A concrete pour fails the 28-day compressive strength test. The test shows 2,800 psi when the specification requires 3,000 psi. What should be the contractor's first action?
Correct Answer
B) Order additional testing including core samples from the affected area
The first step should be additional testing including core samples to verify the actual in-place strength, as cylinder tests may not always represent the actual concrete strength in the structure due to various factors.
Why This Is the Correct Answer
Option B is correct because when cylinder tests fail, the first step should be to verify the actual in-place concrete strength through additional testing, particularly core samples. Cylinder tests can be affected by handling, curing conditions, and testing procedures that may not reflect the true strength of the concrete in the structure. Core samples provide a more accurate assessment of the actual structural concrete strength before making costly decisions about removal or replacement.
Why the Other Options Are Wrong
Option A: Immediately remove and replace all affected concrete
Option A is premature and potentially costly. Immediate removal and replacement should only be considered after confirming that the in-place concrete actually has insufficient strength through proper testing methods like core samples.
Option C: Accept the concrete as the difference is less than 10%
Option C is incorrect because accepting concrete below specification requirements is not acceptable, regardless of the percentage difference. The 10% variance mentioned has no basis in building codes or standards for concrete acceptance.
Option D: File a claim against the concrete supplier
Option D is premature because the contractor hasn't yet determined if the problem is with the concrete itself or with the testing procedures. Filing claims should only occur after proper investigation confirms the concrete supplier is at fault.
Memory Technique
Think 'CORE before CHORE' - get CORE samples before doing the CHORE of removal and replacement
Reference Hint
ACI 318 Building Code Requirements for Structural Concrete, Chapter 26 - Strength Evaluation of Existing Structures, and Florida Building Code Chapter 19 - Concrete
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