Thermographic Evaluation of Concrete Masonry Walls:
Have They Been Properly Reinforced?

Gregory R. Stockton - Stockton Infrared Thermographic Services, Inc., Randleman, NC

ABSTRACT

Infrared thermographers literally walk by more work than they can do. The world is one big radiator, and new, non-traditional applications for infrared thermography are being found every day.

Below, I will deal with the structural inspection of the walls of one type of building: CMU or concrete masonry unit. Fig. 1 is a photograph illustrating typical CMU construction.

Figure 1. Typical CMU wall section.

2. THE NEED

Structural problems in a CMU building are a problem as can be seen in the thermogram of figure 2. This thermogram of a CMU wall section indicates multiple deficiencies. This can only be detected using an Infrared camera operated by a trained thermographer.

Figure 2. Thermogram of a CMU wall section showing multiple deficiencies. (Pilasters are warmer.)

We find many problems with the construction of CMU walls, but judge these defects are almost never caused by fraud. Instead, poor supervision on the job is the cause for the poor quality. Some buildings are effectively grouted, but it takes extreme and costly measures. For years, the only way that a building owner had of looking into a masonry wall was to drill (or hammer) a hole in it. This testing method does not work, because only a small sample is tested. X-ray testing is so slow and expensive, that it is usually cheaper to knock the wall down and start over if its structural integrity is called into question. If the owner really wants to make sure that the grouting and rebar are in the wall, the most popular means is to require the installation of inspections ports or holes, cut in the block faces. These are installed at every lift height and at all grouted vertical pilaster locations as shown in Fig. 3. This is a very costly, time-consuming and sloppy method. That is why infrared is so valuable. It is fast, inexpensive and accurate.

 

Figure 3) CMU wall section with inspection ports.

 

Figure 4) Typical 12” CMU wall construction

Finding pilasters in the middle of the night had worked. Because the lack of heat is uniform, it is the equalizer. Timing turns out to be everything. Areas of higher mass heat up and cool down at a different rate from those of lower mass as shown by comparing the daytime and nighttime thermograms shown in Fig. 5. The walls absorb the Sun’s heat during daylight hours and radiate that energy back into the atmosphere at night. This is why, as with infrared roof moisture surveys, clear nights are preferred so as to see the higher mass [water] in the roof’s substrate. Each wall has a thermal ‘life’ of its own, so we sometimes have to wait for a wall to reach it’s peak delta-T between the different masses; grouted and non-grouted cells.

Figure 5. Thermograms showing daytime and nighttime temperature patterns.

Fig. 6 Time vs. temperature plot of a South-facing CMU wall, over a 24-hour period.

Today, infrared thermography is the best tool for the surveying of a masonry wall to find deficiencies in the structural components and/or the thermal envelope. It is fast, inexpensive, accurate and it will save money on the job in many ways.
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Using the methods described above, CMU walls can be effectively and efficiently surveyed. Once the owner is confident that the specifications will be followed, his designers can stop specifying more grouting than is necessary. This will save the owner on materials and the contractor time on the job. The high costs of other, less effective inspection and verification techniques such as ‘ports’ can be avoided, since the walls can be accurately checked once, after they are erected, but before the resulting repairs can cause delays. Lastly, contractors who are not willing to put qualified supervision on the job and build the building right the first time, will either absorb the expense of making the repairs or hire companies that will build it right to start with.