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

Abstract

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 °C) than cement (around 1450 °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 °C, 60% relative humidity, and 0.04% CO2 concentration. In addition, the effects of the water-to-binder ratio (w/b) 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 w/b 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 w/b 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.

Experimental Investigation of Traditional Clay Brick and Lime Mortar Intended for Restoration of Cultural Heritage Sites

“…Nam et al [36] determined the suitable range of mixing water using a flowability test, depending on the type of hydrated lime and the mixing ratio. The mortar mixing ratios in this research were determined in accordance with those standards and research results [36][37][38], and are presented in Table 2. Figure 4 presents a flow chart of the tests.…”

Utilization of Gaseous Carbon Dioxide and Industrial Ca-Rich Waste for Calcium Carbonate Precipitation: A Review

“…Concrete as the main building material in the world, is manufactured in an amount of 4000 Mt per year (2017) and its market increased by 2.5% annually, while producing approximately 7% of global carbon dioxide emissions [71,72]. For example, the production of 1 kg of Portland cement generates more than 0.8 kg of CO 2 .…”

Historical and Scientific Investigations into the Use of Hydraulic Lime in Korea and Preventive Conservation of Historic Masonry Structures

“…To date, it is known that Korean traditional lime does not have hydraulic properties; hence, it can be defined as air lime, which hardens by the carbonation reaction between calcium hydroxide (Ca(OH) 2 ) and atmospheric carbon dioxide (CO 2 ) while forming calcium carbonate (CaCO 3 ) [6]. This non-hydraulic binder consists mostly of Ca(OH) 2 and is manufactured by slaking the quicklime after burning high quality limestone, which has almost no impurities.…”

“…In addition, lime-based materials are considered philosophically and technically suitable in the field of historic building conservation, compared to Portland cement [22]. Moreover, these materials are eco-friendly due to their low energy consumption and greenhouse gas emissions in the manufacturing process [6,23]. In addition to long-term cost competitiveness, these environmental aspects are also important in preventive conservation.…”

“…One example to support this is that many practitioners and workers believe that long-term sealed curing for air lime mortar is beneficial for developing its strength. This misunderstanding might be caused by the practices involved in using hydraulic materials, and it demonstrates a lack of knowledge that the setting and hardening of air lime is possible only when drying and CO 2 absorption occur [6]. This eventually leads to frequent defects and disputes, making the choice of cement-based materials inevitable.…”