Concrete barriers aiding the fight to reduce road fatalities
Reduction of road fatalities is one of the top 10 goals outlined in the Commission’s White Paper on transport. The EU aims to halve road casualties by 2020 and move closer to zero fatalities by 2050. While there has been a reduction in road fatalities since 2010, the rate at which this is happening has slowed down. The European Road Assessment Programme has indicated the need to adopt improved barrier designs to protect vulnerable road users like motorcyclists. Rubberised concrete has been suggested, however challenges involving its strength and durability are still to be addressed. The SAFER project, with the support of the Marie Skłodowska-Curie programme, worked to develop road barriers made with concrete and recycled materials from end-of-life tyres. The recycled products, when incorporated in concrete mixtures, lead to road barriers with outstanding deformability and energy absorption capacity, paving the way for forgiving road infrastructure. Prof. Diofantos Hadjimitsis, project coordinator, notes: “The use of recycled rubber and steel wires supports the Horizon 2020 transport research and innovation priorities for sustainability and resource efficiency.”
The results are promising
Phase 1 provided the project with the opportunity to ascertain the feasibility of SAFER’s road barriers, prepare reports on the experimental performance of steel fibre-reinforced rubberised concrete material, and conduct numerical analysis and a life cycle assessment. Key overall results highlighted the fact that SAFER’s barriers can be developed with steel fibre-reinforced rubberised concrete, using end-of-life tyre materials. Hadjimitsis adds: “This ensures the circular economy concept is supported and at the same time this enhances the material energy absorption capacity, compared to conventional concrete barriers.” Project researcher Thomaida Polydorou was also able to accomplish additional experimental work. “She investigated the weak zone of the innovative material and from there developed a simple procedure that enhances the bonding action at the interface between the cement paste and rubber particles in rubberised concrete,” reports Hadjimitsis.
Overcoming material challenges
The project’s achievements did not come without challenges. “The main unexpected issue we faced during the SAFER project was the limited workability – flowability – of the material,” highlights the coordinator. This was resolved by additional experimental testing that revealed that the specific gravity and water absorption of the rubber particle sample used in this study did not resemble the expected values, based on the literature. “Determination of accurate rubber-specific gravity is key in designing rubberised concrete mixtures, as the rubber particles replace mineral aggregate by volume,” adds Hadjimitsis. Additionally, while rubber is considered hydrophobic, contamination resulting from tyre recycling processes can significantly alter material behaviour. “So, in this study, the mixture was adjusted based on the actual rubber sample’s properties to achieve adequate workability,” the professor explains. This adjustment enabled the researcher to cast the samples required for the experimental testing rounds. “It is suggested however that specifications are developed for recycled tyre rubber particles used in concrete, to eliminate such difficulties,” he reports. Moving forward, Polydorou will continue working on enhancing the material’s fresh and hardened properties. This will be carried out by applying the treatment method developed and proven to have positive impact on the interfacial transition zone of the material. “Then we will proceed with further improving the SAFER Barrier product,” concludes Hadjimitsis.
Keywords
SAFER, rubberised concrete, road barriers, motorcyclists, end-of-life tyre, transport, vulnerable road users, circular economy
