5 minute read
WASTE The road to sustainability
THE ROAD TO SUSTAINABILITY
The use of waste materials in South African road construction
Advertisement
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.
The 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).
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.”
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.
Construction of road trial section made from recycled tyres.
CASE STUDY ON THE USE OF WASTE PLASTIC
Construction of road sections on Road P159/1 (R80) in City of Tshwane, Gauteng
The CSIR, along with the Department of Science and Innovation (DSI), as well as the plastics and roads industry, have recently worked on a demonstration project in South Africa to evaluate the feasibility of using waste plastic in road construction. The project aimed to identify lowvalue plastic types and evaluate their potential usage in asphalt road surfacing in accordance with South African road design standards and environmental conditions.
The culmination point for the project was the construction of Gauteng’s first “waste plastic” road trial section, currently located on the R80. This trial section was used by the CSIR’s Smart Mobility Cluster for proof-testing plastic-road technology in South Africa. The CSIR has to date successfully completed a full-scale research investigation and laboratory programme that was validated through Heavy Vehicle Simulator (HVS) testing.
The project’s sponsors and key stakeholders from the DSI, Roadmac Surfacing (Pty) Ltd (Raubex Group) and Much Asphalt were crucial in supporting the CSIR’s project team throughout construction.
Although technical findings from the project are still currently being published, the CSIR’s project team stated: “The project has successfully showed potential in using specified waste plastic materials to design rut resistant asphalt mixes without compromising on other asphalt performance requirements. The approach requires the adoption of necessary criteria to establish a consistent source of waste plastic.”
The research project highlights the need to understand the mechanism that improves rut resistance to ensure that this benefit is realised through controlling performance criteria and handling of the asphalt mix. The research identified requirements for measuring additional asphalt properties that would quantify the contribution of the asphalt layer to safety, health and environmental sustainability.
Project team included: Georges AJ Mturi, Johan S O’Connell, Imraan Akhalwaya, Theresa George, Vincent O Ojijo, Tladi Mofokeng, Nonzwakazi Ncolosi, Michandre Smit and Linda Godfrey.
Construction of road trial section made from waste plastic. The end of the road
Feedback from these case studies is aimed at encouraging government and road industry stakeholders to adopt the use of waste materials for environmental benefits, as well as for the improved performance of road surfaces. The technologies will require the development of application guidelines to promote a better understanding of the suitability of waste materials for road projects and therefore lower the risk of premature failure of roads.
