Laboratory based accelerated carbonation approach to simulate long term field carbonation in cementitious mixtures

Abstract Calcium silicate hydrate (C-S-H) 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 C-S-H phases which can be detrimental to the long-term performance of these materials. The study focuses on understanding the physio-chemical changes incurred in C-S-H phases during carbonation and developing an approach to shorten the timescale required for carbonation studies where field carbonation needs to be simulated. For micro scale studies, pure C-S-H phases were synthesized in laboratory and were subjected to varying levels of carbon dioxide (CO 2 ) exposure under controlled conditions. Lime treated soil prepared using bentonite-sand mixture was used to evaluate the effect of carbonation at macroscopic scale. Impact of diffusion of CO 2 was identified based on changes in Ca/Si ratio, pH values and morphology variations and changes in concentrations of calcium carbonate and residual lime in the samples. Observations suggest that carbonation of C-S-H phases in presence of moisture is a multistep process where metastable calcium bicarbonate phases form initially. 30-day exposure to one percent CO 2 was observed to mimic 720 days of infield carbonation due to atmospheric exposure.