The Road Less Travelled

by Isabelle Sambles

45.5 million people use the road each day in the UK. With this statistic in mind and in light of the headmaster's recent choice for his address in the Whole School Assembly, I decided, as the budding civil engineer that I am, to look into the challenges that occur in African countries when they decide to construct roads, and what unconventional concepts can be used.

The first material I researched was tarmac. It is found on almost all of the roads in Britain, and is used because it is long-lasting and doesn’t pick up mud or dust so it is good for the cars. Tarmac is made from tar-grouted macadam, bituminous surface treatments, and modern asphalt concrete and is created at very hot temperatures; due to it containing a substances derived from crude oil, especially bitumen, which is comprised of large molecules, it means that is not very volatile and is very viscous. Thus, once it cools, it will solidify and can withstand the road traffic. However, it is a black material, thus absorbing a lot of thermal radiation. This means that the tarmac will get hot very easily and, once it exceeds 50 degrees, it will start to melt and thus, in the temperatures of the African sun this would not be the best material to use. Furthermore, there is no need for it to have as large of a tensile stress as people do not use the road as frequently.

Before tarmac, concrete was used. Concrete is created in a similar manner; mixing cement, water and crushed rock and sand, the cement binds everything together. Once dry, it can withstand cars and traffic. However, it is more prone to cracking and breaking than tarmac which is why it was replaced.

A more common material used in Africa is laterite, which forms dirt roads. These roads contain a lot of clay which becomes very hard in the dry seasons; however, when wet it can become very slippery and hard to drive on. Therefore, knowing that it rains a lot, especially in the more southern parts of Africa, it is not the best idea to build roads out of this material due to the amount of rainfall they get.

A material which may be better suited might be a bituminous surface. These are used in a lot of developed countries on low-traffic roads, and would be suitable for the roads in Africa. You could use a thin membrane surface: an oil-treated aggregate (coarse particulate material used in construction) which is laid upon a gravel road bed. This will reduce mud and gravel problems. The only issue with this type of surface is that if there is over application of emulsion it can create a slippery surface when wet and the road will “bubble” in the heat.

Another solution which you can use is plastic roads. These roads are being introduced in India to deal with the recycling problems and are created by mixing the recycled plastic in with tar. These have been used in India for 15 years and are proving to be very durable and do not weather. By adding polymers into the roads it also means that the roads don’t buckle and deal with heat a lot better. It is proven that they will melt at over 20% higher temperatures compared to roads made out of tarmac. 

Ideally then the best solution would be tarmac and plastic roads in Africa, but these require factional distillation which is an expensive process and also is a fairly new concept. So practically it is better to use Laterite. However, the poem ‘The Road Not Taken' by Robert Frost is based on the concept that do you go with the track that has been used a lot and is certain to hold and do the job, or do you take the one which will help you in your travels but has less certainty. Thus, in futuristic terms it is better to take a leap of faith and use the tarmac-plastic roads and then see if this increases transport links in the country and helps trade in the economies of Africa.