Low-carbon cement with carbon mineralization products and calcined clays

Emissions of CO2 and other greenhouse gases have increased exponentially since the so-called “Great Acceleration” started around 1950 (Steffen et al., 2015). These gases concentrate in the atmosphere leading to climate change with very serious consequences across the globe. Portland cement (PC) production accounts for 7-8% of global CO2 emissions (Zunino & Scrivener, 2022) and about one ton of CO2 is released for every ton of PC (Reddy & Reddy, 2021). A major part of this emitted CO2 is related to the calcination process of limestone for clinker production. So, one possible way to reduce the environmental impact of PC is to decrease its clinker content by using supplementary cementitious materials (SCMs). An additional route that has been increasingly explored to decrease atmospheric carbon dioxide emissions by industry is based on CO2 mineralization, either through in-situ or ex-situ techniques. In this study, carbonated olivine, the final product of the ex-situ carbon mineralization using olivine-rich rocks, and three calcined clays (“Sant’Elena”, “Red” and “Green”) were used and evaluated as SCMs in three different mixtures of blended cements composed of 50% CEM I 52.5R, 25% carbonated olivine and 25% calcined clays, with a water/cement ratio of 0,5. The starting materials were characterized by X-ray powder diffraction (XRPD) and X-ray fluorescence (XRF) analysis. The reactivity of the starting materials was evaluated with the R3 test. The kinetics of hydration of the three blended cement pastes were analyzed during the first 24 hours through in-situ XRPD measurements. After 7 and 28 days of curing time, the specimens of the three blended cements were subjected to compressive strength test. Portions of these specimens were pulverized and analyzed through XRPD analysis. The obtained results show that carbonated olivine can be used effectively as SCM in ternary blended cements with a content of Portland cement reduced to 50%. The mechanical properties of the blended cements are promising, reaching compressive strength values of 30 MPa at 28 days of curing time. With further optimization of mix design, these ternary cements are promising solutions for low-carbon cement within the 32.5 R resistance class.