Quantitative Analysis of CO₂ Uptake and Mechanical Properties of Air Lime-Based Materials

• Main Authors: Sung-Hoon Kang, Yang-Hee Kwon, Juhyuk Moon
• Format: Article
• Language: English
• Published: MDPI AG 2019-07-01
• Series: Energies
• Subjects: greenhouse gas; global warming; air lime mortar; hydrated lime; CO₂ uptake; carbonation; calcium hydroxide; calcium carbonate; thermogravimetric analysis
• Online Access: https://www.mdpi.com/1996-1073/12/15/2903

In the cement industry, utilization of a sustainable binder that has a lower energy consumption and carbon dioxide (CO₂) emission than Portland cement is becoming increasingly important. Air lime is a binder that hardens by absorbing CO₂ from the atmosphere, and its raw material, hydrated lime, is manufactured at a lower temperature (around 900 &#176;C) than cement (around 1450 &#176;C). In this study, the amount and rate of CO₂ uptake by air lime-based materials are quantitatively evaluated under ambient curing conditions of 20 &#176;C, 60% relative humidity, and 0.04% CO₂ concentration. In addition, the effects of the water-to-binder ratio (<i>w</i>/<i>b</i>) and silica fume addition on the material properties of the air lime mortar, such as strength, weight change, carbonation depth, and pore structure, are investigated. Unlike hydraulic materials, such as Portland cement, the air lime mortar did not set and harden under a sealed curing condition, however, once exposed to dry air, the mortar began to harden by absorbing CO₂. During the first week, most of the internal water evaporated, thus, the mortar weight was greatly reduced. After that, however, both the weight and the compressive strength consistently increased for at least 180 days due to the carbonation reaction. Based on the 91-day properties, replacing 10% of hydrated lime with silica fume improved the compressive and flexural strengths by 27% and 13% respectively, whereas increasing the <i>w</i>/<i>b</i> from 0.4 to 0.6 decreased both strengths by 29% due to the increased volume of the capillary pores. The addition of silica fume and the change in the <i>w</i>/<i>b</i> had no significant impact on the amount of CO₂ uptake, but these two factors were effective in accelerating the CO₂ uptake rate before 28 days. Lastly, the air lime-based material was evaluated to be capable of recovering half of the emitted CO₂ during the manufacture of hydrated lime within 3 months.