Properties of Cement Mortars Subject to Varied Carbonation Treatments at Early Ages

Abstract

Carbonation of cement-based composites at early ages has attracted great interest to achieve mineral CO2 sequestration, as well as to improve the properties. In this study, carbonation of cement mortars of interest (with/without lightweight clinker and fly ash) was investigated from very early ages, with the primary purpose of promoting the proper utilization of carbonation treatment in the concrete industry. To explore the influence of carbonation conditions on the strength, water absorption, carbonation shrinkage, carbonation depth, and gas permeability of mortars at early ages, different carbonation conditions with varying temperatures, CO2 concentration, and carbonation duration were studied. Based on the obtained experimental results, it was found that the influence of carbonation on the properties of different mortar matrices tested was consistent. Improving CO2 concentration from a natural level (∼0.04%) to ∼1.5% could remarkably improve the compressive strength gain of mortars at early ages, and the determined strength gain of mortars with 14 days’ carbonation at ambient temperature and CO2 concentration of ∼1.5% could reach up to 30%–50%. Further rising CO2 concentration from ∼1.5% to ∼20.0% was noted to significantly increase the rate of carbonation shrinkage and almost double the magnitude. Besides, the intrinsic gas permeability and water absorption of mortars could be reduced by accelerated carbonation treatment. The estimated reduction of the intrinsic gas permeability of mortars after carbonation reached approximately 80%–90%. In addition, rising carbonation temperature from ambient temperature to ∼80oC could efficiently improve the early-age strength gain and reduce the gas permeability of mortars in a relatively short carbonation duration (∼4 days). However, overextended carbonation at ∼80oC appeared to compromise the strength gain at early ages.