Q

Is there a relationship between concrete strength and wave speed? How can the acceptable minimum wave speed be determined?

A

Based on information reported in American Concrete Institute (ACI) 228.1, as well as in other codes and specifications, the concrete compressive strength is approximately proportional to compression wave velocity to the 4th power. This means, if σ is the concrete strength, W is the wave speed, and k1 and k2 are constants:

σ = k1 × W4 or W = k2× σ1/4

Those relationships can be used to compare the strength and wave speed of concretes with a similar mix. The following table might offer a rough guide:

fc wave speed fc wave speed
psi ft/sec MPa m/sec
2000 9,249 13.8 2,819
3000 10,235 20.7 3,120
4000 10,999 27.6 3,352
5000 11,630 34.5 3,545
6000 12,172 41.4 3,710
7000 12,650 48.3 3,856
8000 13,080 55.2 3,986
9000 13,470 62.1 4,106
10000 13,830 69.0 4,215

The minimum acceptable strength for the concrete of a drilled shaft project is σA. One of the drilled shafts associated with the project has a wave speed of WM, which is obtained by performing a Pile Integrity Test or Cross Hole Sonic Logging procedure. The measure of strength is σM. This measurement, for example, can be determined by extracting a cylinder. A relationship may be established for the minimum acceptable wave speed of other drilled shafts in the same project. WA is calculated as follows:

WA = WM (σA / σM)1/4