Asphalt Modified by Ethylene-Acrylic Acid Copolymer Ionomers: Fundamental Investigations of Mechanical and Rheological Properties

Abstract

Ethylene-acrylic acid copolymer (EAA) has been demonstrated to be a suitable additive for modifying the properties of asphalt. EAA mixed with metal hydroxides/oxides form EAA-M ionomers, which increase the polarity of EAA, improving its adhesive properties and affecting its mechanical and rheological characteristics. The present work investigates the mechanical and rheological characteristics of asphalt modified by EAA in conjunction with either Ca (OH)2, NaOH, or ZnO. The high-temperature properties of the modified asphalts, including the softening point, and needle penetration, were evaluated. Rheological characteristics of modified asphalts were investigated by rotary rheometer. Moreover, the storage stability at high temperature, morphology and chemical structure were also analyzed. Results indicate that a 4wt% EAA-M ionomer concentration in the base asphalt is adequate for providing the enhanced properties studied. For an equivalent concentration of EAA, the properties of modified asphalts were affected by very small additions of the metal hydroxides/oxides. The best overall mechanical and rheological performance was obtained for EAA-Ca modified asphalt with 4wt% EAA and 2.5wt‰ Ca (OH)2. EAA-Zn modified asphalt provided the most stable high-temperature storage. Compared with 6wt% pure EAA-modified asphalt, which is not stable, the EAA-Zn modified asphalt (2.7wt‰ ZnO) demonstrated reasonable high-temperature storage stability. Compared with asphalt modified with 6wt% pure EAA, the softening point increased from 55.81 °C to 58.05 °C with the addition of 2.7wt‰ NaOH. However, while the mechanical and rheological properties of EAA-Na modified asphalt were very good, its high-temperature storage stability due to the strong reactivity of NaOH, which led to the crosslinking of EAA-Na ionomers, making it difficult to disperse.