Abstract: Conventional ultra high volume fly ash (UHVFA) dam concrete is a kind of promising ecological and energy-saving mass concrete, but its thermal expansion coefficient (TEC) at early age is difficult to measure by a standard testing method. In this work, we test the specimens on a temperature-stress testing machine (TSTM) for the benchmark fly ash (FA) concrete and the UHVFA concrete and separate thermal deformation and autogenous deformation under two curing temperature histories: adiabatic mode and temperature matching curing (TMC) mode. The TECs of the two mass concretes at early age are determined by the strain difference and temperature difference at different ages under the two temperature histories, and a time-varying TEC model is constructed. It is shown that at early age, the TECs of the two concretes are time-varying, first growing up to the maximum at the initial setting time, then rapidly decreasing to the minimum and growing again, and finally tending to be stable. In the heating stage the TEC average of UHVFA is greater than that of FA, while it is smaller during cooling. And in the heating stage, the TEC is smaller at both the initial and final setting times. In general, with the increasing volume of fly ash, the TEC shows a decreasing tendency.

Key words: ultra high content fly ash mass concrete, TSTM test；thermal expansion coefficient (TEC), TEC model