PRACTICAL FATIGUE CHARACTERISATION OF BITUMINOUS PAVING MIXTURES

This paper gives details of the development and later use of the Indirect Tensile Fatigue Test (ITFT) as a routine practical method for evaluating the life-to-crack-initiation of bituminous paving mixtures. Although this test has been used for many years, a recent collaborative project in the UK has led to its significant practical improvement. The project's specific areas of investigation included: (1) mixture design; (2) stiffness modulus measurement; (3) permanent deformation evaluation; (4) fatigue characterisation; and (5) durability testing. The biaxial state of stress occurring in the ITFT is more representative of field conditions than a uniaxial stress state, but complicates calculations of stress and strain. However, linear elastic theory can be applied here, as long as the test temperature does not exceed 30 degrees C. The data also confirm that tensile strain can be used as the principal criterion for fatigue crack initiation. A high correlation was found between results from the ITFT and the trapezoidal cantilever and uniaxial tension-compression tests. The ITFT can characterise a material in as little as two hours, and is very repeatable and reproducible. It is considered to be suitable for a British standard, and a serious candidate for adoption as a European standard. For the covering abstract, see IRRD 889137.