Effects of irregular loading patterns on fatigue life measured in indirect tensile fatigue test: a traffic-based study

Abstract

Loading patterns used in pavement tests are responsible for modeling the traffic loads applied on the road. This paper suggests a framework to aggregate hourly distribution of daily traffic into 3-h loading blocks, keeping fixed the loading times across all blocks but allowing the rest periods to differ block to block. Difference in rest times among loading blocks is a consequence of different headways between heavy vehicles, better reflecting the influence of asphalt self-healing than when fixed rests are used. Field-specific loading patterns are generated by combining the loading blocks, providing irregular shapes compared to the classical loading pattern commonly used in labs. Traffic data of Tehran-Karaj freeway was obtained and analyzed to generate 3 irregular loading patterns representing the traffic conditions of 3 days with different temperatures. Indirect tensile (IDT) fatigue test was performed at the temperature of each experimental day using the classical loading pattern as well as the irregular one corresponding to that temperature. Moreover, for each temperature, the fatigue test was performed at 3 different stress levels predetermined by an Indirect tensile strength (ITS) test. Results show that by applying the irregular loading patterns instead of the classical one, the measured fatigue lives of specimens increase ranging from 19 to 29%. It should be further underlined that the average value of rest periods is constant under both loading conditions, and irregularity caused these improvements. Moreover, the larger percentages of fatigue life improvements are attributed to the tests with lower stress levels as they underwent more irregular loading patterns than the tests with higher stress level.