Materials and Structures最新文献

Pervious concrete (PC), commonly used in urban pavement, is known for its high permeability, which contributes to mitigating the urban heat island effect. However, the low strength and durability of PC limit its use. The objective of this study is to improve mechanical properties and durability of PC by adding cellulose nanofibrils (CNFs). The results showed that CNFs significantly enhanced compressive strength, flexural strength, and salt frost resistance, with optimal performance at 0.15% CNF. At this concentration, compressive and flexural strengths increased by 26.5% and 25.8%, respectively, despite a slight reduction of 10.2% in permeability. CNFs also improved resistance to salt-induced freeze–thaw cycles, reducing spalling and maintaining a higher value of the dynamic modulus of elasticity, particularly at 0.1% and 0.15% dosages. Scanning electron microscope (SEM) analyses revealed that CNFs create a denser, more uniform network of hydrated products, enhancing microstructure and interfacial bonding. This study confirms that CNFs can significantly enhance the mechanical properties and durability of PC.

Chloride penetration resistance is an important indicator of durability, while the tortuosity of the pore structure affects the penetration path of chloride. However, the actual migration paths of chloride are complex and numerous, obtaining the actual migration path is a difficult process. This study proposed to quantify pore tortuosity using the shortest penetration path obtained from pore structure scans, investigated the mechanism of the effect of winter construction curing measures and fibers on the chloride penetration resistance based on the pore tortuosity. Three types of concrete were prepared: plain concrete (C), basalt-polypropylene fiber-reinforced concrete (BP) and steel-polypropylene fiber-reinforced concrete (SP), three curing conditions were set up in severe cold conditions: no winter construction curing measures (NWCM-1), adoption of winter construction curing measures (AWCM-2) and standard curing measures (SCM-3). Pore structure scans were performed and chloride migration coefficient were tested, the shortest penetration path and pore tortuosity were calculated. This study used the chloride migration coefficient as the basis for evaluating durability, experimental results showed that the highest durability was obtained by the adoption of winter construction curing measures. The pore tortuosity was calculated based on the shortest penetration path of chloride, was highly negatively correlated with the chloride migration coefficient, with a relevant coefficient of 0.902. Winter construction curing measures improved durability by reducing the porosity of the material and increasing the pore tortuosity. Adding fibers had the opposite effect.

This paper is the first study to present the long-term performance of a gypsum and cement plasters which can be used to retrofit existing buildings and reduce their energy consumption. It is comprised of high energy storage loaded granules, known as composite PCMs or form-stable PCMs (FSPCMs), containing three types of organic phase change materials (PCM), with phase change transitions between 18 °C and 25 °C. PCMs are effective thermal energy storage systems as they improve thermal comfort of occupants in buildings by reducing temperature fluctuations. As PCMs will undergo many phase transitions throughout their normal life cycle, the effects of thermal cycling on their long-term stability and performance are important considerations in their selection. The limited understanding on the long-term stability and potential for degradation of PCMs has restricted wider use of these materials in the construction sector. In this research, cement mortar and gypsum plaster specimens were subjected to 700 thermal cycles using an environmental chamber. After cycling, experimental results revealed a reduction of latent heat in the solidification process by up to 23% for the pure PCMs and up to 57% for the PCM loaded granules. However, once the PCMs had been incorporated into either the gypsum plaster or cement mortars, there was no significant reduction in the thermal conductivity or the specific heat capacity of these materials. Thermal cycling did not decrease the effectiveness of PCM composites, and so increasing their potential for wider acceptance of these products and use by the construction industry. This will aid the retrofitting of existing low energy efficient buildings to achieve Net-Zero targets.

This study aims to investigate the effects of different design parameters on the low-temperature crack resistance of recycled asphalt mixtures and to provide design guidance for recycled asphalt mixtures. Three material composition factors (reclaimed asphalt pavement (RAP) content, gradation type, and asphalt content) and four mixing process factors (RAP preheating temperature, mixing duration, mixing temperature, and mixing sequence) were considered. Using a single-factor controlled variable method, AC-20 recycled asphalt mixture was designed to study low-temperature crack resistance through a semi-circular bending (SCB) test, the significance of the effects of different factors was analyzed using the orthogonal test, and the fracture surface morphology was observed. Results show that both material composition and mixing processes impact the low-temperature crack resistance of recycled asphalt mixtures. Specifically, lower RAP content, higher asphalt content, higher mixing temperature, longer mixing duration, and mixing sequence I favor improved low-temperature crack resistance. Gradation type and RAP preheating temperature showed non-linear effects, peaking before declining. Material composition, especially asphalt content, has a more significant effect on the low-temperature crack resistance than mixing process factors. To achieve optimal low-temperature crack resistance, it is recommended to optimize the material composition of recycled asphalt mixture and control the RAP preheating temperature to 110 °C, maintain laboratory mixing duration of at least 150s, set the mixing temperature to at least 160 °C, and follow mixing sequence I.

This study examined the potential of using phase change material (PCM)-integrated concrete slabs for long-term thermal-responsive applications in an outdoor environment condition. The objectives were to: (i) evaluate long-term thermal response, snow melting and freeze–thaw reduction efficiency of PCM integrated concrete slabs, (ii) characterize the chemical stability of PCM in cement matrix, and (ii) assess the possibility of PCM leaching into the cement matrix and subgrade soil of the slabs. The experimental program included: (i) outdoor experimentation using large-scale field concrete slabs, (ii) guarded calorimetric (LGCC) tests of cut-bar concrete specimens, (iii) Fourier transform infrared (FTIR) spectroscopic characterization of PCM in mortar and subgrade soil specimens, and (iv) low-temperature differential scanning calorimetric (LT-DSC) tests to assess and quantify the amount of PCM contamination in subgrade soil. Results presented varying degrees of effectiveness after three years of environmental exposure: Micro-encapsulated PCM (MPCM) concrete exhibited considerable success (i.e., ~ 50%) in snow melting while PCM infused in lightweight aggregates (PCM-LWA) concrete failed to provide substantial snow-melting; moreover, both PCM-LWA and MPCM slabs showed diminished resistance to freeze–thaw (F-T) cycles compared to the first-year winter cycle data. Factors contributing to efficiency loss are found to be shell degradation of microcapsules, potential leaching of PCM into subgrade soil (i.e., between 0.2 to 0.3% wt. concentration), and effects of warm temperatures influencing the degree of evaporation, as evidenced with LGCC, FTIR and LT-DSC results. Strategies to enhance efficiency and stability include improved encapsulation techniques, and vascularization methods.

An experimental investigation was conducted at Swinburne University to study the effects of fiber hybridization on the direct shear behavior and mechanical properties of ultra-high performance fiber reinforced concrete (UHP-FRC) members exposed to elevated temperatures. The effect of two key variables on the direct shear performance and mechanical properties of UHP-FRC were investigated. The key variables include: the type of fiber hybridization (hybrid of either hooked end steel fiber (HESF) and straight steel fiber (SSF) only or with jute fiber (JF) as well), and temperature applied on the specimens (room temperature, 200 °C, 400 °C and 600 °C). The direct shear stress—slip performance, ductility and toughness were determined. Furthermore, the thermal–mechanical properties of UHP-FRC such as residual direct tensile strength, residual compressive strength, spalling resistance and mass loss were investigated. Scanning electron microscope micrographs were used to evaluate the microstructure of UHP-FRC matrix reinforced with different types of fiber and the morphological alteration in the surface of JF under high temperatures. The tests results indicate that the residual direct shear stress decreased significantly after exposure to high temperatures. Moreover, thermal spalling occurred for specimens subjected to 600 °C and reinforced with hybrid of HESF and SSF only. While, using hybrid of HESF, SSF and JF was an effective method to prevent the thermal spalling under 600 °C and enhance the residual direct shear stress of UHP-FRC. Preliminary empirical expressions have been developed in this study to predict the shear transfer capacity of UHP-FRC as a function of compressive strength, steel fiber content, natural fiber content and temperature.

Carbonation-induced reinforced steel concrete corrosion is a prominent concern related to engineering design and maintenance. The Durability Index (DI) approach was developed in South Africa to address this concern and enhance the durability performance of reinforced concrete structures. This approach relies on durability index tests, which are associated with transport mechanisms linked to specific deterioration processes. The carbonation of concrete is primarily influenced by the microstructure and transport characteristics of the concrete. Environmental exposure conditions also influence the rate of carbonation. The focus of the research reported here was to develop a carbonation model that could predict the rate of carbonation of concrete exposed to, or sheltered from, rain, with the permeability coefficient (k) from the Oxygen Permeability Index (OPI) test (DI test) as the key unifying variable. The model development was based on natural carbonation data and the drying profiles (experimentally measured) of 48 different concretes. Concrete microstructure was varied by varying the water-to-cement ratio, curing conditions, and by using SCMs. The resulting carbonation model was able to predict the rate of carbonation of concrete, allowing for different exposure conditions. A unique feature of this model is its use of a single material property, the 'k' value, to effectively address both CO₂ diffusion and the drying process within concrete. The model displayed sensitivity towards the influence of variation in CO₂ concentration, concrete microstructure, and the environmental exposure conditions, making this a simplified, effective and practical concrete carbonation prediction model.

This review by Working Group 1 of the RILEM TC 309-MCP discusses recent advances in the beneficial carbonation treatment of recycled concrete aggregates (RCA). The impact of carbonation on RCA properties as well as the microstructure and performance of concrete and other construction materials made thereof is critically reviewed. The increasing focus on environmentally friendly building practices has led to a greater interest in the CO₂ uptake associated with carbonation processing. Furthermore, emphasis is placed on the importance of adopting tailored strategies to optimise the carbonation process based on the quality and type of RCA. Evidence in the literature highlights the beneficiation potential of carbonation processing in improving RCA properties and performance, which translates in variable degrees of enhancement of the performance of concrete or otheinitial; position: relative; float: left; top: 0px; left: 0px; z-index: 1 !important; pointer-events: none;"/>er applications made thereof. The review concludes that, to date, significant techno-economic challenges remain to be addressed to improve the competitiveness of the technology, notably in terms of upscaling and refining life cycle assessment data.

This study systematically investigated the effects of different dosages of an air-entraining admixture (616 AEA) on the fresh and hardened properties of shield synchronous grouting materials. An appropriate 0.075% dosage significantly reduced apparent density by 7.4% and increased air content by 613.3%, while maintaining good flowability and anti-segregation. XRD and thermal analysis revealed the AEA did not alter hydration product composition/formation, indicating its mechanism was introducing air bubbles to modify the pore structure. At 0.075%, an ideal multi-scale pore structure formed, with 28-day of 7.7 MPa and water-to-land strength ratio of 89.6%, meeting engineering requirements. Advanced techniques like low-field NMR, mercury intrusion porosimetry, and ultra-depth imaging comprehensively characterized pore structure evolution, consistently demonstrating increased porosity and larger pores with higher AEA dosages. The findings elucidate the underlying mechanism by which the AEA optimizes the pore structure, providing guidance for mix design optimization and enhancing comprehensive performance for sustainable underground construction applications.

In this work, a novel electromagnetic wave absorption geopolymer was created with efficient utilization of two solid wastes iron tailings and blast furnace slag, meanwhile the mechanism and impacts of iron tailings content, water–solid ratio and specimen thickness on their electromagnetic wave absorption and mechanical property were systematically investigated. It was found the pores, micro-cracks and unreacted particles in the specimens are benefitial for electromagnetic wave absorption but against to compressive strength, even though the compressive strength reaches 69.7 MPa with the iron tailings content 50% and water–solid ratio 0.4. The addition of iron tailings significantly enhances the electromagnetic wave absorption properties of the geopolymers, and increasing iron tailings content improves the number of pores, micro-cracks and the permeability of geopolymers. The electromagnetic wave absorption properties of the geopolymer initially increase and then decrease with the increase of specimen thickness and water–solid ratio. With an iron tailings content 70%, water–solid ratio 0.4 and thickness 30 mm, the effective absorption bandwidth (< -5 dB) was optimized to 10.44 GHz with a minimum reflection loss of −13.34 dB. A new mechanism for electromagnetic absorption in iron tailings has been proposed, in which the electromagnetic wave absorption of geopolymers is mainly dominated by magnetic loss and spatial propagation loss. This study provides higher competitiveness and comprehensive utilisation of iron tailings in the field of electromagnetic wave absorbing building materials, and has great potential for applications in military and other fields affected by high electromagnetic wave frequencies.