Pavements in the Public Domain

Dr Anna-Carin Brink

The aim of this presentation is to provide insight into the geotechnical properties of the materials commonly used in Perth in the construction of pavements, that must be considered during the design. Specifically, where it comes to the Public Domain, the impact of incorrectly designing, for example concrete footpaths and architectural features such as granite setts/pavers are often overlooked, resulting in unsightly failures. The subgrade in Perth consists mostly of Perth Sand which is generally free-draining. Publications on the investigations into adequately testing and controlling compaction of the sand and the development of the Perth Sand Penetrometer (PSP) date back to the 1960s.  Due to the free-draining nature of the sand, compaction can’t be measured as a percentage of modified density, but must be determined using the Density Index.

Dry Density Ratio versus Density Index

Since the 1850s Tamala limestone has been extensively used as basecourse and/or subbase material in Perth.  The quality of the limestone currently available in Perth has largely deteriorated, it breaks down during construction and more than 60% consists of particles passing the 2.36 mm sieve, i.e. sand.  This partly explains why bituminous materials do not stick to limestone. Another reason is due to surface tension causing balling up of standard primes/seals, necessitating the use of anionic emulsions. For the construction of heavy-duty pavements crushed rock is used as basecourse. High quality granite with a resilient modulus of more than 600 MPa is generally available. Due to its low plasticity, it must not be used as a wearing course as it de-densifies and ravels when exposed. Material meeting the requirements of unsealed gravel wearing course must be used for applications such as gravel hardstands. Red asphalt containing 10 mm nominal size laterite aggregate and red iron oxide pigment is used in pedestrian areas and on shared/bicycle paths. Laterite/ferricrete is a weathered pedogenic material with an aggregate crushing value (ACV) of up to 40%, which results in breakdown when used in heavy-duty applications. Although low, the permeability of the laterite allows absorption of binder often resulting in ‘dry’ asphalt mixes with low durability. A concrete pavement is as good as its support meaning all concrete pavements must have a subbase. Concrete footpaths must not be built directly on sand as it is non-cohesive. It pumps through at joints (even in low traffic applications) and erodes, resulting in corner and edge breaks due to loss of support. There is no standard in Australia for the dimensional design of natural stone setts/pavers on top of concrete. Local Authorities may have in-house standards, but most have not been technically verified and are using incorrect terminology and inappropriate details, often resulting in structural failures and trip hazards.

Corner crack in concrete footpath
Failure in natural stone pavers

This presentation will highlight the various elements mentioned above that make up a pavement structure, with emphasis on interpreting and applying the geotechnical properties of the various materials to obtain sustainable pavements in the Public Domain.

About the speaker

Dr Anna-Carin Brink Pavements Lead – Australasia, Arup

Anna-Carin is the Arup Pavements Lead for Australasia. She has a passion for Pavement Engineering and loves to impart the knowledge that she has gained through theoretical and on-site practical experience on diverse projects over various geological, geographical and climatic regions. She is a Chartered Engineer with more than 38 years’ experience.  She has been involved in the design, construction, maintenance and rehabilitation of many road and airport pavements. Designs have varied from unsealed gravel to heavy-duty industrial pavements. She has been based in Perth, Australia since January 2012 and has been working on projects across Australia, New Zealand, Africa and Hong Kong. Since 2001 she has been a member of the International Society for Concrete Pavements, and as a Director on the ISCP Board, since 2006 has gained international recognition with research into the design, construction and maintenance of rigid pavements. She is a recognised expert in the Pavement Engineering industry and has authored and presented several papers and publications over the years, covering topics across rigid and flexible pavements.  She has actively been involved with the technical review of papers for numerous international conferences, as well as Moderator for Podium Sessions. Through her research she has developed industry-recognised innovative and practical solutions to many issues such as the anchor-beam jockey slab transition between flexible and rigid pavement structures.  The Weibull probability density function defining aggregate interlock load transfer at joints in concrete pavements, developed for her PhD, has been incorporated in the cncPave software package; used worldwide.

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