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.
Characterization of Styrene-Butadiene-Styrene Polymer Modified Bitumens—Comparison of Conventional Methods and Dynamic Mechanical Analyses
Rheological properties of styrene-butadiene-styrene polymer (SBS) modified bitumens were studied using conventional test methods (penetration, softening point, kinematic viscosity and Fraass breaking point) and dynamic mechanical analysis (DMA). The study indicated that SBS modification improved the viscoelastic properties of bitumens, which can be demonstrated using DMA but not conventional methods. Significantly improved properties of binders included increased dynamic mechanical moduli and decreased phase angle at high temperatures, as well as reduced complex modulus and increased phase angle at low temperatures. SBS modification also caused reductions in glass transition temperature, Fraass breaking point, and temperature susceptibility. The degree of improvement was observed to be influenced by bitumen source/grade and polymer content/structure. Comparison showed that certain relationships exist between parameters obtained using conventional methods and DMA, such as between penetration and complex modulus, kinematic viscosity and complex viscosity, and Fraass breaking point and glass transition temperature. However, the main conclusion of the study is that conventional test parameters such as penetration and softening point are not suitable for characterization of rheological properties of SBS modified bitumens.