Opportunities for further sustainable practices in concrete pavement design in Australia

Abstract

Sustainable practices are already considered in pavement design decisions for new highways in Australia.  In NSW, it is even more critical where concrete pavement design and construction of highways are widespread in the State, and the asphalt industry is keen to demonstrate its sustainability credentials.

It is typical for concrete pavements to consist of a normal-strength (35 MPa) concrete base, without reinforcement, supported by a lean-mix concrete subbase.  The pavement layers are supported on a durable selected material layer 300 mm thick, and the upper formation layer is applicable for both flexible and concrete pavements.  The 2.5 m wide shoulders are also the same thickness as the concrete base and subbase to allow for continuity of structural support to the base and trafficking of the shoulder during road preservation activities for up to 12 months.  The thickness determination in the Austroads pavement design guide is based on the PCA design model, which has served Australian engineers with a simple, unambiguous, and reliable design procedure for several decades.

For over two decades, concrete pavements have 40 to 75% and 25% fly ash as a replacement for cement in the subbase and base layers, respectively.  While ground slag is sometimes used as a replacement for cement, access to ground slag is less than desirable.  Crushed glass has also been used for sand replacement in subbase and base concrete.  Using recycled materials in concrete pavements is limited by availability and transport costs, and the next area to increase sustainable practices is in the design process.

This paper will explore which design parameters could be reduced, which may result in less concrete and hence lower carbon, and the uncertainty these changes may have on the durability and structural performance of concrete pavement design over a 40-year design period.  The paper will also consider the impact of climate change on pavement performance and larger heavy vehicles regularly having access to the road network in Australia, such as a vehicle with multiple trailers and a gross mass of 130 tonnes.