EVOLUTION OF THE THERMAL-EXPANSION COEFFICIENT OF CONCRETE AS A FUNCTION OF ITS MATURITY AT VERY EARLY AGES

In the first hours after its production and without external loading, the concrete suffers volume changes due to (i) the formation of cement hydrates (autogenous shrinkage), (ii) the heat produced by the reaction, and (iii) air drying. Structural detrimental cracks can appear if these deformations are restrained. The experimental determination of the autogenous shrinkage, without external drying, requires, for each step of hydration, knowledge of the thermal strains, i.e., the thermal expansion coefficient. After a review of the relevant literature, a method is proposed for the continuous determination of the thermal expansion coefficient. This method contains an experimental part and a measurement procedure based on the hypothesis that there is no inter-dependence between autogenous shrinkage and thermal strain. After this calculation, an expression is derived for the thermal expansion coefficient as a function of the concrete maturity. This makes it possible to subtract the thermal strains front the total strains measured, in order to obtain the autogenous shrinkage as a function of the maturity. The method is then applied to a normal concrete.