Test development and material characterization of hot poured crack sealant at low temperature.

摘要

Crack sealing has been used extensively as a routine preventative maintenance practice in flexible pavements. It has been shown that if the cracks can be sealed properly, pavement service life can be extended by three to five years. Thus, the most important issue is how to select a proper sealant material in a specific location. Currently, the material selection is based on the American Society for Testing and Materials (ASTM) standards that have been widely reported to correlate poorly with field performance because ASTM specifications do not reflect the viscoelatic nature of sealants. Therefore, it is indeed an urgent need to develop a performance-based guidelines for the selection of hot-poured bituminous crack sealant. In this study, two new test methods were introduced to measure sealant's low temperature rheological properties: the crack sealant bending beam rheometer (CSBBR) test and the crack sealant direct tension tester (CSDTT) test.;The CSBBR test, which is a modification of the bending beam rheometer (BBR) test currently used in the SuperPave(TM) binder specification, was developed to investigate sealant's low temperature flexural property. The major modification to the SuperPave(TM) BBR test was to double the specimen thickness used in the CSBBR test due to the excessive softness of crack sealant compare to bitumen binder. In the CSBBR test, sealant was subjected to a creep loading for 240s following by a 480s of recovery. The three performance parameters calculated from the CSBBR results to evaluate low temperature flexural property of crack sealant were the stiffness at 240s, the average creep rate, and the dissipated energy ratio.;The CSDTT test, which is a modification from the direct tension tester test currently used in the SuperPave(TM) binder specification, was developed to investigate sealant's low temperature tensile property. The test was modified by redesigning its specimen geometry and loading rate to simulate sealant's in-situ condition. The three performance parameters calculated from the CSDTT results to evaluate crack sealant low temperature tensile property were the extendibility, the strain energy density, and the relaxation modulus decay.;Among these six performance parameters, stiffness at 240s of 25MPa, average creep rate of 0.31 mm/mm/s, and extendibility level at different temperatures were identified and proposed as selection criteria for crack sealant at low temperature. These parameters were used to assess several in-service crack sealants with known field performance. The results show that the proposed tests and performance parameters are highly correlated with sealant field performance when compared to current ASTM specification standards.;In addition to the mechanical characterization of the sealant material, microstructure of the sealants were also investigated by confocal laser scanning microscopy (CLSM), environmental scanning electron microscopy (ESEM), gel-permeation chromatography (GPC), Fourier-transform infrared spectroscopy (FTIR), and thermo-gravimetric analysis (TGA). These techniques reveal the composition of sealant as well as the interaction between the components and are used to assist the understanding of various sealant mechanical behaviors. The results of the microstructure analysis show that with polymer modification, the low temperature tensile property of the sealant improves. However, if the ground tire rubber (GTR) is added, the improvement of tensile property is reduced, but the flexural strength is increased.