Elastic coatings: Crack bridging performance (NT POLY 184)

Abstract

  This test method specifies the determination of the performance of elastic coatings with respect to their resistance to certain repeated movements of a substrate crack. The method is mainly relevant for testing materials which are intended for the bridging, and thereby sealing, of cracks in building constructions of concrete and masonry materials. The description that follows is adapted for such materials. The method is particularly suitable for cases where the cracks alternately widen and narrow due to changes in external temperature. It simulates fairly well such practical conditions, as it relies on the differential thermal movement of two metals for producing the movement of a test crack. The movement is effected by cyclic changes in temperature in a programmable freeze-thaw or heating-cooling type of climate chamber. A test piece is fixed in a certain position on a special metallic equipment and subjected to a cyclic movement in a climate chamber. The equipment described, specially developed for this method, effects a crack movement of a certain rate with respect to the change in temperature. The method can be classified as a fatigue test, involving tensile strength, elasticity and adhesion. The results are expressed as the number of cycles, at specified conditions, to failure identified as partial or complete rupture of the coating along or in the vicinity of the substrate crack.