The Highways Agency (HA), Quarry Products Association (QPA) and Refined Bitumen Association (RBA) all appreciate the need to maximise the durability of asphalt pavements. Therefore, one of the tasks in their jointly funded research project at TRL entitled Performance and Durability of Asphalt Roads was Durability of Asphalt Pavements. One of the principal aims of this task was to identify the techniques and procedures currently considered to produce the best practice and to produce a Best Practice Guide based on that knowledge.
Durability as a concept needs to be clearly defined for any guide on best practice, and it was decided to concentrate on the durability of the whole pavement rather than just that of the asphalt mixture. For this purpose, pavement durability is defined as:
the retention over the structure’s expected service-life of a satisfactory level of performance without major maintenance for all properties that are required for the particular road situation in addition to asphalt durability.
The aim of the Best Practice Guide is to encourage everyone working in the asphalt industry to contribute to making pavements as durable as practical. To enable people to fulfil this aim, they need to know not only the actions they can take to enhance or damage durability, but also how their actions may impinge on the efforts of others. An understanding of the intentions and constraints during other phases should help to produce designs that are buildable, materials that have the potential to perform and a pavement that is fit for purpose.
The desire to achieve longer durability for asphalt pavements is common among those involved in designing, specifying, producing and laying asphalt materials and pavements. Therefore, all parties have to work together in a spirit where positive actions are rewarded and negative actions or omissions are discouraged.
The main aspects that lead to durability are:
The control of water (getting it away from the structure if not actually stopping it ever entering); Limiting the number of and sealing joints (both vertical and horizontal); and adequate compaction (particularly at joints).
These aspects are likely to rise in importance with the predicted changes from global warming, with hotter, dryer conditions in summer but more intense rainfall, and possibly more of it, in the winter. Such conditions will exacerbate the potential for unwanted water to penetrate into the pavement, causing irreversible damage to the asphalt. However, lack of maintenance, particularly of the drainage, can lead to premature failure even if the best practice was followed in design and construction.

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