elastic modulus, and significant brittleness in CAC. However, its dynamic performance shows the opposite advantage. Under impact loads, the energy absorption capacity is enhanced by 32.6–140.3%, compared to ordinary concrete (OC) due to the energy dissipation mechanism of pore platic deformation. Through the modification techniques, such as aggregate pre-treatment (acid washing/coating), incorporation of auxiliary cementitious materials (silica fume increases strength by 16.4%), fibre reinforcement (carbon fibres enhance flexural strength by 33.3%), and replacement with novel cementitious materials (magnesium sulphate cement improves chloride ion binding capacity by 90.7%), the mechanical properties and durability of CAC can be significantly optimised. This paper highlights gaps in current research regarding the high strain rate (>200 s⁻¹) dynamic response, multi-factor coupled durability in marine environments, and the engineering application of alkali-activated materials, providing theoretical basis for future research directions. Full article

The construction industry relies on building materials that provide not only high physical and mechanical performance but also adequate thermal and durability properties. However, several factors still limit the quality and service life of concrete products. The development of the construction industry provides new opportunities for designing efficient construction facilities. To obtain enhanced design capabilities, it is very important to relieve the load on the structure, this can be achieved by reducing the mass of materials without losing strength. This study investigates the enhancement of foam concrete through the combined incorporation of mineral fibers recycled from basalt insulation waste and complex polymer modifiers. The aim was to improve the material’s mechanical performance, durability, and pore structure stability while promoting the sustainable use of industrial by-products. The experimental program included tests on density, compressive strength, water absorption, and thermal conductivity for mixtures of different densities (400–1100 kg/m³). The results demonstrated that the inclusion of mineral fibers and polymer modifiers significantly enhanced structural uniformity and pore wall integrity. Compressive strength increased by up to 35%, water absorption decreased by 25%, and thermal conductivity was reduced by 18% compared with the control mixture. Full article

This study presents an experimental investigation into the seismic performance of seismically deficient reinforced concrete (RC) bridge columns retrofitted with passive and active confinement systems. Four single-cantilever RC columns, representing 1/3-scale bridge piers, were constructed with poor transverse reinforcement detailing to simulate seismic deficiency. One column was left un-strengthened for baseline comparison, while the remaining three were retrofitted using: (1) a CFRP jacket, (2) welded Fe-SMA plates, and (3) bolted Fe-SMA plates. All columns were subjected to quasi-static lateral cyclic push-only loading reaching extreme drift levels exceeding 16% and high loading rates up to 6 mm/s. The study specifically explores the confinement effectiveness of CFRP and thermally activated Fe-SMA plates, comparing their contributions to lateral strength, ductility, energy dissipation, failure mode, and damage suppression. The results show that while the as-built column failed at 3.65% drift due to brittle flexural-shear failure, all retrofitted columns demonstrated significantly enhanced ductility, drift capacity, and post-peak behaviour. The CFRP and Fe-SMA jackets effectively delayed damage initiation, minimized core degradation, and improved energy dissipation. The bolted Fe-SMA system exhibited the highest and full restoration of lateral strength, while the welded system achieved the greatest increase in cumulative energy dissipation of around 40%. This research highlights the practical advantages and seismic effectiveness of Fe-SMA and CFRP confinement systems under extreme drift levels. However, future work should explore full-scale column applications, refine anchorage techniques for improved composite interaction, and investigate long-term durability under cyclic environmental conditions. Full article

Driving the circular economy in road construction requires the effective use of secondary materials like recycled concrete aggregate (RCA) and fly ash (FA). A key obstacle is the performance trade-off in concretes incorporating both materials. This research investigates feasible mix designs for road concrete, using RCA as a full gravel replacement and FA as a cement substitute. Polypropylene fiber (36 mm) and a superplasticizer were utilized to mitigate fresh and hardened state drawbacks. The experimental program included 15 modified mixtures with recycled aggregate and 3 control mixtures with natural aggregate. The workability of all concrete mixtures was kept constant at slump class S1. Road concretes with RCA, containing a 10–12% FA by cement replacement, at least 2 kg/m³ of polypropylene fiber (PF), and 4 kg/m³ of superplasticizer (SP), achieve compressive strength of at least 50 MPa and flexural strength of no less than 5 MPa at the design age. This performance is comparable to that of control mixtures. Furthermore, the abrasion resistance ranges between 0.48–0.50 g/cm², and the brittleness index falls within 0.095–0.100, significantly enhancing the durability of concrete for rigid pavement applications. The conducted cradle-to-gate life-cycle assessment (stages A1–A3) of the constituent materials for 1 m³ of concrete indicates the following environmental impacts: Global Warming Potential (GWP) of 195 kg CO₂ equation, Non-renewable Primary Energy Demand (PENRE) of 1140 MJ, Abiotic Depletion Potential for Fossil resources (ADPF) of 1120 MJ, Acidification Potential (AP) of 0.45 mol H⁺ equation, and Eutrophication Potential (EP) of 0.07 kg PO₄³⁻ equation It is established that the modified compositions not only meet the required performance criteria but also contribute to the goals of resource conservation in road construction. Full article

Nitrogen oxides (NO_x) emitted mainly from vehicle exhaust significantly contribute to urban air pollution, leading to photochemical smog and secondary particulate matter. Photocatalytic technology has emerged as a promising solution for continuous NO_x decomposition under ultraviolet (UV) irradiation. This study developed an eco-friendly permeable concrete incorporating activated loess and zeolite to improve roadside air quality. The high porosity and adsorption capability of the concrete provided a suitable substrate for a TiO₂-based photocatalytic coating. A single-component coating system was optimized by introducing colloidal silica to enhance TiO₂ particle dispersibility and adding a binder to secure durable adhesion on the concrete surface. The produced permeable concrete met sidewalk quality standards specified in SPS-F-KSPIC-001-2006. Photocatalytic NO_x removal performance evaluated by ISO 22197-1 showed a maximum removal efficiency of 77.5%. Even after 300 h of accelerated weathering, the activity loss remained within 13.8%, retaining approximately 80% of the initial performance. Additionally, outdoor mock-up testing under natural light confirmed NO_x concentration removal and formation of nitrate by-products, demonstrating practical applicability in real environments. Overall, the integration of permeable concrete and a durable, single-component TiO₂ photocatalytic coating provides a promising approach to simultaneously enhance pavement sustainability and reduce urban NO_x pollution. Full article

The construction sector is progressively prioritizing environmental norms owing to its substantial role in carbon emissions from clinker manufacture. Industrial waste materials are increasingly used as alternative constituents in cement-based systems, garnering interest as a sustainable strategy. Ceramic waste powder (CWP), produced in substantial quantities with enduring properties, offers a viable alternative. Nonetheless, its elevated water absorption presents issues, requiring modification procedures such as hydrophobization and the use of nanosilica to enhance performance. This study assessed CWP in both raw and modified forms (ground and hydrophobized) as a partial aggregate replacement in concrete. A silane-derived chemical was employed for hydrophobization, with varying amounts of nanosilica. Recent mortar testing encompassed setting time, flow, and density. Durability was evaluated using capillary water absorption, and flexural and compressive strengths were quantified at 2, 7, and 28 days. Mineralogical and microstructural investigations were conducted utilizing XRD and FTIR to monitor hydration phases and reaction processes. Results indicated that unmodified CWP containing up to 1% (wt) nanosilica enhanced mechanical strength; however, elevated nanosilica concentrations diminished early strength. Hydrophobized CWP samples demonstrated improved early strength with nanosilica levels up to 0.5% (wt), but strength diminished at elevated concentrations. Microstructural analysis confirmed reduced portlandite levels and increased C–S–H production, thereby validating the progress of hydration. The regulated and altered application of CWP with nanosilica can improve mechanical performance and durability while promoting ecological sustainability in cement-based systems. Full article

In hydraulic structures such as water control projects, spillway tunnels, and overflow dams that are subjected to high-velocity flow erosion, Concrete is required to exhibit high resistance to abrasion and cracking. While low water-to-binder ratio concrete can meet strength requirements, its inherent high shrinkage propensity often leads to cracking, seriously compromising long-term safety and durability under severe operating conditions. To address this engineering challenge, this study focuses on optimizing concrete performance through the synergistic combination of slag (GGBS) and silica fume (SF). This study systematically investigated the effects of incorporating GGBS (20–24%) and SF (6–10%) in a low water-to-binder ratio system with a fixed 70% cement content on key concrete properties. The evaluation was conducted through comprehensive tests including compressive strength, drying shrinkage, autogenous shrinkage, and hydration heat analysis. The results demonstrate that the blended system successfully achieves a synergistic improvement in both “high strength” and “low cracking risk.” Specifically, the incorporation of silica fume significantly enhances the compressive strength at all ages, providing a solid mechanical foundation for resisting high-velocity flow erosion. More importantly, compared to the pure cement system, the blended system not only delays the onset but also reduces the rate of early-age shrinkage, and lowers its ultimate autogenous shrinkage value. This characteristic is crucial for controlling the combined effects of thermal and shrinkage stresses from the source and preventing early-age cracking. Simultaneously, hydration heat analysis reveals that the blended system retards the heat release process, which helps mitigate the risk of thermal cracking. This study elucidates the regulatory mechanism of the GGBS-SF combination and provides a critical mix design basis and theoretical support for producing high-strength, high-abrasion-resistant, and low-shrinkage concrete in high-velocity flow environments, offering direct practical implications for engineering applications. Full article

Constructed wetlands (CWs), increasingly adopted as nature-based solutions (NBS) for wastewater treatment, require a rigorous assessment of the durability and structural performance of the materials used in their supporting systems. In contrast to the extensive literature addressing hydraulic efficiency and contaminant removal, the structural behavior of CWs has been scarcely examined, with existing studies offering only general references to reinforced concrete and masonry and lacking explicit design criteria or deterioration analyses. This study integrates evidence from real-world CW installations with a systematic review of 31 studies on the degradation of cementitious materials in analogous environmental conditions, following PRISMA 2020 guidelines, with inclusion criteria based on quantified wastewater-related exposure conditions (e.g., chemical aggressiveness, persistent saturation, and biogenic activity). Results indicate that reinforced concrete, despite its structural capacity, is susceptible to biogenic corrosion, accelerated carbonation, and sulfate–chloride attack under conditions of persistent moisture, with reported degradation rates in analogous wastewater infrastructures on the order of millimeters per year for concrete loss and tens of micrometers per year for reinforcement corrosion. Masonry structures, similarly, exhibit performance constraints when exposed to mechanical overloads and repeated wetting–drying cycles. In contrast, emerging alternatives—such as nanomodified matrices and concretes incorporating supplementary cementitious additives—demonstrate potential to enhance durability while contributing to a reduced carbon footprint, without compromising mechanical strength. These findings reinforce the need for explicit structural design criteria tailored to CW applications to improve sustainability, durability, and long-term performance. Full article

This study investigates the influence of silane coupling agents and multi-walled carbon nanotubes (MWCNTs) on the mechanical, durability, and thermal performance of CFRP rebars manufactured using a pilot-scale pultrusion process. The incorporation of additives extended epoxy working time without causing adverse viscosity effects during processing. Silane-modified CFRP rebars exhibited the highest mechanical performance, achieving a tensile strength of approximately 2649 MPa, an elastic modulus of 156 GPa, and improved bond strength with concrete, which is attributed to enhanced fiber–matrix interfacial adhesion. MWCNT-modified rebars showed slightly lower tensile strength but demonstrated superior thermal resistance, retaining the highest proportion of mechanical properties after exposure to 250 °C due to matrix reinforcement and crack-bridging effects. No significant degradation was observed under simulated marine exposure, while gradual reductions (up to ~7%) occurred in alkaline environments, with silane-modified rebars showing the greatest durability. These findings provide mechanistic insights and practical guidelines for optimizing epoxy formulations to enhance the structural and long-term performance of CFRP rebars. Full article

To address the engineering challenge of durability deterioration in concrete structures in the cold and saline regions in northern China, this study investigated PVA fiber-reinforced concrete under combined sulfate attack and freeze–thaw cycles using PVA fiber volume fractions (0%, 0.1%, 0.3%, 0.5%) and salt-freeze cycles (0, 25, 50, 75, 100, 125, 150 cycles) as key variables. By testing the mechanical and microscopic properties of the specimens after salt-freeze, the degradation law of macroscopic performance and the evolution mechanism of microscopic structure of PVA fiber concrete under different volume fractions are analyzed, and the salt-freeze damage evolution equation is established based on the loss rate of relative dynamic elastic modulus. The results show that the addition of PVA fibers has no significant inhibitory effect on the surface erosion of concrete, and the degree of surface spalling of concrete still increases with the increase in the number of salt-freeze cycles. With the increase in the number of salt-freezing cycles, the mass, relative dynamic elastic modulus and cube compressive strength of the specimens first increase and then decrease, while the splitting tensile strength continuously decreases. The volume fraction of 0.3% PVA fibers has the most significant effect on improving the cube compressive strength and splitting tensile strength of concrete, and at the same time, it allows concrete to reach its best salt-freezing resistance. PVA fibers contribute to a denser microstructure, inhibit the development of micro-cracks, delay the formation of erosion products, and enhance the salt-freezing resistance of concrete. The damage degree D of relative dynamic elastic modulus for PVA fiber concrete exhibits a cubic functional relationship with the number of salt-freeze cycles N, and the correlation coefficient R² is greater than 0.88. The equation can accurately describe the damage and deterioration law of PVA fiber concrete in the salt-freeze coupling environment. In contrast to numerous studies on single-factor exposures, this work provides new insights into the degradation mechanisms and optimal fiber dose for PVA fiber concrete under the synergistic effect of combined sulfate and freeze-thaw attacks, a critical scenario for infrastructure in cold saline regions. This study can provide theoretical guidance for the durability assessment and engineering application of PVA fiber concrete in cold and saline regions. Full article