The success of this year’s experiment in reducing the amount of salt in the City of Edmonton’s winter road sand mix may see 3 million fewer pounds of salt spread on Edmonton’s roads next winter.
Primary traction ingredients in the road sand mix are a combination of sand and small rock chips, but salt is a critical element as well, says Blair Buchholtz, Transportation Services’ general supervisor of aggregates and recycling services.
“Salt coats the rock chips and sand particles, enabling them to penetrate a little deeper into ice and packed snow,” he says, “but by far the biggest reason we need it is to prevent huge stockpiles of road sand mix from freezing solid in sub-zero temperatures.”
“We stockpile 138,000 tonnes of the road mix at our various Transportation yards; sand has a low but significant water content, so if we used no salt, we’d be trying to spread Volkswagen–sized lumps of iced sand and rock chips onto our roads,” he jokes.
Long ago, in an attempt to be more environmentally responsible, the City reduced the proportion of salt it uses from 6% to 4%; the proportion has been at 4% for years.
Blair and his Transportation colleagues have talked for several years about the environmental value of notching the salt content down to 3%, but until this past year, they had nowhere to test a large pile of 3% mix to see if it would remain unfrozen in frigid winter temperatures.
The opening of the far northeastern Horse Hills Transportation yard offered Buchholtz, Transportation staff, specialists at the Waste Management Centre of Excellence and a private contractor to collaborate on an experiment in further reducing the salt level.
Earlier attempts at reduced salt content failed because of the inability to guarantee a homogeneous salt percentage throughout a stockpile of mixed material. It was the private contractor which developed a new technology that enabled the City to know the mix would be homogeneous.
The Horse Hill site provided enough space to build a four-foot barrier wall to surround a 2,000-tonne pile of 3% salt mix.
“We inserted a thermistor – like a string of temperature sensors – that allowed us to monitor the inside temperature of the pile, both vertically and horizontally.”
This winter there were a couple of periods when the temperature was -20 Celsius or lower. The 3% mix remained unfrozen.
Blair says Transportation officials still have to process the results of their experiment and discuss whether to implement the lower salt content next winter. But he’s fairly confident.
And once the City has reduced its road mix to 3%, Blair has another experiment in mind.
“I’d dearly like to try an experimental pile of 2% salt next winter,” he says.