Activated Hybrid Cementitious System Using Portland Cement and Fly Ash with Na₂SO₄

Abstract

A number of alternatives have been explored by the cement industry in recent years to reduce CO₂ emissions. One of the alternatives, the subject of this chapter, is an intermediate system between a high volume fly ash concrete and a geopolymer concrete. This concrete includes a hybrid system of 50% OPC–50% fly ash, and an activator. In this study, the long-term durability was studied for laboratory and outdoor cured concretes. It was found that chloride diffusion coefficient was reduced significantly at 90 days and beyond for the activated system compared to control samples (100% OPC and 80% OPC–20% fly ash) of the same water to cementitious content ratio (W/CM). This behavior was exhibited by samples cured under laboratory controlled curing conditions (100% RH and 23 °C). On the other hand, outdoor curing increased concrete permeability for all concretes. Long-term carbonation was also explored and samples under outdoor curing had a significant carbonation depth. Alkali silica reaction problems were mitigated with this activated hybrid system. In order to improve the carbonation resistance of this concrete, a reduction in W/CM seems necessary. Based on these results, activated high volume fly ash systems provide a low CO₂ concrete alternative; however, more studies are needed for establishing specifications and service life prediction models.