Adding dry ice into ultra-high-performance concrete to enhance engineering performances and lower CO2 emissions

Abstract

Developing low-carbon cement-based materials is crucial to address the pressing sustainability concerns the construction industry faces. This study elucidates the effect of adding dry ice on the micro-meso-macro properties of ultra-high-performance concrete (UHPC). The main original points of the method were summarized as follows: simple operation, low technical difficulty, no specific equipment required, and solving the problem that the carbonation curing method is difficult to use in low water-cement ratio concrete. The results show that adding dry ice generates microscopic CO2 bubbles that react with the carbonation of Ca(OH)2 and improve the later-stage strength and electrical resistivity. And adding dry ice reduces the heat of hydration and promotes ettringite formation. The results of microscopic analyses confirmed that increasing the dry ice content results in a decrease in Ca(OH)2; hence more calcium carbonate is formed. It was also observed that the carbon conversion effect became more apparent when the curing period was 28 days. And optical micrograph analysis showed that adding dry ice increased the total bubble content of the matrix and decreased the average bubble diameter, thus affecting the change in macroscopic properties. Moreover, as the addition of dry ice increased from 0 to 15%, the CO2 emission per unit strength decreased from 6.5 to 4.5 kg·CO2·m−3·MPa−1 (30% reduction in CO2 emission). Therefore, adding dry ice to UHPC is an effective way to utilize carbon and is crucial to achieving carbon neutrality in the concrete industry.