Investigations into Properties of Collie Fly Ash that Influence Admixture Sensitivity in Blended Cement Concretes
R.L. Munn and Z.-T. Chang
Appears on pages(s):
carbon type; characterization; chemical admixtures; fly ash; fractional analysis; physical features; sensitivity; sulphur compounds
The construction of concrete slabs-on-ground in Australia requires often requires good control of setting times and bleeding rates in lean concretes using air entraining admixtures to minimize the potential for plastic cracking. Whilst this has been successfully achieved on the East Coast of Australia for decades with fly ash concretes a new source of fly ash from the Collie power station located on the West Coast proved difficult to use. The University of New South Wales undertook an investigation into the cause of sensitivity and variability exhibited by key properties of concretes that contained Collie fly ash. Testing of the basic properties of three Collie fly ash samples and one sample of fly ash from Eraring power station was used to characterize the materials and the samples separated into specific size fractions with further testing undertaken. Testing was undertaken included LOI, density, colour, fineness, carbon content, sulphur content, and physical features using SEM. The investigation concluded that the causes of the admixture sensitive behavior of Collie fly ash concrete is not simply due to the presence of carbon but the high surface area and low density of these carbon particles in association with the presence of oxidisable sulphur compounds.