With the rapid urbanization and growth of construction industry, a large number of concrete structures are demolished and numerous industrial waste by-products are introduced. If the industrial waste such as slag powder and fly ash are efficiently reused to replace Portland cement completely and combined with recycled aggregates from demolished structures, a new kind of concrete, namely alkali-activated recycled aggregate concrete (ARAC) is developed, and thus, the environmental pressure can be effectively alleviated. However, existing researches on durability of this new concrete, especially freeze-thaw resistance, are still limited. Thus, this study mainly aimed at deterioration of ARAC under freeze-thaw cycles. First, the effects of air entraining agent dosage, water-to-binder ratio, alkali dosage, and natural fine and coarse aggregate replacement rates on the air content, slump, compressive strength and resistance to freeze-thaw action of concrete were comprehensively analyzed and discussed. Then, one type of ARAC containing 100 % recycled fine and coarse aggregates achieved a freeze-thaw resistance grade of F300, with its relative dynamic elastic modulus remaining above 98 % after 300 freeze-thaw cycles. Moreover, the influence of freeze-thaw cycles on the hydration products and pore structure of F300 ARAC was elucidated using microscopic tests. The results indicated that as the number of freeze-thaw cycles increased, the composition of hydration products remained unchanged, but their morphology was significantly altered. Freeze-thaw action led to an increase in the internal porosity of ARAC, with the formation of more harmful pores exacerbating the freeze-thaw damage. However, only after 150 freeze-thaw cycles, most of the newly formed pores were harmless or less harmful, causing minor internal freeze-thaw damage. Finally, freeze-thaw damage models, based on mass loss and relative dynamic modulus of elasticity, were proposed for all types of ARAC in this study with correlation coefficients above 0.9, accurately describing the progression of freeze-thaw damage in ARAC. This study can provide a valuable reference for the quantitative design of ARAC performance under freeze-thaw action.

中文翻译：

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冻融循环下碱活化矿渣-粉煤灰掺混再生骨料混凝土的劣化机理


随着快速城市化和建筑业的增长，大量的混凝土结构被拆除，并引入了大量的工业废料副产品。如果矿渣粉和粉煤灰等工业废料被有效地再利用，完全取代硅酸盐水泥，并与拆除结构的回收骨料相结合，就会开发出一种新型混凝土，即碱活化再生骨料混凝土 （ARAC），从而有效缓解环境压力。然而，关于这种新型混凝土耐久性，尤其是抗冻融性的现有研究仍然有限。因此，本研究主要针对冻融循环下 ARAC 的劣化。首先，综合分析讨论了引气剂掺量、水粘结剂比、碱掺量和天然细粗骨料替代率对混凝土含气量、坍落度、抗压强度和抗冻融作用的影响。然后，一种含有 100% 回收细杂骨料的 ARAC 达到了 F300 的抗冻融等级，其相对动弹性模量在 300 次冻融循环后保持在 98% 以上。此外，使用显微镜测试阐明了冻融循环对 F300 ARAC 水合产物和孔结构的影响。结果表明，随着冻融循环次数的增加，水化产物的组成保持不变，但其形态发生了显著变化。冻融作用导致 ARAC 内部孔隙率增加，形成更有害的孔隙，加剧冻融损伤。 然而，仅在 150 次冻融循环后，大多数新形成的孔隙是无害的或危害较小的，造成轻微的内部冻融损伤。最后，本研究针对所有类型的 ARAC 提出了基于质量损失和相对动态弹性模量的冻融损伤模型，相关系数在 0.9 以上，准确描述了 ARAC 冻融损伤的进展。本研究可为冻融作用下 ARAC 性能的定量设计提供有价值的参考。