Evaluation of the Influence of Gradation and Shape of the Aggregate on Skid Resistance of Stone Matrix Asphalt

Based on definitions, skid resistance means the preventive and resistant force which is made by interaction between pavement and the lock wheel. The stone matrix asphalts (SMA) are the warm asphalts mixture which have high strength against skid because the existence of more percentage of coarse aggregate. With consideration of the importance of using the mixtures of SMA as a covering layer which is resistant against skid, and recently particular consideration about using these kinds of mixtures in Iran, so in this research for the evaluation of skid resistance of these kinds of mixtures, the influence of various parameters of asphalt mixtures assessed, such as the amount of bitumen, the kind of aggregate, graduation and the nominal maximum aggregate size (NMAS) and the shape of coarse aggregate in skid resistance of stone matrix asphalt (SMA). Respectively, the influence of microtexture and macrotexture of asphalt specimens was done with the British pendulum tester and sand patch method. From four kinds of lime aggregate, silica aggregate, steel slag and recycling aggregate from the asphalt pavements, and also one kind of bitumen (60/70) with the fiber of rock wool, were used in construction of asphalt specimens of SMA. The mixtures of SMA have four kinds of graduation with nominal maximum size of 19, 12.5, 9.5 and 4.75 mm. The way of design of mixtures of SMA, was used based on the way of proposed in the 425 report which is related to the project of NCHRP9-8. The results of this research showed that the slag aggregates have the better performance in skid resistance than other aggregates. And also the skid resistance of asphalt specimens of SMA has the direct relationship with the increase of the amount of nominal maximum aggregate size (NMAS) and one thing which should be mentioned is that cubic aggregates have 5 to 10 percent more skid resistance than elongate and flaky aggregates.