With regard to update the current Swiss standards, the IVT participates at the international PIARC experiment to compare and harmonise texture and skid resistance measurements. Those measurements took place in 1992. The IVT used three devices: a pendulum tester, a skiddometer and a "Stuttgarter Reibungsmesser" (SRM).
The overall object of the experiment is to develop a formula for converting results produced by the different devices to an international friction rating and thus provide a basis for international standardisation.
The objective of the project is to determine the significance of different measurement methods, to calibrate and to standardise the measurements with regard to the revision of the standard grip.
Following methodology will be used in the project:
1. Formulation of the objectives
The experiment was designed, among other things with the intention to determine the repeatability of friction and texture measurements for each participating device. In addition, a database should be created, which allows to develop and evaluate the relationships between the various devices.
2. Repeatibility of measurement
Each participant in this experiment was instructed repeated measurements for each section perform. Wherever possible, this has been handled so well. The cooperation in this regard as a result worked out great and now allows the database a precise determination of the repetition accuracy of the measuring instruments. The concept of the experiment was based on the need for a wide range of values for factors that could influence the accuracy of measurement.
The skid resistance properties of roads and airport runways are decisive factors for safety. Greatly varying systems and methods for the measurement of skid resistance and surface texture exist. The results of an AIPCR/PIARC large-scale test form a meaningful basis to enable the standardisation of material specifications for roadway construction. In the past, many tests have been carried out in order correlate data from different friction measurements. While good correlations were sometimes obtained, especially for similar types of surfaces, no general correlation was defined. It was recognised that the effects of different surface textures must be taken into consideration if greatly differing measurement methods such as the blocked wheels, variable slip or side force measure (SCRIM) are to be related to each other.
At the IVT at the Swiss Federal Institute of Technology in Zurich, the skid meter has been replaced by the Stuttgart friction measuring apparatus. In the report, the correlation between these two apparatus, both of which were used in the international AIPCR experiment, is investigated.
The database from the large-scale tests was used to derive an international skid, or friction, index. (International Friction Index = IFI). The IFI is an index based on two parameters which requires, for most systems, a texture measurement in addition to the friction measurement.
The choice of the test sections was given much attention. As various textures and frictions were to be related to each other, roads used by traffic with a wide range of texture and skid resistance properties were sought. Also, not only were various skid resistance and texture levels necessary, it was important to have various levels of abrasion and polish. On similar grounds, the inclusion of real travelled roads in two climatic zones (wet and dry) was desired, thus offers from the host countries Spain and Belgium were accepted.
The large-scale test provided the following results:
- Relationship between friction and texture measurements, which must be carried out with different apparatus.
- Quantification of the relation between standard friction and texture measurements.
- Quantification of repeatability and measurement errors.
- Development of an international friction scale so that data from all apparatus can be entered into this scale.