Overview
In Australia, sprayed seals provide a cost effective surfacing on over 80% of the all weather road network. Single/single seals (one binder application followed by one layer of aggregate) are the most common type. The binder is usually (kerosene) cutback bitumen or straight bitumen, with polymer modified binders (PMBs) used on a small proportion of sites where improved properties are required.
The strength of a seal depends on the formation of an interlocking aggregate mosaic. Seals are designed using the Austroads seal design procedure. This is a volumetric approach based on the binder level being about 2/3 the height of the aggregate particles. Aggregate spread rate and binder application rate are determined taking into account a number of factors, including aggregate size and shape, traffic level and composition, the existing surface condition and stone embedment.
The structural component of the pavement is usually unbound granular material. Natural gravel may be used for more lightly trafficked pavements in rural areas. A typical heavy duty pavement (up to 8,000 heavy vehicles per day equivalent to 70 million ESAs) might comprise 200 mm of crushed rock base course and 200 mm of crushed rock subbase course, with the remaining thickness consisting of appropriate lower subbase materials including any capping material over moisture sensitive subgrades.
Construction of a granular base course may require specialist local knowledge, particularly where marginal or non-standard material is used. Appropriate techniques must be used to prepare the surface of the base prior to application of the primer and initial seal coat.
The life of a typical single/single seal may vary between about 7 and 15 years, depending mainly on summer temperature at the site, although a small percentage of seal will last more than 20 years. To obtain adequate life, the correct treatment must be selected for the prevailing conditions and traffic.
How to find the information you are looking for?
You can search the Australian section of the website in two ways. Regardless of which you choose, you should end up with the same answer.
However, each approach gives access to different sorts of extra information along the way.
Publisher's pages
In this approach you visit a page which describes the sort of information avaliable from the publishers - see below
Austroads has the greatest number of guides, specifications, test methods and research reports.
ARRB has some published information which can be accessed directly from this site.
Of the Australian road agencies, VicRoads has by far the largest number of technical notes and other publications and their Bituminous Sprayed Surfacing Manual is particularly recommended.
Key documents
Perhaps the quickest way is to go to the key documents page. There, select the technical area of interest - such as bitumen or treatment selection - and then click on the links.