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The concrete foundations of more than 50 houses
positioned in eastern Canada were examined in the field as well as in
the laboratory in order to diagnose the cause of deterioration observed.
The concrete foundation showed signs of scaling,
spalling and delaminiation.
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The cause of the deterioration was found to
be freeze-thaw action
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The concrete was a poor quality concrete being too porous, too
moist and having a too poor air void structure.
The cause of the poor quality of the concrete is
believed to be an aggregate problem where the sand used at a certain time
had a too fine modulus.
The use of this sand increased the water demand
of the concrete. In order to compensate for the too fine sand limestone
fines was added. However, the limestone fines were also too fine and did
not help the problem, rather the opposite.
Fly ash was introduced to the
concrete at the same times as the limestone fines. It was argued that
this fly ash could have caused an internal sulfate attack in the
concrete and than that was the cause of deterioration. There was,
however, no correlation in the data between the presence of fly ash and
the deterioration observed and internal sulfate attack was neglected as
a deterioration mechanism.
Minor cosmetic scaling from salt crystallization was found at the floor-wall joints and along structural
cracks in some basements. |
