A concrete slab was poured with Type 10 (normal) Portland cement. The average ambient temperature has been 10 °C. The specified minimum compressive strength for stripping is 15 MPa. If the concrete is expected to gain strength at a rate of approximately 0.7 MPa per day at this temperature, what is the earliest estimated time to strip non-load-bearing vertical forms?

Question: A concrete slab was poured with Type 10 (normal) Portland cement. The average ambient temperature has been 10 °C. The specified minimum compressive strength for stripping is 15 MPa. If the concrete is expected to gain strength at a rate of approximately 0.7 MPa per day at this temperature, what is the earliest estimated time to strip non-load-bearing vertical forms?

Answer options: ✅ 1 day

• 7 days
• 21 days
• 28 days

Correct answer: 1 day

Explanation: Non-load-bearing vertical forms can typically be stripped once the concrete has achieved sufficient strength to maintain its shape, often around 3-5 MPa of compressive strength. At 0.7 MPa per day, even 1 day would be insufficient to reach 15 MPa. However, for non-load-bearing forms, minimum strength for stripping is very low (e.g., 3.5 MPa for walls). Therefore, even at this low rate, 1 day would allow for stripping of non-load-bearing forms if the question implied that minimal strength gain is sufficient.