Search Results (560)

Ultra-high-performance concrete (UHPC) has been widely utilised in strengthening and rehabilitating conventional normal concrete (NC) structures due to its exceptional mechanical properties and durability. However, in cold climates, the interfacial bond between UHPC and NC is susceptible to degradation under freeze–thaw cycles, potentially compromising the composite action and long-term performance of strengthened structures. This study systematically investigated the shear behaviour of a UHPC-NC interface with planted reinforcement subjected to various freeze–thaw conditions. The experiments were conducted considering different numbers of freeze–thaw cycles (0, 20, 40, 60, 80, and 100) and salt solution concentrations (0%, 3.5%, and 5%). Direct shear tests were performed to evaluate interfacial failure modes, mass loss, and shear strength degradation. Results identified three characteristic failure modes: adhesive debonding at the interface, mixed failure involving both the interface and the NC substrate, and crushing failure within the NC substrate. Specimens exposed to 3.5% salt solution experienced the most significant deterioration, exhibiting a 35% reduction in shear strength after 100 freeze–thaw cycles. Normally, lower salt concentrations were found to induce greater interfacial damage compared to higher concentrations. The study underscores the importance of increasing the embedment depth of the planted reinforcement to alleviate stress concentration and enhance interfacial durability in freeze–thaw environments. Full article

To address the problem of corrosion, glass fiber-reinforced polymer (GFRP) bars have been introduced as a viable alternative to conventional steel reinforcement in concrete structures. While extensive research has been conducted on the flexural behavior of RC beams reinforced with steel and GFRP bars over both normal-term and long-term periods, studies focusing on fresh concrete beams are almost non-existent. Consequently, this research investigates the impact of steel and GFRP longitudinal reinforcement, as well as the influence of varying concrete compressive strengths, on the flexural behavior of RC beams. The study employs 3-point bending experiments and machine learning (ML) predictive analyses. Specifically, the short-term (fresh) concrete reinforcement compatibility and the effects of steel and GFRP bar reinforcements on beam flexural behavior were examined across three concrete compressive strength categories: low (C25), moderate (C35), and high (C50). A notable contribution of this research is the application of different ML regression models, utilizing Python’s library, for deflection prediction of RC beams. The failure mechanisms of the beams under static loading conditions were analyzed, revealing that composite bar RC beams failed through flexural cracking and demonstrated ductile behavior, whereas steel bar RC beams exhibited brittle failure characterized by shear cracks and sudden failure modes. The ML regression models successfully predicted the deflection values of RC beams under ultimate loads, achieving an average accuracy of 91.3%, which was deemed highly satisfactory. Among the 18 beams tested, the highest ultimate load was obtained for the SC50-1 beam at 87.46 kN. In contrast, while the steel-reinforced beams exhibited higher load-bearing capacities, it was observed that the GFRP-reinforced beams showed greater deflection and ductility, particularly in beams with low and medium concrete strengths. Based on these findings, it is recommended that the Gradient Boosting Regressor, an AI regression model, be utilized to guide researchers in evaluating the load-carrying and bending capacity of structural beam elements. Full article

High-strength concrete (HSC) is widely used in coastal regions, but its durability and structural safety is threatened by chloride ingress in marine environments. This study investigates the effects of different curing methods, normal, steam, and high-temperature autoclave on the chloride resistance of HSC using the electric flux test. A critical chloride concentration of 4.5% was identified, and accelerated deterioration tests were conducted to evaluate mechanical properties development (compressive strength, elastic modulus, toughness, specific toughness) under the various curing conditions. Additionally, the development of hydration products and microstructural characteristics were analyzed to elucidate the mechanisms underlying the observed differences. The results indicate that steam and autoclave curing enhance cement hydration and the initial mechanical properties of HSC but also increase permeability and susceptibility to chloride ion penetration compared to normal curing. Chloride penetration was found to be most severe at moderate chloride concentrations (~4.5%), while higher concentrations resulted in reduced ion migration. Although intensive curing under elevated temperature and pressure improves early strength and stiffness, it accelerates mechanical degradation under chloride exposure, highlighting a trade-off between short-term performance and long-term durability. Full article

This study reveals the evolution of the mechanical behavior of tunnel lining under the influence of heavy rainfall through field monitoring and coupled fluid-solid numerical simulations. Field monitoring shows that after 14 h of rainfall, the maximum vertical tensile stress increment at monitoring point 2 reached 0.55 MPa. The simulation results indicate that when the rainfall intensity is 1.11 × 10⁻⁵ m/s and the rainfall duration lasts for 36 h, the principal stress increment at the sidewall monitoring point is 2.34 MPa (exceeding the tensile strength of C30 concrete of 1.43 MPa). Based on these findings, the suggested threshold for rainfall-induced checks is a single-day rainfall of ≥80 mm or continuous rainfall of ≥10 h. It is recommended to monitor once every 3 days during normal conditions and once every 2 h during heavy rainfall. When the permeability coefficient of the loosened zones increases from 2.05 × 10⁻⁶ m/s to 6.48 × 10⁻⁵ m/s, the principal stress at the sidewall decreases by 41%. It is suggested to reduce the blind drainage spacing on the sidewalls to 3–4 m. The model reproduces the observed stress increment within a 10% error margin. These results may provide a valuable reference for tunnel design, monitoring, and reinforcement in regions prone to heavy rainfall. Full article

Urban underground infrastructure is increasingly challenged by material aging, environmental degradation, and structural deterioration. In response, trenchless polymer grouting technologies employing sustainability-oriented two-component foaming polymers have attracted growing attention. To investigate shear behavior at the polymer–concrete interface, this study conducted direct shear tests on two types of composite interface geometries—curved and planar—formed by bonding two-component foaming polymer to concrete substrates. Five polymer densities (0.33, 0.42, 0.51, 0.58, 0.66 g/cm³), three concrete strengths (C20, C30, C40), three normal stress levels (0.3, 1.0, 2.0 MPa), three shear rates (0.5, 2.0, 5.0 mm/min), and three interface sizes (100, 150, 200 mm) were examined. The results show that both interface types undergo five characteristic stages under shear. Across identical parameter levels, curved interfaces consistently exhibited higher peak shear strength and larger peak displacement than planar ones. When the polymer density is identical, the peak shear strength and displacement of curved specimens are about 1.38 and 1.43 times those of planar specimens, respectively. Similarly, for specimens with the same concrete strength, normal stress, and shear rate, the corresponding ratios of peak shear strength and displacement are about 1.14 and 1.55, 1.96 and 1.43, and 1.43 and 1.36, respectively. Within the tested ranges, the shear stress increases with polymer density, concrete strength, and normal stress, and generally decreases with shear rate. The shear displacement decreases with polymer density, concrete strength, and shear rate, and generally increases with normal stress. As the specimen size increases, the peak shear strength and peak shear displacement of the curved specimens first increase and then decrease, whereas for the planar specimens, the peak shear strength exhibits a nonlinear increasing trend. These findings provide valuable insights to promote sustainable underground infrastructure rehabilitation. Full article

This study presented a comprehensive finite element (FE) investigation into the flexural behavior of RC T-beams strengthened in the negative moment region using near-surface mounted (NSM) carbon-fiber-reinforced polymers (CFRP) rods. A three-dimensional nonlinear FE model was developed and validated against experimental data, achieving close agreement with normalized mean square error values as low as 0.006 and experimental-to-numerical ratios ranging from 0.95 to 1.04. The validated model was then employed to conduct a systematic parametric analysis considering CFRP rod diameter, concrete compressive strength, longitudinal reinforcement ratio, and FRP material type. The results showed that increasing CFRP diameter from 6 to 10 mm enhanced ultimate load by up to 47.51% and improved stiffness by 1.48 times. Higher concrete compressive strength contributed to stiffness gains exceeding 50.00%, although this improvement was accompanied by reductions in ductility. Beams with reinforcement ratios up to 2.90% achieved peak loads of 309.61 kN, but ductility declined. Comparison among FRP materials indicated that CFRP and AFRP offered superior strength and stiffness, whereas BFRP provided a more balanced combination of strength and deformation capacity. Full article

Ultra-high performance concrete (UHPC) and ultra-high toughness cementitious composite (UHTCC) offer superior mechanical properties compared to normal concrete, with UHPC excelling in compressive strength and UHTCC in tensile ductility and crack resistance. This study focuses on UHPC/UHTCC-encased steel tubular (UEST) columns, establishing finite element (FE) models to simulate the axial behavior of UEST columns, conducting parametric studies on stud number, encasement thickness, steel yield strength, and width-to-thickness ratio, and developing a theoretical model considering thin-walled steel buckling to calculate the axial resistance of UEST columns. The proposed theoretical model predicts axial resistance with an average error of 3.4%, providing a reliable design method for engineering applications. Full article

Optimizing concrete production requires balancing ingredient ratios and using local resources to produce an economical material with the desired consistency, strength, and durability. Compressive strength is crucial for structural design, yet predicting it accurately is challenging due to the complex interplay of various factors, including component types, water–cement ratio, and curing time. This study employs a Multi-layer Perceptron Neural Network (ANN_MLP) to model the relationship between input variables and the compressive strength of normal and high-performance concrete. A dataset of 1030 samples from the literature was used for training and evaluation. The optimized ANN_MLP configuration included 16 neurons in a single hidden layer, with the ‘tanh’ activation function and ‘sgd’ solver. It achieved an R² of 0.892, an MAE of 3.648 MPa, and an RMSE of 5.13 MPa. The model was optimized using a univariate sensitivity analysis to measure the impact of each hyperparameter on performance and select optimal values to maximize the accuracy and robustness. Full article

This study investigates the influence of seasonal curing conditions on the compressive strength development of reinforced concrete, focusing on the gap between standard-cured cylinders and in situ structural performance. Concrete mixes with water-to-binder ratios of 0.35, 0.45, and 0.55 were cast under summer, autumn, and winter conditions. Large-scale specimens were instrumented to monitor the internal heat of hydration at center and outer regions, and 91-day core strengths were compared with 28-day standard-cured cylinders. Results revealed that seasonal temperature variations significantly affect hydration kinetics, producing thermal gradients that lead to spatial strength differences. Normal distribution analysis (₂₈S₉₁ values) was used to quantify strength deviations and derive correction factors. Outer-region cores consistently showed lower strengths, confirming them as conservative indicators for design. Based on μ + 2σ, correction factors of approximately 8 MPa are recommended for summer and winter conditions and 5 MPa for autumn, ensuring a conservative estimate of in situ strength. The proposed approach provides a rational, data-driven basis for mix design strength adjustments, improving the reliability of structural safety evaluations and supporting climate-responsive construction planning for durable and safe reinforced concrete structures. Full article

Currently, resin polymer anchoring agents are widely used for bolting support in coal mine roadways to anchor the bolts to the surrounding rock mass. However, due to the relatively low strength of the resin anchoring agent itself, the required anchoring length tends to be excessively long. Based on this, this paper proposes the use of resin concrete as a replacement for resin. Compared to resin anchoring agents, resin concrete offers greater mechanical interlocking force with anchor rods, which can reduce the theoretical anchoring length. To systematically investigate the influence of factors such as the diameter and anchorage length of Glass Fiber-Reinforced Polymer (GFRP) bolt on the bond behavior between GFRP bolts and resin concrete, 33 standard pull-out tests were designed and conducted in accordance with the CSA S807-19 standard. Taking the 18 mm-diameter bolt as an example, when the bond lengths were 2D, 3D, 4D, and 5D, the average bond strengths were 41.32 MPa, 39.18 MPa, 38.84 MPa, and 37.44 MPa, respectively. This represents a decrease of 5.18%, 6.00%, and 9.39% for each subsequent increase in bond length. The results indicate that the bond strength between GFRP anchors and resin decreases as the anchorage length increases. Due to the shear lag effect, the average bond strength also decreases with increasing anchor diameter. Taking a 5D (where D is the anchor diameter) anchorage length as a reference, the average bond strengths for anchor diameters of 18 mm, 20 mm, 22 mm, and 24 mm were 37.44 MPa, 33.97 MPa, 32.18 MPa, and 31.50 MPa, respectively. The corresponding reductions compared to the 18 mm diameter case were 9.27%, 14.05%, and 15.87%. Based on the experimental results, this paper proposes a bond–slip constitutive model between the bolt and resin concrete, which consists of a rising branch, a descending branch, and a residual branch. A differential equation relating shear stress to displacement was established, and the functions describing the variation in displacement, normal stress, and shear stress along the position were solved for the ascending branch. Although an analytical solution for the differential equation of the descending branch was not obtained, it will not affect the subsequent derivation of the theoretical anchorage length for the GFRP bolt–resin concrete system, as structural components in practical engineering are not permitted to undergo excessive bond-slip. Full article

The growing demand for radiation-shielded infrastructure highlights the need for materials that balance shielding performance with environmental and economic sustainability. Heavyweight self-compacting concretes (HWSCC), commonly produced with barite (BaSO₄) or magnetite (Fe₃O₄) aggregates, lack systematic life cycle comparisons. The aim of this study is to systematically compare barite- and magnetite-based HWSCC in terms of life cycle environmental impacts, life cycle cost, functional performance (strength and shielding), and end-of-life circularity, in order to identify the more sustainable and cost-effective material for radiation shielding infrastructure. This study applies cradle-to-grave life cycle assessment (LCA) and life cycle cost analysis (LCC), in accordance with ISO 14040/14044 and ISO 15686-5, to evaluate barite- and magnetite-based HWSCC. Results show that magnetite concrete reduces global warming potential by 19% eutrophication by 24%, and fossil resource depletion by 23%, while lowering life cycle costs by ~23%. Both concretes achieve comparable compressive strength (~48 MPa) and shielding efficiency (µ ≈ 0.28–0.30 cm⁻¹), meeting NCRP 147 and IAEA SRS-47 standards. These findings demonstrate that magnetite-based HWSCC offers a more sustainable, cost-effective, and ethically sourced alternative for radiation shielding in healthcare, nuclear, and industrial applications. In addition, the scientific significance of this work lies in establishing a transferable methodological framework that combines LCA, LCC, and performance-normalized indicators. This enables scientists and practitioners worldwide to benchmark heavyweight concretes consistently and to adapt sustainability-informed material choices to their own regional contexts. Full article

The integration of nanoengineered materials into concrete systems has emerged as a promising strategy for enhancing structural performance and sustainability. This study presents a hybrid experimental-analytical investigation into the use of multilayer graphene as a smart admixture in high-performance concrete. The research combines mechanical testing, microstructural characterization, and a multi-objective optimization model to determine the optimal graphene dosage that maximizes strength gains while minimizing carbon emissions. Concrete specimens incorporating multilayer graphene (ranging from 0.01% to 0.10% by weight of cement) were tested over 7 to 90 days for compressive, tensile, and flexural strengths. Simultaneously, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray analyses revealed crystallinity enhancement, pore densification, and favorable elemental redistribution due to graphene inclusion. A normalized composite objective function was formulated to balance three maximization targets—compressive, tensile, and flexural strength—and one minimization goal—carbon emission. The highest objective score (Z = 1.047) was achieved at 0.10% graphene dosage, indicating the optimal balance of strength performance and environmental efficiency. This dual-framework study not only confirms graphene’s reinforcing effects experimentally but also validates the 0.10% dosage through mathematical scoring. The outcomes position of multilayer graphene as a powerful additive for high-strength, low-carbon concrete, especially suited for infrastructure in hot and arid environments. The proposed optimization approach provides a scalable pathway for performance-based graphene dosing in future innovative concrete formulations. Full article

Ultra-High Performance Concrete (UHPC), characterized by its superior mechanical properties and excellent durability, has emerged as a promising material for the repair and reinforcement of tunnels. This study aimed to clarify the reinforcement mechanism of UHPC for tunnel linings and the improvement in bearing capacity through numerical simulation and theoretical derivation. By simulating normal concrete (NC) and reinforced concrete (RC) eccentrically loaded columns under varying reinforcement configurations and working conditions, the study investigated the failure modes and mechanical behaviors of UHPC-reinforced tunnels. Analytical equations for the compression-bending capacity of UHPC-reinforced columns under secondary loading were established and validated. Subsequently, the influence of key parameters was systematically analyzed. The results show that UHPC reinforcement significantly enhances load-bearing capacity, deformation resistance, stiffness, and ductility, albeit with varying failure modes. Notably, the ultimate load-carrying capacity increases by up to 184.6% for NC columns at 180 mm eccentricity and 286.5% for RC columns at 200 mm eccentricity. Reinforcement effectiveness is highly influenced by eccentricity: inner-side reinforcement proves more advantageous under small eccentricities, whereas outer-side reinforcement outperforms under large eccentricities. Comparative analyses of various parameters reveal that initial strain has the greatest impact on reinforcement effectiveness, followed by UHPC thickness, UHPC strength, and the reinforcement ratio of the reinforcement layer, in descending order of influence. The research provides valuable insights into the application of UHPC in tunnel reinforcement, offering a reliable theoretical and numerical basis for engineering design. Full article

Driven by the pursuit of more sustainable materials, earth construction has seen renewed interest in recent years. However, chemical stabilization is often required to ensure adequate water resistance. While recycled cement from concrete waste (RCC) has recently emerged as a more sustainable alternative to ordinary Portland cement (OPC) for soil stabilization, its environmental impact remains unassessed. A hybrid model, built on collected data and direct simulations, was implemented to estimate energy and carbon emissions of compressed earth blocks (CEBs) stabilized with RCC as a partial or total replacement of OPC. Four operational scenarios were assessed in a cradle-to-gate approach, evaluating the environmental impact per CEB unit, and normalizing it to the CEB compressive strength. OPC CEBs showed up to 9 times higher energy consumption (2.46 vs. 0.24 MJ/CEB) and about 35 times higher carbon emissions (0.438 vs. 0.012 kgCO₂/CEB) than UCEBs. However, replacing OPC with RCC reduced energy consumption by up to 8% and carbon emissions by up to 64%. Although RCC CEBs showed lower mechanical strength, resulting in higher energy consumption when normalized to compressive strength, carbon emissions remained up to 48% lower compared to OPC CEBs. RCC emerged as a more sustainable alternative to OPC for earth stabilization, while also improving the mechanical strength and durability of UCEBs. Full article

This research investigates the feasibility of producing eco-friendly self-compacting concrete (SCC) by partially replacing both fine and coarse natural aggregates with waste marble sludge (WMS), a byproduct of the marble industry. The objective is to evaluate whether this substitution enhances or compromises the concrete’s performance while contributing to sustainability. A comprehensive experimental program was conducted to assess fresh and hardened properties of SCC with varying WMS content. Fresh-state tests—including slump flow, T₅₀ time, and V-funnel flow time—were used to evaluate workability, flowability, and viscosity. Hardened properties were measured through compressive, flexural, and Brazilian tensile strengths, along with water absorption after 28 days of curing. The mix with 10% replacement of both sand and coarse aggregate showed the most balanced performance, achieving a slump flow of 690 mm and a V-funnel time of 6 s, alongside enhanced mechanical properties—compressive strength 48.6 MPa, tensile strength 3.9 MPa, and flexural strength 4.5 MPa—and reduced water absorption (4.9%). A complementary cost model quantified direct material cost per cubic meter and a performance-normalized efficiency metric (compressive strength per cost). The cost decreased monotonically from 99.1 $/m³ for the base mix to $90.7 $/m³ at 20% + 20% WMS (−8.4% overall), while the strength-per-cost peaked at the 10% + 10% mix (0.51 MPa/USD; +12% vs. base). Results demonstrate that WMS can simultaneously improve rheology and mechanical performance and reduce material cost, offering a practical pathway for resource conservation and circular economy concrete production. Full article