Effect of supplementary cementitious materials on reduction of CO2 emissions from concrete

The present study examined the effectiveness of supplementary cementitious materials (SCMs) such as ground granulated blast-furnace slag (GGBS), fly ash (FA), and silica fume (SF), in reducing CO2 emissions from ordinary Portland cement (OPC) concrete. This was done by assembling and analyzing a comprehensive database including 5294 laboratory concrete mixes and 3915 plant mixes. The database covered extensive ranges of compressive strength (8-170 MPa) and substitution levels (3-80% for GGBS, 3-70% for FA, and 3-40% for SF). The system studied for CO2 assessment of concrete based on Korean lifecycle inventory was from cradle to preconstruction, which includes consistent materials, transportation and production phases. The unit binder content and CO2 emissions of concrete in developing the unit strength (1 MPa) were identified using the binder intensity and CO2 intensity, respectively. The value of the CO2 intensity decreased sharply as the substitution level of the SCMs increased up to approximately 15-20%, beyond which the rate of decrease gradually slowed. Overall, the binder and CO2 intensities could be formulated as a function of the individual substitution level of each SCM. The proposed equations hold considerable promise as a guideline for the straightforward determination of (1) the total CO2 emission for a given concrete mix proportion, (2) the unit binder content for a targeted compressive strength, and (3) the type and substitution level of SCMs for a designed strength and targeted CO2 reduction rate.