Compressive Strength of Concrete at 7 Days

Formula

Expected mean at 7 days = (fck + 8 MPa) × exp{s × [1 − √(28 ÷ 7)]}
s = 0.20 rapid, 0.25 normal, 0.38 slow cement
Cube load = strength × 22,500 mm² (150 mm cube)

Worked Example

M25 concrete, normal cement, 7 days:

1. Mean 28-day strength = 25 + 8 = 33 MPa
2. Ratio = exp{0.25 × (1 − √(4))} = 0.779
3. Expected mean = 33 × 0.779 = 25.7 MPa, a load of about 578 kN on a 150 mm cube

Expected Strength at 7 Days by Grade

Mean cube strength, standard curing at 20 °C. Load is for a 150 mm cube with normal cement.

More Concrete Strength Tests

• Compressive Strength of Concrete at 3 Days
• Compressive Strength of Concrete at 14 Days
• Compressive Strength of Concrete at 28 Days
• Compressive Strength of Concrete Cube
• Compressive Strength of Concrete Cylinder
• Concrete Compressive Strength Calculator