Factors Affecting the results of Polished-Stone Value Tests

A study has been made of the factors that affect the results of polished-stone value (PSV) tests. These factors can be separated into those connected with the test procedure itself and those arising from the production of the aggregate and from sampling procedures. The main conclusions that were drawn from this study are as follows: The reproducibility of the test is + 3 units at a 97-per-cent probability level. The repeatability of the test is + 9.3 units at a 95-per-cent probability level. Reproducibility would be improved by rejecting results from tests in which the range of the four individual test results on one aggregate exceed 5 and by specifying an order in which the specimens should be polished and tested. More use should be made of control specimens and further research should be carried out to establish a consistent standard material. Water-washed emery flour can be used in the place of the air-floated flour now specified. Variations in PSV test results can, to a large extent, he caused by variations in the aggregate itself. Tests on single random samples are of very limited value. Tests on properly representative samples are of more value, but a really reliable estimate of the PSV of a source requires calculation of the mean and standard deviation of many test results. The Report discusses ways in which the reproducibility of the PSV test can be improved by amending the test procedure.