Characterisation of Bituminous Macadams by Indirect Tensile Stiffness Modulus

The indirect tensile test (ITT) has been identified as an economic and practical means of measuring the stiffness modulus, or load-spreading ability, of bituminous roadbase. This study aims to provide estimates of stiffness moduli applicable to standard roadbase and basecourse materials used in the UK, and to investigate controversial points that have arisen from the use of the ITT. It considers: the calculation of stiffness modulus using the ITT; the determination of mean stiffness; relationship between stiffness modulus measured using the ITT and measured using a more sophisticated test; relationship between Poisson's ratio and temperature and/or stiffness; the effect of load-pulse shape; and, equivalence of pulse and continuous sinusoidal loading.The issues raised in this report will contribute to the discussion on the standardisation of the ITT, and provide guidance for the setting of target values of stiffness modulus for inclusion in an end-product specification for roadbase and basecourse materials.