| Grade | No. (Ratio) | Compressive strength (MPa) | No. of dams below the standard, 21 MPa (Ratio) | |||
|---|---|---|---|---|---|---|
| Mean | S.D. | Min. | Max. | |||
| Total | 54 (100%) | 22.00 | 3.90 | 13.8 | 38.9 | 19 (35.2%) |
| A | 36 (66.6%) | 23.01 | 3.88 | 16.2 | 38.9 | 8 (22.2%) |
| B | 9 (16.7%) | 19.44 | 3.77 | 13.8 | 25.0 | 6 (66.7%) |
| C | 9 (16.7%) | 20.54 | 2.05 | 17.0 | 22.8 | 5 (55.6%) |