Influence of dry ice on the performance of Portland cement and its mechanism

This study reports on the effect of dry ice on the hydration and hardening behavior of Portland cement. Dry ice was directly added to fresh Portland cement paste, with its dosage fixed at 0 wt%, 0.3 wt%, 0.6 wt%, 0.9 wt%, 1.2 wt% and 1.5 wt%. Results showed that dry ice had little effect on the standard consistency and setting time of cement paste when its dosage was less than 0.9 wt%, but otherwise the standard consistency as well as the setting time was increased. The compressive strength of the paste at 7 days increased slightly when the dosage of dry ice was less than 0.9 wt%, but the compressive strength was reduced with the addition of 0.9 wt% to 1.5 wt% dry ice. For the compressive strength at 28 days, the cement paste with 0.6 wt% dry ice showed the greatest value, being increased by 30.9% compared to the control cement paste, and the compressive strength of the samples with dry ice was all higher than that of the control. In addition, hydration heat, XRD, DTA-TG and SEM results showed that the incorporation of dry ice retarded the early hydration of Portland cement, improved its later hydration, and optimized the hardened structure of the cement paste. These results can provide a reference for the future application of dry ice in Portland cement-based materials. (C) 2018 Elsevier Ltd. All rights reserved.