Summer is a great time to do a thorough inspection of your concrete in confinement buildings. Start with a thorough
cleaning of the building so you can see everything, especially the beams and bottoms of the slats.
The changes in feeding pigs high distiller’s grain diets have led to higher sulfur contents in manure which is resulting in
higher hydrogen sulfide levels in livestock buildings. When this gas is combined with moisture in the building it becomes
sulfuric acid (which is battery acid) that is very corrosive to steel. Cracks in the concrete allow the sulfuric acid to rust the
rebar, destroying the properties of reinforced concrete. The rust molecule is much bigger than the iron molecule it replaces,
and it will continue to break the concrete away from the steel like frost heave in the winter. Concrete has very high
compressive strength but low-tension strength so the rebar is placed where the tension loads are high, but because it is
subject to corrosion, it must be protected with 2-3 inches of concrete. If the rebar moves during the pour it can get close to
the edges where it will begin to rust.
When inspecting, look at each beam column joint for cracks. Cracks along the length of the beams and slats indicate that
the steel rebar is starting to rust and corrode and should be replaced by the next term of the building. Cracks that are
radiating up at an angle from the column beam corners indicate a concrete shear failure and will result in a catastrophic
failure without much warning. The joints of the beams need to be in the middle of the columns. Most of the failures that
have been observed occur when beams are not centered above the column. Because most beams are a standard 10-feet
long, one error in column placement often results in a whole row of beams being off center, which leads to multiple failures.
Slats are the easiest to inspect because they are easier to see. Cracks along the side and bottom of a single slat indicate
that the rebar is corroding, and the slats will need to be replaced within a year or so. If several slats are showing the same
cracks, the situation is more critical and should be replaced as soon as possible.
Well maintained concrete should last the lifespan of the building. The current situations with higher loads from heaver pigs
reminds all of us why we should expect the unexpected.
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