Mechanistically Informed Co-Valorization of Alkaline Industrial Residues and Construction & Demolition Wastes with Industrial CO2 Emissions: A Pathway Towards a Sustainable Construction Materials Value Chain
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Concrete is an essential material used in construction activities, and its manufacturing accounts for 8.6 % of anthropogenic CO2 emissions. In addition to the pollution caused during production, around 1-2 Gt of construction and demolition waste is generated annually. Therefore, it is deemed important to close the loop of the construction industry by valorizing the construction and demolition waste (CDW) and develop circular approaches wherein calcium is recovered from the waste concrete and reused along with captured CO2 emissions to make construction materials. An approach has been developed that involves selective extraction of calcium using different organic and inorganic acids at precise solid-to-liquid ratios and initial concentrations. The efficacy of using organic acids such as acetic or formic acid is contrasted with the use of inorganic acid such as hydrochloric acid for CDW dissolution and the subsequent effects on CO2 mineralization. There is a growing interest in precipitating CaCO3 as its metastable state (vaterite), since vaterite has a niche market, and more recently has been investigated as a supplementary cementitious material (SCM). In this work, the large-scale production of vaterite from calcium salts obtained from leaching CDW with organic and organic acids is demonstrated with a continuous process along with demonstration as an SCM in cement mixes. The successful demonstration of vaterite substitution shows an increase in the strength of concrete at 5% and 10% substitution, paving the way for future research in high-strength concrete using vaterite. Further, in order to reduce dependence on purchasing leaching acid and neutralizing alkali from market, a novel MnO2 and IrO2 electrocatalyst was developed to perform direct electrolysis of brine to co-produce acid, alkali, and hydrogen gas at minimal energy consumption. The techno-economic analysis and life cycle analysis was performed to gain insights into the scalability of the process in different scenarios. Finally, the necessary policy inputs to enable large-scale adoption of were identified. This dissertation, therefore, presents a scientific and technological approach for CDW valorization, its techno-economic and life cycle analysis, and elucidates the system dynamics of the broader construction industry which would allow deployment of such a technology into the market.