The recent trend of civil engineering to make larger structures has brought the increase in number of constructions of massive reinforced concrete members. Since higher strength is required for these structures than for concrete dams, the rich mix concrete must be used for them. Thermal stabilization of these structures is of prime importance, but any of the methods used for preventing thermal cracks in dams is not generally applicable to them for several reasons. The data of thermal properties of rich mix concrete are needed to establish a suitable method.
The thermal diffusivity, coefficient of thermal expansion, and compressive strength of concrete specimens with cement contents from 250 to 700kg/m3 were measured in this study. These properties were influenced considerably by the cement content: with increasing cement content, the diffusivity tends to decrease and the expansion and the strength to increase. Stronger concrete usually exhibits lower diffusivity and higher expansion, so that it is more liable to cracking.
Concrete can be regarded as a composite material composed of cement paste and aggregates. The diffusivity of the paste is lower than that of aggregate and its expansion is higher. Furthermore, the higher the water cement ratio of the paste, the lower the diffusivity and the higher the expansion slightly. For the constant consistency of concrete, however, the higher the water cement ratio, the higher the diffusivity and the lower the expansion, because of the less mix quantity of the paste per unit volume of concrete. To improve the thermal properties, a polycyclic sulfonate, a powerful water reducing agent, was tried in this experiment. As the result of admixing it, a marked improvement in thermal properties was achieved without changing consistency and strength of concrete.