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.
METHODS TO ACHIEVE RUT-RESISTANT DURABLE PAVEMENTS
This synthesis report will be of interest to state, local, and federal agency pavement materials, design, and construction engineers, as well as pavement research engineers and scientists. Those with supervisory oversight for pavement programs will also find it of interest. It describes the current practice for methods to achieve rut-resistant durable pavements. The synthesis documents current experience with permanent deformation of asphalt pavements and identifies methods to improve performance. Information for the synthesis was collected by surveying U.S. and Canadian transportation agencies and by conducting a literature search using domestic and international sources. This report of the Transportation Research Board describes the extent of the rutting problem on the National Highway System, pavement mixture design issues, and the design of rut-resistant mixtures. In addition, alternate mixture types, including stone matrix asphalt and porous asphalt, are discussed, as well as international approaches to mixture design. Finally, the construction of rut-resistant mixtures, including the role of quality control and quality assurance methods, are discussed. A summary of permanent deformation causes and solutions is included in the appendix.
COMPRESSIVE STRESS PULSE TIMES IN FLEXIBLE PAVEMENTS FOR USE IN DYNAMIC TESTING
TRAFFIC MOVING OVER A PAVEMENT STRUCTURE RESULTS IN A LARGE NUMBER OF RAPIDLY APPLIED STRESS PULSES BEING APPLIED TO THE MATERIAL COMPRISING EACH LAYER. THIS CONDITION IS BEST CHARACTERIZED BY DYNAMIC TESTS SUCH AS THE REPEATED LOAD TRIAXIAL TEST OR FATIGUE TESTS. THE SHAPE AND DURATION OF THE COMPRESSIVE STRESS PULSE RESULTING AT DIFFERENT DEPTHS BENEATH THE SURFACE ARE STUDIED FOR SEVERAL FLEXIBLE PAVEMENT SYSTEMS AND VEHICLE SPEEDS VARYING BETWEEN 1 AND 45 MPH. A COMPARISON IS MADE OF THE COMPRESSIVE STRESS PULSES CAUSED BY A VEHICLE MOVING OVER A LAYERED PAVEMENT SYSTEM AT A SPEED OF 1 MPH USING BOTH LINEAR AND NONLINEAR ELASTIC FINITE ELEMENT THEORY. VISCOUS EFFECTS AND INERTIA FORCES ARE NEGLECTED. BECAUSE THE NORMALIZED STRESS PULSES CALCULATED USING THE LINEAR ELASTIC THEORY ARE FOUND TO AGREE CLOSELY WITH THOSE CALCULATED USING THE NONLINEAR THEORY, LINEAR ELASTIC FINITE ELEMENT THEORY IS USED THROUGHOUT THE STUDY. THE RESULTS SHOW THAT THE SHAPE OF THE COMPRESSIVE STRESS PULSE VARIES FROM APPROXIMATELY A SINUSOIDAL ONE AT THE SURFACE TO MORE NEARLY A TRIANGULAR PULSE AT DEPTHS BELOW APPROXIMATELY THE MIDDLE OF THE BASE. TYPICALLY, THE COMPRESSIVE PULSE TIME ALSO VARIES ALMOST INVERSELY WITH VEHICLE SPEED UP TO AT LEAST A SPEED OF 45 MPH, THE CALCULATED STRESS PULSE TIMES WERE EMPIRICALLY CORRECTED FOR VISCOUS EFFECTS AND INERTIA FORCES USING THE RESULTS OF FIELD MEASUREMENTS MADE AT THE AASHO ROAD TEST. CURVES ARE PRESENTED FROM WHICH APPROXIMATE COMPRESSIVE STRESS PULSE TIMES CAN BE SELECTED FOR USE IN DYNAMIC TESTING. /AUTHOR/