Modeling of Fatigue-Strength Development in Cold-Emulsion Asphalt Mixtures Using Maturity Method

Abstract

Emulsion asphalts are cost-effective, environmentally friendly, and sustainable alternatives to hot-mix asphalts. Laboratory curing protocols currently used to simulate field curing of emulsion asphalts have been observed to offer conflicting predictions. This study employed the maturity method to account for the combined effects of temperature and time on fatigue-strength development in emulsion asphalts. An emulsion asphalt, composed of 55% reclaimed asphalt pavement, 45% virgin aggregates, 6.2% bitumen emulsion, and 4% pre-mix water was designed following the Asphalt Institute procedure. A total of 168 specimens from the mix were variously cured at 5 °C, 25 °C, 40 °C, and 50 °C for time intervals of 1, 3, 5, 7, 14, 21, and 28 days, before being tested for fatigue-strengths on the four-point bending test jig. It was observed that fatigue-strengths increased with an increase in cure temperature but decreased with an increase in cure duration. A parabolic hyperbolic fatigue-maturity model was developed from results of specimens cured at 5 °C, 25 °C, and 40 °C and validated with results from specimens cured at 50 °C. A strong correlation was observed between predicted fatigue-maturity and laboratory-determined fatigue-strengths at test strain levels between 125 µm/m and 200 µm/m. The study concluded that the laboratory characterization of emulsion asphalts should consider the curing history of the mix.