Materials and Structures最新文献

The present work investigates the effect of substituting natural coarse aggregates (NCA) with recycled coarse aggregates (RCA) obtained from multiple recycling cycles on the flexural creep of concrete beams under sustained bending loads. Four types of concrete with the same water-to-cement ratio were analyzed: natural aggregates concrete (NC) and three generations of recycled aggregate concrete, where NCA was replaced by RCA in each generation, with volume substitution of 50 and 100%. Creep coefficients and creep deformations velocity were assessed for all concretes In addition, the flexural creep strains of concretes are predicted using Burger’s rheological model, which is the most widely model used to describe the viscoelastic materials properties. The experimental results show that multi-recycling has a negative impact on the flexural creep of concrete. An increase in recycling cycles and RCA content results in higher compressive and tensile creep as well as in the creep coefficient and creep velocity, but using 50% RCA has a lesser impact on this deformation. Finally, the compressive and tensile creep strains predicted using Burger’s rheological model demonstrate good consistency with the experimental investigations results over the assumed range of multi-recycling cycles, RCA volume substitution, and measurement durations.

This study investigated the physicochemical and mineralogical properties of soils used in earthen constructions, with the aim of characterizing the materials of the main types of earthen construction and their source soils from a soil science perspective. Samples from vernacular and modern constructions, together with those from adjacent soils were analyzed, covering traditional techniques such as adobe and rammed earth, as well as compressed earth blocks (CEB). Particle size analysis by sedimentation revealed that vernacular constructions exhibited textural distributions more closely aligned with the optimal ranges reported in the literature with clay, silt, and sand contents that favored cohesion and workability, whereas modern constructions showed greater variability, particularly in the sand fraction, which may result from the mixing of materials. Statistical analyses, including T-tests, one-way ANOVAs, and a MANOVA, did not detect significant differences (p > 0.05) in the particle size fractions (clay, silt, and sand) between construction types or origins, although trends toward higher silt content in vernacular constructions were observed. Furthermore, organic matter content was lower in CEBs, reflecting the greater selection of purely mineral raw material in these structures to ensure their stability. Altogether, these findings indicated that while trends exist in the chemical and textural composition of materials used in vernacular versus modern constructions, soil selection largely depended on local availability and empirical knowledge. Finally, their properties were assessed in relation to their suitability as construction materials.

Physical hardening of asphalt materials subjected to prolonged low-temperature conditions results from the densified shrinkage and increased stiffness caused by molecular rearrangements. It significantly contributes to early low-temperature cracking in asphalt pavements, leading to further distress and raising maintenance expenses. Several engineering dosages (3%, 4%, and 5%) of SBS modified asphalt binders were prepared to clarify the influence of physical hardening on their low-temperature performance. Extended bending beam rheometer test, molecular dynamics simulation, and atomic force microscope were conducted to explore the rheological characteristics and hardening mechanism. Statistical methods were performed to establish the characteristic correlation between macromechanics and micromorphology, and some specific evaluation criteria were proposed. The results show that the higher modifier content indicates the more pronounced deterioration of rheological properties subjected to hardening and a higher risk of low-temperature cracking in service, similar to a longer hardening time and lower temperature. The motion of asphalt molecules exhibits an annealing acceleration state followed by a relaxation steady state during the hardening process. The higher modifier content and lower temperature lead to severe molecular aggregation, while the temperature is the main factor compared to the modifier content. The “bee” structure transits from an integral decomposition stage to a local aggregation stage where the altitude and size grow as the SBS content increases. Grade loss is recommended as the criterion for the hardening characteristics assessment of SBS modified asphalt binders. Mean area and the range between peaks and valleys (R_max) can depict the microstructural properties under the influence of hardening time and SBS content, respectively.

The rising demand for raw materials and the environmental burden of industrial waste have increased interest in sustainable solutions for asphalt pavement engineering. Recycled ethylene–propylene–diene monomer (EPDM) is a promising modifier that combines thermoplastic resilience with environmental benefits. This study investigates the modification of a 70/100 penetration grade bitumen with EPDM and its co-modification with styrene–butadiene–styrene (SBS). A comprehensive experimental program evaluated conventional properties, rheological behavior, aging resistance, thermal susceptibility, elastic recovery, and microstructural features. Results indicated that EPDM improved softening point by 3–5% and increased viscosity, though it also heightened susceptibility to phase separation. Co-modification with SBS provided more pronounced improvements: high-temperature stiffness (G*/sinδ) rose by up to 25% compared to SBS-only modification, non-recoverable creep compliance decreased by more than 70%, and elastic recovery increased by up to 130%. FTIR analysis further showed about 70% lower oxidation indices in co-modified binders, while BBR testing confirmed that all formulations retained satisfactory low-temperature performance (PG 70-16). Overall, the 10% EPDM + 2% SBS binder achieved the most balanced performance across rutting resistance, elasticity, and oxidative durability.

Graphical abstract

Earthen construction offers a low-carbon, locally sourced alternative to fired masonry, yet its widespread use is limited by modest strength and brittle post-peak behavior. Bio-based fibers are a promising low-impact stabilizer, but reported strength gains vary widely because fiber morphology and clay mineralogy are seldom controlled independently. This study isolates those variables by combining pure kaolinite, illite, and montmorillonite clays with well-characterized cellulose fibers whose length-to-diameter ratios span two orders of magnitude. Model clay–sand bricks were assessed through compressive testing, static yield stress measurements, and scanning electron microscopy. Fiber morphology proved decisive. Long cellulose fibers (≈ 100 × clay particle size; ≈ 10 × sand grain size) formed an entangled, well-bonded network that increased compressive strength and post-peak ductility of montmorillonite bricks by up to 120% compared with fiber-free controls, whereas short fibers produced only marginal gains. Reinforcement efficiency also depended on clay mineralogy, with benefits being pronounced in montmorillonite, moderate in illite, and negligible in kaolinite, reflecting differences in fiber–clay adhesion. These results show that effective fiber stabilization of earthen materials requires matching fiber aspect ratio to particle size and selecting clays capable of strong interfacial bonding. The findings provide quantitative guidelines for designing low-carbon, fiber-reinforced earth products and establish a framework for future durability and field-scale studies.

The use of supplementary cementitious materials (SCM) is an important part of the roadmap for reducing CO₂ emissions and extending the service life of reinforced concrete structures. To accelerate the adoption of SCMs, the RILEM Technical Committee 298-EBD evaluates scaled-down cement paste test methods to assess the effect of SCM on resistance to chloride and sulfate ingress and reactivity, which are critical to concrete durability. This review focuses on methods for measuring chloride diffusivity and is divided into four sections: diffusivity models and parameters, diffusion test methods (including NMR and chloride measurements), migration test methods and implications for future research. Key insights highlight the complexities of multi-species ionic and molecular diffusion/migration, including various binding interactions, and compares the different measurement methodologies. The review also addresses the test scale and aggregate effects, noting the pros and cons of testing at the paste, mortar, and concrete scales. The review underscores the need for further investigation into testing protocols and the influence of SCM on chloride diffusion, emphasizing that comprehensive testing across different scales provides complementary information for assessing durability performance.

Large-scale cement-based additive manufacturing, commonly known as 3D concrete printing (3DCP), exhibits greater porosity than traditional cast concrete, with pores mainly concentrated at interface regions, forming interconnected channels that negatively affect their mechanical properties. Additionally, 3DCP has a larger environmental footprint than conventional concrete due to the high cement content in printable mortars (~ 480 kg/m³). One strategy to reduce the environmental footprint is to replace cement with locally available supplementary cementitious materials (SCMs). On the other hand, printing parameters can be optimised to improve the hardened properties of 3D-printed structures. This research aims to assess the feasibility of locally sourced (zeolite and calcined clay) and recycled (mussel shell powder) SCMs in 3DCP mixes, and analyse the effects of printing parameters (filament overlap and nozzle offset) on the mechanical properties. The mechanical properties (elastic modulus, compressive strength, and splitting tensile strength) of 7 mixes were tested at different ages. Results showed that mussel shell powder delayed the binder hydration, decreasing the compressive strength of LC3LCMS and Z40MS cast (by 38.2% and 8.8%) and printed samples (by 11.2% and 13.4%) compared to their counterparts with calcium carbonate at 90 days. Z40 showed the greatest compressive strength results at all ages besides the benchmark samples with metakaolin, achieving a maximum compressive strength of 69.9 ± 1.4 MPa and 53.4 ± 4.6 MPa at 90 days for cast and printed samples, respectively. A 4 ± 1 mm filament overlap improved the mechanical properties and reduced the anisotropy.

This study employs a multi-scale simulation approach to systematically investigate the rupture mechanism and healing efficacy of microcapsules. Firstly, the stress and rupture behavior of microcapsules within virtual specimens of asphalt mixture at different notch tips was analyzed by the semi-circle bending simulation test. Then, based on the simulation results of semi-rigid base asphalt pavement fatigue damage, the equivalent modulus of the representative volume elements for cracks was evaluated, establishing a quantitative relationship between crack quantity and modulus. Finally, the healing effectiveness of microcapsules on pavement structures with varying degrees of damage was assessed based on pavement deflection. The results indicate that reduced capsule wall thickness or increased wall modulus substantially elevates stress levels, with each 1 GPa modulus increase or 1 μm thickness decrease raising average stress by approximately 30 MPa. Under mode-I loading, stresses consistently surpass mode-II values, exhibiting maximum principal stresses approximately double the maximum shear stresses. Rupture probability rises with decreasing wall thickness, and fracture initiates earlier under mode-I loading. Rupture timing follows a Fréchet distribution. Enhanced core material modulus significantly boosts healing efficacy: increasing core modulus from 1 to 9 GPa reduces deflection from 59.56 to 56.48 μm. However, the microcapsule structural strength repair index (MSSRI) demonstrates a quartic polynomial relationship with modulus. The incremental MSSRI gain per modulus unit declines from 0.15 to 0.04, indicating a healing efficacy saturation threshold. This work provides theoretical foundations for microcapsule design. For engineering applications, optimize wall thickness/modulus to control rupture timing, while balancing core material cost against healing efficacy using the modulus-MSSRI relationship.

CFRP cords utilized as external concrete reinforcement follow the curvature in flexural deformation due to their flexibility, preventing debonding that occurs with pre-pregnated CFRP bars. This study investigated the CFRP cord utilization for revitalizing cracked, non-collapsed haunch beam-to-column joints through experimental and numerical methods on large-scale specimens, enhancing the direct applicability of the findings to real-world structures. Since tensile reinforcement has yielded, the cords took a substituting role in the energy dissipation and ductility refinement, restoring the integrity of the system. Two members with haunch angle variations were loaded until tensile-steel yielding, straightened, and epoxy injection retrofitted. Three CFRP cords were attached to the tensile area, and the member was reloaded. The rehabilitation effectiveness was performed by comparing the behavior to two uncracked interchangeable members. A numerical model was developed, and a multi-criteria sensitivity analysis was conducted to evaluate the shifting of the most significant failure behavior parameters. It was demonstrated that the concrete ultimate strain and the initial and post-crack stiffness modulus in compression were the most influential factors, while for non-CFRP-reinforced identical members, the residual stress coefficient and ultimate stress in tension were dominant. The reinforced member was restored and improved significantly in terms of load-carrying capacity of 27% and 32% for (14^circ) and (26.5^circ) haunch, respectively, with the reduced initial stiffness of 30–67%. The findings provide validated, practical strategies for engineers seeking to extend the service life of existing concrete infrastructure, moving beyond laboratory-scale proof of concept to demonstrate a viable and effective conservation technique.

The increasing scarcity of petroleum-based bitumen and its adverse environmental and economic implications necessitate the development of sustainable alternatives for flexible pavement construction. Bio-bitumen is an environmentally friendly substitute for conventional bitumen and is renewable and cost-effective. This study explores the potential of castor oil (CO) and rice husk ash (RHA) as bio-based modifiers in the formulation of castor oil and rice husk ash-modified bio-bitumen (CORMBB). The optimization of CO (5–15%) and RHA (2–6%) content was conducted using response surface methodology (RSM) with central composite design (CCD) and a genetic algorithm-optimized artificial neural network (GA-ANN) model. Binder properties, such as penetration and softening point, along with bituminous mixture performance indicators, including Marshall stability, indirect tensile strength (ITS), tensile strength ratio (TSR), and Cantabro loss, were considered response variables. The GA-ANN model exhibited high predictive accuracy, identifying optimal dosages of 9.02% CO and 5.85% RHA, while RSM yielded 8.992% CO and 6% RHA. Subsequently, the optimized CORMBB (9% CO and 6% RHA) was subjected to storage stability test, X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and dynamic shear rheometer (DSR) analyses to assess, its compatibility of CORMBB, chemical interaction among CO, RHA and base binder (BB), and rheological behavior. The findings indicate that CO enhances flexibility, adhesion, and moisture resistance, whereas RHA improves stiffness, rutting resistance, and aggregate retention. FTIR and XRD results confirmed improved molecular interactions and structural integrity, underscoring the potential of CORMBB as a sustainable, eco-friendly alternative to conventional bitumen. This study provides comprehensive insights into the formulation and performance of bio-modified binders, promoting the integration of agricultural by-products in pavement applications.