Appraisal of the ASR-Induced Development in Recycled Concrete Incorporating a Highly Reactive Coarse Aggregate Through Advanced Imaging Techniques

The use of recycled concrete aggregates (RCA) has been considered as one of the most promising approaches to reducing concrete’s carbon footprint. Thus, RCA have been increasingly incorporated in concrete in many countries, particularly in Europe and Asia. However, RCA are normally considered as a low-quality material, especially regarding its inner-quality variability along with its potential of being contaminated or exhibiting inherited durability-related issues, for instance if it bears unstable mineral phases, which may react with the cement paste’s alkalis, thus potentially triggering the alkali-silica reaction (ASR). This work aims to appraise ASR-induced product formation and the associated deterioration through advanced imaging techniques, i.e., by coupling scanning electron microscopy (SEM), combined with energy dispersive X-ray spectroscopy (EDS), with X-ray micro-tomography (XMT). Recycled concrete mixtures incorporating a highly reactive coarse aggregate type were cast and stored in conditions enabling ASR development. At 1, 3–4, 11, 16, 20, and 24 weeks, the samples were prepared and investigated with SEM/EDS and XMT. Preliminary evaluations show quite promising results in terms of ASR-secondary product formation and composition along with crack generation and propagation. Further quantitative analysis will help to fully describe ASR-induced deterioration mechanisms triggered by highly reactive coarse RCA.