Studies on Effect of Wheel Configuration-Temperature and Type of Binder on Rutting Characteristics of Bituminous Concrete Mix
This report presents the investigation of rutting characteristics of bitumen mixes using plain bitumen (VG-10) and modified binders (CRMB-60 and PMB-70). The report will be of particular interest to engineers in the public and private sectors with responsibility for the design, construction, maintenance and rehabilitation of HMA pavements. The present work is aimed at understanding the properties of mix and the machine parameters which influence the deformation causing ruts for mixes. The rutting was caused on the beam specimens prepared in the laboratory. The study includes the influence of different types of binders, air voids, and along with the applied loads on the rutting characteristics. The results are analyzed to formulate regression equations. It is found that modified binders resist rutting compared to plain binders. PMB-70 binders perform better than VG-10 and CRMB-60 binders under the laboratory induced applied pressures and number of passes.
An Experimental Study of Rutting on Dense Bituminous Macadam of Grading-I (Middle) using Crumb Rubber Modified Bitumen and Waste Plastic Coated Aggregates
Rutting is the permanent deformation in pavement usually occurring longitudinally along the wheel path. Permanent deformation or rutting in bituminous mixes depends on numerous factors such as aggregate gradation, shape and size of aggregate, quantity and quality of binder, volumetric properties of mix such as air voids and Voids in Mineral Aggregates (VMA), film thickness, temperature, construction practices and environmental conditions. Rutting resistance potential of any bituminous mix depends on the properties of its constituents. In this study crumb rubber and waste plastic is used to modify constituent’s properties. Crumb rubber is used to modify bitumen generally termed as crumb rubber modified bitumen (CRMB). Waste plastic is used to form a coating around aggregates. Bituminous mix with CRMB and plastic coated aggregates having proper proportions of crumb rubber and waste plastic gives better results as compared to mixes having any one of the two waste materials. Thus in the areas prone to high rut depth on DBM, for use mainly, but not exclusively, in base/binder and profile corrective courses, modified bituminous mix (having crumb rubber modified bitumen along with plastic coated aggregates) is more suitable than conventional mix due to its high rut resistance. Plastic coated aggregate – crumb rubber modified mix shown negligible increase in rutting even when significant temperature change occurs. Hence such modified mixes could be used in areas having large temperature variations. Thus modified mix with crumb rubber modified bitumen as binder and LDPE coated aggregate, could be successfully used to replace conventional mix for DBM, with advantage of project cost reduction, improvement in performance and environmental betterment
Calibration of Mechanistic-Empirical Rutting Model for In-Service Pavements
Rutting is a major failure mode for flexible pavements. Pavement engineers have been trying to control and arrest the development of rutting for years. Many models are available to relate pavement rutting to design features, traffic loading, and climatic conditions. These models range from purely empirical to mechanistic models. Mechanistic-empirical models (the Asphalt Institute and Shell) were used to predict the development of rutting for 61 Long-Term Pavement Performance (LTPP) test sections. The rutting damage, calculated using these models, did not appear to be a good predictor of the observed rutting depth. A new rutting model was developed and calibrated using the data from the 61 LTPP sections. The model accounts for the plastic deformation in all pavement layers and allows the use of actual axle load and type, rather than the equivalent single axle load, in characterizing traffic.