Concrete mixture proportioning with water-reducing admixtures to enhance durability: A quantitative model

Durable concrete is characterized as concrete with a low porosity, in which the individual grains of cement are tightly packed before initiation of hydration. Such concrete is typically characterized by a low watercement ratio, which is described herein on a volumetric, rather than a mass basis. Low watercement ratio is responsible for improved mechanical properties and for enhanced durability. It is shown, however, that use of a low watercement ratio necessitates either a sacrifice in workability, or the use of high cement content, neither a desirable consequence. The use of water-reducing admixtures is discussed as an alternative. The use of normal-, mid-, and high-range waterreducing admixtures is described in the context of a series of graphs based on the water demand relationships implicit in the ACI 211.1 procedure for proportioning mixtures. By introducing the concept of water-reducer ‘effectiveness’, these graphs can be used to describe the differences among normal, mid-range, and high-range water reducers, and can be used to illustrate the use of water reducers to reduce water content, reduce watercement ratio, and to increase workability.