Fast enhancement of recycled fine aggregates properties by wet carbonation

Abstract

Accelerated carbonation for recycled concrete aggregate (RCA) was one of the effective and economic solutions for improving the quality of RCA and its concrete products. Previously, a fast wet carbonation method was developed and proved to be effective for property enhancement of the coarse fraction of RCA by transforming the carbonation reaction from a gas-solid phase to a liquid-solid phase. Fast carbonation is essential for providing a cost effective and practical method of enhancing the properties of recycled aggregates by waste CO2. In order to investigate the feasibility and effectiveness of the wet carbonation for fine RCA (i.e. < 5 mm), this study presents the results of an experimental investigation by using both laboratory-prepared well-hydrated cement paste particles (RCP) and a real fine RCA derived from demolished concrete. The test results of RCP revealed that a quick 10-min wet carbonation densified the surface layer of the particles, significantly reduced the volumes of the pores less than 10 nm, and increased the carbonation products by 2.6–3.5%. Moreover, the mortar specimens prepared by the carbonated fine RCA showed a 32.6% increase in compressive strength and a 6.4% reduction in drying shrinkage. Replacing 50% river sand by the carbonated fine RCA in the new mortar would not result in significant property deterioration.