Roads recycles rocks

From gravel on the road to… gravel on the road. It doesn’t sound like much, but thanks this pioneering pilot project aimed at recycling the gravel (also called pickle) placed on Calgary’s roads, tons of debris are now being kept out of our local landfills. A simple action that not only saves the environment, but also taxpayer dollars.

It began as an idea 25 years ago - in a time when recycling wasn’t yet a priority in our society - with a Roads Manager sifting rocks through a tilted screen. But what wasn’t practical then is now having great success, with Bryan Savage, N.W. District Manager for Roads, MacGyvering a solution.

“We initially started spit balling about two years ago with the environmental team at Roads on ways to get the pickle out of the catch basins,” says Savage. “The system we are using now came about last year with the purchase of the custom-made screen.”

Believed to be the first of its kind for any municipality, the system is quite simple in its operation. A giant trommel with a cylindric screen, similar to what is used for mining gold, sifts through the gravel and sorts out organic material (dirt) and other things that may have collected on the roads (like shoes!). The smaller stones pass through the screen, leaving the bigger pieces – they must be at least 6.1 mm to be reused. Two brooms sweep the material as it passes through the cylinder brush off any debris. At the end of the process, you are left with two piles – one pile of dirt and one pile of gravel.

The results are impressive. In 2018, Roads put 367.7 tonnes of material through the custom trommel, resulting in 268.6 tonnes coming out as good, re-usable material - meaning 75 per cent can be reused.

The recycled material is mixed with 75 percent of new, unused material. Savage says this year they are trying for a mix of 50/50 mix as the project grows and a larger pile of the pickle mix is sent for recycling.

As is the practice in other cold climate municipalities, 100 percent of the material swept off the roads was previously disposed of. The pickle can’t be repurposed (e.g. for gardens or pathways) because of the salt content, something that also needed to be considered when coming up with this solution.

“There is an environmental standard we need to follow,” explains Savage. “Things like salt and heavy metal content need to be looked at in addition to the fracture [shape] of the rocks required to help them stay on the road.” As part of the pilot, several samples were taken both before and after going through the trommel. The results were promising and determined to be suitable for reuse.

With street sweeping now mostly complete for 2019, the pilot is kicking into gear once again – to sweep and sort the stones swept off the roads and put them back into use for next year. More than 1500 tonnes of pickle have been put aside for recycling this year. Crews are currently busy sifting and anticipate working into August to make their way through the pile.

Trommel Running