Change in microstructure properties of concrete on accelerated carbonation

Abstract

Carbonation of concrete is a complex physicochemical process. The overall volume of the system changes due to carbonation of different hydration products. During carbonation, t products formed on conversion of calcium hydroxide have a higher volume as compared to the initial products, thus the surplus volume fills up the empty space in the capillary system, resulting in a reduced porosity. Supplementary cementitious materials (SCMs) consume calcium hydroxide by pozzolanic reaction, which is the majorly responsible for high alkalinity. Volume change due to CSH transformation is most uncertain, and the type of polymorph formed depends on the calcium-to-silica ratio and water content of the silica gel. Therefore, the change in the microstructure of concrete due to carbonation depends upon the type of cement. In this study, the effect of accelerated carbonation on the microstructure of concrete, made from different cements, was analysed. Change in properties of concrete such as porosity, sorptivity and permeability with carbonation was studied. Accelerated carbonation was carried out at 1 and 3% CO2 concentration. From the results, it can be inferred that irrespective of the type of cement used, the porosity of the system increases on carbonation. Similarly, results were also obtained for sorptivity and air permeability.