09/11/2026
Most people see cracks in concrete and assume the worst but the fact is that not all cracks are the same. Anyone who has worked a lot with concrete will tell you two things about concrete, that it gets hard and that it cracks. Not all cracks indicate distress or failure. Some cracks, may be the result of thermal expansion, or shrinkage, or of rigidity issues in the initial design.
In this case a previous engineer recommended crack gauges to be installed on the underside of a post tension deck. Based on the geometry of the building, construction type, and loading conditions, it is likely that this crack was caused by thermal expansion/contraction and unlikely that the crack gauge will show much movement. The pencil marks are another rudimentary way to make sure that the crack isn't moving laterally. At a minimum the crack gauge is a good way to rule some conditions out, even if they may not always be necessary with a proper understanding of the building.