Standardisation trial of performance tests for bituminous materials

Laboratories in the UK and Australia participated in a trial of BSI draft test methods for the indirect tensile test and the static and dynamic load creep tests. The Nottingham Asphalt Tester (NAT) was used in the UK and the Materials Testing Apparatus (MATTA) in Australia. Precision analysis of the test results was in accord with British Standard 5497:1987. The MATTA results for the indirect tensile test were substantially higher than the NAT results because different methods were used to calculate stiffness modulus. The method of determining stiffness modulus will need to be defined in a revision of the BSI Draft for Development. The precision values obtained for the three test methods appear too large to apply them effectively for end-result specification. The main source of imprecision for the indirect tensile test was shown to be variability between test samples; the variability was typical of that found within a single source of material in UK road construction. Recommendations to improve inter-laboratory variability include more accurate control of the load pulse and improvements in technician training. (A)