What was eating away at cement in western Canada?

There were a lot of strange things afoot throughout Western Canada in the 1920’s, besides the occasional sasquatch sighting. In the world of chemistry, cement was mysteriously getting weaker and weaker. This may seem trivial, but things were getting pretty bad. Sewers were falling apart, irrigation aqueducts were cracking rapidly and even some public buildings were getting brittle.

The National Research Council came to the rescue as they usually do, and organized a team to get to the bottom of all this. The collaboration was between the NRC, the Engineering Institute of Canada and Dr. C.J Mackenzie, dean of the Engineering School of the University of Saskatchewan. The team had two approaches to this conundrum: fortify the cement, or, solve this chemical crime entirely. They did both, but it’s clear the latter was more important in the long-run.

In 1922 they studied a basement in Saskatchewan that was in particularly rough shape because of the cement degradation. They decided to do an analysis of the groundwater in the basement and found out it was teeming with sulphates. There was lots of sodium sulphate and magnesium sulphate, specifically, and further analysis of groundwater in many buildings across Western Canada showed similar results. The rotting buildings themselves had something in common too. A key ingredient in all their cement was tricalcium aluminate.

Putting their clues together the team realized that the sulphates in the water must’ve been tearing apart the tricalcium aluminate in the cement. So the perpetrator that caused so much damage was beneath their feet all along. Tricalcium aluminate is vulnerable to contact from sulphates so the team had to find a way of protecting it from the ever-abundant groundwater. They came up with steam curing, a way to shield the cement from the effects of the water by applying lots of heat and pressure during its creation.

With the mystery solved the group of chemist detectives disbanded, but the NRC would continue research on safeguarding concrete from the elements. They went on to create electrically conductive concrete which has fantastic uses in heating, de-icing and securing the cement itself through electromagnetic shielding. Over the past 90 years they’ve found new ways to test cement and new materials to strengthen it.

By: Jassi Bedi

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