Effect of carbon fibers (length, dosage) on the Marshall and volumetric properties of HMA mixtures

This study investigates the effect of carbon fibers when added to HMA containing recycled concrete aggregate on Marshall properties. It is included to identify the optimum asphalt contents according to the Marshall design method for mixtures containing 20, 40, 60, 80, and 100% coarse recycled concrete replaced with coarse virgin aggregate. Two lengths of 10 and 20 mm of carbon fibers had been added with three percentages of 0.15, 0.25, and 0.35% to the total weight of the mixture. The results showed all mixtures containing recycled concrete aggregate met SCRB 2003 Iraqi standard requirements for wearing coarse type IIIA. Replacement of virgin aggregate by recycled concrete aggregate led to an increase in optimum asphalt contents, in which the maximum increase reached 10.78% over the control mixture when 100% of coarse recycled concrete aggregate was utilized. The Marshall characteristics were altered with carbon fiber, which increased stability. The highest level of stability reached about 38.89% over the control mixture when using 60% recycled concrete aggregate and reinforced by 0.35% carbon fibers had a length of 20mm.