"I have a client who wants me to image a building block wall in search of voids where rebar was incased in concrete as part of the strengthening process. Is there a particular protocol you can point me to that will satisfy the building inspector that no voids exist?"
Solar energy striking the wall is absorbed by the masonry. Hollow or insulated cells create a thermal break or barrier within the cell causing the exterior face shell to heat rapidly. In contrast, the solidly grouted cell acts as a heat sink permitting energy to be conducted through the wall. The emitted energy of the exterior surface is therefore higher in locations of voided cells than that of solid cells. This emitted energy pattern is visible with an infrared camera. This method provides very crisp contrasting data, but is totally dependent on weather conditions and the availability of direct sunlight.
In the daytime, wall sections filled with grout will appear cooler than the other sections. At night, sections with grout will appear warmer than the rest of the wall.
CMU wall section during the day
CMU wall section at night
See these two white papers presented at the InfraMation Conference below:
Use of infrared thermography as a standard in the quality assurance and quality control of grouted masonry construction
Thermographic evaluation of concrete masonry walls: have they been properly reinforced?
