A test procedure to measure the long-term durability of bitumens useed in chipseals on New Zealand roads is described. The proposed test (Opus International Consultants Central Laboratories Test Method No. B309-99) is two tiered, consisting of an acceptance test, used for initial assessment of new bitumens being introduced to the market, and a simple quality assurance test for 'batch to batch' quality control testing. In the acceptance test procedure, high pressure air (at 2,069 kPa or 300 psi) at 60°C is used to oxidise 1.0 mm films of bitumen. The modulus |G*|, measured at 5°C and 9 Hz, using a dynamic shear rheometer, is used as a measure of the extent of oxidation. The frequency of 9 Hz was selected as representative of that experienced by bitumens in the field. An equation is fitted to the modulus data as follows:
Δ(log |G*|) = P (1-exp(-Kft)) + Kt where: Δ(log |G*|) = increase in the log of the modulus
P, Kf, K = constants
To assess durability, the constants P and K are compared to those obtained for standard Safaniya bitumens of the appropriate grade.
The conditions used in the quality assurance test are the same as that used in the acceptance tests except that the test temperature is 80°C and the (suggested) test duration is 48 hours. The extent of oxidation is measured by the increase in modulus (or viscosity) and is compared to benchmark data for that bitumen. The test methods are given in the appendix to the report.