Design of high-volume fly ash concrete for a massive foundation slab

High-volume fly ash concrete was designed for a concrete foundation slab, and a mock-up of 4·5 m × 4·5m × 4·5 m was cast in order to determine the temperature variation of concrete and evaluate the cracking risk of the slab. The addition of a high amount (45%) of fly ash decreased the temperature rise of concrete significantly. The maximum temperature rise of the mock-up was only 41·3°C. Proper thermal insulation measures effectively decreased the cooling rate of the concrete mock-up. The finite-element calculation results showed that the temperature gradient on the surfaces and edges of the mock-up was bigger than its other parts, and the maximum tensile stress appeared on the edge of the upper surface. The cracking risk of concrete was very low because the tensile stress at any position of the mock-up was smaller than the tensile strength of concrete. There was no visible cracking on the upper surface of the mock-up. Decreasing the temperature rise of concrete by adding a large amount of fly ash and decreasing the cooling rate were effective ways to reduce the cracking risk of massive concrete.