Pre-treatment of waste hydrated cement used for replacement of fine aggregate using amine-based CO<sub>2</sub> solvent

Abstract

In the realm of construction and demolition (C&D) waste, a small fraction of hydrated cement waste is typically repurposed to generate supplementary cementitious material or filler for concrete. However, the conventional method of utilizing it in powder form demands significant energy consumption to achieve the necessary fineness. Therefore, this study proposes a method to use a waste-hydrated cement paste as a fine aggregate as well as the pre-treatment method to enhance its properties. The pre-treatment involves carbonating hydrated cement in a fully CO(2)dissolved amine-based CO2 solvent, specifically a monoethanolamine (MEA) solution. This process eliminates vulnerable phases, such as calcium hydroxide, resulting in a higher compressive strength of mortar when incorporating the treated hydrated cement as fine aggregate. Notably, the use of fully CO2-dissolved 1% and 10% MEA solutions during carbonation demonstrates superior performance and increased CO2 uptake. Additionally, the developed pre-treatment method uses MEA CO2 solvent directly, commonly utilized for CO2 capture in industrial flue gas. It is an alternative for solvent regeneration without the need for a heating process, potentially reducing overall energy consumption.