Beneficiation of recycled concrete fines through accelerated carbonation

In the present work, the effects of accelerated carbonation on the physical and microstructural properties of recycled concrete fines are systematically studied. The RCF was prepared by crushing a base CEM I concrete mixture made in laboratory with a water-to-cement ratio of 0.54 and seal-cured for 28 days. The effects of CO2 overpressure, ambient temperature, and duration of carbonation on the CO2 uptake, water absorption, and porosity of RCFs are investigated in a central composite design of experiments. The microstructural and mineralogical changes as a results of carbonation are explored via scanning electron microscopy and X-ray diffractometry. The results show that carbonation under 0.5 bar of CO2 pressure at 80 degrees C leads to the highest CO2 uptake and highest drop in the porosity/water absorption of RCF. The RCF produced under the above conditions was used in comparison with non-carbonated RCF as partial replacement of mortar sand. The mixtures containing 70% sand replacement with carbonated RCF showed a higher initial flowability and approximately 20% higher 28-d compressive strength compared to references containing non-carbonated RCF.