The 6 trillion cigarettes produced every year generate over 1.2 million tonnes of butt litter, and not only do the majority of them end up in the environment, but they're technically toxic waste. Now, researchers at RMIT University in Australia have found a new way to safely dispose of cigarette butts: seal them up inside roads and paths.

The idea comes from the same researchers that last year stashed old butts inside bricks. Not only is that an effective way to keep them from leaching their toxic chemicals into the environment, but they actually make for better bricks too: adding butts halves the amount of energy needed to fire the bricks, and improves the insulation properties of the end result.

Led by RMIT senior lecturer Abbas Mohajerani, the team has since gone on to investigate how asphalt might also benefit from the unusual construction material. First they encapsulated the butts in paraffin wax and bitumen, which locks the lethal chemicals inside and prevents them from leaching into the asphalt and eventually the environment. Then, the encapsulated butts are added to hot asphalt mix.

By testing samples of the butt-enhanced asphalt, the team found that not only could the material handle heavy traffic, it also tended to trap less heat from the Sun. That could help reduce the "urban heat island" effect that warms cities up to uncomfortable levels.

"This research shows that you can create a new construction material while ridding the environment of a huge waste problem," says Mohajerani. "Cigarette filters are designed to trap hundreds of toxic chemicals and the only ways to control these chemicals are either by effective encapsulation for the production of new lightweight aggregates or by incorporation in fired clay bricks."

The research was recently published in the journal Construction and Building Materials.