diameter circle (Figure 3). A black and white 
image was created from the original color image, 
a process called color thresholding. This enabled 
the computer program to determine quantitative 
information regarding the image (granule counts 
and exposed bitumen area). In addition to image 
analysis, manual counts of the granules were also 
conducted. 
4.	Impact Testing. A 5-pound steel missile 
released from a height of 53-inches impacted 
each quadrant of the sample per ASTM D3746. 
The steel missile was held at the top of the drop 
tube with a pin until the sample was ready to be 
impacted. A laser guide was used to align the 
missile with the center of the impact zone. See 
Figure 4.
5.	Post-Impact Weights and Granule Counts. 
Weights of the samples and granule counts at 
each impacted zone were obtained a second time 
for each sample following impact. In addition to 
weighing the full samples using a precise scale, 
granules equal in number to those lost during 
impact were also weighed. Comparisons were 
made between pre- and post-impact images 
(Figures 5 and 6). 
6.	Desaturation. Desaturation is the process 
of removing the bitumen from the membrane 
samples using a solvent to expose the 
reinforcement. One quadrant of each sample was 
desaturated to allow the membrane reinforcement 
to be visually inspected for damage due to the 
impact (Figures 7 and 8). 
www.mrca.org  —  Midwest Roofer
40
TECHNICAL & RESEARCH
Continued from page 39
Figure 2. Weighing of sample.
Figure 3. Granule identification 
through image analysis.
Figure 4. Testing apparatus at left; steel missile within drop tube 
at upper right; and laser spot alignment for missile drop within a 
typical 3-inch diameter circle at lower right. 
Figure 5. Sample 5-MB-G-1 
pre-impact. Orange arrows 
indicate some differences 
between the pre-impact and 
post-impact images. 
Figure 6. Sample 5-MB-G-1 
post-impact. Orange arrows 
indicate some differences 
between the pre-impact and 
post-impact images.
Figure 7. Fiberglass 
reinforcement from a 
modified bitumen base ply.
Figure 8. Polyester 
and fiberglass dual 
reinforcement from a 
modified bitumen cap ply.

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