COUPLINGS IN EARLY-AGE CONCRETE - FROM MATERIAL MODELING TO STRUCTURAL DESIGN

Couplings in early-age concrete are the cross-effects between the hydr ation reaction, temperature evolution and deformation which can lead t o cracking. They involve complex chemo-physical mechanism that operate over a broad range of scales, from nanometer to meter. This paper exp lores these thermo-chemo-mechanical cross-effects from the macroscale of engineering material modeling (the typical scale of laboratory test specimens) to the level of structural design. Set within the framewor k of chemoplasticity, the cross-effects in the constitutive model are derived from Maxwell-symmetries, and characterize the autogeneous shri nkage, hydrate heat and strength growth due to the chemo-mechanical, t hermo-chemical and chemo-plastic couplings. These couplings at a mater ial level can be determined from standard material tests. provided tha t the order of coupling is known. This is shown by considering adiabat ic calorimetric experiments and isothermal strength growth tests, whic h lead to identify an intrinsic kinetics function that characterizes t he macroscopic hydration kinetics of concrete. Finally, an example of application of the model to large-scale finite element analysis of con crete structures is presented, which clearly shows the consequences of thermo-chemo-mechanical couplings for the engineering design of concr ete structures at early ages. (C) 1998 Elsevier Science Ltd. All right s reserved.