Q.: The vertical edges of a number of exterior columns of one of our apartment buildings are breaking away, leaving reinforcing steel exposed, and this steel is corroding. There is also some vertical cracking beginning to occur on the surfaces between the cracked edges. What is the best material to use for repairing the spalled areas? Can we repair the cracks by injecting with an epoxy?
A.: It is too early to plan a repair program. The first thing to do is determine what is happening so that you can consider what measures can effectively eliminate the cause. It could be, for example, that the steel in the columns is suffering from galvanic attack intensified by chlorides. If so, you will want to consider what can be done to prevent corrosion from continuing.This kind of investigation normally requires an expert who can use any of a number of methods to pin down the cause and degree of seriousness of the trouble:
- inspecting and measuring crack widths
- taking cores to determine specific gravity, compressive strength, absorption, percent of voids and chloride content
- sonic pulse velocity tests of soundness of the interior concrete
- electric potential measurements with a half cell to determine the extent of galvanic activity, if any. Normally the expert would start with the easiest tests and perform only those that are necessary. The choice of repair program would depend on the findings.