Properties of flowable high-volume fly ash-cement composite

Coal-burning power plants generate a large amount of fly ash in the United States. A small fraction of the fly ash generated is being utilized in various applications. There is a particular need for further utilization of fly ash. In this paper the results from a recent study on development of a cement composite utilizing relatively large amounts of fly ash are presented. Potential areas of application include waste-disposal site liners and backfills. The flowable fly ash- cement sand composite was investigated for strength and permeability characteristics at various stages of maturity. The independent variables considered were: fly-ash content, sand content, and ratio of water to cementitious materials. Results of this study show that high-volume fly-ash composite can be proportioned to obtain compressive strengths as high as 21 MPa (3,000 psi) at 180 days. For applications requiring strengths less than 3 MPa (500 psi), the mixture with fly ash-cement ratio of 10 and sand-cement ratio of 20 with relatively high water content may be used. For applications where permeability has to be limited to 10^-7 cm/s, water- to-cementitious materials ratio has to be limited to 0.3. The strength of the composite increased significantly with increase in curing time. The splitting tensile strength of the composite was about 7.5% of the compressive strength.