Materials and Structures最新文献

Laminated bamboo is a novel green building material, understanding its mechanical properties at service temperatures is essential for structural safety and optimal design. However, currently there is no constitutive model capable of effectively predicting the compressive stress–strain relationship of laminated bamboo under the influence of service temperatures. This paper examines the influence of service temperature on the compressive stress–strain relationship in laminated bamboo. The compressive properties of laminated bamboo severely decreased as the temperature rises. Based on the fundamental form of the Weibull cumulative distribution, a constitutive model is proposed. Additionally, four constitutive models previously successfully applied to laminated bamboo or other bamboo composites were modified and analyzed for their capability to predict the compressive stress–strain relationship of bamboo-based materials under different temperature. Among all the models, the proposed Weibull model and the modified RA mode have higher accuracy, and both can simulate strain hardening and thermal softening characteristics of laminated bamboo. The findings of this study not only guide the application of bamboo-based engineered materials in actual engineering structures, enhancing the precision and safety of structural designs but also provide valuable references for the research and application of other bamboo composite materials.

Driven by climate change and the quest for new low-carbon construction, there is an urgent need for full-scale, real-time observations in buildings to calibrate and validate behavior and design models. The science related to timber structure design could be improved by processing the vast amount of data on actual responses in real wooden buildings. One of the first 8-storey timber buildings in France was equipped with four three components sensors for permanent instrumentation, from its construction phase through to operation, i.e., once the occupants had moved in. First, the modal analysis of the building was obtained using temporary network, then the modal parameters (frequency and damping) were monitored over several months to observe the dynamic response of this type of buildings. The results show a significant fluctuation in parameters as a function of increasing stiffness, but above all as a function of mass during the construction and moving in phases, due to the lightweight of this type of building compared with more conventional structures (e.g. reinforced concrete or masonry structures). Once the building was in full operation, significant variations appeared depending on weather conditions (temperature, humidity, wind speed), with high sensitivity to wind, especially for damping, revealed by the nonlinear elasticity response observed. Finally, the amplitude of the vibrations was compared with the ISO10137 standard for admissible mechanical vibration, thus validating the design and opening new perspectives for a longer monitoring phase.

As the main solid waste of coal-fired power plants, circulating fluidized bed fly ash (CFBFA) has a huge emission, but its resource utilization in the field of construction materials is limited due to the generation of volume-expanding substances such as caliche and gypsum during the hydration process. A lightweight foamed filler (LFF) was prepared by taking CFBFA as the main material and mixing the foam produced by mechanical foaming to obtain a LFF, which utilizes its internal porosity to alleviate the expansion. The pore structure characteristic parameters such as porosity, homogeneity, pore size distribution, fractal dimension, sphericity, etc. of LFF specimens with different foam doping amounts were investigated from the three-dimensional level using X-CT tomography and other technical means. As the foam doping increases, the phenomena of foam rupture and dissipation and merger and fusion were frequent, which led to the deterioration of the consistency of the morphology of the pores in the LFF materials, and the inhomogeneity of the pore size and the average pore size increased, but the distribution of the pore size conformed to the log-normal distribution. The parameters of the LFF such as the porosity, the homogeneity of the pore distribution, the pore size, etc., were exponentially related to the compressive strength, and relationships of the sphericity with the pore size and homogeneity were quasi-linear.

The shrinkage of concrete cured with plastic film, controlled permeability formwork liner (CPFL) and moisture retention curing film (MRCF) were experimentally measured using the designed test devices. The compressive strain on the inner surface of steel ring was also studied during the steel ring restrained test. The correlation between the development of shrinkage and strain on the steel ring was analyzed from the perspective of concrete creep. The results show that: The surface curing method has a significant impact on the shrinkage deformation and restrained cracking process of concrete. The curing method should be adapted to the characteristics of the concrete body (w/b), otherwise there will be negative effects. CPFL can effectively reduce the drying shrinkage and the risk of restrained cracking of concrete by reducing the local w/b on the surface of concrete. It has a better effect on the low and medium strength grade concrete (C30 and C50), but has adverse effects on high-strength concrete (C80); MRCF can effectively reduce the shrinkage deformation and the risk of restrained cracking through the water supplement effect of the pre-absorbent materials. It has a better effect on the high-strength concrete, while its effect on low and medium strength grade concrete is relatively small. The creep capacity of concrete is closely related to the relative humidity level. It is stronger during the humidity saturation period, and weaker during the humidity decline period.

Steel slag powder-cement composite mortar (SSP-cement mortar), a low-carbon building material with industrial solid waste can effectively utilize SSP. However, the low hydration activity of SSP has a significant adverse effect on its early-age behavior. In this study, the early-age compressive behavior and stress–strain relationship of a high-strength SSP-cement mortar at the first curing period of 7 days were comprehensively studied. The mix proportion parameters include the replacement ratio of SSP R_s, cement strength grade f_ce, mesh of SSP ν, and water-binder ratio W/B. The curing temperature was set at T = 20℃ and T = 80℃. The results indicate that: firstly, at T = 20℃ and T = 80℃, the optimal values for cube compressive strength f_cu are 71.2 MPa and 112.4 MPa, respectively, axial compressive strength f_c are 50.1 MPa and 85.4 MPa, respectively. Secondly, with the increase of R_s, the f_c, elastic modulus E_c, and toughness U, showed decreasing trends, the peak strain ε_cp shows an increasing trend. The trends have weakened at T = 80 ℃. With the increase of f_ce and ν, all the indexes (f_c, ε_cp, E_c, and U) show an upward trend. With the increase of W/B, all the indexes show a decreasing trend and are more pronounced at T = 20℃. Finally, an early compressive stress–strain relationship of SSP-cement mortar was established. Based on the given parameters and curing temperatures, a compressive strength prediction model is provided to guide engineering applications.

Masonry retrofitting systems combining seismic with energy upgrading features are increasingly gaining popularity in the scientific community during the past years since they simultaneously address two of the most pressing needs related to the existing building stock. This is commonly realized by applying textile reinforced mortar (TRM) overlays combined with thermal insulation boards on building envelopes. At the same time, the urge for eco-friendly and environmentally sustainable interventions calls for low-cement or even cement-free solutions. This study aims to combine these requirements by experimentally investigating an integrated seismic/energy retrofitting system that incorporates alkali-activated materials (AAM) based on industrial waste. The system is compared to a counterpart one comprising conventional cementitious materials. The relative position of the strengthening and the thermal insulation layers is yet another parameter of this study. The latter includes tests performed on retrofitted masonry specimens aiming to assess their mechanical performance in terms of masonry-to-overlay bond and flexural capacity. This is achieved by shear bond tests, and in-plane and out-of-plane bending tests, respectively. The results show that the replacement of cementitious binders by alkali-activated ones in TRM jackets is a promising alternative, eliminating cement consumption while ensuring comparable load bearing capacities with ‘conventional’ TRM systems. It is also indicated that the effectiveness of the AAM-based system is improved when the strengthening layer is applied externally, i.e., on top of the insulating boards. However, further research is needed for the optimization of the system’s mechanical and long-term performance.

Ultra-high performance concrete (UHPC) exhibits excellent mechanical properties and durability. However, UHPC requires high content of cementitious materials, associating with high carbon footprints and economic cost. This study aimed to investigate the effects of co-combustion ash of sewage sludge and rice husk (CCA) in UHPC on the hydration mechanism, microstructure, mechanical properties and environmental impact. CCA-based UHPCs were designed by replacing cement or SF with CCA at replacement percentages of 5, 10, 15 and 20 wt%. The results indicated that CCA exhibited excellent pozzolanic reactivity. The maximum compressive strength of CCA-based UHPC exceeded 130 MPa. The total reaction degree of cementitious materials was increased by the incorporation of 10 wt% CCA, thus enhancing the strength development of UHPCs. Besides, additional C–A–S–H gels generated via the pozzolanic reaction of CCA, which increased the length of silicate chain of C–A–S–H gels and refined the pore structure of CCA-based UHPCs. Life-cycle assessment results revealed that replacing 20 wt% cement with CCA could reduce carbon emissions and fossil fuel depletion of UHPCs by 12% and 16%, respectively. Hence, the innovative approach of this study can recycle CCA to manufacture UHPCs with excellent performance and environmental benefits.

The effect of carbonation on corrosion of reinforced steel was investigated in five limestone and calcined clay (LC3) concrete mixtures designed adjusting their cement SO₃ content. Accelerated carbonation tests were carried out according to BS EN 12390-12, while simultaneously the rebar corrosion activity was also monitored using electrochemical tests such as the linear polarization resistance (LPR). This paper reports on the methodology proposed to evaluate the reinforcement's response to corrosion while concrete carbonates. Results showed that LC3 concretes had a significant increase in the carbonation rate and demonstrated a Carbonation Index (C_I) between 0.6–0.9, a parameter defined as the carbonation-depth to concrete-cover ratio, indicating the presence of active corrosion in the rebar, measured in terms of corrosion potential (E_oc) and current density (i_corr). This condition represents an early stage of depassivation because the steel corrosion processes started before the carbonation front reached the rebar (C_I < 1). This finding goes against traditional durability models in which the propagation stage begins when all cover concrete is already carbonated (C_I = 1). Consequently, concrete using very high limestone and calcined clay replacement levels are much more vulnerable to accelerated carbonation.

This study studied the changes in the bond strength of asphalt binders in medium and low temperature areas, focusing on the temperature-dependent mechanism that affects the bond strength of asphalt. The quantitative testing technology independently developed by the team was used to accurately measure the bond strength of three representative asphalt types (Type I, Type II, and Type III), and their change curves in the temperature range of 25 to − 35 °C were plotted. The experimental results show that within this temperature range, the bond strength of the three asphalts all showed significant peaks, and there were significant differences in the temperature and change rate when they appeared. These differences are mainly related to the differences in the asphalt component ratio and brittle temperature. The study also revealed the key influence of the asphalt brittle temperature on its low-temperature performance. The results show that by adjusting the asphalt composition to reduce the brittle temperature, its low-temperature bonding performance can be significantly improved. This study provides a theoretical basis for the selection of asphalt binders in road construction in cold areas, and proposes the importance of using brittle temperature as a screening indicator.

The use of recycled coarse aggregates (RCAs) in concrete often results in a decrease in mechanical properties due to the poor bonding performance between new and old interfaces. This study impregnated RCA with low-alkali sulfoaluminate (LASAC) and magnesium phosphate cement (MPC) to improve the mechanical properties of RCA, and the axial compressive strength and stress–strain characteristics of the recycled aggregate concrete (RAC) were performed. The experimental results showed that LASAC impregnation modification produced thick encapsulation layers and decreased the compressive strength. MPC modified RAC showed good mechanical properties. The thick encapsulation layer caused by LASAC weakened the bonding performance of the interfacial transition zones (ITZs), which led to mechanical properties decreased. MPC modification can effectively improve the ITZs between RCAs and new mortar. Scanning electron microscopy with energy dispersive X-ray spectrometry (SEM–EDS) results showed that LASAC slurries encapsulation layer loosened the ITZs of RCAs and new mortar. The hydration products of MPC acted on RCAs and the new mortar, mainly being clustered on the new mortar to densify the interface between RCAs and the new mortar, which increased the mechanical properties of RAC. Nanoindentation method was used to verify the microscopic mechanical properties between phases in RAC and support the experimental conclusion.