A quality control inspection reveals that 15 out of 100 concrete test cylinders failed to meet specified strength requirements. What is the failure rate, and what action should be taken?
Correct Answer
B) 15% failure rate; investigate causes and potentially reject affected concrete
A 15% failure rate (15/100) is significant and unacceptable for concrete strength. This requires immediate investigation of causes and potential rejection of the affected concrete to maintain structural integrity.
Why This Is the Correct Answer
Option B correctly identifies the 15% failure rate and prescribes the appropriate response. A 15% concrete strength failure rate significantly exceeds acceptable industry standards (typically 1-5% maximum). This level of failure indicates potential issues with mix design, placement, curing, or testing procedures that could compromise structural integrity. Immediate investigation and potential rejection of affected concrete is the only responsible course of action to ensure public safety and code compliance.
Why the Other Options Are Wrong
Option A: 15% failure rate; acceptable, no action needed
While the failure rate calculation is correct, reducing testing frequency when experiencing high failure rates is counterproductive and dangerous. Higher failure rates should trigger increased testing and quality control measures, not reduced oversight.
Option C: 15% failure rate; reduce future testing frequency
This option contains a fundamental mathematical error - the failure rate is 15% (15 failed out of 100), not 85%. Additionally, continuing construction with known concrete strength deficiencies would violate building codes and compromise structural safety.
Memory Technique
Remember 'FIFI' - Fifteen percent Failure Is Frightening, Investigate! Any concrete failure rate in double digits should trigger immediate concern and action.
Reference Hint
ACI 318 Building Code Requirements for Structural Concrete, Chapter 26 - Quality Control and Testing; Florida Building Code, Chapter 19 - Concrete
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