Putting old tyres back on the road, sustainably
Only 20% of rubber tyres are recycled in South Africa, so the reuse of waste rubber in asphalt has the potential to significantly increase this figure and support greater sustainability.
AECI Much Asphalt has supplied several road projects with asphalt mixes containing Ground Tyre Rubber (GTR) in the past year, notably to customers in eMalahleni, Mpumalanga and the Western Cape. The increased attraction of this more sustainable solution has also led AECI SprayPave to manufacture binder containing GTR in-house, using technology that adds significantly to the binder’s shelf life and lowers energy costs.
GTR enables the use of more binder in the asphalt without the risk of bleeding or excessive deformation due to mix viscosity. Increasing the amount of binder provides longer lifespans for roads and lower rolling noise on the asphalt surface.
While this technology is not new to South Africa, it is making paving mixes containing waste tyre rubber increasingly popular.
HOW GTR WORKS IN THE ASPHALT PRODUCTION PROCESS
In the wet process, there is between 18% and 22% GTR in the binder, which constitutes between 5,5% and 7% of the mix. While this does not seem like much, the GTR quantity increases exponentially with the large volumes of asphalt produced for major road surfacing projects.
In the hot mix process, GTR requires production of the binder on-site as its use is time sensitive. Blenders, digestion and header tanks and feeder pumps are required.
In the warm mix process, the binder does not have to be mixed on site and can be hauled to the asphalt production plant and utilised without the need for additional equipment. Warm mix asphalt has the added advantage of a lower energy requirement, translating into less environmental impact.
In 2020, AECI SprayPave commissioned a new mobile blending unit with the capability to produce bitumen at a rate of 25 tonnes per hour, incorporating 25% GTR. It is using between 50 tonnes and 150 tonnes of GTR per month depending on orders for Extended Bitumen Rubber (EBR). EBR blends are produced on a “to order” basis and a significant increase in demand has been noted in the second half of 2021.
The advantages of EBR are:
Longer shelf life
Long-lasting, maintenance-free and moisture-resistant roads
Lower spray temperatures
Reduced carbon footprint, energy consumption and emissions
Reduced viscosity and longer workability (than conventional GTR mixes)