Effect of carbonation on calcium silicate hydrate

Abstract

Abstract Calcium silicate hydrate (CSH) phases precipitated during cementitious reactions are responsible for strength gain in lime and cement-stabilized subgrade layers. Exposure of these treated layers to environmental factors can lead to carbonation of CSH phases and can be detrimental to the long-term performance of these materials. The study focuses on understanding the physio-chemical changes incurred in CSH phases during carbonation and developing a methodology to shorten the timescale required for carbonation studies where field carbonation needs to be simulated. Pure CSH phases were synthesized in accordance with Greenberg et al. (1960) and were subjected to varying levels of carbon dioxide (CO2) exposure under controlled conditions. Impact of diffusion of CO2 was identified based on changes in Ca/Si ratio, pH values and morphology variations in the samples. Observations suggest that carbonation of CSH phases in presence of moisture is a multistep process where metastable calcium bicarbonate phases form initially. 30-day exposure to one percent CO2 was observed to mimic 720 days of infield carbonation due to atmospheric exposure whereas five to seven days exposure to three percent CO2 was found to be equivalent to 720 days of atmospheric carbonation incurred by stabilized samples in field.