ABSTRACT
The design of concrete mixtures involves choosing appropriate proportions of ingredients for particular strengths, long-term qualities, and performance of the concrete produced. Several factors determine these properties. They include the following parameters, which are summarized in Figure 6.1:
• Quality of cement • Proportion of cement in relation to water in the mix (water/cementitious material ratio) • Strength and cleanliness of aggregate • Interaction or adhesion between cement paste and aggregate • Adequate mixing of the ingredients • Proper placing, finishing, and compaction of the fresh concrete • Curing at a temperature not below 50°F while the placed concrete gains strength • Chloride content not to exceed 0.15% in reinforced concrete exposed to chlorides in service and
1% in dry protected concrete
A study of these requirements shows that most control actions have to be taken prior to placing the fresh concrete. Because such control is governed by the proportions of ingredients and the mechanical ease or difficulty in handling and placing the concrete, the development of criteria based on the theory of proportioning for each mix should be studied. Most mixture design methods have become essentially only of historical and academic value. The two universally accepted methods of mixture proportioning for normal weight and lightweight concrete are the American Concrete Institute’s methods of proportioning, described in their recommended practices for selecting proportions for normal weight, heavyweight, and mass concrete, and in the recommended practice for selecting proportions for structural lightweight concrete (ACI Committee 211, 1991a,b; ASTM, 1993; Nawy, 1996).
