High-temperature CO2 for accelerating the carbonation of recycled concrete fines

Abstract

Accelerated carbonation of recycled concrete fines (RCF) is one of the effective ways of improving their poor quality for sustainable reuse in the construction industry. Flue gas containing waste heat that is usually discharged into the atmosphere can be reused to enhance the gas-solid reaction of RCF carbonation. Therefore, this study investigates the influence of high temperature (20–140 °C) CO2 (with a concentration of 20%) on the carbonation performance of RCF, whereby it is demonstrated that the carbonation efficiency is greatly enhanced by increasing the temperature optimally up to 100 °C and achieving 21.65% CO2 uptake. Vaterite and calcite are the main carbonation products of the carbonated RCF (CRCF), especially where calcite becomes larger and more stable with a higher temperature of carbonation. The CaCO3 polymorph affects the rate of cement hydration in which the vaterite plays an important role in enhancing the early-age cement hydration reaction, whereas the calcite in the CRCF has less impact due to its more thermodynamically stable characteristic. Overall, it is concluded that the higher carbonation degree of CRCF results in better performance as a cement substitute. Cement paste containing CRCF at 100 °C possesses a shorter setting time, higher heat of hydration, and a comparable 28-day strength to that of pure cement paste.