Under what condition should test results be discarded?

Test results should be discarded when the fracture occurs outside the middle third of the span length by more than 5% of the span due to the fact that such a scenario indicates that the load and stress applied to the specimen are not evenly distributed. This can lead to an inaccurate representation of the material's true strength, affecting the reliability of test results. The middle third of the span is where bending moments are minimized and results are most consistent, allowing for a more accurate assessment of concrete strength under normal loading conditions.

When fractures occur outside of this optimal region, it signifies that a significant portion of the specimen may be subjected to abnormal stress, which does not reflect the material's behavior under standard conditions. This guideline is essential for maintaining the integrity of concrete testing and ensuring that results are valid for quality assurance and structural design purposes.

The other conditions, while important in evaluating test results, do not necessarily warrant discarding the results. For example, fractures occurring in the middle third may still provide valid data, and specifications regarding dimensions or alignment may still allow the specimen to be acceptable based on specific testing standards.