Concrete mixture proportioning for desired strength and reduced global warming potential

In this research, formulae for predicting compressive strength and global warming potential (GWP) per cubic meter of concrete are proposed. These equations allow for prediction of properties based on the water-to-binder ratio for concrete mixtures containing cement as the only binder, as well as for concretes containing Class F fly ash (FA) and ground granulated blast furnace slag (GGBS) as partial cement replacement. To meet multi-criteria demands of mechanical properties and lower GWP, a method for obtaining the optimal water-to-binder ratio, for given replacement level, is presented. In this research, optimization is based on a direct ratio of GWP to compressive strength, but the methodology has the potential to be extended to other environmental impact categories and material property relationships. For the classes of concrete examined, the analyses showed that high levels of cement replacement with GGBS may provide the best, hence resulting in the lowest, ratio of GWP to compressive strength for the mixtures examined. Additionally for the classes of concrete examined, the results showed that optimal water-to-binder ratios for the best ratio of GWP to compressive strength occurred at relatively high strengths (∼50-70 MPa). Yet, the majority of concrete used in countries such as the U.S. is lower strength concrete (<∼35 MPa). For the mixtures examined, it was shown that the concrete mixtures of low compressive strength (i.e., high water-to-binder ratios) containing only cement as the binder provided a lower ratio of GWP to compressive strength than some of the mixtures containing large quantities of replacement binder suggesting replacement of cement as a binder may not always be the most sustainable solution for low strength concretes.