 Shell, a world leading provider of bitumen products and services, looks at the benefits of using modified bitument for road paving
Polymer Modified Bitumens (PMBs) are widely hailed as the universal panacea to all pavement problems; this is a fallacy in the same way that supercars are automatically considered the best cars in the world. By this I mean that PMBs will address many of the problems of the road, but not all, just as a supercar is great on high-speed straights and corners but not as a family car to take three children to school – the product must be meet the requirements for which it is to be used.
Maximum value
In order to extract the maximum value out of any PMB you must ensure that the lower layers of the road are properly constructed, compacted and drained and that the traffic loading, climate and desired life of the pavement is understood. Once all of this is ensured then the choice of PMB can be made. In choosing a PMB many clients/contractors ask the following questions: - How can you claim that the use of PMBs is more sustainable?
- Why should I pay more for some products, aren’t they all the same?
- What has changed so that I now need to use a PMB rather than Penetration grades?
- Have you any proof that PMBs provide the benefits you claim?
- If PMBs are so great, why are they not specified for all wearing courses?
- What is the next step after PMBs?
Sustainability
PMBs, such as the Shell Cariphalte range, are more sustainable in that if they are properly designed into the overall structure, then pavement life can be significantly extended, saving money in whole life terms, reducing the amount of construction materials used, reducing energy consumption and reducing the number of vehicle movements associated with construction and maintenance (thinner structures and longer maintenance periods). Added into this must be the consideration of which PMB to use as they are certainly not all the same. This requires that the PMB supplier be clearly able to demonstrate which mechanical properties of the PMB, and therefore asphalt, are improved by the modification; this necessitates that a PMB supplier, such as Shell, be used that can demonstrate this type of information, provide technical support as required, and can demonstrate a long track record – Shell has been supplying PMBs for more than 40 years.
Proof that PMBs really work is always difficult to come by as it is rare that a modified and unmodified section of road are laid together so that they experience exactly the same conditions. However, the Asphalt Institute in the US produced a book, entitled ‘Quantifying the Effects of PMA (Polymer Modified Asphalt) for Reducing Pavement Distress’, which provides a lot of convincing independent evidence to this effect. Additionally, there are many instances around the world where PMBs have been used because other solutions have failed and the PMBs have stood up to the onerous conditions.
The need for PMBs is increasing all the time with the increasing traffic volumes, axle loads, tyre pressures and temperatures, all of which have a detrimental effect on the pavement, as well as with the environmental drive towards all industries being sustainable.In the long term it is entirely feasible that we will move towards PMBs not just in all surface courses but in all bound layers of the road (such as Shell Cariphalte Base) to ensure that we get the maximum performance with the minimum thickness and reduced disruption due to maintenance.
Functionality
Today PMBs are becoming widespread, with developing nations using them to build their infrastructures as well as developed nations using them for maintenance – this leads to the question of what is next?
The next generation of PMBs adds functionality beyond improved mechanical properties, an example of this is Shell Cariphalte Fuel Resisting, a PMB designed to provide all the benefits of a traditional PMB such as resistance to permanent deformation (rutting) and fatigue cracking, as well as significantly increased resistance to damage by fuel, particularly important in areas such as airports where loose material, caused by a fuel spillage, could cause Foreign Object Damage. Beyond this next generation of multi-functional PMBs, Shell are beginning to ask the question what else can we make a road do beyond carrying goods and vehicles from point A to point B.
The answer to this question forms the basis of our extensive research and development programme where we have bitumen, asphalt and pavement experts working with our customers to find the solutions of tomorrow. |
