This paper evaluates the complex nature of recycled concrete aggregates that are susceptible to damage due to recycling. The study was carried out by microstructural assessment techniques beyond the standard testing methods normally specified for aggregates. The laboratory produced recycled concrete aggregates were investigated using fluorescent microscopy and image analysis. Contrary to common opinion, microstructural studies showed that adhered mortar (AM) is not always the primary parameter determining the quality of the recycled coarse aggregate. Sandstone coarse aggregate originally had defects in the form of voids and cracks. Further processing of the recycled coarse aggregate changed the microstructural profile of the material and enhanced their properties. The unusual results of the performance tests carried out on the recycled aggregate concretes could be explained with the findings of microscopic level investigations.
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