Potential for CO2 mitigation and economic benefits from accelerated carbonation of construction and demolition waste

Abstract

Transitioning to zero-waste cities may help achieve low-carbon goals. The unprecedented generation of construction and demolition (C&D) waste poses a significant obstacle to the sustainable development of the built environment, particularly for megacities in emerging economies. Among the common C&D wastes, concrete debris has high alkalinity and can be used for CO2 sequestration via mineralization. However, previous studies have almost exclusively considered the CO2 uptake potential, while ignoring the emissions associated with the energy and material consumption for carbonation. The lack of understanding in this domain poses a great challenge to industrial applications due to environmental and economic uncertainties. Thus, this study aims to evaluate the net emission reduction and economic efficiency of using concrete debris in 14 global regions via life cycle assessment and life cycle costing to fully consider the inputs and outputs in carbonation systems, which can compensate for the biased results of historical studies. The results show that the average unit net CO2 benefits and economic benefits from the industrialization of carbonated recycled concrete aggregates (cRCA) technology vary considerably between countries, with CO2 benefits (ton CO2 emission/ton CO2 uptake) ranging from 0.7 in Brazil to 2.6 in Pakistan and economic benefits (USD/ton concrete debris) ranging from 18.5 in the USA to −5.6 in Pakistan. We found that, even with cRCA technology, only a few countries can obtain net negative CO2 emissions and positive economic value simultaneously, which indicates that the production process should be further adjusted to reduce avoidable emissions and increase potential economic benefits before it is promoted. Given the heterogeneity of economic and spatial contexts across countries, the study proposes targeted strategies for the transport, production, and trade processes of various types of regions to optimize the situation. But in general, restructuring the transportation network and relocating recycling plants are the most effective options for improving economic and environmental benefits. CO2 sequestration via concrete debris carbonation will become promising when strategies are tailored to local conditions.