Not knowing much about Post Tensioning Slabs, I would have to say that it might be good there is a crack, it would allow the moisture to get out, right?
Just my theory. ha. ha.
Just thought I would note that some forms of cracks usually occur due to improper design and construction practices, such as:
Omission of isolation and contraction joints and improper jointing practices.
Improper subgrade preparations.
The use of high slump concrete or excessive addition of water on the job.
Inadequate or no curing.
Concrete, like other construction materials, contracts and expands with changes in moisture and temperature, and deflects depending on load and support conditions. Cracks can occur when provisions to accommodate these movements are not made in design and construction.
Most random cracks that appear at an early age, although unsightly,m rarely affect the structural integrity or the service life of concrete.