When a concrete floor or foundation appears damaged, it’s time to conduct a crack evaluation. But what do you look for? 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 take action. Unless you’re a concrete 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.

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. However, 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 thermograph, 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).

For some concrete repairs, the best repair material is simply high quality concrete. However, manufacturers have developed some excellent repair materials that include various polymers leading to higher bond strength and durability. Most repair materials today are polymer-modified concrete, meaning that the basic material is a Portland cement and aggregate mixture with a polymer (typically latex) added.

A couple of important factors in selecting a repair material are:
• Prior to deciding what repair material to use, make sure you know what the intent is: Are you trying to bond a crack together or just cover it up?
• Does the mortar need to stick to overhead or vertical surfaces? Or, can it be very flowable to pour into forms or cracks?
• How quickly do you want the repair to achieve full strength?
• Do you want to use a one-part material or are you willing to use a two component material that may be more difficult to work with but has superior properties?

One of the most important characteristics of a good repair material is very low shrinkage. The concrete matrix has already gone through its shrinkage, so if the repair material shrinks, it will de-bond and the repair will fail.

How important is bond strength? Usually very important—most repairs will be considered failures if the repair material doesn’t bond to the concrete matrix. A big part of getting good bond is surface preparation.

Consider the dimensional characteristics of the repair material: Drying shrinkage can de-bond a repair. If the repaired area will be under load, the elastic modulus should be similar. Thermal coefficients (the rate at which the material expands or contracts with temperature) should also usually be similar.

• Does the repair material need to be freeze-thaw resistant?

• Does the repair material need to allow water vapor transmission? Water vapor pressure from within the matrix of the concrete can create very high pressures— easily strong enough to de-bond many repair materials.

• How important is compressive strength or flexural strength? How about abrasion resistance?

Cleaning concrete periodically will extend its service life and enhance its beauty. It can be difficult to tell when concrete is in need of cleaning because the dirt and grime can build up so slowly.

However, once the process is done, the results of freshly cleaned concrete are very noticeable.

There are multiple ways to clean concrete depending on the type of surface, such as exterior slabs, floors or countertops. Each requires a different procedure to avoid damaging the surfaces.

Maintaining concrete consists of four steps:

• Cleaning Concrete on a regular basis (at least once per year) to remove normal dirt and grime build up and to remove rust or other stains.

• Repairing Cracks in Concrete: To maintain a structurally sound surface and minimize water intrusion through cracks, which can cause problems with the sub grade.

• Sealing joints in the concrete: To minimize water intrusion through the joints
• Eliminate dirt collecting in the joints.

• Eliminate weeds sprouting up through the joints.

• Sealing the concrete surface so it repels water and dust proofs the surface.

Some sealers offer other benefits as well, including high resistance to abrasion, resistance to UV sunlight, resistance to dirt and grime, oil, grease, rust, acid, chlorine, fertilizer stains, sprinkler water residue and mildew, as well as stains from most other organic matter.

What your concrete is exposed to will effect your choice of a sealer. For decorative concrete, the same steps as above will apply, but we visit the web site or contact the technical department of the decorative product manufacturer you have chosen.

For instance, if you used a concrete topping or dressing, or a certain brand of colored concrete, or a spray on decorative finish, the technical departments of these companies will have real world experience with what works best for their products. ❑