Concrete Reinforced with Tire-Derived Fibers, an Innovative Take on Recycling

As plenty of landfills full of old tires can attest, recycling these automotive components is still a pending issue. In fact, just in Europe, up to 70% of tires are dumped in this type of deposits, so finding new ways of processing this waste could do with some imaginative thinking. The most innovative and sustainable building materials, however, no longer seem to be a thing of the future. The University of Sheffield in the United Kingdom has come up with a technology project where the textile fibers from old tires are embedded in the concrete mixture to provide increased fire resistance.

One of the characteristics of concrete is that, when this kind of material suffers the high temperatures of a fire, a process called spalling kicks in, compromising the structural integrity of a building. In order to prevent it, over the past few years, the use of propylene fibers has become an increasingly common solution for concrete reinforcement. So far, however, specifically manufactured propylene was used, which is an energy intensive process. Thus, the researchers at the University of Sheffield have devised a technique that allows using recycled propylene from old tires. By using their technology, they can separate the propylene strands from the tire rubber and later spread them evenly across the concrete mixture. According to the results published in the journal Fire Technology, the fibers from used tires are just as efficient as manufactured propylene, albeit with a significantly lower environmental and financial cost.       

Why does concrete crack in a fire?

Concrete always contains a certain amount of moisture that, when exposed to high temperatures, evaporates and pushes the material outwards, causing explosive fractures. When propylene fibers are added, though, they can melt leaving micro-grooves that channel the steam. Most of the construction concrete has been reinforced with steel. A fire can trigger a destructive spiral, as the pressure of the steam causes concrete spalling that reveals the underlying steel, which is weakened furthermore by the high temperatures. This compromises the structure and can lead to the collapse of the building.      

Asphalt reinforced with tires… and plastic bottle caps

In addition to reinforcing concrete with propylene against fires, there are other projects exploring the potential of this material in the manufacturing of asphalt mixtures, although by adding propylene from other sources besides old tires. That is the approach used in the POLYMIX project carried out by the Spanish Technology Institute of Plastic jointly with ACCIONA. In their first tests, they used a mixture of propylene sourced from used tires and bottle caps, polyethylene packaging, and polystyrene hangers to asphalt one and a half miles of a road.

Eighteen months after the asphalt was put into place, the developers of this technology project certified that the material provides improved resistance to high temperatures and road traffic thanks to its reduced plastic deformation. The main advantage offered by POLYMIX is that it integrates plastics from a range of sources and allows to build roads with less environmental impact, as well as more durability. The project was awarded the Life 2015 prize in the Environment category of the EU Green Week celebrated in Brussels.

Source: Science Daily, AIMPLAS