THE INFLUENCE OF CEMENT SOURCE AND SLAG ADDITIONS ON THE BLEEDING OF CONCRETE

Excessive bleeding of plastic concrete can result in problems with finishing and a weak surface layer particularly on flat slabs, a reduction in the bond between the steel and the concrete and ana increased risk of the occurrence of plastic settlement cracks. Bleeding is controlled primarily by the fine material in the mix in particular, the quantity and reactivity of the cement. The partial replacement of OPC by ground granulated blast furnace slab(ggbs) leads to a reduction in the rate of hydration and, as most other worker have reported, an increase in bleeding. However the authors have found that if comparisons are made on the basis of an equal 28 day compressive strength, and not on equal water/cement ratio as is usually the case, there are little if any differences between the OPC and the slag cement concretes. The reason for this believed to be due to the increase in the overall cement content of the slag cement concretes which is necessary inorder to achieve parity in strength at 28 days with the OPC concretes.