CHARACTERIZATION OF LOW TEMPERATURE CREEP PROPERTIES OF CRACK SEALANTS USING BENDING BEAM REHOMETRY Prepared
Crack sealing has been widely used as a routine preventative maintenance practice. Given its proper installation, crack sealants can extend pavement service life by three to five years. However, current specifications for the selection of crack sealants correlate poorly with field performance. The purpose of this research was to develop performance guidelines for the selection of hot-poured bituminous crack sealants at low temperature. In this part of the research, the creep behavior of crack sealant at low temperature is measured and performance criteria for material selection were developed. Because various pavement and State agencies are well acquainted with and own the Bending Beam Rheometer (BBR), which was developed during the Strategic Highway Research Program (SHRP), an attempt was made to utilize the same setup to test hot-poured bituminous-based crack sealants. Testing conducted in this research project indicated that the standard BBR was inappropriate for testing soft bituminous-based hot-poured crack sealant, even at-40°C. The measured deflection exceeded the BBR limit, for some sealants, after only a few seconds of loading. To address this issue, the moment of inertia of the tested beam was increased by doubling its thickness (from 6.35mm to 12.7mm). For the new beam dimensions, it was found that only 4% of the beam center deflection is due to shear, a value deemed acceptable for sealant evaluation and comparison. In an effort towards developing a robust testing procedure, 15 sealants from various manufacturers were included in the study and tested between –4°C and –40°C. In addition, five sealants, which have known field performance, were tested to validate the laboratory results and establish specification thresholds for the selection guidelines. Since stiffness calculation in the BBR test method requires that measurements be made within the linear region of viscoelastic behavior, validation of this theory was conducted for crack sealants. This was found to be generally the case with crack sealants, which allowed for the use of the time-temperature superposition. If the temperature-superposition principle is applied, the stiffness at 240s at a given temperature can be used to predict the stiffness after 5hr of loading at a temperature that is 6°C lower. With the assumption of linear viscoelastic behavior, sealants performance can be characterized through stiffness, average creep rate, and dissipated energy ratio. Stiffness was found to be sensitive to temperature changes and could be used to differentiate between sealants. The measurements of the average creep rate and the dissipated energy ratio …
STATE-OF-THE-ART SURVEY OF FLEXIBLE PAVEMENT CRACK SEALING PROCEDURES IN THE UNITED STATES
Abstract : A survey of all 50 United States was conducted in September of 1990 to determine the state of the art of crack sealing procedures on flexible asphalt concrete pavements. The results were tabulated and a summary report prepared. A meeting was held at the U.S. Army Cold Regions Research and Engineering Laboratory to discuss the draft report; the comments and suggestions received were incorporated into this report. At the meeting the group identified the need for a trade organization to develop uniform specifications and terminology and to promote proper equipment, methodology, materials, training and education in the pavement crack sealing industry. Crack sealing, Pavement routing, National survey.
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME