The evaluation of the crack-bridging ability of exposed roof coatings

Abstract

A major problem with single-layerin situ applied or prefabricated roofing membranes, exposed to intensive solar radiation in subtropical climates, is their long-time ability to bridge over working cracks. A performance test, suitable for accelerated testing and evaluation of the crack-bridging ability of roofing membranes, exposed to real climatic conditions and experience gained with its use are described. The testing device consists of a reinforced concrete slab measuring 100 cm × 50 cm × 5 cm on free-moving horizontal supports. A transverse crack of controlled width is induced at mid-length. The membrane under test can be applied before or after inducing the crack. Crack opening and closing is caused by differential thermal movement between the concrete slab and two black aluminium profiles enclosed in “solar boxes”, connected lengthwise at both sides of the slab. The crack opens on sunny days to about 0.7 mm during daytime and closes at night. Typical temperature variations, and resulting crack widths recorded during the calibration period, are discussed. Included also are results of comparative tests perormed with the device on different roofing materials. It was concluded, from experience gained so far with the device, that for a designated crack-width movement the crack-bridging ability of different roofing membranes can be compared and evaluated after only a few months of summer exposure.