Rut Resistant Asphalt Pavements
The author of this article examines the causes and potential cures of asphalt pavement rutting. He explains that rutting on the asphalt pavement surface commonly is the result of an unstable asphalt mix, heavy vehicle traffic, and high pavement temperatures. He notes that this type of rutting is often observed at intersections, bus stops, freeway off ramps, or under extreme loading situations on airport runways or dock loading facilities. He explains how an engineer can determine if rutting in the asphalt pavement surface is due to distress throughout the entire pavement structure or due to failure in the asphalt layer only. He suggests that asphalt mixes can be designed to resist rutting with the proper selection of materials, good construction practices, and use of appropriate mix design methods. Good compaction practices during construction will improve rut resistance by increasing the interlock of aggregate particles in the mix.
Evaluation of permanent deformation of unmodified and SBS modified asphalt mixtures using dynamic creep test
Abstract Recent researches show that there is a serious need for more accurate methods to evaluate polymer modified asphalt mixtures. In this research, dynamic creep test was conducted on unmodified and SBS modified samples, using UTM25 machine to this end. During this work it was attempted to compare the permanent deformation potential of the coarse graded mixtures with dense graded mixtures. Having determined the type of gradation with lower permanent deformation, the amount of polymer to improve the mechanical behavior of the samples made with this type of gradation was investigated. Finally the creep behavior of the samples was estimated by the Zhou three-stage creep model. Based on the obtained results, dense graded mixtures had higher permanent deformation susceptibility than coarse graded mixtures. Moreover, 5% of SBS polymer had better effect on improvement of permanent deformation resistance than 4% and 6%. The mathematical models of creep curves showed that lower stress levels in dynamic creep test can not show the real behavior of asphalt mixtures and particularly the modified mixtures.
A RELIABILITY-BASED MIX DESIGN AND ANALYSIS SYSTEM FOR MITIGATING FATIGUE DISTRESS
A reliability-based mix design and analysis system has been developed for mitigating fatigue distress in asphalt pavements. Design decisions consider not only fundamental mix properties but also the level of design traffic, the temperature environment at the site, the pavement structural section, laboratory testing and construction variabilities, and the acceptable level of risk. This paper describes the mix design and analysis system, discusses its calibration, illustrates its use, and assesses the consistency of current California design practice vis-a-vis the control of fatigue distress. It reveals possible inconsistencies in current California design practice, discusses effects of construction variability, highlights advantages of rich-bottom pavement structures, and illustrates the integration of mix and structural components into a reliability-based mix design process.