Effects of supplementary cementitious materials on the freeze-thaw resistance and carbon footprint of blended cement concrete

Increased use of supplementary cementitious materials (SCMs) is limited by variability in their compositions and reactivities, since these factors significantly affect concrete properties and durability. Traditional durability testing is time-consuming, making it infeasible to apply widely to emerging SCMs. This paper develops and applies a computational method to screen many blended cements containing coal fly ash and granulated blast furnace slag to identify those that have higher potential to produce high freeze-thaw resistance and low CO2 emissions concrete, varying SCM chemical composition, reactivity, and replacement levels. This is achieved using the Panoramix algorithm, which integrates thermodynamic modelling, random sampling, grid search algorithm, a freeze-thaw prediction model, and life cycle assessment (LCA) to probabilistically explore the design space, thereby rigorously accounting for uncertainties in raw material properties. A novel SCM reactivity database is developed and used here, enabling application of Panoramix to blended cement concretes. The modelling results show that at constant air content (4%), increasing the replacement levels of coal fly ash and granulated blast furnace slag decrease the mean value of the freeze-thaw resistance indicator but increase its variance, due to their broader chemical composition ranges than Portland clinker. At constant air void system quality and content, higher values of the freeze-thaw resistance indicator are calculated at increased SCM reactivity levels, and reduced climate change impacts are calculated at increased SCM substitution levels. The results indicate that a balance between higher freeze-thaw resistance and lower CO2 emissions can be approached using high reactivity SCMs and low clinker-to-cement ratios. The methodology used here facilitates multi-objective concrete selection considering environmental impacts and durability performance.