Materials and Structures最新文献

Composite performance in concrete structures requires steel–concrete bonding. Environmental conditions prone to alkali–silica reaction (ASR) steadily impact the mechanical properties of concrete, including its bond strength. This research aims to investigate the effect of reactive aggregate size on the bond strength of concrete in ASR environmental conditions. To this end, four mixtures were prepared with different combinations of reactive and non-reactive fine and coarse aggregates. Then, Reinforced Concrete (RC) blocks with 12 and 16 mm rebars were cast with these various mixtures. These specimens were immersed in NaOH solution at high temperature for 3 or 6 months to accelerate the ASR. Subsequently, the pull-out test (POT) was performed to evaluate the bond strength of the concrete blocks. The results showed that with the passage of time and intensification of the ASR, the ultimate bond stress decreased. Also, with the decrease in reactive aggregate size in the concrete mixture, the ultimate bond stress loss intensified. The ultimate bond stress of the 12 mm rebars embedded in the RC blocks where reactive gravel was solely used decreased by 5.8% and 8.2% compared to RC blocks where reactive sand was solely used, after 6 months of immersion. Moreover, the variation in the reactive aggregate size or immersion duration did not affect the failure mode of the specimens with the same diameter rebar. However, by changing the rebar diameter from 12 to 16 mm, the ASR caused a variation in the failure mode of the specimens. Finally, a proposed bond-slip model was employed for the pull-out specimens by adjusting the coefficients within the CEB-FIB model.

Modeling concrete at elevated temperatures is essential to understanding the behavior of structural elements during fire, particularly with respect to spalling. To accurately predict temperatures and pore pressures, models must be validated against experimental data. However, most models in the literature focus on replicating experimental outcomes and often rely on input parameters sourced from the literature or determined by empirical tuning. To explore this further, a study of five models was conducted as part of the activities of the RILEM Technical Committee 256-SPF. On the theoretical side, state-of-the-art formulations are reviewed and similarities and differences between implementations are discussed. Using input parameters from various test reports, simulations of temperatures and pore pressures were performed and compared with test results for two types of concrete. While all of the models gave satisfactory results, they did so only when permeability values were applied that were significantly lower than those obtained from the standard tests. Since this trend was consistent across all models, it suggests that the permeability of concrete under heating conditions differs from that measured in standard material tests. As noted by some researchers, gas permeability in concrete is altered by the presence of water, probably due to swelling and rehydration. Identifying an accurate permeability value for these conditions remains an open research challenge.

This paper comprehensively studies the interface characters and behaviors of asphalt-aggregate by laboratory tests and molecular dynamics (MD) simulations. To accurately build the molecular model of asphalt-aggregate interface system and explore the nano-scale adhesion mechanism, the physicochemical composition of SARA components (saturate, aromatic, resin, and asphaltene) is characterized by macro–micro tests including SARA components separation and elemental analyzer. The mineral composition of aggregate is analyzed by X-ray diffraction test. The adhesion work, diffusion behavior and relative distribution of SARA components on aggregate surface are analyzed based on MD simulations. The results show that the influence of aggregate type on adhesion work is higher than that of asphalt type. The interfacial adhesion strength law obtained by pull-off test is highly consistent with the simulation results. Diffusion behavior is related to the polarity and proportion of SARA components and mineral types. Polar components have strong adhesion to minerals and are concentrated near the surface of minerals, and they are easily adsorbed on the surfaces of alkaline minerals such as calcite and albite. The adsorption characteristics of mineral surface will be affected by the proportion of SARA components.

The air-void system of concrete is of paramount importance to ensure freeze–thaw durability. Pumping induces detrimental changes in the air-void system of concrete by dissolving the air bubbles in the surrounding water when pressure increases due to the pump action. This research work investigates the influence of shear rate and air-void size distribution on air dissolution with time of cement pastes under pressure. Steady-state shear rheology at different shear rates was applied on samples of different air-void size distributions but similar air contents. Due to the low capillary number of the mixtures, the application of pressure caused a decrease in viscosity. With increased applied shear rate and increased fineness of the air-void size distribution, the decrease in viscosity was more abrupt, indicating that the air dissolved almost immediately. Coarser air-void size distributions and lower shear rates caused a more gradual decrease in viscosity and thus a slower air dissolution. All experimental air dissolution times were lower than the calculated time needed for dissolution by pure diffusion. These results on the combined effect of pressure, duration, shear rate and air-void size distribution create the basis for a deeper understanding of the behavior of the air-void system of concrete during pumping.

In recent years, the linear amplitude sweep test (LAS) and the time sweep (TS) test under dynamic shear are widely used to evaluate the damage resistance of paving asphalt. This paper attempts to demonstrate the possibility of using the LAS test as the accelerated fatigue protocol for damage resistance estimation of asphalt from perspectives of crack initiation and propagation. Both the finite element (FE) simulation and experimental work based on fracture mechanics are conducted for this purpose, followed by the verification on the traditional TS fatigue test. The FE model of the cylindrical asphalt sample is created by means of the FRANC2d/L software to identify the cracking mode under the crack propagation phase. The LAS test results show that the damage evolution behavior follows the two-phase crack growth (TPCG) model and the crack propagation is governed by mode-I cracking, which is consistent to the FE-based numerical simulation. The TS test results show that the TPCG model in the LAS protocol can be utilized to reasonably distinguish the crack initiation and propagation resistance of different asphalts. The polymer modification on asphalt can significantly improve its fatigue damage resistance.

Extreme loads can arise from accidents such as vehicle collisions or airplane crashes, as well as deliberate acts of terrorism or military attacks involving blasts and fragmentation. Blast overpressure can also occur accidentally, for example, from explosions of hazardous materials such as gas. Distinguishing between accidental and deliberate loads is crucial for designing appropriate protection measures. The repercussions of extreme loading events can be devastating, leading to injuries, loss of life, economic setbacks, and significant social disruption. These consequences result not only from the direct effects of impacts or explosions, but also from secondary factors such as structural collapse, which is particularly concerning due to its potential for widespread devastation and substantial losses. Efforts to enhance the protection of concrete structures have focused on understanding the properties of construction materials and how structures respond to impact and blast loads. This document presents a comprehensive overview of RILEM TC 288-IEC, aiming to provide essential guidance for designing concrete structures to withstand extreme dynamic loads. This emphasizes the importance of a thorough understanding and accurate modelling of loading scenarios and material behaviour. By implementing the strategies outlined in this document, engineers can enhance the safety and resilience of structures facing such challenges.

This study aims to establish a hybrid method combining the finite element method (FEM), the mechanical–electrical model, and a back-propagation artificial neural network (BP), to simulate the piezoresistive pavement. First, the tire-pavement FEM model with piezoresistive units was established considering the viscoelasticity of the pavement materials. Subsequently, the mechanical responses of the piezoresistive units under various tire and environmental loads were converted into electrical resistance outputs via the mechanical–electrical model. Finally, BP was trained using simulated data to address challenges associated with the back-calculation of tire loads. Results indicate that the electrical resistance of the piezoresistive unit in complete contact with the tire illustrates an overall rising trend as tire load increases, which is attributed to changes in contact stress. However, the adjacent piezoresistive units display an opposite trend, which can be used to determine the lateral position of the tires. Additionally, electrical resistance shows a non-linear decrease with increasing temperature. The single-hidden-layer BP with 13 neurons was validated to demonstrate higher accuracy compared to multi-hidden-layer BP. Moreover, the Genetic algorithm-optimized single-hidden-layer BP (GA-S-BP) shows further improved performance, achieving an MSE of 1.91 and an MAPE of 8.5%, and a low probability of underestimating tire loads. The GA-S-BP designed in this study can effectively predict tire loads within permissible levels to realize the function of piezoresistive pavement.

In recent years, substantial progress has been achieved in the development of multifunctional cement-based composites, targeting improved energy efficiency and environmental sustainability while minimizing material depletion. Leveraging the high thermal capacity of these materials facilitates controlled heat storage and release, providing versatile applications in renewable energy management and heat regulation, influencing structural integrity and long-term resistance. Recent research has integrated phase change materials (PCMs) into these composites to harness their superior thermal energy density. This comprehensive review examines the latest experimental research findings on these hybrid materials, emphasizing their thermo-physical behaviour and influence on structural properties and durability. Furthermore, it provides an overview of PCM characteristics and their integration into cement-based matrices. It critically analyses the interaction between PCMs and the cement matrix, explaining effects on structural performance, hydration processes, and freeze–thaw mechanisms. Furthermore, the paper explores recent experimental techniques and protocols for measuring and assessing the structural and thermo-physical properties of these composites. By identifying key trends, the review aims to provide valuable insights into the design and optimization of cement-based composites with PCMs, ultimately enhancing energy efficiency and resource conservation.

While the assessment of the quality of clay calcination for use in cements is important to ensure optimal performance, the currently available test methods, such as lime-reactivity, R3, XRD, TGA, etc. do not meet the requirements for a quick and cost-effective quality control at industrial clay calcination units. This paper proposes the use of a combination of methylene blue and density measurements to obtain reliable assessment of the quality of calcination of kaolinite-rich clays. Seven different clays calcined within the temperature range of 400 °C to 1000 °C were studied using these techniques and the results were compared with traditional methods. The results clearly demonstrate that the degree of conversion of kaolinite to metakaolin can be effectively obtained by measuring the residual kaolinite-content using the methylene blue test. A 50% reduction in the methylene blue value indicates the presence of under-calcined clay. Additionally, the formation of the spinel phase, which is the first unreactive product that forms upon over-calcination, can be identified by density measurements, as it is associated with higher density values. The proposed test methods can be implemented at clay-calcination units without the need for expensive equipment and highly-skilled technicians. The methods are seen to be sufficiently quick and reliable for a continuous monitoring of the calcination quality at short intervals.

This recommendation is an outcome of the work carried out by RILEM Technical Committee 309-MCP “Mineral Carbonation for the Production of Construction Materials”. To facilitate exchange in the rapidly developing field of mineral carbonation for construction materials, technical terminology covering specific terms of common interest is proposed. This terminology was developed in an iterative feedback process within the technical committee.

The presented terminology is recommended for use in the field of mineral carbonation technology applied to the production of construction materials and products.