Recycling of calcined carbonated cement pastes as cementitious materials: Proposed CCUS technology for calcium looping

Abstract

In this study, calcined carbonated hydrated cement pastes (HCPs) were used to partially replace ordinary Portland cement (OPC) as a cementitious material. Calcined carbonated HCP can be derived from carbonated HCP after the release of CO2 for the carbon capture, utilization, and storage (CCUS). Calcined carbonated HCP was produced by calcining carbonated HCP at 1000 °C, also used in calcium looping. The crystal phase compositions of the HCP, carbonated HCP, and calcined carbonated HCP were identified. Various hardening and microstructural tests on the composite cement paste mixtures blended with calcined carbonated HCP were performed. The initial results showed that the HCP could sequester CO2, forming various calcium carbonates. After carbonated HCP calcination, the main nanocrystalline phases of calcium silicate hydrate (C-S-H) and calcium carbonate decomposed, forming lime and wollastonite. The 28-day compressive strength of the calcined carbonated HCP–OPC mixtures increased with the replacement ratio up to 20%, owing to the filler effect of wollastonite. The microstructural analysis revealed that the portlandite, C-S-H, and monocarboaluminate phases were formed after hydration. Finally, by recycling demolition waste, this study proposed a technology roadmap for CCUS to achieve this goal, and a life cycle assessment was conducted to evaluate and compare the environmental impacts of producing 1 t of calcined carbonated HCP–OPC mixtures and plain OPC paste.