Soundness Test Failure and Retest Pressure
A 5-cycle sodium sulfate soundness test on 1/2 in. crushed gravel gives 14% loss, exceeding the 12% maximum in the specification. The producer requests a retest, arguing the sodium sulfate solution was near the end of its life and the oven temperature fluctuated. Records show the solution specific gravity was 1.151 (target range typically 1.151–1.174 for sodium sulfate) and the oven cycled between 230°F and 250°F during drying. The lab has a magnesium sulfate option available. The producer offers to supply a new sample from a different stockpile.
1. Assess the validity of the original test and the retest request.
Read the worked answer
The original test has documented control problems: solution specific gravity at the low end of the acceptable range (1.151) and oven temperature cycling above the specified drying range. Both can bias results. The specific gravity being at the lower bound means the solution may be less aggressive, which would tend to understate loss-so a 14% failure is not explained by a weak solution. Oven fluctuation above range can cause cracking and overstate loss. Given the control deviations, a retest with documented, in-range conditions is reasonable-but the retest must use a properly prepared, representative sample and controlled solution and oven conditions, not simply a more favorable stockpile.
2. How should the retest be designed, and can magnesium sulfate be substituted?
Read the worked answer
Retest with a freshly prepared sodium sulfate solution verified in range (specific gravity per the method, typically 1.151–1.174, confirmed by hydrometer), oven temperature controlled within the specified drying range, and a properly reduced representative sample from the same material under evaluation. Do not substitute magnesium sulfate to get a passing result-the two salts give different loss values and the specification names sodium sulfate. Substitution would not be a valid compliance test. Run the full 5 cycles and report the result with all control data.
3. If the valid retest also fails, what is the appropriate disposition?
Read the worked answer
Report the material as nonconforming to the soundness requirement. Do not average the two failing results to pass, and do not shop stockpiles to find a passing sample. The accepting authority decides disposition (reject, use in a less demanding application, or blend) per the specification. Document both tests, the control deviations, and the retest conditions so the record is transparent.