INFLUENCE OF CEMENT BLEND AND AGGREGATE TYPE ON STRESS-STRAIN BEHAVIOR AND ELASTIC MODULUS OF CONCRETE

This technical paper presents the results of an experimental investigation in which four aggregate types--granite, dolomite, andesite, and quartzite--were used in concretes made with four cement types--ordinary portland cement (OPC) and blends of OPC with silica fume, slag, and fly ash. The influence of these mix variables on short-term stress-strain behavior and concrete elastic modulus E was evaluated. Results indicate that E was markedly dependent on aggregate and cement type, and that age played an important role. Andesite and dolomite yielded considerably stiffer concretes than granite or quartzite. Silica fume produced concretes of similar or slightly greater stiffness than OPC, but slag and fly ash reduced stiffness, particularly at early ages, on an equal strength or water-cement ratio (w/c) basis. The most plausible mechanism to explain the results would be that silica fume densifies the interfacial zone between paste and aggregate, while slag and fly ash do not have the same ability in this regard. A practical design approach for engineers to estimate concrete E for the various combinations of materials is also given.