Effect of carbonation on strength development of cement-treated Toyoura silica sand

It is well known that the strength of cement-treated soil increases over the course of several years. In general, the long-term increase in strength is attributed to the pozzolanic reaction between the cement paste and the soil. The carbonation of cementitious material can also increase its strength. In this study, the effect of carbonation of cement-treated sand on its strength was investigated. Specimens of cement-treated Toyoura silica sand were cured under three conditions: sealed, natural, and accelerated carbonation. The CO2 concentrations under the three curing conditions were 0%, 0.03%, and 5%, respectively. The measured strengths of the specimens cured under sealed conditions were almost constant after 28 days, whereas those of the specimens cured under the natural and accelerated conditions increased beyond 28 days because of carbonation. These results indicate that carbonation is one of the main reasons for the long-term increase in the strength of cement-treated sand. Based on thermal analysis, the effect of the CO2 concentration on the strength and elastic modulus can be explained by the formation of CaCO3.