Experimental and Numerical Investigation on the Microstructure and Failure Characteristics of Concrete Using Strengthened Recycled Coarse Aggregate

A method to strengthen recycled coarse aggregate (RCA) by applying a fiber reinforced coating layer is proposed. The composition of the strengthening layer is explored, and the crushing index of the strengthened RCA (SRCA) is reduced by 37.4%. Microstructure investigations demonstrate that the new interfacial transition zone (ITZ) in SRCA made concrete (SRC) is densified, which contributes to the strength improvement. The failure mode of SRC is distinct from that of reference group, and distributed cracks are generated without forming major cracks. The compressive strength of SRC is increased by 29.7% at 28 days. Elaborative numerical analyses by considering all the existing phases demonstrate that, for reference group, the cracks initially develop in new ITZ and then propagate in all the other four phases. While for SRC, the damage localization in both new and old ITZs is negligible until 80% post-peak, and the cracks prevailingly develop in new mortar.