ABSTRACT
Abstract For the estimation of thermal cracking detailed knowledge about the behaviour of early age concrete under high tensile stresses is necessary. For the calculation of restraint stresses during the hydration process the crack development and the pronounced viscoelasticity must be taken into account. Test results of axial tensile tests, creep and relaxation tests under high tensile stresses wil be reported. Finally a model based on linear creep theory is presented which is applicable for the prediction of creep and relaxation at early age concrete. Keywords; Degree of Hydration, High Tensile Stresses, Cracking, Creep, Relaxation, Principle of Superposition
In massive concrete structures high temperatures are generated in course of the hydration of concrete. In case of restraint high tensile stresses may develop with the consequence of cracking. For the estimation of the occurrence of cracking, models for the material properties of concrete at early age are essential. Such models comprise:
- temperature development T(t) in the structure - degree of hydration a(T(t)) - mechanical properties, such as the tensile strength
f .^ (Qf), compressive strength f^W and modulus of elasticity E^^(a)
- crack development - creep and relaxation under high tensile stresses
The material models must be developed on basis of experiments. For this axial tensile tests, creep and relaxation tests under high initial tensile stresses in the ascending branch of the stress-strain relationship were performed.
