Design of seals has seen significant development in many countries in the past two decades, particularly in South Africa. Nevertheless, selection of emulsion grade and type for various seal designs and cold asphalt mixes is not being done systematically. Design of emulsions has advanced based on empirical information and experience of consultants and producers. In order to establish a framework for seal selection, the most relevant causes of seal failure were first analysed. This required differentiation between construction related failures and in-service failures. Fattiness, ravelling and fatigue cracking ranked as the three dominant seal failure mechanisms. Secondly, the environmental factors that affect seal performance were identified, including underlying layer support, traffic (speed, volumes and tyre pressure) and climate (temperature, rainfall and humidity). Finally, taking account of the environmental influences, the binder properties that affect the performance of seals were evaluated. This includes sprayability, breaking-rate (for emulsions), drain-down, wettability (adhesion), fatigue, cohesion and other rheological properties. Using these requirements, a preliminary performance selection framework of binders for seals was established and is discussed. Guidance is provided for taking account of climate during and after construction as well as traffic conditions in the binder selection procedure. (a) For the covering entry of this conference, please see ITRD abstract no. E217100.
Abstract