Concrete slab poured - How to recognize possible frost damage?

Hello,
this is only a possible defect. I hope this is the right section for this.

So we are currently building. The base slab was poured last week. But then the frost came. It got down to minus 7 degrees here. Allegedly, the concrete was mixed with cement with higher heat of hydration. It was also supposedly covered. However, the tarp partly blew away in the wind.

So my question is: How can I recognize damages on the slab?

On deep, possibly wide cracks. But only after drying. Small shrinkage cracks, I believe up to 3 mm deep, are okay; more details are stated in the [DIN].