Eindhoven University of Technology, the Netherlands, Department of Masonry structures

As part of the research project concerning crack control in veneer walls the influence of hardening conditions on the physical behaviour of masonry has been investigated. If cracks are allowed, the crack width should be limited to an acceptable value. If not, movement joints are needed. For the spacing of movement joints as well as for the crack width, design rules should be based on information about the detailing of the veneer walls (geometry, restrained deformation) and on the physical and mechanical characteristics of the masonry used (shrinkage, creep, relaxation, tensile strength). Until now, no such scientific based design rules have been developed. In this research the influence of hardening conditions on the physical and mechanical properties of mortar (and masonry) were studied, with a focus on the shrinkage by hardening, drying and wintertime outdoor conditions. Mortar made in steel moulds (according to European Standards) has been investigated under different moisture conditions during hardening and compared to mortar hardened between clay bricks. The properties of mortar prisms, brick-mortar couplets and wallettes were investigated for the evaluation of the influence of water suction and restrained deformation by the bricks. During the test period the weight, the deformation and the strength of the specimens were determined. In the experimental research a significant influence of the hardening conditions (moisture conditions and clay brick contact) on the characteristics of mortar and masonry was found. In some cases shrinkage was reduced by a factor 2. Consequently, covering masonry and pre-wetting may reduce cracking and may allow a larger spacing of movement joints. The strains measured in the clay brick masonry couplets and wallettes were not higher than 0,15 mm/m. Therefore it is not necessary placing movement joints in this type of masonry because of shrinkage by hardening and drying and thermal contraction in wintertime.

Key words
Mortar, hardening conditions, movement joints, crack control