A modified direct tension test (DTT) for bituminous crack sealant characterization at low temperature

The main purpose of this research was to develop performance-based guidelines for selecting hot-poured bituminous crack sealants at low temperature. Hot-poured bituminous crack sealing has been widely accepted as a routine preventative maintenance practice, and with proper installation, it is expected to extend the pavement service life three to five years. However, the current specifications for the selection of crack sealants correlate poorly with field performance; hence the need for this study. Measuring the mechanical properties of crack sealant at low temperatures is one of the criteria used in the development of performance-based guidelines. A modified direct tension test (DTT) was used. The DTT modification includes specimen geometry (which allows specimens to be stretched up to 95%), the extension rate, as well as the specimen preparation procedure. Tensile force was applied to the dog-bone specimen, with its effective gauge length of 20.3mm, and was pulled at a deformation rate of 1.2mm/min. Nine sealants were tested at various temperatures, and three performance parameters were suggested as indicators of sealant performance: Extendibility, strain energy density (SED), and percent modulus decay. Extendibility is used to assess the degree of deformation undergone by a sealant at low temperature before it ruptures or internal damage is observed. The SED is the area under the stress-strain curve and is used to measure the work expended in deforming the material. The percent modulus decay infers the viscoelastic properties of sealant. These three performance parameters were analyzed and successfully used to distinguish among sealant behaviors and predict their performance. Due to its simplicity, the extendibility parameter is recommended for use in the newly developed crack sealant performance grade system.