Quantifying the global warming potential of low carbon concrete mixes: Comparison of existing life cycle analysis tools

One of the most feasible approaches to reduce the carbon footprint of concrete, a critical contributor to global CO2 emissions, is to consider the high-volume replacement of cement with supplementary cementitious materials (SCMs). However, this approach currently has two issues: 1) low early-age strength, 2) inconsistent carbon accounting. To address these issues, we investigate the micro- and macro-scale performance of a series of low-carbon concrete mixes and analyze their global warming potential (GWP) using 5 unique LCA tools. We report that the cumulative heat, when normalized to the total water content, exhibits correlations with key performance metrics such as open porosity (R2 = 0.83) and compressive strength (R2 = 0.92). In addition, all LCA tools suggest that high-SCM mixes (55-70% replacement), broadly, can reduce the GWP values for concrete by -50% (from -450 to -240 kg CO2-eq/m3). However, depending on the mix and the LCA tool used, for GWP values, the relative variation can be as high as 30% (-50-80 kg CO2-eq/m3). Finally, we normalize the compressive strength to the GWP metric using an 'Integrated Strength Eco-Efficiency' (I-SEE) coefficient, which can be a potential parameter for simultaneously assessing concrete's performance and environmental impact.