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- What Causes Damage to Concrete?
Typical Concrete Problems and Why They Occur
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Concrete Crack Repair Evaluation
The typical reason for evaluating concrete is that it is somehow damaged—we seldom evaluate the condition of perfect concrete but just accept that it is functioning. So what are we looking for when we go out to evaluate damage? Start by deciding whether the damage is structural or superficial. A large diagonal crack across a concrete beam is serious and means it is time to call an engineer—don't take on the responsibility of structural work unless you know what you are doing. Document any structural problems you observe and contact the owner immediately. Just being there could impart some responsibility to you if there was a failure and you didn't take some action.
This doesn't look so bad on the surface, but the rust tells us that the reinforcing steel is deteriorating. The only solution is to remove the unsound concrete and replace with new. The Pascoe Group
If it appears that the concrete structure is not in danger of collapse, evaluate it in a series of steps. The first step is a simple visual examination:
- Is the damage local or widespread?
- Is the damage superficial or does it go deeper into the concrete matrix?
- Is there damaged (corroded) reinforcing steel?
- For cracks, are they still moving?
- For surface delamination, can you define it as thin scaling or deeper spalling or is it an overlay delamination?
- What more extensive testing is needed?
- Do you have information about the initial construction (mixes, construction drawings, specifications)?
A good tool to have at this point in the investigation is a hammer and some spray paint. Pinging the concrete surface with the hammer will reveal delaminated areas that can be outlined with the paint. Delaminated areas send back a dull hollow sound instead of the hard ringing of sound concrete. Also be sure to have a tape measure to determine the extent of the repairs. Take lots of notes and photos—even video if that would more easily document the problems.
At this point you will begin to get a feeling for the cause of the damage. But if you need more information you might have to resort to some destructive and nondestructive evaluation techniques. The first step is just to break away any damaged concrete to determine how deep the damage goes. If you need more information, you can drill core samples for analysis in the lab or by a petrographer (someone who studies hardened concrete using microscopy).
Non-destructive evaluation (NDE) techniques include radar, infrared thermography, and impact-echo. These can reveal a lot about the condition of the concrete and any reinforcement without having to open it up.
For a detailed description of how to conduct a condition assessment, get ACI Committee 364's report, Guide for Evaluation of Concrete Structures before Rehabilitation (ACI 364.1R-07).