Abstract
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.
Highlights
Boris Radovskiy (TRB 2003) reviewed the history of Voids in Mineral Aggregate (VMA) and average film thickness where he stated that the minimum voids in the mineral aggregate (VMA) requirement has been a property proposed since the late 1950’s for use in asphalt mix design specifications, but difficulties in achieving VMA in mixtures have led to several new research studies
The same can be noted for binder layer (19mm) mixes for the effect of asphalt cement content on VMA where at optimum asphalt content (5%), VMA is slightly more than (10%) which is not satisfied for binder layer (13%) as shown in the same figure
It is obviously can be noted that the relation is linear where increasing asphalt cement content will increase film thickness, this effect is expected because increasing asphalt content will increase voids filled with asphalt which in turn increases VMA
Summary
Level 1 design is a volumetric mix design where aggregate characteristics and mixture volumetric properties, such as air voids and VMA, are the basis for the selection of gradation and asphalt binder content. They stated that previous researchers recognized the relationship between voids, aggregate surface area, binder film thickness and stability for dense graded asphalt concrete mixes.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
