A novel carbonate binder from waste hydrated cement paste for utilization of CO2

A novel carbonate binder for utilization of CO2 was prepared with dehydration of waste hydrated cement paste. The effect of water-solid ratios (w/s) varying from 0.175 to 0.275 on carbonation properties of the carbonate binder was evaluated and its phase composition and microstructure before and after carbonation were characterized. The results showed that the compressive strength of carbonate binder exposed to a CO2-rich environment for 2 h maximized at 82.6 MPa with w/s of 0.225 while the CO2 uptake was 27.2% which were on a par with that of carbonated pure dicalcium silicate (C2S) and carbonated steel slag. Analysis of phase composition and microstructure of the carbonate binder before and after carbonation revealed that the major phase beta C2S (beta-C2S) in the dehydrated waste hydrated cement paste transformed into granular texture carbonation products (calcite and aragonite) with a size of less than 1 mu m. The carbonation products closely packed to form a large number of mesoporous which result in high compressive strength. The total CO2 uptake of carbonate binder in the whole preparation process was equal to that of the waste hydrated cement paste but it processed higher mechanical properties. It will provide a novel method to prepare high carbonation reactivity cementitious materials and improve the recycling rate of waste concrete which are benefit to utilization of CO2, energy conservation and environmental protection.