Predictive Service Life Tests for Roofing Membranes

April 29, 2005
Publication: Tenth International Conference on the Durability of Building Materials and Components, Royal Institute of Technology, Leon, France
Author(s): Cash, Carl G. Arthur Davies David Niles Bailey D.M. Delgado A.H. Paroli R.M.

Abstract: Twelve roofing membranes, including poly [vinyl chloride], asphalt glass-felt built-up, thermoplastic polyolefin, atactic polypropylene polymer modified asphalt, styrene-butadiene-styrene block copolymer modified asphalt, and ethylene-propylene-diene rubber membranes were exposed to oven heat, ultra-violet and condensing humidity environment, and two and four-year outdoor exposure at United States Department of Defense sites in Phoenix, Arizona (hot and dry climate); Key West, Florida (hot and moist climate); and Champaign, Illinois (moderate mid-continent climate). Selected mechanical properties were measured before and after each exposure. Each membrane was rated before and after exposure and the membranes were ranked as to relative performance in these physical tests. The physical tests performed include load-strain, dynamic impact resistance, moisture absorption, and glass transition temperature. Identical test methods were used for each membrane to make the physical properties directly comparable. With the exception of the TPO (thermoplastic polyolefin) membrane samples, the mean changes in the load to first peak of the membranes at each site had a 0.994 correlation with the before exposure, after oven heat aging, and after condensing ultra violet exposures. The TPO membrane load to first peak more than doubled after two years of exposure and then dropped dramatically after four years of exposure. The overall results show that testing membrane samples before and after oven heat aging and condensing ultra violet exposures do not accurately predict the final ratings of a dissimilar group of membranes exposed outdoors in a broad variety of climates. These accelerated aging techniques have shown to often be valuable when used to evaluate similar membranes. The single parameter that seems most useful in tracking weathering is the water absorption test. The average percent water absorbed by the membranes increase in direct proportion to exposure time with a linear coefficient of 0.999. We hope to be able to conclude this six-year study as soon as the samples finish weathering and report our results to interested parties.