Strength gain by concrete in cold weather 2

[gp238]

I have a reinforced concrete basement wall for a new home poured by a contractor at Amherst, NY on December 14th. The high and low temperatures on that day were 32 and 20 degree. The high & low tempreatures on the next day were 40 and 24. The water-cement ratio of concrete was 0.54 and type III cement was used with super-plastisizer and 5-8 % entrapped air. After 7 days I tested the concrete strength of the wall by a Swiss rebound hammer. I tested at least at 20 different points and the correlated compressive strength was 1000-1200 psi. Also, when I tapped the surface of the wall by a small hammer it left a dent on the wall. When I contacted the contractor about the problem, he informed me that the concrete supplier has tested one cylinder from the batch and the 7-day strength is 2000 psi. In my opinion , the tested cylinder is not cured at the site and thus does not reflect the in-situ strength of the concrete wall. I am very worried about the basement wall and hesitant to let the builder start framing. Could you or someone please advice me.
Thanks!
gp238

 

[BigH]

Ron - thanks - I've been dinged a few times on EM posts so see thread noted above.