Effect of nanomodification of cement pastes on the CO2 uptake rate

This study investigates the effects of nano-TiO2 addition on the CO2 uptake rate of cement pastes as a function of CO2 concentration. 16x4x4 cm prismatic samples of 0.5 water/binder (w/b) cement paste with and without nano-TiO2 particles were used. These samples were placed inside a controlled environment with three initial CO2 concentrations (25%, 50%, and 100% CO2) during eight 1-hour cycles. CO2 concentration in the chamber was constantly monitored with a CO2 sensor, and was refilled each hour to the targeted concentration. CO2 uptake results showed that nano-TiO2 addition enhances the CO2 uptake rate of cement pastes, enabling the capture of more CO2 with lower CO2 concentrations, thus making the process more efficient. Using nanoparticles reduces the porosity of cement pastes. Typically, a decline in porosity produces a decrease in the samples' diffusion of CO2, implying a lower carbonation rate coefficient. However, data showed that nanomodified samples absorb more CO2 faster while the porosity is decreased, which is counterintuitive. 3D X-ray results suggest that the nanomodification of cement pastes increases the pore surface area while reducing the overall porosity. Thus, the carbonation rate coefficient does not directly depend on the pore volume but on the pore surface area.