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Elliot Lake Mall Collapse: A Preventable Tragedy

 

On June 23, 2012 the Algo Center Mall in Elliot Lake, ON suffered from a partial structure failure when a segment of its rooftop parking lot collapsed into the building. Slabs of concrete crashed through the upper level of a lottery kiosk near the food court to the ground floor. Over 20 people were seriously injured and two died in the collapse. There is currently an ongoing investigation and a $30 million class action lawsuit against the mall, the goverment of ON, the city of Elliot Lake, W.R Wright and Asssociates (the engineering firm that surveyed the mall parking lot), and Eastwood Malls, Inc. The mall has since been demolished.

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What Went Wrong

 

The main issue with this mall was water leaking and corrosion. When the mall was originally built the owners decided against waterproofing the concrete in order to save time and money. This was an extremely poor decision as using a waterproof membrane to protect the concrete parking lot could have prevented the tragic collapse.

 

By the 1990s there are already signs of water leakage and damage in the mall's structure. A few years later they had to shut down some stores to repair water damage and mold issues. One of the restaurants in the mall actually had to close because a piece of the roof had fallen. Despite these serious warning signs, the mall owner's continued to provide only temporary fixed for the water damage.

 

There were two critical errors made during the planning stages. Firstly, the parking lot for the mall was located on the roof of the building without efficient  waterproofing, and secondly the structural inefficiency of the hollow concrete slabs which prevented the installation of effective waterproofing later on.

 

To learn more about the details of this tragedy click here.

 

How it Went Wrong

 

The main culprits of this tragic event were salt (de-icers) and water. Together they inflict catastrophic blows to the structural integrity of any unprotected concrete structure. To explain why this happens take a look at the chart below:

 

Factors

How They Cause Damage

Salt Melts and Freezes Ice

Salt only melts snow and ice, it doesn't get rid of them. As it melts snow and ice the salt mixes with them forming salt water, which has a lower freezing temperature than normal water. This means that it seeps into the porous concrete and as the temperature drops, the salt water eventually freezes in the concrete causing it to expand and crack. These cracks eventually will lead severe structual damage. This same process happens with just water but salt accelerates the process.

Salt Causes Crystallization and Subflorescence

As saltwater evaporates from the concrete, the salt remains in its cracks. Eventually, the salt recrystallizes in the pores of the concrete, causing a permanent expansion in the concrete, which reinforces cracks and structural damage.

Salt and Rebar Metal

Most concrete contains rebar metal (aka steel), which salt naturally corrodes. It does this because it contains magnesium chloride, sulfate and hydrogen carbonation ions that will essentially attack concrete. This corrosion causes rust, which creates pressure on the surrounding concrete. As the concrete gets more cracks it becomes more susceptible to salt, which creates a vicious cycle and makes it break down faster.

 

Lessons Learned

 

The simple solution to this catastrophe would have been to invest in waterproofing the concrete right when they built the mall, and to continue to properly upkeep the waterproof membrane that they would have used. So if you're an engineer or a business owner looking to construct a new building, be sure to invest in a waterproof membrane, the short term cost far outweighs the long term risks of not getting one.

 

Waterproofing Concrete Floor

 

Before grinding to expose the crack crack joint repair
After water proof membrane waterproof membrane

 

 

 

 

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