Thanks for your prompt response. My inquire was for Michigan DOT bridge project. MDOT specification requires minimum three days of curing or 70% of 3500 psi (28 days compressive design strength) prior to placement of any additional concrete on substructure concrete. Contractor is asking for exception to this requirement providing compressive strength of concrete of poured concrete > compressive stress due to subsequent pour. I am looking for a min compressive strength of concrete where you can validate stress/strain relationship and compare stress due to loads vs. compressive strength.
You're welcome. 3 days or 2500 psi; in mNy places 3 days means 72hours where the temperature under the covers is 40 degrees or higher. That's to a very burdensome requirement. If it's early into the project, tell the contractor no - unless it's a dire emergency - they'll think they can get away with everything the want.
