Effect of Recycled Aggregate on the Durability of Concrete: A Critical Narrative Review of Mechanisms, Conflicting Evidence and Service-life Implications

Abstract

Recycled aggregate derived from construction and demolition waste is central to the decarbonisation and circularity agenda of the concrete industry, yet its consequences for long-term durability remain the principal obstacle to unrestricted structural use. This review critically synthesises the evidence on how recycled aggregate alters the transport-controlled and physicochemical deterioration of concrete, and examines why the literature remains discordant after more than a decade of intensive experimentation. Peer-reviewed research retrieved from open scholarly databases and indexes was appraised for methodological adequacy, comparability and evidential strength, and organised around deterioration mechanisms rather than around individual studies. The synthesis identifies adhered mortar, and the multiple interfacial transition zones it generates, as the common material origin of most durability penalties, but argues that the magnitude and even the direction of reported effects are governed less by replacement ratio than by four decisions that are rarely controlled consistently: the basis on which recycled and natural aggregate concretes are compared, the treatment of aggregate moisture and water compensation, the descriptor used to characterise aggregate quality, and the choice of accelerated rather than natural exposure. Evidence for increased carbonation depth, chloride ingress and drying shrinkage at high replacement levels is strong and internally consistent; evidence for freeze-thaw and sulfate behaviour is genuinely mixed, with several studies reporting neutral or favourable outcomes attributable to mix-design compensation rather than to aggregate quality. Accelerated carbonation of recycled aggregate is the best-supported treatment, improving transport properties substantially, but its consumption of alkalinity reserve, its interaction with supplementary cementitious materials and its long-term effect on reinforcement passivation remain insufficiently resolved. Field and structural-scale evidence is scarce, and probabilistic analyses indicate that cover requirements derived from natural aggregate concrete may be materially unconservative. Priorities include standardised comparison protocols, long-duration natural exposure programmes and treatment validation at structural scale.