Accelerated Carbonation Curing as a CO2 Sequestration and Water Conservation Technique

Abstract

Global warming has become one of the biggest problems for a sustainable future ever since the start of industrial era. CO2 is a major greenhouse gas which is responsible for global warming, with cement industry contributing towards 5% of worldwide CO2 emissions. CO2 sequestration is described as long-term storage of atmospheric CO2 in stable forms, and is identified as one of the solutions to further mitigate higher levels of CO2.The ability of cement to react with the atmospheric CO2 makes the cement-based materials viable carbon sinks. The process of interaction of cement with atmospheric carbon dioxide is called natural carbonation. Instead of natural carbonation, the process of deliberately supplying CO2 to the cement system during very early ages of strength development is called accelerated carbonation curing (ACC). During ACC, the captured CO2 gas is passed over freshly cast concrete for a certain duration, pressure and relative humidity. In this process, CO2 reacts with unhydrated cement components (calcium silicates) and hydrated cement compounds (calcium hydroxide and C-S-H) to form CaCO3 that is stored as stable precipitate in concrete. The objective of this research work is to evaluate the performance of concrete when subjected to ACC. The testing programme is divided into various subparts. In the first part, the performance of carbonation cured concrete was evaluated vis-à-vis water curing in terms of mechanical properties, permeation properties and microstructural changes of concrete, with special emphasis on surface characteristics.ACC was carried out for a period of 6 hours after initial preconditioning of 2 hours and followed by water spray for three days. The microstructural analysis of the mixes indicated considerable modification of the concrete surface by adopting carbonation curing. It was observed that calcium carbonate formed during the carbonation process gets accumulated in the concrete pores, thereby refining the pore structure and improving the permeation characteristics of concrete.