Highway engineering & construction

’ Aggregate gradation of asphalt mixtures has significant effects on both volumetric and physical properties of these mixes. The aggregate gradation can be characterized by severalmethods, one of them is the gradation hump ratio. Gradation hump ratio is defined as the relative slope between two segments of the gradation curve before and after a certain sieve.This study aims to determine the effects of variation of gradationhump ratio measured at different sieves, type of coarse aggregate, and percentage passing the No. 200 sieve on the properties of hot asphalt mixes. To achieve these objectives, asphalt mixes of different conditions according to the studied variables are prepared and investigated. The investigated mixesare composed of crushed dolomite or limestone as a coarse portion, siliceous sand as a fine portion and limestone dust as a mineral filler.Analyzing the study results, it can be concluded that increasing gradation hump ratio greatly increases the required optimum asphalt content (OAC) and highly changes the Marshall mix properties. While, the change of mix gradation keeping constant hump ratios causes lower change in OAC andconsiderable variation in other mix properties. It is noticed thatthe increasing hump ratio increases the sensitivity of the investigated mixes to variation of asphalt content. It can be also concluded that the effect of changing the gradation hump ratioare similar for the two considered coarse portion types.