Changjiang Kou

1. Noise pollution, a critical urban environmental issue, disrupts daily life and contributes to psychological and physiological disorders [1]. Approximately one-third of people are disturbed by tr...

The increasing generation of construction and demolition waste (CDW) and the overexploitation of natural aggregates (NA) have necessitated sustainable solutions for recycled aggregate concrete (RAC). This study proposes an innovative inorganic–organic combined modification method using water glass (WG) and sodium methyl silicate (SMS) to enhance the performance of recycled coarse aggregate (RCA) and RAC. A comprehensive experimental program was conducted, including crushing value tests, capillary water absorption, compressive and splitting tensile strength analysis, nanoindentation and Fourier transform infrared spectroscopy (FTIR). The results demonstrated that the combined treatment of 40% WG and 10% SMS significantly improved the RCA properties, reducing water absorption by up to 46.47% and increasing the compressive strength of the RAC by 34.8%. Through mechanistic analysis, it was found that after treatment with SMS solution, a hydrophobic film formed on the surface of the RCA, thereby preventing the transmission of moisture. The interface transition zone between the RCA and the new cement mortar was enhanced, consequently improving the mechanical properties of the RAC. This study contributes to improving the properties of recycled aggregate and recycled aggregate concrete, and to the understanding of the mechanism of combined modification.

The diameter of basalt fiber influences the reinforcement of basalt fiber asphalt mixtures. However, the performance evaluation and mechanistic analysis of asphalt mixtures reinforced with varying fiber diameters have been insufficiently studied. AC-13 asphalt mixtures were designed and prepared with four different fiber diameters 7 μm, 16 μm, 25 μm, and an equal-mass mixture of these. The reinforcement mechanisms were analyzed using the equal cross-section theory. Results indicate that the incorporation of 7 μm and mixed-diameter basalt fibers significantly enhances the pavement performance of the asphalt mixtures compared to the control group without fibers. Additionally, it is shown by triaxial shear tests that the cohesion of the asphalt mixtures with the aforementioned two diameters of basalt fibers is strengthened by 61.5% and 55.5%, respectively. The dynamic modulus values in the high-frequency range are found to be positively correlated with fiber diameters. Since the fiber mass content and modulus were held constant, a decrease in diameter was observed to lead to an increase in fiber quantity. This is manifested by a multiple-fold increase in the total transformed cross-section (TTC_R) index for 7 μm fiber asphalt mixtures, as described by the equal cross-section theory. It is concluded that the performance improvement of the asphalt mixtures can be further enhanced under the same fiber content and cost conditions by optimizing diameter parameters.

The poor quality of recycled coarse aggregate (RCA), particularly its high water absorption and low strength, has long restricted the development of recycled aggregate concrete (RAC). In this study, a novel combined spraying treatment method integrating cement slurry and a methyl sodium silicate (MSS) solution was proposed to improve the comprehensive performance of RCA. The effects of the treatment on RCA properties, including crushing value, water absorption, dynamic water absorption, apparent density, micromorphology, and contact angle, were systematically investigated. Furthermore, the treated RCA was incorporated into concrete to evaluate the mechanical strength, water absorption, and interfacial transition zone (ITZ) properties of the resulting RAC. The results indicated that cement slurry treatment alone significantly reduced the crushing value of the RCA by 30.1% but had little effect on water absorption. Conversely, MSS solution treatment reduced RCA water absorption by 29.6% without affecting its strength. The combined spraying method successfully enhanced both strength and water absorption performance. When applied in the RAC, cement slurry-treated RCA improved compressive and splitting tensile strengths, while MSS-treated RCA notably reduced water absorption. RAC prepared with combined-treated RCA achieved further strength improvement, and although its water absorption was not as low as that of MSS-only treated RAC, it still showed a substantial decrease compared to untreated RCA. Nanoindentation and microstructural analyses revealed that MSS enhanced the ITZ by forming a hydrophobic molecular film and reacting with new mortar, inhibiting water transport and improving RAC durability. An optimal MSS concentration of 10% was identified for achieving the best combined performance in strength and durability.