Effects of carbonation treatment on the crushing characteristics of recycled coarse aggregates

Abstract This work investigated the effects of the carbonation treatment on the crushing characteristics of recycled concrete aggregates (RCAs). Single-particle crushing test was conducted on more than 300 RCAs and carbonated RCAs (C-RCAs) with particle sizes of 20–30, 30–40, and >40 mm. The results indicated that the single-particle crushing test of the C-RCA had a four-stage crushing cycle which was on repeat because of the presence of natural aggregates. Carbonation treatment increased the crushing stresses and reduced the water absorption (WA) of the RCA. The stress at the initial crack and maximum stress of the C-RCA were higher than those of the RCA, and carbonation treatment exerted a greater influence on the former than on the latter. A weak linear relationship was detected between the two stresses and the physical properties (WA and attached mortar content) of the C-RCAs and the RCAs. Moreover, CO2 could be captured more effectively with smaller RCAs. Compared with RCAs with different particle sizes, the C-RCA with particle size of 20–30 mm showed significantly improved stress at the initial crack and maximum stress. By contrast, the >40 mm C-RCA had little difference from the RCA. The microhardness and scanning electron microscopy analyses of the C-RCA mesostructure agreed with the results of the WA, stress at initial crack and maximum stress of C-RCA, confirming that the carbonation treatment of RCA enhanced not only the original interfacial transition zone but also the attached mortar in the RCA, although the former was more significantly enhanced than the latter.