Utilization of nano-ZrO2 to improve the efficiency of carbonation curing of cement-based materials

Nanomaterials are characterized by large surface areas and ultrasmall particle sizes, which affect their micromorphologies. In this study, the impact of nano-ZrO2 on the efficiency of carbonation curing was systematically investigated to compare the mechanism for nano-ZrO2 in the hydration and carbonation reactions occurring during sealed and carbonation curing and the effects on the micro- and macroscopic properties. The experimental results showed that the hydration rate and degree of carbonation increased gradually with increasing nano-ZrO2 content. The effect of nano-ZrO2 on the hydration rate was more significant in the early period (0-72 h); the impact on the carbonation curing efficiency was more significant in the later period (28 days). After 28 days of carbonation curing, the compressive strengths of samples doped with 0.5% and 1% nano-ZrO2 were higher by 7.5% and 4.9%, respectively, compared to those of the samples without nano-ZrO2. Moreover, the resistivities of the samples doped with nano-ZrO2 were higher than that of the control sample (NZ-0%-CC). The efficiency of carbonation curing was mainly attributed to optimization of the substrate micromorphology by the nano-ZrO2. The addition of nano-ZrO2 decreased the orientation of the calcium hydroxide (CH) crystals in the mixture and reduced their sizes, leading to an increase in the reactivity of the CH. Moreover, with increases in the amount of nano-ZrO2 added, the calcium carbonate content of the carbonation product increased slightly. Thus, nano-ZrO2 improved the efficiency of concrete carbonation curing; high carbonation, high strength and high durability were realized by adding a small amount of nano-ZrO2 for microscopic morphology optimization.