An assessment of microcracks in the interfacial transition zone of recycled concrete aggregates cured by CO2

The effect of carbonation on the properties of recycled concrete aggregate (RCA) was investigated in this study. RCAs with diameters of 10-20, 20-30 and 30-40 mm were carbonised for 0, 7, 14 and 28 days. Scanning electron microscopy was used to measure the average microcrack width (W-c) in the interfacial transition zone (ITZ) of the aggregate and mortar in RCA, and the dependencies amongst W-c in the 117 area and the mechanical properties of recycled aggregate concrete (RAC) were assessed. Experimental results show that carbonation treatment modifies the 117 microstructure. W-c rapidly and slowly decreases during the early and later stages of CO2 curing, respectively. W-c of ITZ after 28 days of CO2 curing corresponds to 14.1-16.9% of that without CO2 curing. The small aggregate and large specific surface area can facilitate the absorption of additional CO2 by using RCA during carbonation and accelerate the decrease in W-c. Moreover, the mechanical properties of RAC (e.g. compressive strength and modulus of elasticity) increase with the decrease in W-c. (C) 2019 Elsevier Ltd. All rights reserved.