RECYCLING / BSM TECHNOLOGY
- Date: Next dates to be confirmed
- Location: Virtual (MS Teams platform)
- Facilitator: André Greyling
- Presenter: Dave Collings and André Greyling
This training module takes a ”helicopter view” of pavements, what they are, what purpose they serve, which materials are used for construction, how these materials behave in pavement layers and why roads need ongoing maintenance and rehabilitation. It is an introductory course for those wanting to understand the basics of pavement engineering without being blinded by science.
At the end of this training, delegates will be familiar with the following concepts
- a basic understanding of the relevant technology applicable to different pavement materials
- the meaning of structural capacity and how it is determined
- the leading role played by Mother Nature in pavement engineering
- why pavements are constructed in layers using different materials
- the characteristics of different materials that are used to construct pavement layers
- where specific materials should be used in a multi-layer pavement structure
- how structural capacity is affected by changing the thickness of layers
- options for achieving the same structural capacity using layers of different materials
- estimating the initial construction cost and life-cycle cost for different pavement structures
Hot mix asphalt is not always the answer
The world today has been conditioned to believe that road pavements are constructed with hot mix asphalt (HMA), the more the better. But, the Romans never had HMA and many of their roads have endured for over 2000 years, albeit with some maintenance interventions. They were built using granular material comprised of gravel sourced from local pits and hard stone from quarries, either in small blocks or painstakingly broken down by hand. Both HMA and stabilising agents were still millennia away. Why have these pavements performed so well? Using today’s mind-set, how is such an achievement possible without HMA?
This training module starts by looking at those early roads and finding answers to these questions. The Romans were unlikely to have had the mathematical skills that allowed them to model pavement structures. How did they get it right? Undoubtedly they learned as they went along using trial-and-error and building on experience. The result is that we now have some magnificent long-term pavement performance (LTPP) data to analyse and use to understand how pavements function. And it is the understanding of pavements constructed with granular material that provides the building blocks for what happens when the properties of granular material are enhanced by some form of treatment, especially bitumen stabilisation.
The starting point in determining the competence of any pavement structure is the definition of purpose; what loads will the pavement have to carry and over what period of time. The concept of “structural capacity” in terms of repeated axle loads of a specific magnitude is explained together with methods commonly used to estimate this important number that becomes the target for designing a pavement.
Behaviour of pavement materials
Different ways of achieving this target are then explained, starting with an appreciation of Mother Nature’s role in pavement engineering. Since all pavements serve the purpose of protecting the subgrade (Mother Earth) from the loads to be applied, it is important to understand what happens “down there”. This is all covered under the section dealing with granular materials, their behaviour and how they fail when they cannot carry the applied load. The concept of “modular ratio” is explained in detail since this is Mother Nature’s primary influence on how layers of material in a pavement structure respond to applied loads and how they protect the subgrade.
The different technologies available for treating granular material are then covered, commencing with HMA and cement stabilisation. The behaviour of pavement layers that receive such treatment is explained together with their respective distress mechanisms. Bitumen stabilisation is then addressed. This relatively new method of treatment receives a detailed explanation, focusing on the properties of bitumen stabilised material (BSM) and why such material cannot be grouped in the same category as other treated material, especially HMA. Its closest relative is untreated granular material, which reinforces the need to appreciate the behaviour of granular material, something the Romans clearly understood better than today’s generation of pavement engineers.
For those who want more, three other training modules are on offer. These modules are all focused on cold recycling and bitumen stabilisation, explaining the various aspects of the technology in detail. A practical hands-on approach is adopted to assist delegates to understand the reasons for following certain procedures to obtain results, as well as the ability to interpret the results to arrive at a meaningful conclusion. These modules include:
- Laboratory training. How to design for bitumen stabilised materials (BSM mix designs);
- Pavement design training. How to determine an appropriate pavement rehabilitation structure by recycling / bitumen stabilisation; and
- Application training. How to use a recycler to achieve the required pavement.