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 test has been defined in a British Standards Institution (BSI) Draft for Development and it is considered to have the potential for inclusion in a future end-product specification. The objectives of this study are 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. This report considers the definition of ITT stiffness modulus, the determination of mean stiffness, curing, comparison with a more sophisticated test, the selection of Poisson's ratio and the effect of load-pulse shape and its equivalent sinusoidal, loading frequency. Estimates of the stiffness moduli of newly laid, standard macadams used in the UK have been determined and the specification of bituminous materials by stiffness class is discussed. It is recommended that an expert panel is convened to resolve the issues raised in this report and that a data-base should be established to collect information on the performance properties of materials laid in UK road contracts. (A)
Abstract