Accelerated carbonation treatment of recycled concrete aggregates using flue gas: A comparative study towards performance improvement

CO2 source is one of the limiting factors for popularizing the accelerated carbonation technology in recycled concrete aggregates (RCAs) improvement. In this paper, the feasibility of using flue gas (CO2 content of 20 %) from cement plant as alternative CO2 source to improve RCAs was systematically studied and evaluated. Results showed that the carbonation extent and physical properties of the RCAs treated by flue gas were obviously improved and were comparable to those treated by commercial mixed gas with CO2 content between 20 % and 100 %. Based on the results of thermal gravimetric (TG), fourier transform infrared (FTIR) and X-ray diffraction (XRD) analysis, calcium hydroxide and calcium silicate hydrates in RCAs were significantly transformed into calcium carbonate at the optimal gas flow rate (5 L/min) after 168 h of treatment. The workability, compressive strength and flexural strength of concrete incorporating carbonated RCAs treated by flue gas were comparable with those treated by mixed CO2 gas, but were much better than those of concrete containing non-carbonated RCAs at all the replacement rate. Finally, the environmental impact and economic feasibility using flue gas to improve RCAs were evaluated based on a combined waste recycling system. All indicated that flue gas could be effectively utilized as CO2 source to improve RCAs.