Transformation of industrial solid wastes into carbon-infused infrastructure materials

Abstract In this study, we developed a recycling technique for converting solid waste together with carbon dioxide into a new type of carbon-infused waste-derived concrete. Using fly ash as an example, the concrete was instantaneously consolidated from a semi-dry fly ash mixture via compaction molding and was then cemented and hardened via hydration and accelerated carbonation. We examined the roles of Na2CO3 activation and accelerated carbonation on the reaction chemistry, phase assemblage, mechanical properties, and microstructure of the new waste-derived concrete. The addition of Na2CO3 accelerated the hydration of fly ash mixtures, but an excessive dosage (2% addition) appeared to curtail the hydration. The accelerated carbon curing (up to 4 h) improved the mechanical strength and microstructural integrity of the fly ash concrete, which performed more efficiently upon the addition of Na2CO3 to the mixtures. The Na2CO3-activated mixtures produced diverse hydration products because of the increased alkalinity and the dissociated CO32− ions. The accelerated carbonation transformed the initial hydration products and thus promoted continuous hydration as well as natural carbonation. The microscopic crystalline phases developed through carbonation were merged well with the hydrated matrix phases. The cured matrix demonstrated pronounced calcium features and a wide range of phase compositions because of the synergy of Na2CO3 activation and carbonation. Being deposited on and intermixed with the original hydrated matrix phases, the in-situ formed carbonate-based products acted as cementing agents to form a new cementitious and cohesive microstructure in the waste-derived concrete, without consuming conventional cements. Through a series of laboratory experiments, this method was technically evaluated, indicating that it has the potential to be used for converting large quantities of solid waste from the waste site, along with carbon dioxide, into new types of cement-free carbon-infused waste-derived concrete for cleaner urban and infrastructural development.