Effects of thermal shrinkage on built-up roofing

Abstract

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Thermal-shock resistance for bituminous built-up roofing membranes :

“…The difference in the values of the linear thermal expansion coefficients in respect to the orientation of the felt in a built-up membrane has been report [2], The values of the engineering properties and those of the Thermal-Shock Resistance Factors reported here also reflected the anisotropic behavior of a built-up roofing membrane. The difference in value of these properties between the "machine" (longitudinal) and the "across machine" (transverse) directions of both the organic and asbestos based felts appeared to be sufficiently large as to result in differences in performance in field service.…”

“…The linear thermal expansion measurements were made on duplicate dumbbell-shaped specimens prepared as described in section 2.1, using a 5-inch gage length in accordance with a procedure described by Cullen [2].…”

“…Moseley [1]-^has indicated that tension splits which occur in the built-up membrane are frequent causes of failure. Cullen [2] suggested that the thermal movement which occurs in a bituminous built-up roofing membrane due to rapid temperature changes is often a contributing factor in tension splits.…”

“…Moseley [1]-^has indicated that tension splits which occur in the built-up membrane are frequent causes of failure. Cullen [2] suggested that the thermal movement which occurs in a bituminous built-up roofing membrane due to rapid temperature changes is often a contributing factor in tension splits.He proposed the utilization of a Thermal-Shock Resistance Factor [3] to predict the ability of a built-up membrane to tolerate, without rupture, the forces induced by such temperature changes [4] The higher the breaking load, the lower the apparent linear thermal expansion coefficient and the lower the modulus of elongation the more resistant the membrane will be to rupture under thermal changes. These parameters were combined in a Thermal-Shock Resistance Factor given by the following equation ( The development of the Thermal-Shock Resistance Factor has been reported, and values for three conventional built-up membranes were given at temperatures of -30°F (-34 .4°C ) , 0°F (-17.8°C), 30°F (-1.1°C), and 73°F (22.8°C) [6].…”

“…Therefore, it appears that the ability of components of the roof system to conduct heat to and away from the roofing membrane will, by regulating the amount and rate of temperature change of the membrane, affect the service life of the membrane. The thermal diffusivity of the substrate would appear to be a relevant factor in the ThermalShock Resistance Factor and may be Included by rewriting equation (2) where TRSF 3 _S Ma K = thermal conductivity of the substrate p = specific heat of the substrate d = density of the substrate.Based on the foregoing comments the authors suggest the above equation (3) as a possible useful revision of the Thermal-Shock Resistance Factor and feel that it should be tested by further investigations of the engineering behavior of the whole roof assembly and of the interrelationship of its components under different thermal exposures. ACKNOWLEDGMENT…”