Couplings in early-age concrete: From material modeling to structural design

Couplings in early-age concrete are the cross-effects between the hydration reaction, temperature evolution and deformation which can lead to cracking. They involve complex chemophysical mechanism that operate over a broad range of scales, from nanometer to meter. This paper explores 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 framework of chemoplasticity, the cross-effects in the constitutive model are derived from Maxwell-symmetries, and characterize the autogeneous shrinkage, hydrate heat and strength growth due to the chemo-mechanical, thermo-chemical and chemo-plastic couplings. These couplings at a material level can be determined from standard material tests, provided that the order of coupling is known. This is shown by considering adiabatic calorimetric experiments and isothermal strength growth tests, which lead to identify an intrinsic kinetics function that characterizes the macroscopic hydration kinetics of concrete. Finally, an example of application of the model to large-scale finite element analysis of concrete structures is presented, which clearly shows the consequences of thermochemo- mechanical couplings for the engineering design of concrete structures at early ages. c 1998 Elsevier Science Ltd. All rights reserved.