Abstract
Bonding strength between asphalt and aggregate is considered an important feature that governs the future performance of flexible pavements. This study investigated five factors that have the potential to affect this bonding strength. Two asphalt penetration grades (60/70 and 85/100) in addition to various types of substrates (limestone, granite, marble and basalt) were used to prepare specimens to be tested by the Binder Bond Strength (BBS) test. Three aging levels (unaged, short-term aged and long-term aged) with four types of modifiers (Crumb Tire Rubber, Nano Silica, Nano Clay and Microcrystalline Synthetic Wax) were implemented for two specimen conditioning methods (dry and wet). Statistical analysis was performed to measure the influence of these factors on the asphalt-aggregate bonding strength. The results showed that aggregate type and modifier type had the most effect on the bonding strength with relatively no effect of binder type. Moreover, long term aging and two types of modifiers (Nano Silica and Crumb Tire Rubber) were found to significantly increase the Pull-Off Tensile Strength (POTS), which is a measure of the asphalt-aggregate bonding strength. Failure type was mainly cohesive in the dry condition then transformed to adhesive when specimens are exposed to moisture.