“Concrete always cracks!”

When concrete cures, it shrinks by about 1%. This happens because water from the wet concrete mix is chemically bound during the hardening process (it does not evaporate!). Therefore, large concrete slabs require at least some rebar and evenly spaced contraction / control joints to limit cracking.

Control Joints

The grooves we all know from our sidewalks are examples for such joints. On floor slabs like we have here, we usually cut small grooves into the surface at columns and at regularly spaced distances. You can see some of those in the atrium floor and the second floor, but they were omitted on the third floor.

Also, any structural floor deflects a small amount under its own and other structural weights. In this case, we have a CLT wood-concrete composite floor system that spans perpendicular to the hallway direction. Floor deflection then creates tension at the top of the floor along the center row of columns, which is the cause for small structural cracks.

The cracks you see on the floor have been widened so that they could get filled in easily, which makes them more visible than would usually be the case.

Long story short: These cracks are normal to any concrete construction and control joints would have prevented them.

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