By Ronald Ahrens
Too many bad things can happen at a grain elevator. For one, construction crews and elevator workers face the risk of falling. For another, grain dust can explode. And it’s even possible for a worker to be trapped in a silo.
Then there’s the problem of blowouts. We have written before on Our Grandfathers’ Grain Elevators about blowouts.
One had occurred on a Tillotson Construction Co. job, probably in 1955, at Blencoe, Iowa.
And it turned out, during our visit to the 1950 Tillotson elevator run by Consumer’s Supply Co-op in Canyon, Texas, there was the story to tell of a blowout.
Those weren’t just stretch marks on that corner silo. Well, actually, yes, they were.
As Dewayne Powell explained when he showed me around, the blowout in a single silo had occurred sometime before his tenure, which goes back eight years.
Tillotson Construction Co.’s records specify the bearing pressure of the walls at 3.1 tons per square foot. Somehow, the concrete must have deteriorated, leading to the failure.
The elevator’s importance to the Co-op is underscored by the fact that repairs were made. Powell said Gunite was used. I searched for a definition of Gunite and found this passage from the Shotcrete entry on Wikipedia:
Dewayne Powell leads the way into the elevator’s basement.
“Shotcrete, then known as gunite (/ˈgənīt/), was invented in 1907 by American taxidermist Carl Akeley to repair the crumbling façade of the Field Columbian Museum in Chicago (the old Palace of Fine Arts from the World’s Columbian Exposition).[1]
“He used the method of blowing dry material out of a hose with compressed air, injecting water at the nozzle as it was released.
“In 1911, he was granted a patent for his inventions, the “cement gun”, the equipment used, and ‘gunite,’ the material that was produced.”
Whatever the term, the repair was nicely done. But Powell said he’d heard stories of chaos the blowout caused. Aside from this disaster, the 68-year-old elevator has held up quite well.
Our Grandfathers' Grain Elevators 
Elevator bin blowouts can be caused by a number of reasons or combinations thereof. A blowout during the slipform construction process however can be the most devastating because it can endanger the stability of the entire bin structure or even the entire project if the failure is large enough. Causes may include:
1.Improper cement mixture which requires consistent mixtures of the specified materials including water, the placement of such at the proper consistency, as well as adequate vibration of the poured cement when introduced into the concrete formwork so as to insure elimination of air pockets.
2.Incorrect placement or lack of insertion of the structural reinforcing steel grid (vertical and horizontal bars) that provide the actual strength of the bin wall structure (the concrete is the ‘binder’ that holds the steel in place)
3.Imbalance of the entire slipform operation whereby the formwork gets ‘out of plumb’ causing the bin pours on one end or side to be compressed while the opposite side of the imbalance is elongated and weakened because the reinforcing steel becomes spaced incorrectly.
4.Correct ‘set time’ of the poured cement so that the cement is sufficiently dry and bonded enough to be self supporting by the time the slipforms have been lifted/vertically elevated beyond the bottom edge of the formwork. This entails continuous monitoring during the slipping operation by inspectors that examine the finished wall surfaces from hanging scaffold erected at the bottom of the formwork.
5.And last, but not least, the elements of weather must be within spec – ie; hot temps, rain, snow cold or freezing temperatures all or any of which can affect the final outcome of the poured in place product in not within tolerance.
To further add to the complexity of constructing a grain elevator is the utilization of unskilled labor as most of the labor employed for constructing is procured from the surrounding local area of the project and has not ever been involved in slipform construction. The training of the workers is done
by the appointed management personnel on an ‘learn as you do it’ basis.
Consider then how all of these factors somehow miraculously come together to rapidly build a towering monument structure that must withstand all of the pressures from within and without its walls over the eternal test of time. Also, it is not difficult to understand how a latent blowout occurs many years after the initial construction as one or more of the above listed blowout causes was not done correctly or the stresses placed upon the structure by wind, rain, earth settlement, improper bin filling management, build up of pockets of grain dust, etc.have caused a weakness in the bin wall that has taken time to develop.
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