HEINRICH METZEMACHER Industrieverband Werktrockenmortel e.V., Koln

In order to evaluate the resistance of masonry to cracking in the presence of slowly developing restraint forces, information is needed on the level of stress imposed and the stress-strain behaviour with regard to tensile strength. Whereas numerous publications are available on shrinkage as a main cause of tensile stresses leading to cracks and the stress-strain behaviour under tensile stressing, for some time definite data have been lacking on the visco-elastic behaviour of the material, the long-term stress reduction by relaxation. The reasons for this are the difficulties arising in the tests, mainly the very small stresses and strains, and in particular the fact that unavoidable shrinkage processes are superimposed on the relaxation. For the solution of this problem a mathematical equation has been developed and tests on mortar and masonry specimens have been carried out.