WASTE
THE ROAD TO SUSTAINABILITY The use of waste materials in South African road construction The Council for Scientific and Industrial Research has recently been involved in several new research initiatives geared towards providing alternative waste material products, specifically to be used by the asphalt pavement industry in South Africa.
T
he research focus of the CSIR has been centred around creating a more inclusive and sustainable approach to future road construction, particularly through increasing the potential for job creation, increasing economic benefits, producing better performing roads and trying to resolve South Africa’s environmental challenges. One of the CSIR’s recent successes has been around the adoption of locally produced waste alternatives (opposed to importing costly conventional road and waste products).
CASE STUDY ON THE SUSTAINABLE USE OF RECYCLED TYRES Construction of a road section in Roodepoort, Gauteng
In 2019, the CSIR in collaboration with Much Asphalt (Pty) Ltd successfully constructed a road trial section in Roodepoort using locally available micro-fillers and recycled tyres. The project came to fruition when both products under development were successfully paved into a controlled road trial section, after a year of combined laboratory development and rigorous evaluation. The 200m long trial section includes a 60mm modified enrobés à module élevé (EME) base layer and a 40mm modified bitumen-rubber asphalt layer that was constructed over a cleaned gravel base. This layer was treated with a SS60 tack-coat prior to paving. The location of the trial section specifically allows for continual performance monitoring, which includes up-to-date details on the distribution and volume of traffic that moves across the section. Georges Mturi, CSIR’s project manager speaking on the success of the project: “During both the development and trial phase, several performance characteristics were evaluated as predictors of in-situ performance, which served as the baseline for the performance evaluation that were set to run on a three-month basis for a period of one year after construction.” In this regard, he adds “The evaluations and visual inspections have shown that after nine months of traffic and environmental exposure, the layers are performing as expected.”
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Construction of road trial section made from recycled tyres. To date, no edge breaking is present where heavy vehicles are moving onto and off the surfacing, no permanent deformation is present on the surfacing (particularly at stopping locations and where regular vehicle turning takes place) and, lastly, there are no signs of any deflection or temperature-induced crack formations taking place. Joanne Muller, regional laboratory manager at Much Asphalt says, “The developed and trialled technologies aimed at improving the performance properties of standard 10/20 based EME, while also acting as a viable replacement product for standard styrene-butadiene styrene (SBS) modified A-E2 binder, without detracting from pavement performance. These are deemed effective as they can assist industry practitioners in their endeavour to provide long-lasting pavements to society.” Overall, the project is aimed at assisting bitumen users, asphalt manufacturers and other intermediary bitumen suppliers. It is expected that the technology will enable the correction of poor bitumen to pass performance specifications. Additionally, the technology may also improve the performance of standard bitumen from one grade to another, especially in the event of national bitumen shortages. It is also important to highlight that a major benefit of this invention would be an increase in the recycling rates of waste tyres in South Africa, which will ultimately lead to better-performing roads and a greener environment.
