A team of engineers at RMIT University in Melbourne have found a novel use for the trillions of cigarette butts that litter our streets.

By coating discarded butts in paraffin or bitumen, the team can mix them into asphalt concrete, making a new building material. this new asphalt mixture can create cooler, greener pavements in cities and towns. By lowering the asphalt’s density, pavements become more porous, draining surface water away. Another useful property is the asphalt’s lower thermal conductivity. By soaking up less of the sun’s heat, the cool pavements could cut the ‘urban heat island’ effect felt in many cities.

Working in the department of civil and infrastructure engineering, Dr Abbas Mohajerani and his team have been experimenting with cigarette butts as building materials. Around 6 trillion cigarettes are made worldwide every year, leaving more than 1.2 million tonnes of waste. Together, they are one of the most common types of litter on the planet.

Comparing coatings

Before engineers can work with the cigarette waste, they must first encapsulate the butts in something. Cigarette filters trap hundreds of toxic chemicals that, when thrown away, are no longer contained.  Coating the butts stops the filters getting wet and leaking their toxic chemical load into water systems.

In this experiment, Mohajerani’s team tested the efficiency of different coatings. They compared coating butts in bitumen or paraffin wax before mixing into asphalt. Paraffin proved suitable for pavements experiencing light traffic conditions alone. Asphalt containing bitumen-coated butts could safely withstand light, medium and heavy traffic conditions.

“In this research, we encapsulated the cigarette butts with bitumen and paraffin wax to lock in the chemicals and prevent any leaching from the asphalt concrete. The encapsulated cigarettes butts were mixed with hot asphalt mix for making samples,” Mohajerani said.

Recycling butts into bricks

This is not the first time he has experimented with cigarette butts to make novel building materials. In 2016, he gained worldwide notoriety for recycling discarded butts into house bricks. “I have been trying for many years to find sustainable and practical methods for solving the problem of cigarette butt pollution,” he said. “This research shows that you can create a new construction material while ridding the environment of a huge waste problem.”

Mohajerani’s team found that adding cigarette butts to clay house bricks cuts the energy needed to fire them by almost 60%. In addition, bricks made with cigarette butts were lighter and better insulators. This helps reducing household heating and cooling costs. Rather than encapsulating butts in a waxy material, here it is the firing process that traps harmful chemicals.

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