Q&A with EIC's David Barker - Challenges in constructing unbound granular pavements
- December 01, 2022
- Construction and commissioning
Question: From the contractor's point of view, what are the key challenges in constructing an unbound granular pavement?
DB: I think the key construction challenges are:
- finding the right skill set in people onsite
- achieving consistent moisture content that’s in the right range
- surface preparation for sealing
- achieving the required performance based primarily on specification conformance, particularly on construct only projects
- on brown field projects in particular, programming the works around weather, seasons and public access and road openings.
Having people onsite who have developed an understanding of each material type and the importance of achieving consistent moisture content both horizontally and vertically is a challenge but one we are constantly working on.
A lot of the pavement materials come to site after they’ve been run through a pugmill for moisture control, so there is some level of moisture control when doing that. Achieving consistent dryback throughout the layer is really important and is a critical part of the pavement performance. This also needs to be done to ensure consistency across a lot both vertically and horizontally.
For sprayed seal roads getting the right surface preparation and texture is critical to seal performance and is a real balancing act with how much work you put into slurrying and compacting and then how much sweeping you do. This is something that takes time and expertise to get right, particularly considering I think as an industry we often expect too much from a sprayed seal.
Lastly, the thing that has always stuck with me on granular pavement construction is that it takes time. You can’t just place it, compact it, put some black stuff on the top and expect it to work.
Question: How do you account for the variabilities in material and moisture content in the field?
DB: Our teams track the delivered moisture content day by day to allow us to make adjustments at the quarry and to calibrate against what we’re seeing onsite.
I want moisture content to be right, but it is the consistency across a lot and day-to-day that I really want to see happen. If the moisture is consistent and rolling patterns are consistent, then the compaction will be consistent and we give the pavement the best chance of performing consistently.
The development of technology that can measure moisture content, or even indicate its consistency, over a large area in real time would really be a benefit in this regard.
About EIC’s involvement with SPARC Hub research
CIMIC Group’s engineering and technical services business EIC Activities is the major industry partner to the Smart Pavements Australia Research Collaboration (SPARC) Hub, in conjunction with Monash University, the Australian Road Research Board (ARRB) and Austroads, which represents the Australian and New Zealand transport agencies.
We are working to make pavements safer and more economical with a lower environmental footprint. Our sponsorship of nine innovations includes a focus on smart sensing, construction and maintenance monitoring.
Delivering smarter, more sustainable transport pavements
SPARC Hub aims to advance and transform the Australian pavement manufacturing industry by addressing short, medium and longer-term transport challenges.
Through high-quality, collaborative research in innovative materials, smart technologies and advanced design, construction and maintenance methods, they are working to make Australia's transport pavements smarter and more sustainable.
EIC Activities was invited to be a contributor to research topics and facilitated CIMIC Group funding of nine research projects.
The research projects focus on unbound pavements with thin surfacing, advances in bound pavement bases, smart sensing, construction and maintenance monitoring including:
- Subgrade model incorporating unsaturated soil behaviour, cyclic loading, and climatic effects and test methods
- Unbound pavement material model incorporating unsaturated soil behaviour cyclic loading, and climatic effects and test methods
- Temporary (short duration) pavement design parameters based on short durations and relatively low number of standard axles
- Fibre (plastic/steel/graphene) as potential reinforcement in continuously reinforced concrete pavements (CRCP). Provide a review of graphene as potential reinforcement CRCP
- Quantifying the benefits of intelligent compaction for unbound/subgrade pavement performance
- Use of L-band radiometer or other suitable sensing techniques for remote moisture measurements unbound materials and soil subgrades
- Remote sensing and advanced analysis of measurements of density through the possible use of appropriate sensing techniques, including LIDAR and GPS
- Enhanced road safety through smart sensing for road construction, planned interruptions/worksites and interaction with autonomous vehicles
- Microwave dry-back of granular pavements.
Read more about SPARC Hub research projects here.