I'm posting this for a friend who isn't very computer literate. She is in the middle of pool construction and she had her concrete decking poured after a rain about 10 days ago. The weather has been steadily increasing from the 70's to upper 80's/low 90's since the pour if that matters. Today she noticed 4 hairline cracks, the widest being about 4 feet wide. A picture is below. Is this normal or should she be concerned? Thank you.