The objective of this study is to investigate the effect of fly ash as a filler replacement on the mechanical properties of asphalt–aggregate mixtures. Utilization of fly ash, which is the by-product of coal-fired power generation, is of great importance from an environmental and economical point of view. In this study, a dense bituminous mixture composed of calcareous aggregate was selected as the reference mixture. It was observed that there was a definite increase in Marshall stability and decrease in flow values, especially when calcareous filler was replaced by Soma-type fly ash, which was one of the three types of fly ashes used. The mechanical properties, namely elastic strain, elastic modulus, and permanent strain, of the asphalt mixtures were determined by carrying out fatigue tests with a UMATTA tester for three types of fly ashes, portland cement, lime, and control specimens. The changes in mechanical properties are important in the sense that they affect the behavior of asphalt concrete pavement under applied loads. This mechanism can be explained basically by bitumen extension. The fatigue life of fly ash specimens, especially Soma fly ash, was found to be considerably higher than that of calcareous filler specimens. Based on this study, it is demonstrated that fly ash can be used effectively in a dense-graded wearing course as a filler replacement.

In recent years, research has been devoted to the control of permanent deformations in flexible pavements. In order to prevent rutting, fatigue, and low-temperature cracking, different types of polymer modifiers have been utilized. The use of polypropylene (PP) fibers as a modifier in pavement mix that can be found locally and at low cost compared to other modifiers is an attractive option. This paper reports on the Marshall design and the optimum bitumen content for asphalt concrete with the addition of polypropylene fibers. Different types of PP fibers were used in order to determine the optimum bitumen content and the optimal PP fiber dosage. Marshall specimens were tested using the universal testing machine to determine the creep behavior of dense bituminous mixtures under repeated loading. The results from the analysis of the tested specimens show that the addition of polypropylene fibers improves the behavior of the specimens by increasing the life of samples under repeated creep testing.