The construction industry generates substantial volumes of construction and demolition waste (CDW), including aggregates and fine particles classified as recycled concrete powder (RCP). This study investigates the sustainable reuse of RCP by evaluating its combined use with metakaolin (MK) as supplementary cementitious materials in both binary and ternary mixtures with Portland cement, aiming to reduce environmental impact without compromising mortar performance. The experimental program assessed two particle sizes of RCP, along with MK, and various replacement levels, which were pivotal parameters in the study. A series of binary and ternary mixtures were prepared with different proportions of RCP and MK, considering replacement levels ranging from 10 % to a maximum of 30 %, using RCP alone or in conjunction with MK. The mortars were analyzed in both fresh and hardened states, focusing on critical properties such as consistency index, compressive strength, splitting tensile strength, elastic modulus, water absorption, density, void index, and capillary water absorption. Furthermore, a microstructural analysis was conducted using scanning electron microscopy (SEM), and a cement consumption efficiency index, along with CO₂ emissions data, was calculated to provide a comprehensive evaluation of performance and sustainability. The findings demonstrate that RCP with a particle size comparable to that of cement (RCP1) significantly enhances both physical and mechanical performance, particularly in ternary mixtures with MK due to its pozzolanic activity, where the silica (SiO₂) and alumina (Al₂O₃) components react to form additional hydrated products, thereby improving the properties of mortars. For instance, the ternary mixture comprising 15 % RCP1 and 15 % MK attained compressive and splitting tensile strength of 29.26 MPa and 3.36 MPa at 28 days, respectively, compared to the reference mixture, which yielded 27.96 MPa and 3.33 MPa. Conversely, larger particle sizes (RCP2) and higher replacement levels led to a decline in performance across all evaluated parameters. Ternary mixtures containing RCP1 also exhibited a higher cement consumption efficiency index and lower CO₂ emissions per MPa. Notably, the mixture with 15 % RCP1 and 15 % MK showed the most favorable indicators overall, with cement consumption and CO₂ emissions measured at 12.08 kg/m³·MPa and 10.01 kgCO₂/m³·MPa, respectively. These results suggest that the synergy between RCP1 and MK enhances particle packing and matrix density, which in turn improves the structural properties of the mortar. The incorporation of MK compensates for the limited reactivity of RCP, especially at higher replacement levels, while the utilization of RCP1 offers significant sustainability benefits by reducing Portland cement consumption. This study demonstrates that the combination of RCP and MK in ternary mixtures presents a technically viable and sustainable alternative for mortar production, optimizing cement use and reducing CO₂ emissions. The innovative application of CDW-derived RCP in construction materials represents a practical approach to promoting more sustainable practices within the industry.

中文翻译：

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提高砂浆性能：二元和三元共混物中再生混凝土粉末和偏高岭土粒度的比较研究


建筑行业会产生大量的建筑和拆除垃圾 （CDW），包括被归类为回收混凝土粉末 （RCP） 的骨料和细颗粒。本研究通过评估 RCP 与偏高岭土 （MK） 作为补充胶凝材料在二元和三元混合物与波特兰水泥的混合物中的联合使用，调查了 RCP 的可持续再利用，旨在在不影响砂浆性能的情况下减少对环境的影响。实验程序评估了 RCP 的两种粒径以及 MK 和各种替代水平，这是研究中的关键参数。用不同比例的 RCP 和 MK 制备一系列二元和三元混合物，考虑替代水平从 10% 到最大 30% 不等，单独使用 RCP 或与 MK 结合使用。对新鲜和硬化状态的砂浆进行了分析，重点关注关键特性，如稠度指数、抗压强度、劈裂拉伸强度、弹性模量、吸水率、密度、空隙指数和毛细管吸水率。此外，使用扫描电子显微镜 （SEM） 进行了微观结构分析，并计算了水泥消耗效率指数以及 CO₂ 排放数据，以提供性能和可持续性的全面评估。研究结果表明，粒径与水泥 （RCP1） 相当的 RCP 显着提高了物理和机械性能，特别是在与 MK 的三元混合物中，由于其火山灰活性，其中二氧化硅 （SiO₂） 和氧化铝 （Al₂O₃） 成分反应形成额外的水合产物，从而改善砂浆的性能。 例如，含有 15% RCP1 和 15% MK 的三元混合物在 28 天时分别达到 29.26 MPa 和 3.36 MPa 的抗压和劈裂拉伸强度，而参考混合物的抗拉强度为 27.96 MPa 和 3.33 MPa。相反，更大的粒径 （RCP2） 和更高的置换水平会导致所有评估参数的性能下降。含有 RCP1 的三元混合物也表现出更高的水泥消耗效率指数和更低的每 MPa 二氧化碳排放量。值得注意的是，RCP1 含量为 15 % 和 MK 含量为 15 % 的混合物总体指标最有利，水泥消耗量和 CO₂ 排放量为 12.08 kg/m³·MPa 和 10.01 kgCO₂/m³·MPa 的 10 个值。这些结果表明，RCP1 和 MK 之间的协同作用增强了颗粒堆积和基体密度，进而改善了砂浆的结构特性。MK 的掺入补偿了 RCP 的有限反应性，尤其是在更高的替代水平上，而 RCP1 的使用通过减少波特兰水泥的消耗提供了显着的可持续性优势。这项研究表明，RCP 和 MK 在三元混合物中的组合为砂浆生产提供了一种技术上可行且可持续的替代方案，可优化水泥使用并减少二氧化碳排放。CDW 衍生的 RCP 在建筑材料中的创新应用代表了在行业内促进更可持续实践的实用方法。