Stone Matrix Asphalt (SMA) is a gap-graded mix that is gaining popularity worldwide. SMA does not application in Iraq; in order for adopt the use of SMA mixtures particularly on high volume roads such as highways and urban intersections in Iraq. So, the new methodology has to be evaluated using Iraq materials and conventional laboratory methods to insure good performance in the Iraq's highway. The purpose of this study is to evaluate the effect of additives type and content on the performance of stone matrix asphalt mixtures. A detailed
laboratory study is carried out by preparing asphalt mixtures specimens using aggregate from Al-Nibaay, (40-50) grade asphalt from dourah refinery and two types of fiber (carbon fiber and polypropylene fiber) with percentages (0.2, 0.3, 0.4, 0.5%) by weight of total mix and two types of polymer (phenol and polyethylene) with percentages (7.5, 10, 12.5, 15%) by weight of total mix were tested in the laboratory. Compacted mixtures were tested to evaluate the effects on SMA bulk specific gravity, maximum specific gravity, void content, Marshall
Stability, Indirect Tensile Strength (ITS) and permanent deformation. Three different tests temperatures (20, 40,60C°) were employed in the creep test and two temperatures (5, 25 C°) were used in indirect tensile test to investigate the susceptibility of these mixes to change in temperature. The results clearly indicate the importance of using the proper type of stabilizing additive. According to the study results, polymers additives were found to be more effective than fibers
additives. SMA Mix modified with phenol additives can be used in cold and normal temperature area, whereas SMA Mix modified with polyethylene additive can be used in high temperature area.