11 - Carbon dioxide sequestration on recycled aggregates

Abstract

Carbon dioxide (CO2) is the predominant greenhouse gas on earth, and its atmospheric concentration is increasing at an exponential rate due to human activities. Cement production contributes about 7% of the total worldwide CO2 emissions, and thus finding a practical way to reduce the greenhouse gas emission is essential. Recycled concrete aggregate differ from natural aggregate (NA) as the former contains hardened cement mortar. The adhered cement mortar on recycled concrete aggregate has higher porosity and water absorption and lower strength than NA. It has negative effects on the mechanical properties and durability of fresh and hardened concrete made with recycled concrete aggregate. However, the adhered cement mortar rich in calcium hydroxide and calcium silica hydrate is considered to be a potential calcium source for CO2 sequestration, forming thermodynamically stable carbonate minerals. In the past decade, a major research effort was to study the influencing factors affecting the effectiveness of active carbonation of construction and demolition waste. In this section, active carbonation techniques adopted for crushed concrete aggregate and waste cement derived from the construction and demolition waste and the resulting properties of the CO2-cured recycled concrete aggregate are discussed. In addition, the mechanical properties, durability properties, and microstructure of CO2-cured recycled aggregate concrete are also reviewed in this section. We conclude that the mineral carbonation of construction and demolition waste is a technically feasible, economical, and environmentally friendly approach of a future carbon sequestration strategy.