Performance of blended cement concretes prepared with constant workability

摘要

The use of supplementary cementing materials, such as silica fume, fly ash, blast furnace slag, and natural pozzolans, has been promoted by their technical and economic advantages. However, in certain parts of the world, where these materials are not available locally, their utilization is solely based on their technical superiority. The practice in such regions is to replace part of the cement with the selected supplementary cementing materials while maintaining constant water-to-cementitious materials ratio. In such cases, the advantage of a reduction in the water requirement of certain materials is not utilized. In the reported study, fly ash, silica fume, or a highly reactive finely pulverized fly ash replaced part of the cement. The concrete mixtures were designed for a constant workability of 75-100 mm slump. The performance of ordinary Portland cement (OPC) and silica fume (SF), fly ash (FA) and very fine fly ash (VFFA) cement concretes was evaluated by measuring the compressive strength development and reduction in both compressive strength and pulse velocity after exposure to moisture and thermal variations, and sulfate (SO_4~- = 1%, 2%, and 5%) solutions. The effect of curing regime, namely water ponding and application of a curing compound, was also evaluated. It was noted that the water requirement of FA cement concretes was less than that of OPC and SF cement concretes. Consequently, the mechanical properties and durability characteristics of the former cements were better than those of the latter cements. It was also noted that a longer curing period, prior to the application of a curing compound, is beneficial to OPC, SF, FA, and VFFA cement concretes. Curing with water tended to improve the quality of OPC, SF, FA, and VFFA cement concretes; and as the curing period increased the quality improved further.