Resources

The British Pendulum Tester (BPT) is used to assess the skid resistance of road surfaces. There are concerns that on chipseal surfaces the instrument may not deliver accurate or consistent results, recorded as British Pendulum Numbers (BPN). As a result, a study was carried out between 1992 and 1994, over a 30 month period, in four phases.

Phase 1 established, by means of an inter-laboratory comparison, that measurements of chipseal surfaces had large repeatabilities and reproducibilities. This phase was carried out on test panels simulating road surfaces.

Phase 2, after testing more panels made from three grades of chip each selected from four quarries, could establish no consistent relationship between BPN, chip source or chip size. However, an indicative relationship could be established between BPN and the micro- and macrotexture of the chips as quantified by the methods of the standard ASTM E770-80.

Phase 3 involved training two operators to employ an identical test procedure, and for both operators to minimise permitted variations in procedure. Repeatabilities and reproducibilities for these two operators were found to be significantly improved than those found in the first phase of the work.

Phase 4 examined the pattern of variation of skid resistance (measured by the BPT) over road surfaces so that an appropriate sampling pattern could be proposed. A statistically significant pattern was found that showed:

• consistency of BPN over a 50m length of road
• lower BPN in the wheeltracks compared to the shoulders and between wheeltracks, and
• on some curves, differences in the BPN measured in a radial direction compared to BPN measured longitudinally, ie in the direction of traffic.

Keywords: Aggregates, British Pendulum Tester, chip, friction, grade, New Zealand, pavements, Pendulum Number, repeatability, reproducibility, roads, samples, skid resistance, surfaces, texture