doiSerbia

Influence of acid treatment and carbonation on the properties of recycled concrete aggregate

Radević Aleksandar (Faculty of Civil Engineering, Belgrade)
Despotović Iva (Belgrade University College of Applied Studies in Civil Engineering and Geodesy, Belgrade)
Zakić Dimitrije (Faculty of Civil Engineering, Belgrade)
Orešković Marko (Faculty of Civil Engineering, Belgrade)
Jevtić Dragica (Faculty of Civil Engineering, Belgrade)

Recycled concrete aggregate (RCA), obtained by crushing of original (old) concrete, consists of natural aggregate grains and a cement mortar matrix. The presence of old adhered cement mortar, which has higher porosity than natural aggregate, causes unfavourable properties of RCA. The research conducted in order to improve the quality of RCA and to enable its greater application in the construction industry is presented in this paper. Therefore, RCA was subjected to quality improvement treatments with hydrochloric acid and carbon dioxide (accelerated carbonation). The first procedure was aimed at partially removing the adhered cement mortar and the second at reinforcing the cement matrix. The physical, mechanical and chemical properties of all three types of RCA were tested. After the pre-soaking acid treatment (0.1 mol/dm3 HCl), RCA showed reduced water absorption (up to 3%); the process of accelerated carbonation also led to reduced water absorption (13–20%) as well as to improved mechanical properties (∼10%). A scanning electron microscopy investigation revealed that the carbonation process, as expected, significantly reduces porosity of RCA. The overall results show that if RCA is obtained by crushing of compact, high- -quality concrete, the procedures of aggregate quality improvement are not necessary.

Keywords: accelerated carbonation, pre-soaking in acid, recycled concrete aggregate