Effectiveness of Super-plasticizer on High Volume Fly Ash Concrete

This research project was aimed to determine the optimum super-plasticizer dosage
for producing highly workable, high strength, low porosity and low gas permeability
concrete containing high volume fly ash ( 60%) as partial cement replacement. The
trial mix with 100% cement was initiated with a water cement ratio of 0.27, which
gave very dry mix with negligible slump value. The mix resulted quite poor quality
hardened concrete cubes. Then on the next trial, the mix was also not very
successful. Finally a mix with 0.4 water cement ratio yielded targeted results and
chosen as the final mix water ratio. Super-plasticizer dosage of 0%, 0.5%, I%, 1.5%,
2%, 2.5% and 3% were tested. It is found that super-plasticizer dosage in the range
of 1.5% to 2.5% has given the optimum characteristics of concrete including
strength, porosity and the gas permeability up to 90 days and 1.5% yields the
optimum dosage of super-plasticizer.