Materials and Structures最新文献

Effective utilization of supplementary cementitious materials to substitute high Portland cement contents in cementitious systems is a promising approach towards decarbonizing the cement and concrete industry. In this study, ultrafine ground granulated blast furnace slag (UFS) was combined with a locally available and medium-grade metakaolin (MK) to prepare low-Portland cement content binders. First, UFS was obtained from ultrafine grinding of a commercial slag, and analyzed for amorphous content, surface chemistry, and reactivity using R³ method. MK and UFS blends at MK/UFS ratios of 80/20, 70/30, and 60/40 were used to replace 50 and 60 wt% of Portland cement in mortars and pastes. The compressive strength of mortars was monitored from 1 to 91 d. The heat evolution of pastes was recorded by isothermal calorimetry, and the microstructure of selected pastes was analyzed through thermogravimetric analysis, quantitative X-ray diffraction, and scanning electron microscopy. The results showed that ultrafine grinding of slag induced changes in its size, surface area, amorphous content, and surface chemistry, leading to higher reactivity of UFS compared to slag. Using MK-UFS blends with MK/UFS of 70/30 and 60/40 in mortars provided comparable 3-d, and higher 28- and 91-d, compressive strengths compared to the mortar made with Portland cement only. Formation of more reaction products, such as calcium–(alumino)–silicate-hydrates (C–(A)–S–H) and carboaluminates, and refinement of the microstructure in the mixtures containing MK-UFS contributed to the enhanced strength development of these mixtures.

This study proposes a multi-phase synergistic conductive network design strategy, innovatively utilizing industrial solid waste iron tailings sand (ITs) as a low-cost, eco-friendly conductive phase alongside carbon fibers (CFs) within an alkali-activated geopolymer matrix. This approach develops geopolymer mortar (TCAGM) with integrated superior mechanical properties and self-sensing functionality. Through Response Surface Methodology-Box-Behnken Design (RSM-BBD), the alkaline activator modulus (A), sol–gel ratio (B), and CF volume fraction (C) were optimized, overcoming the performance-cost-sustainability trade-off inherent in conventional self-sensing materials. The optimal mix proportion (A = 1.42, B = 0.82, C = 0.4%) achieves high electrical conductivity (1.98 × 10⁻²(Ω ·cm)⁻¹, stable without degradation) and piezoresistive performance (− 0.0157 MPa⁻¹, fluctuation within ± 5%). The multi-scale conductive network (long-range CF pathways + short-range ITs electron hopping + ionic transport) not only reduces CF dosage by 20–60% and raw material costs by 20% through ITs substitution but also enhances electromechanical performance. This work establishes a sustainable paradigm for high-performance, low-environmental-impact intelligent construction materials.

The creep behavior of bamboo culms under long-term loadings was investigated in the present work. Phyllostachys aurea bamboo samples were subjected to four-point flexural creep tests at loads corresponding to 30%, 50%, and 80% of the bamboo's short-term bending strength. Creep and recovery behavior were evaluated for each loading level at room temperature over 398 days, allowing the attainment of primary, secondary, and tertiary creep stages. The failure of one creep test sample occurred at 73 MPa, and the failure mode due to creep was described. Creep mechanisms assessed included node flexibility, cylindrical bending, and shear. Node flexibility contributed 50–74% of total deflection, cylindrical bending contributed 24–48%, while shear contributed less than 2%. A four-element Burgers mechanical model was proposed, matching the experimental results for all loading levels. A viscous coefficient parameter of 4.3 to 30× 10³ GPa.day was inferred, corresponding to the linear dashpot (eta_{1}). These models estimated the bamboo culm deflection over time and predicted failure at a 40% increase in deflection. Overall, this study provided comprehensive insights into the long-term structural behavior of bamboo culms for use in design and engineering applications.

The influence of concrete cover thickness on corrosion-induced crack initiation and propagation in reinforced concrete structures is investigated, employing advanced 3D imaging and material analysis techniques. Two cylindrical specimens of small cover (SC) with diameters of 50 mm and large cover (LC) with 75 mm were fabricated. Distinct patterns are observed in crack initiation and propagation dynamics between the SC and LC samples. Specifically, crack initiation in the SC sample occurs independently of void proximity to reinforcement bars, whereas in the LC sample, crack initiation is closely associated with voids and corrosion products, indicating the influence of thicker concrete cover on crack initiation patterns. Raman spectroscopy analysis highlights the prevalence of iron hydroxide compounds in regions of crack initiation and growth in the SC sample, emphasizing the role of pore saturation in crack initiation. X-ray Computed Tomography (CT) imaging provides additional insight into the impact of concrete voids on crack propagation. The sample with a higher concentration of voids (SC) notably aids in the propagation of cracks by facilitating their movement through existing void spaces. Additionally, Scanning Electron Microscopy (SEM), mapping, and Energy Dispersive X-ray Spectrometry analyses reveal substantial differences in corrosion product distribution between the SC and LC samples, with the SC sample demonstrating higher quantity and deeper penetration of corrosion products. The presence of iron hydroxides, particularly lepidocrocite and goethite compounds, in the LC sample’s leak-off zone indicates their significant influence on crack propagation behavior. Understanding the crack initiation and propagation mechanisms provides valuable insights for corrosion mitigation strategies in reinforced concrete structures.

Basalt fibers can significantly enhance the deformation resistance and structural strength of asphalt materials through mechanical reinforcement, but their crack repair capacity is limited. To further control the development of micro-cracks into macro-cracks, it is a feasible approach to repair micro-cracks with microcapsules. Therefore, this study selects microcapsules to carry out composite modification on fiber-modified asphalt mastic so as to improve its repair capacity. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA) were used to characterize the morphology, chemical structure, and thermal properties of the microcapsules. Self-healing tests, dynamic shear rheology (DSR), and bending beam rheology (BBR) were carried out to test the self-healing ability and rheological characteristics of the modified asphalt mastic. The results indicate that the microcapsules possess well-defined spherical structures with distinct concave-convex textures on their surfaces, which enhance their interfacial adhesion with asphalt. Alkyl glycidyl ether (AGE) and epoxy resin are successfully encapsulated within the microcapsules, which maintain thermal stability at 150 °C. Self-healing test results confirm that the content of the microcapsules and the healing time positively influence the repair capacity; however, increased damage severity diminishes the self-healing ability of the asphalt mastic. The optimal self-healing temperature is 25 °C. Rheological test results demonstrate that the compositely modified asphalt mastic exhibits a higher modulus and improved rutting resistance, although it shows slightly reduced fatigue resistance and low-temperature crack resistance. Notably, the asphalt mastic modified with 4% microcapsules displays the best overall performance.

To investigate the degradation of bond performance between rebar and concrete in cracked RC structures under the combined effects of salt freezing and fatigue loads, 11 sets of pullout specimens with cracks were subjected to alternating actions. Pullout tests were then performed to assess the bond strength deterioration. The deterioration mechanism was analyzed, and a bond-slip constitutive model considering effect of crack width under alternating salt-freezing and fatigue conditions was established. The results showed that salt-freezing damage in concrete progressed under alternating actions, leading to a continuous decline in bond fatigue performance. Larger initial crack widths resulted in more significant reductions in peak bond strength. After three cycles of alternating actions, the ultimate bond strength decreased by 41.39% for specimens without initial cracks and 48.07% for specimens with an initial crack width of 0.05 mm. Specimens with a 0.10 mm initial crack failed during the fatigue loading phase of the third cycle. All specimens exhibited a combined pullout-splitting failure mode. The salt-freezing cycles and fatigue loads jointly accelerated the degradation process. Initial cracks provided pathways for saline solution to penetrate the interface and cause stress concentration in cover concrete, thereby further weakening the interface's fatigue performance. Consequently, the degradation of bond performance under alternating actions was accelerated by initial cracks. The adverse effects were more distinct as the crack width increased.

Delithiated β-spodumene (DβS), an industrial by-product from lithium refining, has demonstrated potential for enhancing mechanical properties of geopolymers due to its pozzolanic characteristics. Understanding the behavior of DβS-based geopolymer paste at different alkaline activator ratios from a microstructural perspective provides critical insights into the potential suitability of DβS for geopolymer mortar and concrete. This research evaluates the influence of varying Na₂SiO₃–to–NaOH ratios on the compressive strength and microstructural attributes of geopolymer paste made with 25% DβS and 75% fly ash. The findings reveal that the paste made with DβS and fly ash exhibits the maximum compressive strength at a Na₂SiO₃–to–NaOH ratio of 2, similar to that of the paste made with only fly ash. The generation of the amorphous sodium aluminosilicate hydrate phase is enhanced with increasing Na₂SiO₃–to–NaOH ratios. The highest amount of the sodium aluminosilicate hydrate phase formation in the DβS/fly ash and fly ash pastes occurs at ratios of 2 and 2.25, respectively. The findings of this study provide an insight to incorporate DβS as an alternative to FA in geopolymer binders and suggest the optimal alkaline ratio range for use in geopolymer mortar and concrete. This strategy not only enhances geopolymer properties but also mitigates the environmental issue of DβS disposal of in landfill.

Ultra-high performance concrete (UHPC) faces challenges in optimizing workability, strength, and durability while maintaining sustainability. Calcium sulfoaluminate (CSA) cement, known for its high early strength and low carbon footprint, offers a promising alternative binder. However, its application in UHPC requires further optimization to balance mechanical performance and shrinkage resistance. This study developed a novel UHPC using solid waste-based calcium sulfoaluminate cement (SCSA) and investigated the feasibility of substituting silica fume (SF) with steel slag micro powder (SSMP). The physical properties, hydration process, volume stability, microstructure and carbon footprint of the novel UHPC system were systematically examined. The results demonstrated that the SSMP enhances the mechanical strength of UHPC at all ages, with an 80% replacement increasing compressive strength by 25.9% at 3d, 18.8% at 7d, and 13.4% at 28d compared to the control group. XRD, TG, and MIP results indicate that SSMP further promotes hydration by generating C–S–H through its cementitious activity and pozzolanic reactions. Furthermore, when the SSMP replacement ratio does not exceed 40%, it effectively reduces the autogenous shrinkage of UHPC, addressing a key limitation of conventional UHPC. Microstructural observations show that the addition of SSMP reduces harmful pores, and enhances ettringite crystal interlocking. Moreover, carbon footprint analysis indicates that SCSA-UHPC is a greener material with lower carbon emissions, while the incorporation of SSMP as a replacement further reduces carbon footprint by utilizing solid waste. However, the SSMP content should be controlled, as excess content compromises workability and volume stability. These findings highlight the potential of SCSA-UHPC as a sustainable and high-performance material, providing new insights for low-carbon construction applications.

This study introduces an effective approach to tackle the environmental challenge posed by construction waste, employing photocatalysis with nano-titanium dioxide (TiO₂) to modify recycled clay brick sands (RCBS) and recycled glass sands (RGS). The primary objective of this research is to leverage the distinct characteristics of these recycled fine aggregates and enhance their efficacy in nitrogen oxide (NOx) reduction. Following modification with nano-TiO₂, the microstructure of RCBS underwent notable transformations, as evidenced by the presence of Ti–O bonds, which confirm the effective infiltration and adhesion of the catalyst. Conversely, RGS exhibited minimal surface alterations after treatment. When the modified aggregates were incorporated into the photocatalytic mortar, the study revealed that the 28-day compressive strength diminished with an increasing substitution rate of natural river sand, reaching a decrement of 24.94% at full substitution. Nevertheless, the NOx degradation efficiency improved with higher substitution rates, attaining 78.6 μmol/m²h at full substitution, which represents a 7.78-fold increase compared to a 25% substitution rate. Significantly, a synergistic effect was observed when NT-RCBS and NT-RGS were combined at an optimal mass ratio of 75:25. This combination resulted in a NOx degradation rate of 103 μmol/m²h, marking a 71.7% enhancement compared to the direct incorporation of TiO₂ at 2% by weight using what. Additionally, this approach reduced TiO₂ usage by 50%. This study not only advances sustainable construction practices by upcycling waste materials but also offers economic advantages through cost reduction. The findings underscore the potential of photocatalysis in modifying recycled aggregates for high-value applications, thereby contributing to environment and resource conservation.

In recent years, nanomaterial have garnered significant interest for enhancing engineered cementitious composites (ECC). This study employs response surface methodology (RSM) to conduct multi-objective optimization of the mechanical properties of nanomaterial-reinforced ECC (NR-ECC), aiming to determine the optimal dosages of silica nanoparticles (NS) and carbon nanotubes (CNTs). A central composite design (CCD) was utilized to formulate 13 mixtures with varying NS (1–3%) and CNTs (0.1–0.2%) contents. Three quadratic response surface models were developed and validated to predict uniaxial compressive strength, uniaxial tensile strength, and peak tensile strain, demonstrating high accuracy (R² = 0.94–0.98) and statistical significance (p < 0.05). Multi-objective optimization identified the optimal contents as 1.698% NS and 0.155% CNTs, which were experimentally validated with errors below 5%. The results indicate that NS enhances matrix density and interfacial properties, while CNTs facilitate multi-scale crack bridging. The optimal mixture improved compressive strength, tensile strength, and tensile strain by 9.89%, 27.75%, and 32.45%, respectively, compared to the baseline. This study provides a reliable modeling and optimization framework that supports the efficient design of high-performance NR-ECC for practical engineering applications.