Harnessing CO₂ and in-situ nanoparticles to strengthen and decarbonize Portland cement-based concrete

The production of ordinary Portland cement (OPC) is responsible for nearly 8% of global anthropogenic CO₂ emissions. A promising strategy to address this challenge is to improve concrete performance, thereby reducing the amount of cement or concrete required in construction. This dissertation presents two innovative methods that significantly enhance the compressive strength of concrete, offering a practical pathway toward more efficient and sustainable cement-based construction.

The first approach—biomolecule-regulated slurry carbonation (BioCarb)—utilizes concrete as a CO₂ sink through a mineralization process in which CO₂ reacts with calcium-rich cement phases to form calcium carbonate (CaCO₃), thereby enabling permanent CO₂ storage. Unlike existing carbonation methods, the BioCarb process introduces CO₂ into a lightly pre-hydrated cement slurry prior to mixing, in the presence of a multifunctional biomolecule that regulates the carbonation reaction. This biomolecule (i) chelates calcium ions to accelerate carbonation, (ii) controls the nucleation, morphology, and crystallinity of CaCO₃, (iii) promotes the formation of reactive silica gel, and (iv) disperses the resulting CaCO₃ nanoparticles. As a result, CO₂ uptake reaches levels at least 25 times higher than existing and the 28-day compressive strength of the produced cement mortar is enhanced by more than 20%.

The second approach enables the in-situ formation of silica nanoparticles using low-cost, environmentally friendly precursors. This strategy overcomes two major challenges that have hindered the practical use of nanoparticles in concrete: high cost and poor dispersion. The in-situ synthesized silica acts as both a nucleation site and a reactive pozzolan, resulting in a 10–15% increase in 28-day strength while allowing for a 10% reduction in clinker content, with strength retention of 90–95% compared to the control. Mercury intrusion porosimetry revealed a 35% reduction in critical pore diameter.

Together, these two approaches offer a scalable and cost-effective solution for reducing cement consumption and decarbonizing concrete production. Both methods rely on inexpensive, widely available chemicals and require only minor modifications to current workflows—such as sealed pre-mixers and access to standard CO₂ or silicate supplies. Their compatibility with existing ready-mix infrastructure makes them well-positioned for rapid industrial adoption, paving the way for significant reductions in greenhouse gas emissions across the built environment.