Is it possible to get superhigh cylinder strengths at seven or 28 days by vibrating concrete test cylinders or somehow jimmying them?
It is difficult but not impossible to get overly high strengths. If cylinders were stored at excessively high temperatures their strengths at seven days would probably be high. These strengths might in some cases give a false sense of security about the quality of concrete in the structure. The strengths of such cylinders at 28 days would, however, be likely to be low because the acceleration of early strength gain is usually done at the expense of later strength. Vibration of high slump mixes that should be rodded would probably not cause an increase in strength, but possibly it could cause a decrease.