To better understand the synergistic effects of combined fibers on mechanical properties and durability of recycled aggregate concrete (RAC), different types of fibers with various lengths and mass ratios were adopted in this study. Experimental investigations were conducted to study the 28-day compressive strength and strength loss after exposed to salt-solution freeze–thaw cycles and the coupled action of mechanical loading and salt-solution freeze–thaw cycles. The microstructure was also characterized to evaluate the mechanism of this synergistic effect. To determine the effectiveness of the combined fibers on improving the mechanical properties and durability of RAC, the synergistic coefficient was proposed and applied for various combinations of fibers. The results indicate that the incorporation of fibers slightly decreased the 28-day compressive strength of RAC, but combining different sizes and types of fibers can mitigate this negative effect. Moreover, the incorporation of fibers greatly improves the freeze–thaw resistance of RAC. The combining different fibers exhibited a synergistic effect on the enhancement in properties of RAC, which could not be predicted with only one simplistic rule of fibre mixtures. In addition, microstructural characterization shows that the bonding strength of the interfacial transition zone (ITZ) between the fiber and cement matrix is mainly determined by the chemical bonding force which is due to the hydration reaction between fiber surface and cement matrix.

中文翻译：

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聚丙烯和玻璃纤维对再生骨料混凝土力学性能和耐久性的协同作用

为了更好地了解复合纤维对再生骨料混凝土 (RAC) 力学性能和耐久性的协同作用，本研究采用了不同长度和质量比的不同类型纤维。进行了实验研究，以研究暴露于盐溶液冻融循环以及机械载荷和盐溶液冻融循环的耦合作用后 28 天的抗压强度和强度损失。还表征了微观结构以评估这种协同效应的机制。为了确定复合纤维对提高 RAC 机械性能和耐久性的有效性，提出了协同系数并将其应用于各种纤维组合。结果表明，纤维的掺入略微降低了 RAC 的 28 天抗压强度，但结合不同尺寸和类型的纤维可以减轻这种负面影响。此外，纤维的加入大大提高了 RAC 的抗冻融性。不同纤维的组合对 RAC 性能的增强表现出协同效应，这是无法仅用一种简单的纤维混合物规则来预测的。此外，微观结构表征表明，纤维与水泥基体之间界面过渡区（ITZ）的结合强度主要取决于由纤维表面与水泥基体之间的水化反应产生的化学结合力。但结合不同尺寸和类型的纤维可以减轻这种负面影响。此外，纤维的加入大大提高了 RAC 的抗冻融性。不同纤维的组合对 RAC 性能的增强表现出协同效应，这是无法仅用一种简单的纤维混合物规则来预测的。此外，微观结构表征表明，纤维与水泥基体之间界面过渡区（ITZ）的结合强度主要取决于由纤维表面与水泥基体之间的水化反应产生的化学结合力。但结合不同尺寸和类型的纤维可以减轻这种负面影响。此外，纤维的加入大大提高了 RAC 的抗冻融性。不同纤维的组合对 RAC 性能的增强表现出协同效应，这是无法仅用一种简单的纤维混合物规则来预测的。此外，微观结构表征表明，纤维与水泥基体之间界面过渡区（ITZ）的结合强度主要取决于由纤维表面与水泥基体之间的水化反应产生的化学结合力。仅用一种简单的纤维混合物规则是无法预测的。此外，微观结构表征表明，纤维与水泥基体之间界面过渡区（ITZ）的结合强度主要取决于由纤维表面与水泥基体之间的水化反应产生的化学结合力。仅用一种简单的纤维混合物规则是无法预测的。此外，微观结构表征表明，纤维与水泥基体之间界面过渡区（ITZ）的结合强度主要取决于由纤维表面与水泥基体之间的水化反应产生的化学结合力。