Mark G. Vangel
James J. Filliben
Statistical Engineering Division, ITL
Walter J. Rossiter
Building Materials Division, BFRL
Adhesively-bonded EPDM (a rubber material) is widely used for low-slope industrial roofing. There are two main types of adhesive systems for seams on these roofs: a liquid adhesive, and several varieties of tape adhesive. Liquid adhesive is widely used, but it is volatile and relatively expensive to apply. An objective demonstration that tape adhesives are at least as reliable as the liquid will greatly increase the use of these adhesives. A consortium of NIST, professional roofing trade associations, and roofing adhesive manufacturers was formed, in part, to perform such a study.
The chosen measure of performance for the experimental seams is creep lifetime; i.e. the time-to-failure under a constant load. In Phase I of this investigation, specimens from two tape systems and a liquid adhesive were tested in creep-rupture at various loads. The main conclusion of this phase was that the tape-bonded seams appear to perform at least as well (in terms of creep life) as adhesive-bonded seams.
Phase II of this investigation concerns the performance of tape-bonded seams under laboratory simulations of field preparation conditions. A 25-1 fractional factorial experiment involving application factors was designed and analyzed, for each of 22combinations of material factors. The application factors are
The figure displays the means of eight replicates
for ordered factor combinations, with the material
factors indicated by plot symbols. The average
lifetime for liquid adhesive specimens is taken from
Phase I of this study. It appears that if
tape systems are well prepared (primed, cleaned,
etc), then tape-bonded seams can be expected to have
creep-life at least comparable to that of
well-prepared adhesively-bonded seams.
Figure 18: Creep-rupture lifetime of tape-bonded EPDM seams for various combinations of application conditions.
Date created: 7/20/2001