CO2 Sequestration Eciency within the Porous Matrix of Concrete - Advanced Physicochemical, Transport, and Engineering Modeling

Carbon dioxide sequestration in concrete is a mineralization process in whichgaseous or dissolved carbon dioxide penetrates the pore network of a cementitious matrix and reacts with alkaline hydration products, primarily calcium hydroxide, calcium silicate hydrate, calcium aluminate hydrates, calcium oxide, and magnesium-bearing phases. The principal stable product is calcium carbonate,although amorphous silica gel, decalcied calcium silicate hydrate, aragonite, and vaterite may also form depending on the chemical environment.The sequestration eciency of concrete is governed by a coupled system ofgas diusion, liquid-phase dissolution, ionic transport, capillary saturation, mineral dissolution, carbonate precipitation, pore-structure evolution, heat transfer,and mechanical damage. Consequently, concrete carbonation should not be represented only as a one-dimensional moving-front problem. A more accurate description requires a nonlinear thermo-hydro-chemo-mechanical reactive-transportframework.This study develops an advanced theoretical framework for evaluating carbon dioxide sequestration inside the porous matrix of concrete. The framework combines chemical equilibrium, reaction kinetics, multicomponent mass transport,eective diusivity, pore-size distribution, evolving porosity, and mineral availability. The theoretical carbon dioxide storage capacity is separated from the actualuptake, carbonation degree, and process eciency. The eects of water-to-binderratio, relative humidity, carbon dioxide concentration, pressure, temperature, curing regime, supplementary cementitious materials, steel slag, y ash, recycledconcrete aggregate, biochar, calcium hydroxide, and nano-additives are analyzed.The theoretical analysis indicates that the highest carbonation eciency is notassociated with maximum moisture or maximum carbon dioxide pressure alone.Instead, it occurs within an optimum moisture interval in which sucient liquidwater is available for carbon dioxide dissolution and ionic mobility, while the porenetwork remains suciently unsaturated to permit gaseous diusion. Mineralcarbonation can densify the pore structure, increase early compressive strength,and permanently stabilize carbon dioxide as carbonate minerals. However, excessive carbonation may reduce pore-solution alkalinity and increase the risk of reinforcement depassivation. Therefore, the engineering design of carbon-sequesteringconcrete must optimize both carbon uptake and structural durability.