What does concrete spalling look like?
Saturday, April 18, 2020
Spalling is the deterioration of a concrete surface over time, with crack lines forming first, then chunks of concrete falling out as the problem advances. It is caused by moisture penetrating the layer of concrete covering the reinforcing steel in the beam, column, or foundation pier. Eventually the steel begins to rust inside the beam and, because rust is slow but very powerful expansive process, cracks appear at the surface over the reinforcing steel. It‘s a progressive deterioration, because the open crack allows more moisture to accelerate the corrosion--formally known as ferrous oxide scale--which opens the crack further.
Spalling in concrete beams starts as long horizontal cracks.
As it progresses further, chunks of concrete start to fall out. The fix is simple but labor-intensive: each crack line has to be jack-hammered open to expose the surfaces of the steel reinforcing bars. The rust is then cleaned away with a chemical solution like Ospho®, shown below, and stiff brush, coated with an anti-corrosion solution, and then a special concrete/mortar mixture is packed into the damaged area and smoothed out along the surface.
Simply patching the cracks without repairing the steel, like in the photo below, is a temporary fix and the cracks will reopen.
Spalling can also occur at concrete columns, slabs, curbs, chimney caps, and window sills, as shown below.
A similar type of spalling can occur in brick mortar lines when steel reinforcing ladders are used in the wall, like in the photo below. To read more about it, go to our blog post What would cause long horizontal lines of brick mortar to fall out?
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