The effect of nearby dynamite blasts, pile driving, or the simultaneous operation of machinery or vehicles on fresh or newly cast concrete is often questioned. Particle velocity of earthborne vibrations has been found to be the best measure of potential damage to structures, and we believe the same approach can be applied to fresh concrete. Field measurements to record displacement and frequency of vibrations are needed to calculate particle velocity. Many electronic sensing instruments are available to record needed data at the job site.

TRANSITORY VIBRATION LIMITS FOR FRESH OR IMMATURE CONCRETE

Permitted peak particle velocity, inches per second = 0.1;
Age of concrete at which vibration occurs: Less than 10 hours.

Permitted peak particle velocity, inches per second = 4.0;
Age of concrete at which vibration occurs: 10 to 24 hours.

Permitted peak particle velocity, inches per second = 7.0;
Age of concrete at which vibration occurs: More than 24 hours.

The limited evidence does not justify the general conclusion that fresh concrete will not be damaged by nearby blasting, jarring, and other transitory vibrations. The possibility exists that fresh concrete exposed during the first 24 hours to shock of unknown but presumably very great intensity through detonations or pile driving can suffer a loss in compressive strength. Therefore we suggest the above conservative guidelines.