The stock of control stone used for calibration in the polished stone value (PSV) test, which determines the suitability of aggregate for use in the road surface course, ran out in 2008. An alternative aggregate was procured and initial testing confirmed its suitability for use as PSV control stone. Subsequent use by UK laboratories revealed that the mean PSV of the new source had been overestimated and a revised value was introduced. Extensive round-robin testing of the aggregate confirmed its revised PSV. The round-robin testing also demonstrated the suitability of a proposed alternative control stone, sourced in Germany.
The 2011 UK PSV control stone has a mean PSV of 49.0 and is available for use in the PSV test. The PSV of the German control stone was confirmed as 54.5 or 55.0.

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