Effect of moisture content on properties, microstructure and carbon sequestration of CO2-cured cement mortar mixed with chelator

Abstract

Chelator has the effect of improving the mineralization curing degree of cement-based materials. However, the moisture content in the pores of concrete will affect the permeability and dissolution of CO2 as well as the complexation and migration of Ca2+ by chelator, thus influencing the performance of CO2-cured concrete containing chelator. To obtain optimal moisture content for CO2-cured cement mortar mixed with chelator (CMC), the effects of the residual water cement ratio (RW) on the properties, microstructure, and carbon sequestration of CO2-cured CMC was investigated in this paper. The findings showed that the reduction of RW was beneficial for improving the mechanical properties and impermeability of mineralization curing CMC, but excessive reduction of RW weakened the action effect of chelator on accelerating the development of compressive strength. The optimal RW for mineralization curing ordinary cement mortar was 0.15 to achieve the fastest development of its mechanical properties, while the optimal RW for CMC was 0.2. It was also found that chelator was beneficial for shortening the curing period of CO2-cured mortar by more than half. Chelator significantly improved the aperture structure of CO2-cured mortar with a RW of 0.2 and promoted the transformation of larger to smaller pores through increasing the porosity of pore size between 0.01 and 0.02 μm by 7.1% and decreasing the portion of pores above 1 μm in the mortar by 24.2% after mineralization curing for 48 h. The reduction of RW was conducive to the permeation and diffusion of CO2, significantly enhancing the capacity of carbon sequestration of CMC. The RW was decreased from 0.5 to 0.2, and the carbon sequestration rate of CMC was increased by 551.6% after 48 h of mineralization curing. Meanwhile, compared to CO2-cured ordinary cement mortar, the carbon sequestration rate of CMC could be increased by 9.7% and 12.1% after 4 h and 48 h of curing, respectively.