TECHNICAL & RESEARCH a height of 53-inches and impacted the samples one time in each quadrant. The steel missile equates to a 2-inch diameter hailstone, as both have an impact energy of 30.0 J [22 lbf-ft]. Sample weights, granule counts, and exposed bitumen measurements were taken both before and 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 Procurement All 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: ½-inch thick gypsum and ½-inch thick wood fiber, along with polyisocyanurate insulation. The ages of the samples varied, consisting of new, approximately five years old, and approximately ten years old. All the samples came from in-service roofs from Midwest environments (in lieu of artificial weathering), with the exception of the new samples which were fabricated for the purposes of this testing. Testing Procedure The testing procedure consisted of the following seven steps: 1. Initial Documentation. A total of 18 samples were received and consisted of the following: a. (3) 16”x16” modified bitumen with gypsum cover board – 10 years old b. (3) 16”x16” modified bitumen with wood fiber cover board – 10 years old c. (3) 16”x16” modified bitumen with gypsum cover board – 5 years old d. (3) 16”x16” modified bitumen with wood fiber cover board – 5 years old e. (3) 16”x16” modified bitumen with gypsum cover board – new f. (3) 16”x16” modified bitumen with wood fiber cover board – new All samples were labeled, using a sample naming convention consisting of sample age, membrane type, cover board type, and sample number (i.e. 5-MB-G-2), and then photographed. 2. Test Sample Preparation. All samples were neatly trimmed to a size of 12-inch x12-inch in the laboratory and graphically divided into (4) 6-inch x 6-inch quadrants with 3-inch-diameter circles as impact zones (Figure 1). The as- received samples were larger than the test sample size to eliminate any negative edge effects from the removal process. Each zone was used for a different purpose throughout the testing process. Zone 1 (upper left) was used for image analysis and manual granule counts, Zone 2 (upper right) for image analysis, Zone 3 (lower left) for image analysis and desaturation, and Zone 4 (lower right) for image analysis and cross-section microscopy, all of which as described in the following steps. 3. Pre-Impact Weights and Granule Counts. Weights and granule counts were obtained for each sample prior to impact. Weights were obtained using a scale (Figure 2). Granule counts were obtained through a process called “image analysis” which uses a computer program to analyze a high-resolution photograph to identify features of interest (granules) within a 3-inch Continued on page 40 Figure 1. Sample trimmed and divided into four quadrants with 3-inch diameter impact zones.
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