Materials and Structures最新文献

This paper aims to develop a novel method of preparing self-sensing concrete with recycled coarse aggregate (RCA) impregnated by polyvinyl alcohol (PVA) solution containing nano carbon black (Nano CB). The four-electrode method was adopted to investigate the influence of modified RCA substitution ratio, temperature and water content on the electrical resistivity of as-fabricated modified RCA concrete. In addition, the effects of modified RCA substitution ratio and loading rate on the piezoresistivity were explored. The results indicate that the modification have successfully attached Nano CB to the surface of RCA, and the micro-pores on the RCA surface have been filled with PVA/ Nano CB slurry, meanwhile, the water absorption decreased by 28.8%, and the crushing value decreased by 42.3%. The workability and compressive strength of concrete are improved by the modification of RCA as well. As the RCA substitution ratio increases, the resistivity of concrete first decreases slowly, then sharply and finally stabilizes. The percolation threshold of modified RCA concrete is approximately 60% substitution ratio of modified RCA (1.76 wt.% Nano CB by weight of cement). Moreover, the conductivity of modified RCA concrete possesses positive temperature sensitivity and humidity adaptability. Under cyclic loading of stress, the order of the maximum FCR value and the stress sensitivity of modified RCA concrete is: percolation zone > conductive zone > insulation zone. The specimens with modified RCA substitution ratio of 60% (in percolation zone) exhibit the best piezoresistive response compared to specimens with substitution ratios of 40% (in insulation zone) and 80% (in conductive zone). In addition, regardless of the modified RCA substitution ratio, the stress sensitivity of specimens decreases with the increase of loading rate.

In response to the challenges of natural resource depletion and the need to reduce energy consumption in buildings, the demand for sustainable materials and energy-efficient construction practices has become critical. This study aims to evaluate the hygrothermal performance of walls constructed from wood aggregates-cement concrete and to compare their effectiveness with that of conventional walls under different climates. The numerical model for heat and moisture transfer through wood concrete walls, implemented using MATLAB software, is validated through a long-term in-situ measurement on a wood-cement concrete building over a 12-month period. Monitoring of temperature and relative humidity takes place both inside and outside the building, as well as at three specific positions within the walls. Thermo-physical parameters of wood concrete necessary to feed the model are initially determined through in-lab experimental characterization. Comparisons between the measured and numerical results demonstrate the ability of the adopted ‘reduced heat, air, and mass’ model to accurately replicate the hygrothermal behavior of wood-concrete walls under real climatic conditions. After successfully validating the model, the hygrothermal performance of the wood-cement wall under different climate conditions is evaluated. The assessment incorporates key parameters such as the decrement factor, time lag, and interstitial condensation. Focusing on the center position of the wall, the study demonstrates that the bio-based wall achieves up to 6% more temperature reduction than the conventional wall and maintains more stable RH levels, fluctuating around 70%. Furthermore, no condensation is observed in any of the climates studied, highlighting the material’s suitability for sustainable building designs.

Due to the vast landscape of low carbon concretes that have been or can be developed, traditional empirical methods are impractical for comprehensive assessment of concrete performance. Here, we describe Panoramix 1.0, a Python-based tool that can predict physical and chemical properties of hydrated cements, and durability and environmental impacts of concretes. Applying it to CEM I concrete as a case study, we investigate the cement composition effects on the freeze–thaw resistance indicator (time to critical saturation degree, t_CR). Results indicate that chemical composition of raw materials including Fe₂O₃ may influence freeze–thaw resistance, which is usually not considered in the current scheme of durability assessment. The results also show how the design space (i.e., feasible cement compositions) could be found for different types of concrete at specified minimum freeze–thaw resistance. We validate Panoramix by comparing its ranking of 28 concrete samples in terms of freeze–thaw performance (t_CR) with experimental data for relative dynamic modulus of elasticity (RDME) reported in ten publications and measured using procedures from four different standards. By combining the composition-freeze–thaw resistance modelling with a life cycle assessment model, we show that the climate change impact (100-year global warming potential) per m³ CEM I concrete can be reduced from 313 to 286 kg CO₂-eq. by decreasing the clinker-to-cement ratio while reducing t_CR from 7 to 5.5 years.

This paper investigates the regression statistics of the size-effect method to obtain fracture parameters of quasi-brittle materials. The correct nonlinear regression model and assumptions are established and verified using a large dataset of size-effect tests extracted from the literature. The effect of model transformation on the change in error structure is then investigated. Three different transformations are considered, including the one leading to the linear regression recommended by RILEM (Mater Struct 23:461–465, 1990). The behavior of the nonlinear least squares estimators of the fracture parameters corresponding to the untransformed space, i.e., peak load P versus specimen size D, and to each of the three transformations are discussed. Monte Carlo simulations on generated data show that the transformations lead to the violation of model assumptions and to highly skewed error distributions prone to artificial outliers. The paper also shows that the estimator corresponding to the RILEM recommendation is asymptotically biased. The estimators corresponding to the other transformations are found either asymptotically biased or do not possess the minimum variance property. Finally, simulations show that the least squares point estimates of the unknown fracture parameters differ when a model transformation is used, and that the difference is statically significant. The fitting of the fracture parameters through the size-effect method should only be obtained in the space (P vs. D) for which the nonlinear least squares estimator is asymptotically unbiased, mean square consistent, and has minimum variance. The linear regression plot suggested by RILEM should be avoided for the statistical inverse problem of the size-effect method.

Concrete has emerged as a promising solid-based sensible heat storage (SHS) material due to its favorable balance of thermal properties, cost-effectiveness, non-toxicity, and widespread availability. This state-of-the-art review examines the applications of concrete-based SHS across diverse domains, including buildings, concentrated solar power systems, and industrial power generation. It also investigates the thermal properties of concrete relevant for SHS applications and explores the design considerations for concrete SHS systems and reviews the current research landscape and the role of numerical modeling and simulation techniques in optimizing the performance of concrete SHS systems. Various computational methods, such as transient modeling, finite element method (FEM), computational fluid dynamics, and simplified lumped capacitance models, have been employed to analyze and enhance the design of these systems. As research and development continue in this field, several future trends are anticipated.

In this study, a novel idea of using calcium carbide residue (CCR) as an activator to prepare cementless ultra-high performance concrete (UHPC) was proposed. Ground granulated blast furnace slag (GGBFS) and silica fume (SF) were used as single or composite precursors, activated by CCR, to prepare a series of mortars, which were cured under standard curing, hot water curing and combined curing, respectively. Workability and compressive strength of mortars were tested and the mix proportion of mortar suitable for preparing UHPC was selected. With addition of the steel fiber at a volume dosage of 2%, cementless UHPC was successfully prepared, which had high slump spread (660–701 mm) at fresh state and ultra-high compressive strength (120–175.4 MPa) and splitting tensile strength (10.6–20.4 MPa) after combined curing. Furthermore, the microstructure of cementless UHPC matrix was detected by a variety of microscopic testing methods. The results show that the pozzolanic reaction between Ca(OH)₂ and SiO₂ was significantly accelerated by thermal curing, especially with the addition of SF, which helped produce more C-(A)-S–H gels and a small amount of C-(A)-S–H crystals such as tobermorite and xonotlite, resulting in the refinement of pore structure and significant improvement of compressive strength of the cementless UHPC matrix. In addition, the cost and CO₂ emissions of CCR activated cementless UHPC were considerably lower than those of cement-based UHPC and other cementless UHPC reported in literature.

Previous studies on the moisture buffering characterization of hemp concrete have shown some discrepancies and difficulties for comparison. The aim of this paper is to raise warning points and define a robust protocol for Moisture Buffer Value (MBV) measurement of vegetal concrete. The applicability of the NORDTEST protocol was assessed by two round robin tests (RRT) on an industrial hemp concrete. Seven laboratories participated to the RRT. The first RRT specified a method for the conditioning of specimens prior to the MBV test, without added recommendation. Based on the shortcomings of the first RRT, a second RRT was performed with additional recommendations. For the test, the specimens should be representative of in-situ ones regarding exchange surface and orientation versus moisture flux. RRT2 confirmed that the exchange surface finishing widely affects the MBV results. Moreover, it underlined the effect of air velocity and the least efficiency of climate chambers with Peltier technology. The results obtained following this more detailed protocol were comparable between laboratories, suggesting their robustness to assess MBV of vegetal concrete.

In this paper, compressive tests of RC columns strengthened with cementitious grout under small eccentric compression were performed to explore the strengthening response. The effects of reinforcement position and thickness on the failure modes, bearing capacity, ductility, and stiffness of the columns were analyzed. Results indicated that the bearing capacity and corresponding deflection of the columns increased gradually with the increase of reinforcement thickness, and the enhancements in bearing capacity of compressive-side strengthened columns were obviously greater than that of the tensile-side strengthened columns. Simultaneously, the ductility coefficients presented a decreasing trend with the increase of reinforcement thickness while the influence of reinforcement position on the ductility coefficients of the columns did not show consistent variations. Moreover, the stiffness degradation rate of the compressive-side strengthened columns was slower than that of tensile-side strengthened columns, and the stiffness degradation rate of the columns decreased with the increase of the reinforcement thickness. Thereafter, a rational calculation method for predicting the bearing capacity of the columns strengthened with cementitious grout under small eccentric compression was proposed.

Adobe block walls are prone to out-of-plane collapse under seismic actions. Current research on the in-plane seismic performance of adobe block walls is relatively comprehensive, while studies on out-of-plane seismic performance and the relationship between in-plane and out-of-plane seismic performance are lacking. This paper conducted in-plane cyclic loading tests and out-of-plane airbag monotonic loading tests on adobe block walls, obtaining the out-of-plane failure modes, load-bearing capacity, deformation characteristics, under different in-plane damage conditions. Based on this, theoretical analysis was used to derive a method for calculating the load-bearing capacity of adobe block walls in the out-of-plane direction and establish an empirical relationship between in-plane damage severity and out-of-plane load-bearing capacity. The research findings indicate that adobe block walls experience bending tensile failure along the bottom horizontal mortar joint when subjected to uniformly distributed out-of-plane loads. The difference between the cracking load and peak load is relatively small. The wall displaces linearly along the height direction, with the maximum out-of-plane displacement occurring at the top of the wall. There is a clear interaction between in-plane damage severity and out-of-plane strength of the wall. As the in-plane damage severity increases, the out-of-plane load-bearing capacity of the wall decreases by 6.25% to 34.87%.