Research: Painting the town … concrete

Acrylic additives can improve the bonding and durability of concrete and mortar mixes.

But it’s a huge leap from there to the idea that the concrete trucks of the nation might become a destination for the many thousands of litres of unused acrylic latex paint that end up at municipal recycling sites, according to the Natural Sciences and Engineering Research Council (NSERC).

The idea, however, is familiar to Moncef Nehdi, a civil and environmental engineer at The University of Western Ontario.

Nehdi was turned on to the potential of paint-concrete mixes when, a number of years ago, he was asked to take a preliminary look into the topic by the City of London.

Promising news from this early work reached the Vancouver-based Product Care Association. They contacted Nehdi, who based on their interest and that of the Ontario Centre for Materials and Manufacturing, proposed an in-depth investigation.

With matching funding from NSERC under a program that funds universities to work collaboratively with private sector partners on ideas of interest to industry, Nehdi, a colleague and students set out to perform the first-ever comprehensive study of paint-concrete mixes.

“The results from the two-year project were amazing,” said Nehdi. “Essentially all our objectives were achieved.”

“The paint improved the durability of the concrete, and in virtually every aspect, from the mechanical properties of the concrete mixture to its workability and handling, to worker and environmental safety (the potential harmful components were stabilized and did not leach out over the long term), the process and product met or exceeded standards.”

There was only one exception, according to the researcher.

“The compressive strength of the concrete decreased, but we solved this by lowering the water to cement ratio or using high-shear mixing.”

Nehdi said that the project lays the groundwork for large-scale municipal use of latex paint in sidewalks and other concrete structures, an idea he and others are eager to advance to the next stage.

“Currently waste latex paint forms the largest volume of liquid waste collected at household hazardous waste collection sites in Canada,” he said.

“If implemented, our technology can recycle most of this waste, with the added value of enhancing the durability of municipal concrete infrastructure and eliminating the cost of alternative disposal of the paint.”

And will the paint actually colour the town? Not really. When all the tints are mixed together, the concrete still looks very much like … concrete.