Materials and Structures最新文献

The stacking voidage of coarse aggregate is a key parameter influencing the performance of concrete. However, its governing mechanisms related to particle morphology, gradation, and the sidewall effect remain unclear. This study aims to clarify how these three factors affect stacking voidage and to identify pathways for its reduction. Real aggregate models were reconstructed using image analysis techniques (AIMS and laser scanning), and the packing process of coarse aggregates in a cubic mold was simulated using the Discrete Element Method (DEM). In addition, a three-graded mixing experiment with real coarse aggregates was conducted to investigate the effect of gradation on the stacking voidage. The results show that stacking voidage consists of a basic component (P_S) and two additional components (P_W, P_G). P_S is primarily determined by aggregate morphology, with sphericity and angularity as the main influencing factors. P_W represents the increased voidage caused by the container sidewall effect, while P_G denotes the reduction in voidage due to aggregate gradation. The greater the particle size difference between aggregates, the larger the decrease in P_G. In concrete columns up to 1000 mm, the contributions of morphology, gradation, and the sidewall effect to overall voidage were 57.17%, 30.51%, and 8.31%, respectively. The sidewall effect depends strongly on container size. The proposed equation (P = P_S + P_W – P_G) clarifies the influence mechanism of these three controllable factors on aggregate stacking voidage, offering a theoretical basis for predicting stacking voidage and improving aggregate packing for high-quality concrete.

This study investigates the Alkali-Silica Reaction (ASR) behavior in Ground Granulated Blast Furnace Slag (GGBFS) mortars activated with NaOH (GGBFS-NaOH) and LiOH (GGBFS-LiOH). AAS mortars incorporating feldspar-based reactive aggregates were prepared with varying molar concentrations of each activator. Accelerated mortar bar tests (ASTM C1260) showed that GGBFS-NaOH samples showed expansion beyond the threshold limit of 0.1% within four days of exposure at 10 M concentration, whereas GGBFS-LiOH samples showed negligible expansion ((le) 0.02%) throughout the test period. Microstructural analysis confirmed the presence of ASR gel and microcracking in GGBFS-NaOH mortars, particularly near the interfacial transition zone. In contrast, LiOH activation resulted in the formation of dense lithium-silicate layers and stable C–A–S–H gels, effectively mitigating silica dissolution and crack development. Thermodynamic modelling corroborated these findings, showing that GGBFS–LiOH favored stable C–A–S–H and Stratlingite phases that immobilize alkalis and minimize expansion, whereas GGBFS–NaOH formed C–S–H, AFm, and zeolites, indicating greater alkali mobility and ASR risk. Thus, the study offers a characterization-driven mechanistic insight into the enhanced ASR resistance of LiOH-activated systems.

This paper evaluates the effect of adding Blast Furnace Dust (BFD), a by-product of the steel industry, on the multifunctional performance of porous asphalt mixtures designed for self-healing permeable pavements. Porous mixtures were prepared with six different BFD percentages (i.e., 0%, 2%, 4%, 6%, 8%, 10% by weight), as substitutes for fine aggregate. The physical, mechanical, hydraulic, electrical, thermal, and self-healing properties of the porous asphalt mixtures were subsequently evaluated. The effect of the chemical, mineralogical, and physical properties of both the aggregate and BFD on microwave heating and healing efficiency was also examined. The healing capability of the mixtures was quantified by measuring the three-point bending strength of specimens before and after microwave-induced healing. X-ray micro-computed tomography (micro-CT) was also employed on core samples to assess the distribution of BFD and the internal porosity. Results showed that the lower density of BFD reduced air void content when used as a fine aggregate replacement. At 4% BFD, hydraulic permeability approached that of the reference mixture, due to its good void distribution and connectivity, as evidenced by µCT reconstruction analysis. Electrical resistivity and thermal conductivity were unaffected by BFD incorporation. Mechanical properties and durability improved under both dry and wet conditions, while energy efficiency during microwave exposure also increased. The highest heating rates were observed in BFD and fine aggregate components. Healing indices generally decreased from the third cycle onward; however, the 4% BFD mixture maintained a high healing index for an additional cycle without adverse effects. In short, incorporating BFD into porous asphalt mixtures improves mechanical performance, durability, and microwave heating efficiency, while supporting multifunctional pavement design and promoting sustainability.

This study aims to understand the effects of the curing temperature on the phase assemblage and the distribution of aluminum-bearing hydrates (AFm and AFt), and how these affect external sulfate attack. Mortars were prepared with Portland cement (PC) and slag-Portland cement at a water-to-cement (w/c) ratio of 0.5. Specimens were cured at 20 °C, 40 °C and 60 °C for 28 days prior to full immersion in sodium sulfate solutions at 50 g/L. The results showed that curing at higher temperatures shortened the latent period before expansion in both PC and slag systems. High-temperature curing altered both the pore structure and the phases embedded in the C–(A–)S–H matrix, leading to more expansion and degradation. Expansion occurred much later and to a lesser extent in slag-Portland mortars due to lower contents of fine monosulfoaluminate (X-ray amorphous) in the C–(A–)S–H, compared to Portland cement mortars.

Autoclaved lightweight concrete (ALC) are widely used in non-load-bearing walls due to their lightweight, thermal insulation, and low cost. However, their low strength, high water absorption, and poor impact resistance limit their application in load-bearing structures. Although several reinforcement strategies have been proposed, the role of interface materials in optimizing the ALC-concrete system remains unclear. This study systematically investigates the performance of four interfacial treatments: no treatment (N), mortar material (MM), cementitious penetration crystallization material (CPCM), and wall hardener material (WHM). The investigation employs bidirectional shear experiments (BSE), fracture experiments (FE), and water absorption experiments (WAE), combined with theoretical modeling and finite element analysis (FEA). The results indicate that the MM-treated interface exhibits the best shear properties, while the N-treated interface demonstrates superior flexural properties due to enhanced bonding from concrete slurry penetration. The MM treatment also minimizes the water absorption of ALC. Furthermore, this study proposes a calculation method and a finite element model (FEM) for the interface shear ultimate bearing capacity, providing a theoretical and simulation framework for enhancing ALC strength and expanding its application in load-bearing structures.

In order to improve the seismic performance of structures and realize the self-recovery of building structures after an earthquake, shape memory alloy (SMA) and engineered cementitious composite (ECC) have been widely researched and applied to structures. This study systematically examines the bond-slip behavior between ribbed SMA bars and ECC through 25 sets of central pull-out tests under monotonic and cyclic loading conditions. The ribs of SMA can significantly improve the bond property with ECC. Increasing the cover thickness and enhancing ECC strength significantly improve the ultimate bond strength. Specifically, expanding the cover thickness from 2d to 4.5d results in a 27% bond strength improvement, while upgrading the matrix strength from E30 to E50 achieves a 31% enhancement. Conversely, enlarging the bar diameter from 6 to 10 mm reduces the ultimate bond strength by 23%, and extending the anchorage length from 5 to 10d causes a 27% reduction. Under cyclic loading conditions, the bond strength exhibits a 22% enhancement and demonstrates notable recovery characteristics. Through systematic analysis of experimental data and comparison with other models, a constitutive model was used to describe the bonding properties of SMA to ECC and verified by comparing with experimental curves.

Compared with natural aggregates, the water absorption behavior and particle shape of recycled concrete aggregates (RCA) are the main factors affecting fresh behavior. Based on the excess paste theory, the discrete element method (DEM) was employed to simulate the role of RCA in fresh concrete, explicitly accounting for its particle morphology and water absorption behavior. The DEM model was calibrated and validated by using slump flow tests under varying superplasticizer dosages (0.5–1.0%), water to binder ratios (0.409–0.479) and mortar paste volume. The DEM model achieved prediction errors within 10% under high flowability condition. Based on the calibrated model and the assumed time-dependent water absorption of RCA, the theoretical rheological properties of mortar were derived to predict the fresh behavior of concrete at different absorption times. Compared with 90 s of water contact, the yield stress of the mortar increased from 33.78 to 43.94 Pa after 1200 s, while the plastic viscosity rose from 6.48 to 8.36 Pa·s. The slump flow of concrete decreased from 570 to 501 mm. The results indicated that the water absorption behavior of RCA influenced the fresh properties of concrete with time by increasing the mortar’s yield stress and plastic viscosity while reducing the paste film thickness. The proposed DEM model provides an approach for analyzing and predicting the time-dependent workability of recycled aggregate concrete.

This study presents a novel approach to designing low-carbon cementitious composites by integrating nature-inspired topologies and hybrid binder systems. Leveraging 3D-printed triply periodic minimal surface (TPMS) formworks made from recyclable Polylactic Acid (PLA) material, two-phase cementitious composites are fabricated using high-performance cementitious (HPC) mortar and geopolymer mortar (GPM). Two configurations are investigated: one with cement-based mortar as the outer part and geopolymer as the core part (HG) and the other with the reverse arrangement (GH). Mechanical tests, including uniaxial compression and direct tension, are conducted on individual mortars and composite cubes. Experimental results demonstrate that the HG configuration exhibits superior mechanical performance and enhanced ductility compared to GH, owing to the confinement effect of the outer high-performance mortar. Finite element simulations using a simplified concrete damage plasticity model can capture internal stress distribution and damage evolution, validating experimental observations. This TPMS design strategy enables performance optimisation through functional grading and highlights the potential of hybrid material systems for achieving mechanical efficiency and sustainability in cementitious composites.

This study presents a systematic investigation into the role of corundum aggregates (CA) in enhancing the thermal resilience of metakaolin and silica fume-based geopolymer (GP) mortars. The primary objective was to improve the high-temperature performance of GP mortars by replacing standard sand (SA) with thermally stable CA by focusing on mechanical properties, microstructural integrity, and thermal compatibility under exposure to temperatures up to 1000 °C. Seven mix designs incorporating metakaolin, silica fume, potassium silicate, SA, and varying proportions and gradations of CA were prepared and evaluated. The experimental program included compressive strength, mass and volume changes, capillary water absorption (CWA), pore structure, and nanomechanical assessments. Advanced characterization techniques such as X-ray Diffraction (XRD), Thermogravimetric (TGA) and Derivative Thermogravimetric (DTG) analyses, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), porosimetry, and nanoindentation, were employed to investigate phase transformations and microstructural evolution. A one-way ANOVA at a 5% significance level and Tukey’s Honest Significant Difference (HSD) post-hoc test were conducted to statistically assess the influence of CA content and gradation on strength and mass loss. The results revealed that CA incorporation markedly enhanced thermal stability and strength retention. The SA0-CA50-M mix achieved 83 MPa at 1000 °C, representing 143% strength retention and a 302% improvement compared with SA50-CA0. A finer CA gradation (SA0-CA50-S) further improved performance, yielding 139 MPa with 264% strength retention. Higher CA content reduced shrinkage by up to 40% and decreased porosity from 30.43% to 16.18% through sintering. Nanoindentation confirmed a ~ 20 GPa increase in elastic modulus and a 3.5 GPa rise in hardness near CA particles. Microstructural analyses (SEM, XRD, FTIR) revealed the development of thermally stable crystalline phases, confirming superior structural integrity. ANOVA results validated that improvements in strength and mass loss were statistically significant.

Under water-rich geological conditions, tunnel engineering is highly prone to water leakage, which poses serious threats to construction and operational safety and has adverse environmental impacts. In this study, a novel permeable crystalline grout material (PCGM) was developed using a combination of a cementitious crystalline capillary waterproofing material (CCCW, XYPEX) and nano-SiO₂ (NS) for synchronous grouting in tunneling. Through systematic testing of both slurry and consolidated body properties, the effects of water-to-cement (W/C) ratio, XYPEX content, NS content, and polycarboxylate superplasticizer (PCS) content on the density, viscosity, setting time, bleeding rate, stone content, mechanical strength, and permeability of PCGM were investigated. Additionally, the microstructure, hydration products, and pore structure evolution of the PCGM underwent analysis. The results demonstrated that the synergistic incorporation of CCCW and NS effectively improved the basic properties of the slurry and enhanced the mechanical properties and impermeability of the consolidated bodies. Across mix designs, the stone content of the PCGM reached 100%, and the setting time was reduced markedly. The NS content played a dominant role in the initial stage of mechanical and permeability performance, whereas the XYPEX controlled the 28-d performance. Multi-objective optimization determined the optimal mix proportions of PCGM to be W/C ratio = 0.4, 3 wt% XYPEX, 1 wt% NS, and 0.3 wt% PCS. The catalytic-complexation-precipitation mechanism of XYPEX and the nano-filling effect of NS synergistically refined the pore structure of PCGM. These findings could provide a scientific basis for the application of green, high-performance impermeable grouting in tunnel engineering under water-rich conditions.