The specification for aggregates for use on New Zealand roads includes the British Polished Stone Value (PSV) test. This test and the acceptance criteria were adopted in New Zealand in the 1990s, based on British experience that they were the best available method of predicting the on-road friction performance of aggregate. However, research performed by a number of people in New Zealand has shown that the prediction of performance by the PSV test is extremely variable.
The Wehner-Schulze (WS) test method, developed in Germany in the 1960s and commonly used there, can test samples taken from the road. This research, which was carried out between December 2009 and August 2010, aimed to assess the potential of the WS test for predicting chipseal surface friction.
The chipseal samples taken from New Zealand roads could not be used for testing because their very high texture imposed too much stress on the equipment. Therefore, hand-placed chips were tested (a specified variation in the test method). Six New Zealand quarry aggregates, covering a range of on-road friction performance, were used to assess the WS test. The test results showed that PSV and WS test results on the hand-placed samples were highly correlated. Therefore, in this form the test is not a better predictor of on-road friction than the PSV test.