Stiffness and fatigue evaluation in cyclic tests with rest periods for asphalt mixtures with or without fly ash

Abstract

Fatigue of asphalt materials is evaluated in the laboratory by continuous cyclic loading tests, whereas in the field loading is intermittent. Due to such distinction in the nature of loading and possible differences in material behaviour, further study of the effect of rest periods (RPs) on stiffness and fatigue life is of paramount importance. This paper aimed to investigate the effects of rest periods (RPs) on the fatigue life and on the stiffness evolution of asphalt mixtures, including the use of fly ash. The materials used in this research are: three asphalt binders; two granitic aggregate sources from different quarries; fly ash from a thermal power plant. Stiffness and fatigue tests were performed using a servo-hydraulic press. Stiffness characterisation was performed using complex modulus tests at five different temperatures and six different frequencies. Fatigue tests were performed at 19 °C, considering different maximum strain amplitudes in the specimen. Tests with recovery time (5 RPs of 4 h each) were performed. Complex modulus during all fatigue tests was tracked using small, short-period loadings (compared to fatigue loading) during rest. The results show that after significant stiffness decrease during loading, there is a great (about 90% of the total decrease) stiffness recovery during the 4 h RPs, but this recovery is not associated with an increase in the number of cycles to failure in tests with rest. This indicates other phenomena, probably reversible, are responsible for part of the stiffness change during loading.