Effect of Changing Theoretical Maximum Specific Gravity on Asphalt Mixture Design
Keywords:Theoretical maximum specific gravity of a bituminous paving mixture (Gmm), rice test, percent air voids, optimum asphalt content, limestone, basalt
The value of theoretical maximum specific gravity of bituminous paving mixture (Gmm) plays a significant role in the performance of paving mixes. The Impact of (Gmm) can be noticed on properties of bleeding, rutting, raveling, and fatigue. Calculation of Gmm is fundamental to the design process of asphalt concrete mixes. It can be measured either directly by using the standard Rice test method (AASHTO T209, ASTM D2041), or can be estimated indirectly based on the effective specific gravity of aggregate mixtures, and specific gravity of asphalt. In the latter case exact determination of percentage air voids, and optimum asphalt content values is pivotal in estimating the true value of Gmm. This paper aims to study the Impact of changing theoretical maximum specific gravity for asphalt mixture on the characteristic of asphalt mixes. To achieve this objective an extensive experimental program was designed. Two types of aggregates (limestone and basalt) as well as four mix gradations were used to conduct the study. Based on the study results, it has been found that the measured air voids content using Gmm value measured by rice test (AVm) is lower than the estimated air voids content (AVe) in about 20% and 9% for limestone and basalt, respectively. Consequently, the optimum asphalt content values based on the laboratory-measured Gmm (ACm) are lower than those which were determined by using the estimated Gmm (ACe) by about 7% and 2% for limestone and basalt, respectively. Therefore, it is recommended to use the rice test in determining the theoretical maximum specific gravity of asphalt mixture in Egyptian code.
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