Adding risk to a model for reseal intervention due to binder ageing.

The maximum life a seal can achieve is controlled by the rate at which the binder hardens through reaction with oxygen in the air. When hardening reaches a critical viscosity level (dependant on the local climate), the seal cracks or loses aggregate. A model was developed to predict maximum seal life (reseal intervention point) by combining a binder hardening model and a distress viscosity model. Inputs for the two models were site temperature parameters, binder durability (resistance to hardening) and seal size. The current paper describes the addition of a risk factor to the model. The risk factor is an indicator of the level of risk an asset manager is prepared to accept by delaying resealing at a site past the first signs of distress. Risk factors were developed for the sites in the distress viscosity database and a correlation exercise carried out to develop a new distress viscosity model. Intervention times calculated using the new model compared well with reported intervention times for Local Government (LG) and State Road Authority (SRA) roads. Guidelines were prepared to assist users assign risk factors to particular sites. The model should help asset managers obtain the optimum economic life from their sealed surfacings. (a) For the covering entry of this conference, please see ITRD abstract no. 0612AR242E.