Saturday, March 31, 2012

Corrosion Jacking

Allow me to explain a funny phenomenon that can have a horrific impact on your building. As shown below, here is a short wall along a building's roof.

short concrete wall at building roof

Note that the wall has a few cracks in it. You can tell where they are because water has entered the cracks.

When water is inside of these cracks, it can come into contact with the reinforcing steel (rebar). When this happens, the water that exits these cracks is brown in color. The origin of this color is the corrosion on the rebar.

stained water exiting crack

A close up of this staining can be seen below.

close up of staining

What does all of this mean? As steel corrodes, it expands. Because the steel is encased by concrete, there is no room for the steel to expand. Something has to give. Typically, it is the concrete itself. Weak in tension, the concrete spalls with results similar to those shown below.

spalled concrete with exposed rebar

spall at horizontal surface

The spalled concrete must be patched and other cost repairs may be required.

In the case above, we recommended that the half wall be cleaned and a parge coat be applied to smooth out the surface before hot rubberized waterproofing be applied as a permanent solution.