b'TECHNICAL & RESEARCHa height of 53-inches and impacted the samples onef.(3) 16x16 modified bitumen with wood fiber time in each quadrant. The steel missile equates tocover boardnewa 2-inch diameter hailstone, as both have an impactAll samples were labeled, using a sample naming energy of 30.0 J [22 lbf-ft].convention consisting of sample age, membrane Sample weights, granule counts, and exposedtype, cover board type, and sample number (i.e. bitumen measurements were taken both before and5-MB-G-2), and then photographed. after the impact to capture any changes the impact caused. Desaturation of the membrane samples was then conducted to remove the bitumen and make visual observations of the membrane reinforcement. Additionally, microscopy of the cross sections was performed on portions of each sample at the areas of impact. Sample ProcurementAll samples were provided by MRCA T&R Committee members and consisted of two-ply modified bitumen membranes applied in cold adhesive, all from a single manufacturer. The samples contained two cover board types: -inch thick gypsum and -inch thick wood fiber, along with polyisocyanurate insulation.Figure 1. Sample trimmed and divided into four quadrants The ages of the samples varied, consisting of new,with 3-inch diameter impact zones. approximately five years old, and approximately2.Test Sample Preparation. All samples were ten years old. All the samples came from in-serviceneatly trimmed to a size of 12-inch x12-inch in roofs from Midwest environments (in lieu of artificialthe laboratory and graphically divided into (4) weathering), with the exception of the new samples6-inch x 6-inch quadrants with 3-inch-diameter which were fabricated for the purposes of this testing. circles as impact zones (Figure 1). The as-Testing Procedure received samples were larger than the test The testing procedure consisted of the followingsample size to eliminate any negative edge seven steps: effects from the removal process. Each zone was used for a different purpose throughout the 1. Initial Documentation. A total of 18 samples weretesting process. Zone 1 (upper left) was used received and consisted of the following: for image analysis and manual granule counts, Zone 2 (upper right) for image analysis, Zone 3 a. (3) 16x16 modified bitumen with gypsum cover(lower left) for image analysis and desaturation, board10 years old and Zone 4 (lower right) for image analysis b. (3) 16x16 modified bitumen with wood fiber and cross-section microscopy, all of which as cover board10 years old described in the following steps. c. (3) 16x16 modified bitumen with gypsum cover3. Pre-Impact Weights and Granule Counts. board5 years old Weights and granule counts were obtained for each sample prior to impact. Weights were d. (3) 16x16 modified bitumen with wood fiberobtained using a scale (Figure 2). Granule counts cover board5 years old were obtained through a process called image analysis which uses a computer program to e. (3) 16x16 modified bitumen with gypsum coveranalyze a high-resolution photograph to identify boardnew features of interest (granules) within a 3-inch Continued on page 40'