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.

Introduction

In order to reduce environment impact of CO2, a number of measures have been taken, such as reducing CO2 emission [1,2] and sequestrating CO2 by using cementitious materials [3]. However, the construction industry annually consumes 4.3 billion tons of ordinary Portland cement (OPC) for making concrete, resulting in a great amount of CO2 emission that accounts for around 7% of global CO2 emissions. To reduce carbon footprint of cement industry, a number of studies focused on developing low-carbon cement [4–۷]. In addition, other relevant research has been performed, which included CO2 curing [8–۱۳], CO2 strengthening recycled aggregates [14–۱۹], as well as the transformation of carbon dioxide to carbonate as chemical additives [20–۲۲]. X.Y. Pan [11]studied the strength and permeability of CO2 surface treatment on oneday age of cement mortar. After 24 h of CO2 treatment, the results showed that the compressive strength was increased slightly, the impermeability of cementing material was improved, while water absorption was reduced by 15–۳۰%. KOU [23] studied the effect of carbonization on recycled aggregates, and their results showed that CO2 curing increased the physical properties of recycled aggregates: the longer the curing time, the better the degree of carbonation and the higher the quality of aggregate. W. Kunther [24] investigated the effect of bicarbonate ions on the deterioration of mortar bars in sulphate solutions and found that the presence of bicarbonate ions significantly reduced mortar swelling. J.G. Jang [25] studied the effect of sodium bicarbonate on the performance of cement slurry, and they found that the addition of NaHCO3 caused the internal carbonation of cement slurry, resulting in the consumption of Ca(OH)2. Besides, the compressive strength was increased with the addition of 5% NaHCO3; however, the strength degraded for higher concentrations. Rodger [26] found that Li2CO3 accelerated the early hydration rate of sulphoaluminate cement. Other studies [27–۲۹] found that lithium carbonate significantly shortened the setting time of sulphoaluminate cement, and improved its early compressive strength and flexural strength. Although there have been a number of studies on the influence of CO2 curing or carbonate salts on hydration and hardening of Portland cement, little research has been carried out on how dry ice, as an alternative form of CO2, affects the process of Portland cement hydration. This study investigates the effect of dry ice on the hydration kinetics, compressive strength, chemical compositions, and microstructure of Portland cement paste.