THE USE OF FLY ASH, SILICA FUME, SLAG AND OTHER MINERAL BY-PRODUCTS IN CONCRETE

Abstract

Portland cement is a highly energy-intensive product, and therefore, in an energy-hungry world considerable efforts are being made to find substitute materials for the partial replacement of cement in concrete. Some of the most promising substitutes or supplementary cementing materials are high- and low-calcium fly-ashes, ferrous- and non-ferrous slags and condensed silica fume. This paper presents a state-of-the-art review on the use of these mineral by-products in concrete, and the role of these materials in the less developed countries. The physical and possolanic properties of the supplementary cementing materials are outlined, and their effect on the properties of fresh and hardened concrete discussed. Particular emphasis is placed on the use of condensed silica fume, a relatively new addition to the family of supplementary cementing materials. The contribution of superplasticizers to achieving high-strength concrete incorporating fly-ash and silica fume is mentioned. Reference is made to the currently available specifications for these materials both in North America and Europe, and their limitations discussed. The advantages and limitations in the use of supplementary cementing materials as separately batched ingredients at a ready-mixed concrete plant, versus the use of blended cements are discussed, and North American trends in this field are mentioned briefly. It is emphasized that additional quality control measures are needed when fly-ash, slag and silica fume are incorporated in ready-mixed concrete. This is especially so when chemical admixtures are also incorporated in concrete made with supplementary cementing materials. (Author/TRRL)