Experimental Fracture Toughness Study for Some Modified Asphalt Mixtures

The use of modifiers or additives in the asphalt mixtures is a suitable and common method for improving their mechanical properties especially under high temperature service conditions. However, for cold climates which the pavement of roads usually experience subzero temperatures, the overall failure mechanism of asphalt layers may be occurred mainly due to elastic brittle fracture and growth of initiated cracks inside the pavements. Fracture toughness is the most important parameter for characterizing the crack growth and failure of cracked materials and structures such as the asphalt pavements. Hence, the main aim of this research is to study the effect of different additives including Poly phosphoric acid (PPA), Styrene butadiene styrene (SBS), Anti striping agent (ANTI), Crumb rubber (CR) and FT-paraffm wax (Sasobit) on the low temperature mode I fracture resistance of asphalt mixtures. A series of asphalt samples with different percentages of the mentioned additives were manufactured in the shape of semi circular specimens containing vertical edge cracks. The test samples were then loaded monotonically using a symmetric three-point bend fixture at a constant subzero temperature of -15 degrees C. The value of mode I fracture toughness (K-IC) were determined by recording the critical fracture loads of tested specimens. It is shown that all the investigated additives increase the low temperature fracture toughness of the asphalt mixture and the maximum increase in the value of K-IC occurs when the sasobit and CR additives are used.