Assessment of Realkalisation and Carbon Dioxide Uptake of Cement Composite Using Granulated Absorbent

Abstract

Fossil fuel usage has increased rapidly since the late 19th century with industrialization, and global warming and climate change have accelerated as a result of greenhouse gas emissions. The cement industry, as a major industrial producer of greenhouse gases, is responsible for 5–8% of man-made CO2 emissions. The carbonation reaction that occurs between CO2 and the reactive compounds from cement-based materials can form stable carbonates from CO2. Thus, CO2 sequestration technology using cement composites can offer an effective option for carbon capture and utilization projects. Carbonation is a process in which the CO2 in the atmosphere (0.03% by volume) diffuses into concrete and alters the hydrated cement paste. Carbonation itself does not cause the deterioration of concrete, but it changes the pH of the pore solution in the concrete. However, because of changes in the pH, the steel reinforcement inside concrete starts to corrode, and the increase in the volume of the steel reinforcement causes the concrete to crack. For this reason, studies on carbonation have focused on increasing the carbonation resistance of concrete; but recently, it has become more popular to uptake CO2 using concrete for environmental reasons. Studies have mainly conducted accelerated CO2 curing in the early age by using gamma-C2S and the mineral carbonation of waste concrete. In this study, calcium hydroxide, a reactant of CO2, was granulated and added to a cement composite to consume more CO2 in the atmosphere during the carbonation reaction by increasing the amount of calcium hydroxide by the same volume of concrete structures. In addition, this method restores the dropped pH in the carbonated area and increases the watertightness by supplying alkali activity and Ca+ ions to the non-carbonated area. To achieve the purpose of this study, calcium hydroxide was granulated, and a granulated CO2 absorbent was prepared using the wet granulation method. The granulated CO2 absorbent was added to cement composites to produce various specimens. The physical properties and durability of the specimens were evaluated, and the efficiency of CO2 uptake was compared. The hydration products were confirmed by XRD and FTIR, and the efficiency of CO2 uptake was evaluated by comparing the amount of precipitated calcium carbonate by the carbonation reaction using TGA. As the amount of granulated CO2 absorbent increased, the strength of the cement composite decreased in the early curing stage, but the long-term curing age showed similar results to those of the control group containing no absorbent. The results of a chloride penetration test showed that the chloride penetration resistance increased with an increase in the amount of chloride added. In the carbonation depth test, the recovery of the pH around the granulated CO2 absorbent was confirmed. The efficiency of CO2 absorption increased as the amount of granulated CO2 absorbent increased. Through XRD and FTIR, the phases of the hydration product and the calcium carbonate by carbonation were confirmed. A quantitative analysis by TGA confirmed the efficiency of CO2 uptake by the increase in the amount of calcium carbonate according to the amount of granulated CO2 absorbent. Finally, porosimetry test results showed that the micropores were reduced by the addition of granulated CO2 absorbent.