Using IR to verify construction details of commercial facilities is another use of the technology. With the right conditions, thermography can be successfully used to verify placement of reinforcement grout in concrete masonry unit (CMU) walls.
Editors Note: While thermography can detect the presence of grout in hollow cell masonry, it typically cannot detect the steel reinforcement bar. Once the grout has been detected, another detection mechanism must be used to determine if the bar is present.
In buildings that are under construction, these patterns typically show up best either early in the morning or later in the evening. Due to differences in thermal capacitance, grouted cells require more thermal energy to change temperature vs. those that are empty and filled with air. As energy is absorbed by the wall from the surrounding environment (including that of solar loading on the outside surface), the grouted columns take longer to heat up in the morning, but stay warmer, longer, into the evening. Cell columns that are empty, warm up relatively quickly in the morning, and cool off more rapidly in the evening. This creates a distinct, qualitative, pattern across an entire elevation of a building where grouted cells can appear cooler in the morning but warmer in the evening when compared to the rest of the wall.
These theoretical principles are the same physics that allow a building thermographer to inspect low-slope roofs for moisture intrusion, permit a NDT technician to identify flaws within a composite material, or create circumstances for a plant thermographer to identify liquid and sludge levels in storage tanks.
This type of inspection can be conducted almost anytime the wall is in a thermally transient condition. Ideally it is done during construction, and before the roof is in place, as deficiencies can be corrected relatively easily prior to the building being occupied. Having said that, these patterns can also show up on finished structures as well. Not having the roof in place means all 4 walls may be subjected to the solar loading transients.
In existing buildings (an example seen here), where there is often a temperature difference in place from inside to outside, increased thermal conductivity through the grouted cells can, at times, also help enhance this pattern. Grouted cells may have a different thermal conductivity than those filled with air. As such, if the conditioned space on the interior happens to be warmer, you will see an increase of heat transfer through the grouted sections that show up warmer on the outside in the right conditions.
As with most IR applications, the ease with which this type of inspection can be conducted is always dependent on environmental conditions, such as solar loading on South or West facing walls during an evening inspection, as well as structural variances within the building system. If, however, the right situation presents itself, using IR to verify the structural integrity of CMU walls can be successfully accomplished.