A contractor needs to remove concrete forms from a beam. The concrete was placed 5 days ago and has reached 70% of design strength. What is the appropriate action?
Correct Answer
B) Remove sides but leave bottom support
ACI standards allow removal of beam sides when concrete reaches sufficient strength (typically 70%), but bottom forms and supports must remain until the concrete reaches adequate strength to carry its own weight plus construction loads, usually 7-14 days.
Why This Is the Correct Answer
Option C correctly follows ACI standards for form removal timing. At 70% design strength (typically achieved in 3-7 days), concrete has sufficient strength to resist lateral pressure, allowing safe removal of side forms. However, the beam still needs bottom support to carry its own weight plus any construction loads until it reaches higher strength levels, typically requiring 7-14 days total.
Why the Other Options Are Wrong
Option A: Remove forms immediately
Removing all forms immediately would be unsafe because while the concrete has reached 70% strength for lateral support, it still needs bottom support to carry structural loads and prevent deflection or cracking.
Option C: Wait for full 28-day cure
Waiting until 7 days minimum is unnecessarily conservative for side form removal, as 70% strength is already adequate for removing sides, and this approach doesn't address the different requirements for side versus bottom support.
Memory Technique
Think 'SIDES FIRST' - sides come off when strong enough to hold shape, bottoms stay until strong enough to hold weight
Reference Hint
ACI 318 Building Code Requirements for Structural Concrete, Chapter 6 - Formwork and Shoring, or Florida Building Code Chapter 19
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