2021 A Subbase Odyssey

The subbase layer has a critical role in the design of concrete pavements. Australia is unique in its routine application of a lean mix concrete subbase layer to much of the heavy-duty concrete pavement highway network, the result of which is a reluctance to adopt any alternative (“why fix what isn’t broken”). Rightly or wrongly this mindset has led to lean mix concrete being specified in many concrete paving applications such as track slab, and non-lineal assets such as ports and intermodals, industrial pavements, etc. Notwithstanding local practice, subbase types overseas vary significantly, as do performance outcomes. This paper will present a summary of typical subbase specifications for various types of concrete pavements along with several typical overseas practices. Due to local industry pressures, such as fly ash and other SCM availability, constrained budgets and concrete pavement rehabilitation techniques, there is a need for renewed consideration of other subbase types in Australia. This paper seeks to outline those instances where an alternative subbase type should be considered or seemingly provides a better engineering or ‘whole of life’ outcome. Aurecon’s experience across ports, highways, airfields, rail, and intermodals enables us to provide a unique insight into the design, construction and operational considerations that are necessary when selecting the appropriate subbase type for a given situation. The outcome of this paper is intended to be a better industry understanding of the risks of alternative concrete pavement subbase types, along with identifying opportunities to benefit the concrete pavement industry now and into the future.