Austroads releases new structural design method for flexible pavements

A new structural design method has been published by Austroads for flexible pavements containing lightly bound cemented materials.

Ross Guppy, Austroads’ Transport Infrastructure Program Manager said the scarcity of quality, cost-effective road‑building materials is an increasing national challenge.

“Treating granular materials with chemical binders is becoming commonplace as reserves of high‑quality materials are exhausted or their haulage over long distances is cost‑prohibitive,” he said.

“Adding a small amount of cementitious binder to non-standard granular materials can produce a fit‑for‑purpose base or subbase at a significantly lower cost than the use of crushed rock that complies with standard specifications.”

He said cementitious binders can also be added to gravels complying with standard specification and can improve rut resistance for moderate to heavy traffic roads or high rainfall environments.

“These lightly bound cemented materials are particularly useful in pavement rehabilitation and heavy patching but they have been used for new pavements,” he said.

Austroads found Queensland Department of Transport and Main Roads has intermittently used cement stabilisation of pavement materials for many years. The use of lightly bound cement bases has recently increased in the state, particularly in North Queensland.

An examination of some of these pavements in Queensland found that with sufficient base thickness and subbase support a low strength material pavement, such as this, can be constructed as the right method will reduce the possibility of micro or macro-cracking.

Austroads’ structural design method was informed by field deflection testing, lab testing and analysis.

This method can be used on pavements with lightly bound cemented materials and heavily bound cemented materials in the post-fatigue cracking phase of life.

The design method includes a new elastic characterisation method and design charts to select lightly bound cemented base thickness to prevent the development of cracking.

The research also outlined the need for a national test method for mixing, compacting and curing of unconfined compressive strength specimens to improve consistency of results across jurisdictions.