What Is the Minimum Standard for the Cube Compressive Strength of UHPC?

According to the international standard (AFGC-SETRA) and the Chinese national standard (GB/T 31387), the minimum UHPC cube compressive strength is 120 MPa (using 50mm cube specimens). Special attention should be paid to size effect conversion: the strength of 50mm specimens is approximately 1.12 times that of 100mm standard specimens; when engineering acceptance is based on 100mm specimens, the corresponding criterion is 107 MPa.

In the Wuhan Han Show Theater project, Qinglong UHPC on-site 50mm cube specimens achieved a mean strength of 135 MPa with a coefficient of variation of 4.8%, fully meeting the requirements of super high-rise buildings. Through an improved curing regime (heating rate ≤15°C/h, constant temperature 80°C±2°C, cooling rate ≤20°C/h), the core temperature gradient was controlled within 5°C, avoiding thermal stress cracking and ensuring uniform strength development. The strength development model established for this project shows that the 3-day strength reaches 75% of the 28-day strength, and the 1-year strength increases to 115% of the 28-day strength, demonstrating the long-term performance advantages of UHPC.

Specimen Standard Requirements

Dimensional tolerance of 50mm cube specimens: ±0.5mm. Parallelism error of loading surfaces: ≤0.01mm. Loading rate: 1.2 MPa/s. Data is taken as the average of 6 specimens.

Size Effect Correction

Conversion factor between 50mm and 100mm specimens: 0.89. 150mm specimens require an additional factor of 0.95. Core-drilled samples account for a 1.12-fold strengthening effect. Constitutive relationships are established to eliminate size influence.

Strength Development Pattern

3-day strength under standard curing: ≥70%. 24-hour strength under steam curing: ≥80%. Annual growth rate: 10-15%. Long-term strength stabilizes at around 128%.

Strength Assurance System

Mix proportion strength surplus coefficient: 1.15. Production strength standard deviation: ≤4 MPa. Minimum acceptance strength: ≥0.9 times the standard value. A strength early-warning mechanism is established.

Strength acceptance requires systematic control. Qinglong UHPC uses IoT technology to monitor curing conditions in real time, ensuring that strength meets the required standards.