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Per ACI 308, concrete reaches approximately 65% strength at 7 days and 99% at 28 days under standard curing conditions. The critical period is the first 7 days: keep the surface moist, cover with plastic sheeting or curing compound, and protect from freezing. Driving on a new driveway at day 3 or removing forms at day 2 causes surface scaling and cracking that is visible for the life of the pour.
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