Mechanical and healing properties of asphalt mixes reinforced with different types of waste and commercial metal particles

Improper disposal of metal waste in landfills is one of the primary means by which metals, mainly produced in different industrial sectors, reach the soil and ground water. These can migrate to surrounding ecosystems and bio-magnify in plants and animals endangering human food chain. At the same time, the addition of metal particles in asphalt mixes produces a series of beneficial effects, such as enhancing their mechanical performance, durability and electrical conductivity making possible applications, such as ice/snow melting and cracks healing by electromagnetic induction. The present investigation assesses and compares the use of two different types of waste metal fibres (recovered from old tyres and shavings from machining industry) and two other types of commercial particles (steel wool and steel grit) regarding their effect on volumetric, mechanical and healing properties of asphalt mixes. Results showed that, with a proper design, the improvement in such properties by using waste metals is comparable to that obtained by using commercial particles. It was also found that fibres from old tyres are especially suitable for low structural layers (base and sub-base), while the use of metal shavings is particularly recommendable in superficial course layers.