Researchers in RMIT University in Australia have figured out a novel way to cut environmental hazardous waste and make urban roadways cooler. Mix old cigarette butts into the asphalt.
Why? It seems the cigarette butts (CBs) aren't biodegradable because their filters are made of cellulose acetate, a plastic-type material made from wood. They collect toxic substances such as cadmium, arsenic, zinc, iron and copper while the cigarette is in use, but once discarded and exposed to water, the filters release the metals into the environment but don't break down themselves.
This doesn't sound like a huge problem except it turns out about 1.2 tons of cigarette butts are produced globally per year and estimates are that weight will double by 2025. The Central Minnesota Water Education Alliance says 32 percent of storm drain litter is tobacco products.
The CBs make their way to storm water routes, eventually escaping into surface waters. Once in the water, the CBs can be mistaken for food by animals, release poisons, and foul land areas. It's a landfill, water, and beach nightmare.
Dr. Abbas Mohajerani, leader of the research at RMIT's School of Engineering, has done similar work mixing butts with concrete and found the combination made for better cement bricks. So he turned his focus to asphalt.
The RMIT team found that by encapsulating the butts with paraffin wax, then adding them to an asphalt mix not only trapped to toxic chemicals but also reduced the bulk density of the asphalt.
The result is an asphalt mix that meets standards for road pavement durability, but as importantly it reduces heat conduction. Decreasing the amount of heat that pours off the pavement in turns reduces the Urban Heat Island effect.
The urban heat island (UHI) effect is a phenomenon where surfaces such as concrete and asphalt absorb and hold solar energy - in the case of concrete, up to 2,000 times more heat that the equivalent volume of air - which then affects winds, precipitation, and air pollution. By using paving materials with less thermal conductivity properties, we reduce the effects of global warming.
Dr Mohajerani says bitumen (asphalt) has been used to store nuclear material in France for many years. "We actually saturate and encapsulate the cigarette butt, and we don't use them on the surface of the pavement, we use them in the second layer. The encapsulation prevents the leeching of those chemicals. The water cannot reach inside the filters so chemicals cannot escape from the filters."
The RMIT project ran for five years and has gained the support of the Australian government. "This research shows that you can create a new construction material while ridding the environment of a huge waste problem," says Mohajerani.