Investigation of Fracture and Crack Propagation Characteristics of Asphalt Mixtures Modified with Polyphosphoric Acid Based on Semi-Circular Bending (SCB) Test

One of the most common methods to enhance performance of asphalt binder and mixtures is using polymeric and mineral additives. The polyphosphoric acid (PPA) is one of additives used to modify asphalt binder's characteristics during last two decades. In this research, to investigate the effect of this additive on fracture and crack propagation characteristics of asphalt mixtures, asphalt mixture specimens were fabricated by implementing with asphalt binder modified with three different dosages of PPA: 0.5, 1 and 1.5% by weight of asphalt binder. The semi-circular bending (SCB) test was performed on these specimens at five different test temperatures including -10, 0, 10, 25 and 40 degree of centigrade. The major output of this test was force-displacement curve. The Maximum force, fragility, fracture energy and toughness were determined for all specimens based on force-displacement curve. Also, notch mouth opening displacement was measured by using pictures captured during the SCB test. To compare asphalt mixture behavior, an index was presented in this research as fracture energy divided by noth mouth opening displacement. At a constant temperature, the greater index shows better performance of asphalt mixture. The results have shown that adding PPA at low temperatures is not useful but at moderate temperatures it can increase fracture properties of asphalt mixture. The optimum content of PPA at the moderate temperatures is determined between 0.5 to 1%.