In 2010 Transport Scotland published a new surface course specification (TSIA No 35, 2018), known as TS2010. The specification requires a three stage approval process which includes laboratory testing, off-network trial and an on-network trial (a Type Approval Installation Trial (TAIT)), after which the material is approved for further use dependant on six month in-service GripTester measurements. The disadvantage of such a TAIT is that materials will have to wait up to six months before being given approval and much longer before the long term skid performance of these materials are known. The aim of this study was to see if the Friction After Polishing (FAP) test, conducted using the Wehner-Schulze machine (W-Sm) can be used as an alternative for predicting what level of skid-resistance TS2010 materials will provide whilst in service and the test’s potential to be used for approving TS2010 materials.

Results from all specimens were compared with other factors such as SCRIM, traffic levels, road site categories, material age and texture depth. Analysis of these results indicates that it may be possible to predict, with a reasonable level of accuracy, the high speed friction (Est. L-Fn100) of TS2010 materials. It was not possible however to generate a model based on the data collected during this study that could predict the in-service skid performance of TS2010 materials as measured using SCRIM.

Recommendations include developing a protocol for preparing untrafficked specimens to ensure grit is applied in a consistent manner for any future W-Sm testing. The use of W-Sm friction measurements should also be considered at Stage 2 of the TAIT process.

 

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