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The prevalence of splitting in built-up roofing during recent years has prompted special studies to be undertaken by the Division of Building Research to determine the causes for these serious failures. The determination of certain engineering properties of the components used in built-up roofing and the complete membrane have received special attention. To determine these properties, a roller-coating technique was developed to prepare membranes and a special grip arrangement was constructed for the tensile studies. These studies were made at 75 F and at −20 F, using two rates of straining.
The results emphasize the secondary role of the bitumen in the strength of the membrane. At both temperatures the felts contribute 80 to 90 per cent of the strength of the membrane, although the actual strengths increased by 70 to 250 per cent as the temperature changed from 75 F to −20 F. The small amount of creep and of notch sensitivity also serve to confirm the secondary role of the bitumen.
Jones, P. M.
Organic Materials Section, Division of Building Research, National Research Council, Ottawa,