Optimization of cement and fly ash particle sizes to produce sustainable concretes

In the drive to produce more sustainable concretes, considerable emphasis has been placed on replacing cement in concrete mixtures with more sustainable materials, both from a raw materials cost and a CO2 footprint perspective. High volume fly ash concretes have been proposed as one potential approach for achieving substantial reductions in cement usage, but their usage is sometimes hampered by reduced early age strengths and dramatically increased setting times. One limitation of the current industry practice is that portland cements are generally only optimized for their performance in a pure cement, as opposed to a blended cement, system. In this paper, a new approach of optimizing the particle sizes of the cement and fly ash for achieving desired performance in a blended product will be presented. By appropriately selecting the particle size distributions of cement and fly ash, equivalent 1 d and 28 d strengths may be achieved with about a 35% volumetric replacement of cement with fly ash, while maintaining the same volume fraction of water in the mixture, thus providing an actual 35% reduction in cement content.