Low-CO2 emission strategies to achieve net zero target in cement sector

Cement industry is one of the largest contributors to greenhouse gas emissions accounting for about 7% of global CO2 emission. As global cement demand continues to rise exponentially, the industry is taking numerous effective steps to meet net-zero emission targets by limiting global warming to 1.5 degrees C by the end of the century and improve the ecological system. Worldwide, about 2.9 billion tons of CO2 were emitted in 2021 from cement production and the industries are expected to achieve the net-zero target by 2050. The reduction of CO2 emission remains a major challenge for the cement industry as the manufacturing processes and the current infrastructure allow little margin for the reduction in CO2 emission, considering the age-old and conventional Portland cement chemistry. To achieve a net-zero emission target, several effective measures are being explored to mitigate CO2 emissions from cement industries, viz., use of alternative fuels, reducing clinker-to-cement ratio, improving energy efficiency, carbon capture, utilization, and storage (CCUS) techniques etc. Apart from these, production of low-carbon cement different from Portland clinker chemistry has the potential to make a big difference in mitigating CO2 emission. Carbonatable calcium silicate-based cement, is found to be a promising alternative to OPC and reduces about 70% of total CO2 emission from cement production. This paper thoroughly reviews the different low-carbon emission approaches (both direct and indirect) such as reducing clinker factor, lowering the clinkerization temperature by using fluxes and mineralizers (such as CaF2, BaO, SnO2, P2O5, Na2O, NiO, ZnO etc), producing low temperature clinker, use of supplementary cementitious materials (SCMs) in concrete and capturing the emitted CO2 through mineral carbonation, direct air capture (DAC) etc for future alternative lowcarbon cements. Various commercialized technologies for reducing CO2 emissions (CarbonCure, Solidia, Heidelberg, Novacem, Carbicrete and CO2-SUICOM) with their technology readiness levels (TRLs) are also discussed.