QUALITY ASSURANCE
ROCKS PUT TO THE TEST:
A PROFICIENCY TESTING PROGRAM
Nearly 30 laboratories affiliated with quarrying operations have recently participated in the third round of a rocks proficiency testing program to assess the strengths and purities of construction materials. Proficiency Testing Australia co-ordinated the program and analysed the results.
P
roficiency testing is a means of determining the performance of individual laboratories for specific tests or measurement and an external audit of their quality control procedures. A standard proficiency testing program compares the measuring results of different laboratories on identical samples. Proficiency Testing Australia (PTA), one of Australia’s largest proficiency testing providers, can service the construction materials industry by offering proficiency testing programs for aggregate, soils, concrete, rocks, cement, asphalt and bitumen. PTA recently announced the completion of its third Rocks Proficiency Testing Program. The program was approved by International Accreditation New Zealand and organised with the technical assistance and sample supply of Gayani Samaradiwakara of Golder Associates’ Melbourne Laboratory. The aim of the program was to assess laboratories’ abilities to competently perform the prescribed analyses. Twenty-nine participating laboratories participated in this program in April 2021. All but two of the laboratories were in Australia, with the overseas participants in Bulgaria and Peru. All of the laboratories submitted their results by the due date. Each laboratory was allocated a unique code number for the program to ensure confidentiality of results. All participants performed the required testing by either Australian Standards or ASTM methods, eg: • AS 4133.4.1 Determination of point load strength index - (clause 3.3 Axial test). • AS 4133.4.2.2/1.1.1 Determination of Uniaxial Compressive Strength/ Determination of the moisture content. • AS 4133.4.3.2 Determination of deformability of rock in uniaxial compression. • ASTM D3967 Splitting tensile strength on
intact rock specimen. Laboratories were requested to perform the tests as per PTA instructions and record their findings on a PTA-supplied results sheet. Two or four cylinders (nominally 50mm diameter x 150mm length) were supplied to each laboratory. Cylinders had the identification A or B, depending on the tests performed by each laboratory. Prior to sample distribution, a number of randomly selected samples were analysed for homogeneity. Based on the results of this testing, the homogeneity of the samples was established.
STATISTICAL ANALYSIS OF PARTICIPANTS’ RESULTS PTA used a robust statistical approach to assess the laboratories’ testing performance. A list of summary statistics appears at the bottom of each of the tables of results and consists of: • The number of results for that test/sample (No. of Results). • The median of these results, ie the middle value (Median). • The uncertainty of the median; a robust
Up to four 50mm (dia) x 150mm (l) rock cylinders were supplied to each laboratory.
estimate of the standard deviation of the Median. • The normalised interquartile range of the results (Normalised IQR).
The results by lab of the Rocks Deformability – Density test as per AS 4133.4.3.2.
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