ACI 318 values for common f'c
| f'c (psi) | Ec (ksi) | fr (psi) | n = 29,000 / Ec |
|---|---|---|---|
| 2,500 | 2,850 | 375 | 10.2 |
| 3,000 | 3,122 | 411 | 9.3 |
| 3,500 | 3,372 | 444 | 8.6 |
| 4,000 | 3,605 | 474 | 8.0 |
| 4,500 | 3,824 | 503 | 7.6 |
| 5,000 | 4,031 | 530 | 7.2 |
| 6,000 | 4,415 | 581 | 6.6 |
| 7,000 | 4,769 | 627 | 6.1 |
| 8,000 | 5,098 | 671 | 5.7 |
| 10,000 | 5,700 | 750 | 5.1 |
| f'c (MPa) | Ec (GPa) | fr (MPa) | n = 200 / Ec |
|---|---|---|---|
| 17 | 19.4 | 2.56 | 10.3 |
| 20 | 21.0 | 2.77 | 9.5 |
| 25 | 23.5 | 3.10 | 8.5 |
| 28 | 24.9 | 3.28 | 8.0 |
| 30 | 25.7 | 3.40 | 7.8 |
| 35 | 27.8 | 3.67 | 7.2 |
| 40 | 29.7 | 3.92 | 6.7 |
| 45 | 31.5 | 4.16 | 6.3 |
| 50 | 33.2 | 4.38 | 6.0 |
| 60 | 36.4 | 4.80 | 5.5 |
| 70 | 39.3 | 5.19 | 5.1 |
Values computed from the ACI 318 equations above. Measured Ec varies with aggregate type by roughly ±20%.
| Concrete | lb/ft³ | kg/m³ |
|---|---|---|
| Normalweight, plain | 145 | 2,320 |
| Normalweight, reinforced (dead load) | 150 | 2,400 |
| Sand-lightweight | 105 to 120 | 1,680 to 1,920 |
| All-lightweight | 90 to 105 | 1,440 to 1,680 |
Typical ranges. Properties of steel, aluminum and wood are on the material properties page.
For normalweight concrete ACI 318 gives Ec = 57,000√f'c in psi, or 4,700√f'c in MPa. For 4,000 psi concrete that is about 3,600 ksi (25 GPa), roughly one eighth of steel.
Use the general form Ec = wc^1.5 × 33√f'c (psi), with wc the unit weight in lb/ft³ between 90 and 160. In SI, Ec = wc^1.5 × 0.043√f'c (MPa) with wc in kg/m³.
n = Es / Ec, with Es = 29,000 ksi for reinforcing steel. For 4,000 psi concrete, n = 29,000 / 3,605 ≈ 8. It is used to transform steel area into equivalent concrete in cracked section analysis.
Plain normalweight concrete is about 145 lb/ft³ (2,320 kg/m³). Reinforced concrete is usually taken as 150 lb/ft³ (2,400 kg/m³) for dead load.