What's the name of the little note in front of the concrete floor?

The small piece of paper in front of the cement floor is called expansion joint.

Expansion joints are used to prevent cement roads from expanding with heat and contracting with cold due to weather changes. Let the whole cement floor have room to "stretch its legs" when it expands, so that it is not easy to arch or crack.

Concrete, referred to as "concrete" for short, refers to the general name of engineering composite materials bonded by cementing materials.