Evaluation of Carbonation Degree of Hardened Cement Paste with Different Water-Cement Ratio in Wet-Dry Cycle

Abstract

One of the global environmental problems, CO2 emissions from cement production intensifies in these decades. To solve this problem, countermeasures for CO2 emissions using waste concrete, which has ability to absorb CO2 due to contain calcium-silicate-hydrate (C-S-H) and portlandite (Ca(OH)2), are in the spotlight recently. However, considering the limited time before recycling as roadbed materials, it is important to increase CO2 absorption efficiency so that as much CO2 as possible reacts with waste concrete. In this study, hardened cement paste powders (HCPWs) with the water-to-cement ratios of 0.4, 0.5 and 0.6 were evaluated for the degree of carbonation under various humidity conditions. HCPWs were pulverized to a particle size of 0.6 to 1.18mm and put in desiccators keeping constant humidity condition of RH60 and RH80. In addition, desiccators were prepared with RH60-80 cycle (wet-dry cycle) of 30 minutes, 1 hour, 2 hours and 4 hours to determine the degree of carbonation promotion according to periodic humidity changes. The degree of carbonation of HCPWs were measured by thermogravimetric analysis (TGA). The result shows that the degree of carbonation was improved as the water-cement ratio increased, because the higher the water-to-cement ratio, the more open pores were contained. In addition, vaterite and aragonite caused by the decomposition of C-S-H were the most produced under RH60-80 cycle conditions. This is considered to be because the reaction area with CO2 was increased by weakening the C-S-H by repeating drying and wetting.

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