Produce low-CO2 silica fume hybrid high-strength concrete using dry ice (solid CO2) as a CO2-utilized admixture

Concerns about high-strength concrete (HSC) have increasingly grown in tandem with the building industry's rapid development. However, the high CO2 emissions, high hydration heat, and high autogenous shrinkage of HSCs considered key issues that limit their wide application. In this study, various proportions of dry ice (solid CO2) were added to concrete to optimize HSC. The test results indicated that adding solid CO2 decreased the hydration heat and autogenous shrinkage and increased the mechanical properties and surface electrical resistivity of HSC. This is primarily attributed to the physical and chemical effects of solid CO2 in HSC curing. At 28 d of curing, the sample containing 3 wt.% solid CO2 exhibited the most significant optimization effect. This is attributed to the fact that, at lower solid CO2 content (3%), the production of carbonation products compensates for the loss of strength caused by the reduction of hydration products. In addition, the addition of solid CO2 caused a decrease in the initial temperature, which delayed the hydration reaction and reduced the autogenous shrinkage. Adding solid CO2 led to an increase in acidity and promoted the formation of AFt, further reducing the autogenous shrinkage. And the more solid CO2 added, the greater the reduction in CO2 emissions for the mixture. Therefore, adding solid CO2 can play a role in optimizing the performance and promoting the sustainability of HSC and can contribute to the objectives of low CO2 emissions, low hydration heat, and low autogenous shrinkage of HSC.