Materials and Structures最新文献

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.

The existing recommendations for the experimental investigation of the bond characteristics along interfaces comprising Textile-Reinforced Mortar (TRM) overlays and various types of substrates ignore the effect of out-of-plane stresses. This study investigates the in-plane and out-of-plane bond of two TRM systems with masonry substrate, employing the Single-Lap/Single-Prism (SL/SP) and the Modified Hinged Beam (MHB) set-up, respectively. The two systems shared the same cementitious matrix and comprised either Alkali Resistant (AR)-glass or carbon dry fibers textile (named GTRM and CTRM, respectively), while they had comparable axial rigidity. The failure mode of the specimens was due to slippage of the textile form within the matrix, regardless of the examined TRM system as well as the used set-up. Based on the comparison of the maximum textile axial stress obtained from the SL/SP and MHB tests for each TRM system, it was found that the normal stresses developed during bending enhanced the bond capacity of the CTRM system by almost 30%, whereas they had no apparent effect on the bond capacity of the GTRM system. The results of the current and previous related studies suggest that the bending stiffness, E_fibI_fib, of fibers is a parameter that could be correlated with the effect of the normal stress, in case dry fiber textiles are considered. Finally, it is concluded that for both adopted TRM systems the Cohesive Material Law calibrated based on the response curves obtained from the SL/SP and MHB tests is affected by the type of both the bond test and the textile’s fibers.

Cathodic protection using galvanic anodes is a proven technique to control or prevent corrosion of steel in reinforced concrete structures. However, huge variations have been observed in the properties of various galvanic anodes available in the concrete repair market and their resulting performance. This work assessed the performance of five commercially available galvanic anodes using an earlier developed Galvanic Anode Performance (GAP) test. In addition, a methodology to estimate the guaranteed minimum service life (SL_min) of galvanic anodes in concrete systems exposed to specific environmental conditions is developed. This methodology involves the determination of electrochemical capacity (i.e., total electrical charge drawn) of galvanic anodes and the corrosion rate of galvanic anodes using potentiostatic scans. It was found that the average SL_min of the five anodes tested under severe laboratory exposure conditions (Relative humidity of 100% and temperature of 25 ± 2 °C) ranged from about 3 months to 7 years – indicating huge variation in the quality of various galvanic anodes. The analysis of the physico-chemical characteristics of the encapsulating mortar of pristine and aged galvanic anodes showed that the average SL_min depends on the pH, activator content, total pore volume, and critical pore entry diameter of the encapsulating mortar and is irrespective of the mass of zinc. Also, the failure mechanisms of galvanic anodes observed during the GAP test are conceptualized and correlated to the properties of encapsulating mortar. Finally, a set of prescriptive and performance specifications for the selection of galvanic anode systems to achieve a target service life of repair is presented.

This paper explores the computational modeling of transient heat conduction in thermal energy storage (TES) systems for buildings made of cementitious composites with microencapsulated phase change materials (PCMs). Addressing solid ↔ liquid phase transitions, the study examines numerical approaches and homogenization techniques to define effective thermal properties. Discussion spans both numerical and analytical homogenization models, followed by a comprehensive exploration of approaches to incorporate phase change effects into the numerical solution of transient heat conduction problems. Challenges such as enthalpy-temperature hysteresis and supercooling phenomena are addressed, proposing alternative formulations for stable solutions and improved convergence. The paper highlights the complexities of phase change phenomena and emphasizes the need for ongoing research to enhance modeling techniques for practical applications.

Compared with the traditional semi-rigid base layer asphalt pavement, assembled base layer asphalt pavement has the advantages of fast construction and low cost. The cooperative deformation ability between the base plates has an important influence on the assembled road, and at this stage, there are fewer studies that consider the lateral cooperative action of the assembled base layer and the mechanical response under the settlement of the plates. Therefore, this paper reveals the influence law of rebar articulation on the cooperative deformation and plate displacement of assembled roads from the base layer plate structure. This paper establishes a pavement structural model using ABAQUS finite element software and does a sensitivity analysis of the hinged base slab under various load conditions. A thorough examination of the base's collaborative deformation capacity and uneven settlement is carried out, utilizing the assembly-type hinged base as the foundation. The study's findings indicate that the articulated base layer is influenced to varying degrees by the plate modulus, thickness, and traveling load. Variations in the plate modulus and load cause the tensile stress at the plate's bottom to increase by 3.5% and 28%, respectively, while the thickness of the plate causes the tensile stress to decrease by 77.44%. The reinforcement's articulation improves the assembled subgrade's capacity for load transmission, resulting in displacements of the slab under various load positions being reduced by 0.35 mm, 0.92 mm, and 1.59 mm, respectively. The inhomogeneous settlement of the soil base had a significant impact on the corners of the slabs and the asphalt surface layer, but the articulation of the reinforcing bars led to a 7% reduction in slab displacement and a 21% reduction in surface layer shear stress. Soil-base dehollowing had a negative impact on the subgrade slab’s settlement, which was especially significant for the location of the slab corners.

To achieve the organic combination of rainwater resource recycling and urban construction, this study innovatively prepares a dry cement-based water absorbing material (DCWAM) using superabsorbent polymers (SAP) and expanded perlite (EP). A systematic study based on response surface methodology focuses on mechanical properties, water absorption properties, and deformation properties to achieve optimization of DCWAM mix proportions. Moreover, the influence of SAP and EP on the microstructure characteristics of DCWAM is revealed through SEM and XRD analysis. Experimental results show that with the addition of SAP and EP, the flexural strength initially increases and then decreases, while the compressive strength shows a decreasing trend. After water absorption, the above properties decrease by 50.67% and 46.03%, respectively, resulting from the accelerated internal crack development caused by the water absorption expansion of SAP and EP. The addition of EP increases the water absorption rate of DCWAM, slows down the development of cracks under external forces, and improves deformation performance. For SAP, the early water absorption rate is reduced, but it can achieve more sustainable water absorption, thereby improving the final water absorption rate. When 0.3% SAP and 17.5% EP are added, the water absorption rate reaches its maximum, which is 38.4% of its own weight, about 20 times that of ordinary cement paste.

Corrosion of steel bars is a major issue for the management of existing reinforced concrete structures, since affecting many ageing structures and infrastructures and introducing risk for safety and reliability, as well as high maintenance costs. Intervention strategies should be planned and carried out according to the effective state of deterioration and to the expected evolution of performances over time. The critical parameters needed to evaluate these performances are the intensity and pattern of the corrosion attack, referring to both extension and depth of the attack. However, this information is rarely available and hard to predict when dealing with real structures. This paper presents a field investigation on existing corroded structures characterized by different environmental conditions. Corroded bars were removed from structural elements, the corrosion patterns were studied, and then the bars were tested to determine their mechanical properties. The objective of this study is to increase the knowledge of the effects of corrosion in natural environments and to propose a method to relate easy-measurable environmental conditions with the characteristics of the expected corrosion attack, which need to be further validated.

A significant amount of CO₂ is released into the atmosphere during mining and production of construction materials, negatively affecting the environment. Reabsorption of the CO₂ into new construction materials could compensate for some of the negative impacts. This study aims to explore the CO₂ uptake capacity of waste concrete fines (WCF) and their role in lowering the environmental impact of concrete. It examines the effects of various factors such as source, composition, and grain size distribution on the CO₂ uptake capacity of WCF. The CO₂ sequestration potential and the degree of carbonation of WCF fractions were measured by thermogravimetric analysis (TGA). The results showed that the WCF from thermomechanical beneficiation had the highest CO₂ uptake, followed by the WCF from ready-mixed concrete sludge. This was due to the higher content and reactivity of calcium oxide (CaO) in these materials, which is derived from the hydrated cement paste. The WCF from different sources and processes exhibited different chemical and mineralogical compositions, which affected their CO₂ sequestration capacity. WCF showed CO₂ uptake potential ranging from 4.9 to 18.2% based on the source, size of the WCF and production method of RCA. The study suggests that CO₂ uptake by WCF could offset about 10–28% of the net carbon footprint associated with concrete production.

The bond strength at the interface between seawater sea sand concrete (SWSSC) and fiber-reinforced polymer (FRP) tubes is critical but remains understudied. This paper examines the improvement of bond behaviour between SWSSC and carbon-glass hybrid FRP tubes using a surface sand coating technique. Four different grading of sand coating were used to alter the surface roughness. Push-out tests were conducted on the specimens to determine the bond strength and failure modes. It was found that increasing surface roughness through sand coating significantly enhances bond strength, making it up to 239 times stronger than that of uncoated samples. However, although the coating with the largest particle size and broader particle distribution showed a slightly higher bond strength compared to other types, the difference was not statistically significant. Therefore, it can be concluded that, regardless of the coating grading, sand coating significantly improves the bond strength with no notable difference in their effectiveness level. The findings of this study provide valuable insights into the use of hybrid FRP tubes with sand-coated surfaces, offering a practical solution for enhancing bond strength. These insights can inform future construction practices aimed at developing more durable, sustainable, and environmentally-friendly materials, helping to reduce the carbon footprint of the construction industry.

Previous studies have shown the feasibility of using recycled aggregates in new concrete production. However, the recycling of fibre-reinforced concrete (FRC) introduces a novel challenge: the emergence of a new aggregate type that can be identified as recycled aggregate with embedded fibres. Therefore, in this study, in order to investigate the differences, the mechanical properties and microstructures of polypropylene fibre-reinforced concrete (PPFRC) made of natural coarse aggregate, coarse recycled aggregate and coarse recycled aggregate with embedded fibres were compared. Polypropylene fibre contents of 3 and 9 kg/m³ (0.33% and 1.0% by volume, respectively) were chosen for all concretes. The mechanical properties, including stress–strain behaviour in compression and flexural behavior, were tested. Scanning electron microscopy (SEM) was used to examine the microstructure and elucidate the effects of different aggregates on PPFRC properties. The results indicated that recycled aggregate with embedded fibres did not enhance compressive strength and elastic modulus compared to recycled aggregate without fibres. However, when the fibre content is low, its contribution to flexural behavior is significant, even surpassing that of PPFRC made with natural aggregate.