A working party was set up in 1973 to determine the causes of failure of a number of rolled-asphalt wearing-courses by sliding on their base-courses; failures normally occurred shortly after completion of construction. The interim report of the working party published in 1976 (see IRRD abstract no 219217) analysed 56 failures from which it was clear that a number of factors were contributing to slippage. The laboratory has since carried out an extensive programme of testing on construction sites. Early results from this programme are presented which indicate that pavement stiffness is important but which also confirms that other non-structural factors increase the risk of failure. Cores taken from the surfacings established that slippage is strongly associated with a lack of shear strength near the interface between the base-course and the wearing-course. This lack of strength is produced during construction. The report describes a full-scale experiment designed to identify any interaction between pavement stiffness and effects related to surfacing temperatures during laying and early service life. From laboratory tests an assessment of the role of the binder has also been made. The results of these investigations are discussed in relation to the working party's original analysis and the major causes of slippage failure identified. (Author/publisher)
Abstract