Properties of CO2-cured cement incorporating fly ash and slag subjected to further water curing

In the present work, the synergetic effect of fly ash (FA) and ground granulated blast furnace slag (GGBS) on the compressive strength and microstructure development of mortars subjected to CO2 curing coupled with further water curing was investigated. The calcite content in pure cement was first increased and then decreased, while it decreased gradually in cement incorporating FA and GGBS during further water curing. Ettringite was interlocked with calcium carbonate and MC and was only observed in pure cement paste. Two distinct forms of C–S–H were observed in pure cement with one being interlocked with calcite, while the other one was pure amorphous phase. The incorporation of FA and GGBS showed a negative effect on the polymerization decrease of silica-rich phase. FA showed a negligible effect on the decrease of porosity, while GGBS had a positive effect on it. A positive correlation was found between the increase of compressive strength subsequent to water curing and three parameters, i.e., crystal size of calcite, carbonation degree and capillary pore percentage after CO2 curing, where the carbonation degree had a negative effect, while the other two parameters had a positive effect. The incorporation of GGBS and FA had a positive effect on the strength increase rate during further water curing. Notably, GGBS showed a more obvious effect on the strength development during further water curing and normal curing at later age. When GGBS content was lower than 10 % or cement content was lower than 10 %, the increase of FA content had a positive effect on the strength increase.