Recycling construction solid waste is an immediate need due to the substantial amount of construction waste that occupies valuable land and poses environmental hazards. In response to challenges related to the performance and interfacial transition zone (ITZ) when using recycled aggregate (RA) in concrete, a modified formulation with low calcium phosphate (CaP) content was developed to enhance RA's performance. It was found that when the mass ratio of CaP to RA reached 0.001 g/g, the physical properties of RA were significantly improved through a precoating treatment, resulting in a 31.52 % increase in the compressive strength of recycled aggregate concrete (RAC) compared to the control group. An in-depth analysis of the mechanism of action of CaP revealed that the active layer formed by CaP on the RA surface promoted the slow hydrolysis-hydration coupling reaction through the sustained release of Ca2+ and PO₄3- ions. This process and the solid-phase reactions of C-S-H gel, carbonation products, and sulfate ions effectively improved the pore structure, increased the specific surface area by 47.36 %, and reduced crack width by 78.95 %. Furthermore, the bond strength test between modified RA and freshly hardened mortar showed a 30.29 % increase in bond strength, directly demonstrating the effectiveness of CaP in enhancing the ITZ in RAC.

中文翻译：

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磷酸钙改性对再生骨料与混凝土界面过渡区的影响


由于大量的建筑垃圾占用了宝贵的土地并对环境造成危害，因此回收建筑固体废物是当务之急。为了应对在混凝土中使用再生骨料 （RA） 时与性能和界面过渡区 （ITZ） 相关的挑战，开发了一种磷酸钙 （CaP） 含量低的改性配方，以提高 RA 的性能。研究发现，当 CaP 与 RA 的质量比达到 0.001 g/g 时，预涂处理显著改善了 RA 的物理性能，导致再生骨料混凝土 （RAC） 的抗压强度与对照组相比提高了 31.52%。对 CaP 作用机制的深入分析表明，CaP 在 RA 表面形成的活性层通过持续释放 Ca2+ 和 PO₄3- 离子促进了缓慢的水解-水合偶联反应。该工艺以及 C-S-H 凝胶、碳酸化产物和硫酸根离子的固相反应有效地改善了孔结构，比表面积增加了 47.36 %，裂纹宽度减少了 78.95 %。此外，改性 RA 和新硬化砂浆之间的粘结强度测试显示粘结强度提高了 30.29%，直接证明了 CaP 在增强 RAC 中 ITZ 的有效性。