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<p>The asphaltic mixture consists of three main parts: the aggregate, the binder and air voids between the granules. The percentage of air void is important, where high air voids will produce crack sensitive pavement due to oxidation of asphalt or filling the voids by water which will cause striping of aggregate. The asphalt content is important too, where low content will increase stiffness of pavement and high content will increase skidding problems, therefore; the sum of air voids and asphalt content is called Voids in Mineral Aggregate (VMA), where it had been found by several researchers and transportation departments that VMA depends on maximum aggregate size where, for 19 mm maximum aggregate size, VMA is 14% and 13% for 12.5 mm aggregate size. Besides VMA, it had been found that average thickness of asphalt film coating the aggregate of 8 microns will produce durable mixture. VMA limit has not been included in Iraqi standards, therefore, this study focused on collecting literatures on these parameters, analyzing mixtures prepared under current standards to evaluate VMA and film thickness where, for surface course (12.5 mm aggregate size) VMA was 10% and film thickness was 9 microns and for binder course (19 mm aggregate size) VMA was 10% and film thickness was 9.6 microns. The final conclusion was to use VMA and film thickness as parameters in the design of asphaltic mixture as well as current standards and the study included the necessary equations to be used in the calculations of VMA and average film thickness.</p> |
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