Rut

Abstract: A re-examination and simplification of the original rut index concept for predicting rut susceptibility in aggregate bases is presented to eliminate some of the disadvantages of the original approach. The rut index can be determined from the results of a single cyclic load triaxial test performed at a confining stress of 6 psi, rather than at two confining stresses as originally proposed. The principal stress ratio to be used in the test varies from 2 to 6, depending on the structural strength of the pavement section. The resilient and permanent deformation characteristics of river gravel, granitic gneiss, shale, limestone, and quartzite aggregates were determined using the cyclic load triaxial test. Variables investigated included density, gradation, moisture content, and aggregate shape and surface characteristics. The revised rut index concept was used to evaluate and compare the relative permanent deformation behavior of these various unbound aggregates. The cubic-shaped, smooth rounded river gravel was found to be more than two times as susceptible to rutting as the crushed aggregates tested. The crushed aggregates were angular, blade, and disc shaped and had relatively rough surfaces. These aggregates generally performed similarly with respect to permanent deformation, although the visual appearance of the two blade-shaped aggregates was not as nice as the others. The use of a simple, slow triaxial shear test as a practical alternative to the conventional dynamic test was studied for evaluating the resilient and permanent characteristics of unbound base materials. The slow triaxial shear test was found to be suitable for evaluating the resilient modulus, but appeared not to be appropriate for evaluating permanent deformation characteristics.

Abstract: The construction, instrumentation, and response to vehicle trafficking of an unpaved road on soft ground are described. The road is comprised of an unreinforced section, three sections with different geotextiles, and a section with geogrid. The performance of the unreinforced section compares reasonably well, at large rut depths, to prediction using the analytical approach most commonly used in current design practice. Inclusion of a geosynthetic between the base course layer and subgrade soil led to a significant improvement in trafficability. The improvement was greatest for the thinner base layer of 25 cm, and diminished with increasing layer thickness. Reasonable agreement was, again, observed between the field performance and analytical predictions at large rut depths. The analytical approach was found to significantly overpredict the number of vehicle passes to develop a 5 cm rut. The lack of agreement at small to moderate rut depths is attributed to compaction of the base course layer in response t...

Abstract: The objectives of this study were 1) to identify the material properties, mix design parameters and construction procedures that affect rutting, 2) to provide information necessary to produce hot mix asphalt (HMA) mixtures that will perform satisfactorily, and 3) to provide information to identify those mixes with a tendency to rut under today's heavy traffic loadings. Forty-two pavements were sampled from fourteen states across the United States. Rut depth measurements were made across each pavement to quantify the amount of rutting occurring at each site. The mix design information, construction records and traffic counts were also obtained. A detailed laboratory testing program was performed on samples of the asphalt mixture from these rutted and good performing pavements. The data were analyzed to determine material and mixture properties and to identify procedures that are necessary for construction of rut resistant HMA pavements. Among the conclusions from this study are the following: (1) 69% of the pavements evaluated that were designed with the Marshall method utilized a 50-blow compactive effort. This resulted in high asphalt content and led to low in-place voids after traffic and subsequently rutting. (2) 33% of the sites had no construction history available, only 38% of the sites utilized laboratory compacted samples of the asphalt mixtures from the mixing plant during construction to verify that the air voids were within an acceptable range, and 53% of the sites that measured voids in laboratory compacted samples had voids less than 3%. (3) Most of the rutting occurred in the top 3-4 inches of the HMA. (4) In-place air void contents above 3.0% are needed to decrease the probability of premature rutting throughout the life of the pavement. (5) The shear strength of the recompacted mix as indicated by the GTM roller pressure had the best correlation with rutting of any single factor. (6) If the in-place air voids are above 2.5%, the angularity of the aggregate as measured by percent of coarse aggregate (plus No. 4) with 2 or more crushed faces and NAA Uncompacted Voids for the fine aggregate (passing No. 4) are highly correlated to rate of rutting. (7) The properties of the asphalt cements extracted from the mixtures are not closely related to rutting. (8) A rate of rutting of 0.00023 in. per square root ESALs delineated between good and rutted pavements for the pavements evaluated. (9) Rutting on high volume roadways can be prevented if angular coarse and fine aggregates are used and if the air voids in the mixture do not fall below approximately 3.0%.

Abstract: Rutting is a major form of pavement distress in asphalt pavements. The main concern with rutting has been related to driving safety. Many highway agencies and researchers suggested that pavement rutting could lead to vehicle hydroplaning and loss of skid resistance in wet weather. However, to date no theoretical basis has been established for an analytical assessment of the severity of rutting for the purpose of pavement maintenance and rehabilitation. Most highway agencies classify rut severity on the basis of engineering judgment or field experience. This paper presents an analytical procedure to assess the severity of rutting based on vehicle skidding and hydroplaning analysis. It considers theworst-case scenariowhere a rut is filled with water and analyzes (1) if a car will hydroplane at a given speed; and (2) the length of braking distance required for the car traveling at the given speed. A finite-element simulation model is adopted to perform the analysis. For a given rut depth filled with water, the computer model computes the hydroplaning speed for a typical passenger car, and the required braking distance for the car traveling at a known speed. It was found that depending on the rut depth and the surface frictional property of a pavement, the severity classification of a rut may be governed by either hydroplaning risk or safety requirement of braking distance. The traditional method of using the same set of critical rut depths for all pavement sections in a road network is not ideal for effective handling of rutting maintenance. DOI: 10.1061/(ASCE)TE.1943-5436.0000336. © 2012 American Society of Civil Engineers. CE Database subject headings: Pavements; Maintenance; Skid resistance; Vehicles; Finite element method. Author keywords: Rut depth; Pavement maintenance; Skid resistance; Hydroplaning; Braking distance; Tire tread depth; Finite element method.