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. Since the replacement of cement by fly ash in a concrete mixture is often accompanied by a significant decrease in the water-to-cementitious materials ratio by mass (w/cm), the concurrent reduction in cement content may be significantly less than the replacement level. As an example, a w/cm=0.3 concrete with a 40 % volumetric replacement of fly ash for cement actually may only achieve about a 25 % reduction in cement content relative to an equivalently performing mixture based solely on portland cement with a water-to-cement ratio (w/c) of 0.42. 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 by fly ash, while maintaining the same volume fraction of water in the mixture, thus providing a 35 % reduction in cement content.
Citation: Cement and Concrete Composites
Pub Type: Journals
Blended cement, high volume fly ash, particle size distribution, strength, surface area, sustainability.