NSF Convergence Accelerator Track I: Revolutionizing the manufacture of Portland cement concretes towards a circular and carbon-negative future

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Concrete is the most widely used construction material in the world. However, current production of ordinary Portland cement (OPC)-based concrete contributes to three main challenges that our society is facing today: climate change, resource depletion, and solid waste. This convergence research will establish a pathway to address all these challenges by leveraging the synergy of circular economy principles and a revolutionary manufacturing method of concrete which converts concrete into one of the largest sinks for CO2. Through a biomolecule-regulated carbonation (BioCarb) technology, this new manufacturing method transforms cement slurry into an effective CO2 absorbent, which can absorb and permanently store 25 to 50 times more CO2 in fresh concrete than existing technologies. More importantly, the compressive strength of the produced concrete can be drastically increased by in-situ produced nanoparticles. Similarly, calcium-rich industrial wastes – such as recycled concrete fines, steel slag, and coal ashes – can be converted into carbon-negative supplementary cementitious materials, which can substantially reduce the amount of OPC needed for concrete production. In addition, the functional biomolecules used in BioCarb will be extracted from agricultural waste, which provides a new solution to decarbonize chemical admixtures used in concrete. If successful, this project can unlock the enormous potential of concrete for permanent storage of CO2 as carbonate minerals and decarbonize all ingredients of concrete. As a result, the CO2 footprint of concrete will potentially be reduced by more than 50%. If the proposed technology is deployed at full scale, over 2 billion metric tons of CO2 can be reduced per year globally, and more than 3 billion metric tons of solid wastes can be converted into useful cementitious materials and aggregate every year and avoiding extraction of the same amounts of natural resources.Concrete can serve as a CO2 sink through mineralization processes, in which CO2 react with calcium-rich minerals in concrete to produce CaCO3 and permanently store CO2. However, key challenges including diffusion barriers and marginal strength improvement impede existing technologies to reach full potential of concrete for CO2 sequestration. To fully unlock this potential, we propose a breakthrough technology, BioCarb, to maximize CO2 uptake while n-situ produce nanoscale performance enhancers before concrete hardens. This is achieved by using a biomolecule as small-dose additive, which regulates the carbonation process of calcium-rich minerals through: i) chelating with calcium to facilitate the carbonation of the minerals, ii) controlling the crystal nucleation, orientation, size, and polymorph of calcium carbonate, and iii) enabling uniform dispersion of the produced CaCO3 nano- and micro-particles. As a result, much more CO2 can be absorbed by concrete directly without compromising performance. More importantly, the metastable CaCO3 produced through BioCarb can react with the cement to form new minerals or dissolve and re-precipitate to function as a binding phase in concrete. As a result, a novel calcium silicate hydrate-CaCO3 hybrid binder can form in the concrete, leading to improved mechanical strength, volumetric stability, and durability. Similarly, this process can be used to process other calcium-rich solid wastes and convert them into carbon-negative supplementary cementitious materials and aggregate for maximal substitution of cement and naturally extracted aggregate, respectively. This implies an even bigger potential for decarbonization. A convergent research approach is employed in this project to transit BioCarb into practical use, by fusing multiple disciplines – civil engineering, material science and engineering, environmental engineering, chemistry, food science and processing, and environmental justice – and the end uses of BioCarb and full life cycle considerations for the environmentally and economically sustainable production of concrete.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.