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Carpenter Red Seal Exam Prep · Question

For a concrete beam that achieved 70% of its specified 28-day compressive strength (f'c = 30 MPa) at 7 days, what would be the typical minimum required strength (in MPa) before stripping all formwork and re-shoring falsework for subsequent loads, according to common practice and CSA A23.1 recommendations?

While specific requirements vary by engineer, a common guideline for stripping load-bearing forms and removing shoring is when the concrete has achieved at leas

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Question: For a concrete beam that achieved 70% of its specified 28-day compressive strength (f'c = 30 MPa) at 7 days, what would be the typical minimum required strength (in MPa) before stripping all formwork and re-shoring falsework for subsequent loads, according to common practice and CSA A23.1 recommendations?

Answer options:

  • 15 MPa
  • 21 MPa ✅ 22.5 MPa
  • 30 MPa

Correct answer: 22.5 MPa

Explanation: While specific requirements vary by engineer, a common guideline for stripping load-bearing forms and removing shoring is when the concrete has achieved at least 75% of its specified 28-day comprehensive strength (f'c). So, 0.75 * 30 MPa = 22.5 MPa. This ensures adequate strength for self-support and partial construction loads.

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