Chert in concrete aggregate 1

[let]

We have 6 concrete cooling towers (wet/dry cycles are common) that are fast deteriorating by spalling. We suspect that chert was used in the aggregate and that it is causing chunks to pop at the surface. I need information on the behavior and composition of chert. The chert near the surfaces are poping now, but how about the chert that is deep in the wall? (12 thick and thicker) is that chert also deteriorating inside?. How is best to repair? Can a waterprofing coat with a high-tech material help? or retard deterioration of the cooling towers. The are about 5-years old. Your insights will be appreciatted

 

[Ron]

You will first need to characterize the chert. The common reactive form of chert is chalcedony. This is usually a relatively soft, greenish tinted material present in limestone/dolomitic strata.

Most often, this chert is reactive only near the surface where it exerts enough stress to cause surface popouts, but not enough to cause serious internal problems in thicker sections of concrete. Surface coatings may serve to exacerbate the problem, not correct it.

The reactants can be characterized by a petrographic evaluation of the concrete and its deterioration potential can be assessed from this exercise.

 

[let]

Thank you Ron. A petrographic analysis will be underway. The chert we have is actually light brown (tan). Is this a different type of chert?. Your answer seem to imply that there are other cherts that have different mechanical or chemical behavior. Your opinion is appreciated.