2003 Volume 52 Issue 6 Pages 571-575
The consolidation mechanism of calcium silicate with water under carbonation was investigated. CaSiO3 powder was activated by mechano-chemical treatment for 24h in air with a vibration ball-mill. The cakes of the vibration ball-milled CaSiO3 added with a fair amount of water were carbonated at 50°C in 0.33MPa CO2 for 0.5 to 6hrs. in order to obtain the specimens carbonated to different degrees. The microstructural development in this carbonation process was observed by transmission and scanning electron microscopy and 29Si-MAS NMR, and the pore size distributions of the consolidated bodies were evaluated by mercury intrusion and N2 gas adsorption methods. By this carbonation treatment, dense consolidated bodies were obtained which exhibited high compressive strength. In the carbonated specimen, needle like crystals of aragonite precipitated to fill up macro-pores, and particles coalesced to form continuous matrices. The results of 29Si-MAS NMR showed that Q2 structure of SiO2 component assignable to single silicate chains transformed into Q4 structure indicative of three-dimensional SiO2 networks. These experimental results suggest that carbonation-induced consolidation would be caused by poly-condensation of SiO2 component in CaSiO3.
