Heat and moisture transfer in early age cement paste

International audienceThe hydration reactions within a cementitious material are both exothermal and thermoactivated. Thus at early age, an increase in the medium temperature is observed because of the heat of hydration release. Moreover, concrete is a granular assembly composed of inert phases (sand, aggregate...) and a reactive phase (pure or composed cement paste). The evolutions of early age concrete temperature and moisture are thus influenced by the cement paste as well as the inert phase thermophysical properties (common aggregates, lightweight aggregates or even concretereinforcing bar). The role of the boundary conditions can also be of great importance. Consequently, the hydration kinetics can be heterogeneous in the medium, yielding temperature and moisture heterogeneities able to influence the cement paste hydration degree.In this paper, we propose to study the influence of aggregates on the hydration kinetics of pure or blended cement pastes containing fly ash at early age. The first part is dedicated to the determination of the blended cement paste hydration properties (apparent activation energy, chemical affinity function). Then, the temperature, moisture and hydration degree fields are numerically computed by means of a 2-D transfer model applied to a square medium submitted to boundary conditions of the second kind. The calculation is carried out by taking into account the reaction water consumption, heat release and the influence of aggregates. The computation shows that the fields can exhibit strong heterogeneities depending on the thermophysical properties of aggregates, and that fly ash can help limiting the medium temperature increase