Determination of optimal mix from the standpoint of short term aging based on asphalt mixture fracture properties using response surface method

Over the years, asphalt pavement materials age, causing binder embrittlement which adversely affects pavement service life. This paper employed Response Surface Method (RSM) to determine the optimal mix from the standpoint of short term aging based on mixtures' fracture properties obtained from the Semi-Circular Bending (SCB) test. In order to short term age the mixtures, an experimental matrix was designed based on the central composite design. Aging temperature, aging duration and duration in humidity and ultraviolet chamber were considered as short term aging factors or independent variables (IV). The maximum force, deformation at maximum force, strain at maximum force, stiffness, fracture energy, maximum stress at failure, fracture toughness, velocity of fracture initiation, fragility index, and velocity of crack growth as the SCB test outcomes or dependent variables (DV) were analyzed using RSM. The results showed that the effects of IVs on the DVs change with changes in either binder type or binder content. For instance, the maximum fracture energy of mixtures produced with binder A60 were 3197.8 and 2599.1 J/m(2) at 10 and 30 degrees C, respectively, while the corresponding values of mixtures produced with binder B80 were 5112 and 1725.9 J/m(2) at 10 and 30 degrees C, respectively. Aging up to some level exhibited beneficial impacts on mixtures' fracture properties, which was considered as the optimal mix. The short-term aging level of optimal mix for the mixtures with stiffer binder was lower, compared to those produced with softer binders. For example, aging temperature to achieve optimal mix for mixtures prepared using binder A60 was 124 degrees C at 20 degrees C, while the corresponding value for mixtures produced with binder A80 was 142 degrees C at the same temperature. Crossing the optimal mix, made the mixtures become brittle, which was not desirable especially at lower temperatures. (C) 2018 Elsevier Ltd. All rights reserved.