ABSTRACT
The calculation of thermal stresses and estimation of the cracking risk demands a lot of input data, such as the thermal and mechanical proper ties of the concrete. However, the most important concrete properties at early ages as the E-modulus and relaxation are changing continuously in a very wide range. Their developments cannot be predicted by generally valid formulas. This renders stress-computations for concrete at early ages vulnerable to unrealistic results. Because of this two ways have been pursued in the last few years:
2.1.1 Restraining Laboratory Tests
Restraint stresses and the cracking tendency of a concrete due to tempera ture changes as well as shrinkage are tested in direct restraining tests with special equipments (cracking frame or Temperature-stress testing machine). By this the influence of different concrete constituents, mixes and temperature on the development of the restraint stresses and on the cracking tendency can be directly measured.
