Evaluation of properties of high-volume fly-ash concrete for pavements

The work reported in this paper is based on a laboratory study of superplasticized high-volume fly-ash (HVFA) concrete suitable for pavement construction. Three control concrete mixtures having 400 kg/m(3) of ordinary portland cement (OPC) and water-cementitious material (w-cm) ratios of 0.30, 0.34, and 0.40 were prepared. Other concrete mixtures were then prepared by substituting 20, 30, 40, 50, and 60% fly ash in all control mixtures. Compressive and flexural strengths at ages of 7, 28, 90, 180, 256, and 365 days, drying shrinkage, and abrasion resistance of concrete were measured for all the mixtures. The laboratory test results showed that HVFA concrete mixtures containing 50-60% fly ash can be designed to fulfill the requirement of strength and workability suitable for cement concrete pavement construction. At all w-cm ratios, the concrete mixture containing 60% OPC and 40% fly ash developed maximum strength at the age of 90 days and beyond. However, a maximum increase in the strength of concrete at 365 days over the 28 days strength was observed in the mixtures containing equal amount of OPC and fly ash. Drying shrinkage of concrete decreased with decreasing w-cm ratio and increasing fly-ash content. Among all the concrete mixtures, the mixture with w-cm ratio of 0.30 and containing 60% fly ash showed least shrinkage. Abrasion resistance of concrete, measured by the sand-blasting method, decreased with increasing fly-ash content and decreasing compressive strength. However, abrasion resistance of HVFA concrete mixture with 60% fly ash at 0.30 w-cm ratio was adequate from concrete-pavement considerations.