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This research used laboratory evaluations to study the effect of using low-density polyethylene (LDPE) additive on the fracture toughness of asphalt concrete mixtures. LDPE was mixed with asphalt at 160[degrees]C and incorporated into the mixture. LDPE content of 1.5, 3, and 4.5% by total weight of asphalt was adapted. Fracture toughness evaluation was based on the J-integral concept. Innovative semicircular specimen geometry (76-mm radius and 57-mm thickness) is employed in fracture toughness evaluation. Notches with different depth-to-radius ratios were introduced at the middle of the flat surface of each specimen. Three-point bend loading was used to allow the separation of the two surfaces as a result of tensile stresses at the crack tip. Application of the J- integral concept revealed the fracture toughness superiority of the LDPE-modified asphalt concrete mixtures as compared to the unmodified mixture. The fracture toughness is sensitive to the LDPE concentration. Mixtures modified with 4.5% LDPE experienced the highest fracture toughness. LDPE modification has also enhanced the physical properties of asphalt cement. The LDPE-modified asphalt concrete mix displayed a significant increase in both indirect tensile and compressive strength. DOI: 10.1061/(ASCE)MT.1943-5533.0000106 CE Database subject headings: Asphalts; Concrete; Toughness mixtures; Polyethylene. Author keywords: Asphaltic mixtures; Low-density polyethylene; Physical properties.

The effect of polypropylene application method on long-term aging of hot mix asphalt (HMA) was investigated. Three different application methods were considered within this paper, namely, the coating method (where aggregate surface was coated with polypropylene), the dry method, and the wet method. Constant polypropylene content of 0.7% by weight of total mix was adapted. Laboratory aging program was set up to simulate the aging process of asphalt pavement occurred in the field. The mechanical properties of aged and unaged mixtures prepared using the three different polypropylene application methods were evaluated based on Marshall quotient, the indirect tensile strength, fracture energy, and unconfined compressive strength. Experimental testing has revealed the enhancement in the mechanical properties of HMA when polypropylene was added. The polypropylene additive has managed to counteract the effect caused by long-term aging of HMA. A comparison between the three polypropylene application methods indicated that the coating method has caused a considerable improvement in the indirect tensile strength and fracture energy of HMA under aged and unaged conditions. Marshall quotient and compressive strength of tested mixtures have shown less dependency on the polypropylene application method. DOI: 10.1061/(ASCE)MT.1943-5533.0000105 CE Database subject headings: Asphalt; Polypropylene; Cracking; Aging; Mechanical. Author keywords: Hot mix asphalt; Polypropylene; Marshall quotient; Fracture.