Abstract
The cause of blistering in modified bituminous roofing membrane systems was investigated. Membrane samples were removed from several existing modified bituminous roofs containing blisters. Their mechanical behavior was characterized by tensile tests. Gas content within the blisters were collected in canisters in the field & their chemical composition was determined by quantitativelyh by Gas Chromotography Mass Spectroscopy. Mechanical testing indicates that blister formation does not seem to depend on the strength of the modified bituminous membrane. Also, the existence of blisters did not reduce the strength of the membrane, at lesaast not where the blister remainted intact. GC/MS revealed that the gas within the blisters was composed mainly of air and water vapor, with a negligible amount of volatile organic compounds. The relative humidity of the blister gas ranged from 30-75%. These findings indicated that the mechanism of blister formation and growth in modified bituminous roofs is possibly the same as that in built-up roofing where water vapor promotes blister growth by exerting cyclie pumping action to the blister following the dirunal changes in temperature. The physical properties of the membranes and the mopping asphalt were also studied. The polymer contnet in the mod bit membranes was determined by infrared spectroscopy to be 6-11 weight percent. The blending between the polymer and the asphalt was found to be uniform in most cases as examined by ultraviolet florescent microscopy. Both polymer content and blending were not signicantly affected by a combination of aging, weathering and stesses. The softening points of the mopping asphalts exceeded the upper limit of Type IV asphalt in most cases. The high values may be due to aging of the asphalts. The quantity of mopping asphalt was determined to be 1-2mm or 1-2 kg/m2 from examination of polished cross-sections of the membranes using an optical microscope. The high values indicated that the application temperatures might have been too low and hence the viscosity of the asphalt too high in many cases. These factors could promote mopping skips. Visual examination of the membrane surface inside the blisters revealed three types of failure surfaces: cap shet / mopping interface, discontinuities in moppinog and uncoated spot. They were due to mopping at improper viscosity and proo wetting between the mopping asphalt and the membranes.
The cause of blistering in modified bituminous roofing membrane systems was investigated. Membrane samples were removed from several existing modified bituminous roofs containing blisters. Their mechanical behavior was characterized by tensile tests. Gas content within the blisters were collected in canisters in the field & their chemical composition was determined by quantitativelyh by Gas Chromotography Mass Spectroscopy. Mechanical testing indicates that blister formation does not seem to depend on the strength of the modified bituminous membrane. Also, the existence of blisters did not reduce the strength of the membrane, at lesaast not where the blister remainted intact. GC/MS revealed that the gas within the blisters was composed mainly of air and water vapor, with a negligible amount of volatile organic compounds. The relative humidity of the blister gas ranged from 30-75%. These findings indicated that the mechanism of blister formation and growth in modified bituminous roofs is possibly the same as that in built-up roofing where water vapor promotes blister growth by exerting cyclie pumping action to the blister following the dirunal changes in temperature. The physical properties of the membranes and the mopping asphalt were also studied. The polymer contnet in the mod bit membranes was determined by infrared spectroscopy to be 6-11 weight percent. The blending between the polymer and the asphalt was found to be uniform in most cases as examined by ultraviolet florescent microscopy. Both polymer content and blending were not signicantly affected by a combination of aging, weathering and stesses. The softening points of the mopping asphalts exceeded the upper limit of Type IV asphalt in most cases. The high values may be due to aging of the asphalts. The quantity of mopping asphalt was determined to be 1-2mm or 1-2 kg/m2 from examination of polished cross-sections of the membranes using an optical microscope. The high values indicated that the application temperatures might have been too low and hence the viscosity of the asphalt too high in many cases. These factors could promote mopping skips. Visual examination of the membrane surface inside the blisters revealed three types of failure surfaces: cap shet / mopping interface, discontinuities in moppinog and uncoated spot. They were due to mopping at improper viscosity and proo wetting between the mopping asphalt and the membranes.
Date
3/1998
3/1998
Author(s)
NRCA / NRCC
NRCA / NRCC
Page(s)
38
38
Keyword(s)
blistering; SBS modified bitumen; physical properties; mechanical test; asphalt
blistering; SBS modified bitumen; physical properties; mechanical test; asphalt