Q.: Construction of a 5-story building about 100 yards from a working quarry is under consideration. How damaging would the quarry blasting operations be to the concrete?
Should concrete be allowed to reach some minimum age before it is exposed to shocks from blasting?
We want to know whether we would have to work out a careful schedule, perhaps in cooperation with the quarry operators.
There have been a number of studies that show that concrete is remarkably resistant to damage from jarring and vibration at early ages and that some jarring and vibration may make it stronger. Nevertheless, there must be some amount of jarring that would be too much.
A.: In "Damage Effects of Pile Driving Vibrations," Highway Research Board Record, Number 155, 1967, John F. Wiss has discussed how to make measurements of displacement and frequency of vibrations. From these measurements a peak particle velocity can be calculated which is a guide to whether the jarring or vibrating is excessive. The allowable peak particle velocities are:
Age at which vibration occurs, hours
Permitted peak particle velocity, inches per second
less than 10
10 to 24
More than 24
If you could make some measurements at the jobsite when blasting is being done you could use Wiss's method to calculate what the peak particle velocities are. Then you would know whether you have to take any precautions and if so, how long your concrete must be kept vibration-free.