Carbonation of a concrete using a large amount of blast furnace slag powder

Abstract

Pastes of a low-carbon concrete in which ground-granulated blast-furnace slag was hardened by activators were subjected to accelerated carbonation to investigate the changes in the pore structure and composition of hydrates. The carbonation rate was more strongly correlated with Ca/(Si + Al) of calcium silicate hydrates (CSH) than with Ca/Si, with the rate being higher with a decrease in Ca/(Si + Al). Carbonation reduced the porosity but increased large-diameter pores, and a mixture with a higher carbonation rate showed more significant coarsening of pores. It was also found that different reactions occurred in different region of the paste. A mechanism was suggested whereby CSH in the inner products is strongly affected by carbonation to decompose to an amorphous silica gel, with the released Ca transferring out of the grains to form CaCO3. In the outer products, the Ca/Si of CSH was reduced by carbonation similarly to the inner products, but the decomposition did not proceed to a silica gel as long as Ca(OH)2 remained to be present.