Characterization of Low Temperature Mechanical Properties of Crack Sealants Utilizing Direct Tension Test

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. This was accomplished by measuring the mechanical properties of crack sealant at low temperature and then developing performance criteria for material selection. The modified direct tension test (DTT), crack sealant direct tension test (CSDTT), simulates the in-situ loading behavior of crack sealants in the laboratory. A modified dog-bone specimen geometry, which allows specimens to be stretched up to 95%, is recommended. This new specimen geometry also facilitates sample preparation. Tensile force is applied to the dog-bone specimen, with its effective gauge length of 20.3mm, and is pulled at a deformation rate of 1.2mm/min. Fifteen sealants were tested at various temperatures, and three performance parameters are suggested as indicators of sealant performance: extendibility, percent modulus reduction, and strain energy density. Extendibility, which is used to assess the degree of deformation undergone by a sealant at low temperature before it ruptures or internal damage is observed, is recommended as a measured parameter to be included in the performance-based guidelines for the selection of hot-poured crack sealants. Extendibility thresholds were defined as function of low service temperatures. The CSDT is conducted at +6oC above the lowest in service temperature because of the relatively high test loading rate compared to in-situ crack sealant movement rate.