Skid resistance index

The skid resistance of the pavement surface may be measured by a considerably great number of devices on the basis of different principles. This fact renders the direct comparison of the results almost impossible. 

For harmonising the results obtained from all permitted skid resistance devices, the SRI has been invented. SRI is an objective estimate of skid resistance that is independent of the 

According to CEN EN 13026-2, the permitted devices for friction measurements are those that have their measuring principle and procedure described in CEN/TS 15901-1 (2009) to CEN/TS 15901-13 (2011) (Table 16.2). 

For the determination of SRI, it is necessary to also measure the surface texture depth profile, according to CEN EN ISO 13473-1. This is achieved by the use of appropriate laser devices or other optical non-contact devices (high-resolution three-dimensional [3D] devices may also be used) placed at the front or at the back of a survey vehicle. 

In the case that the mean texture depth (MTD) is known by the volumetric technique (sand patch method) according to CEN EN 13036-1 (2010), the mean profile depth (MPD) may be estimated by the following equations  

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The measurements taken by each device are not completely comparable. For this reason, the limiting values of skid resistance values set by national specifications should be differentiated for every device recommended to be used. This problem can be resolved by expressing the skid resistance value obtained with respect to the Skid Resistance Index (SRI) (see Section 16.3.6). 

The last property is related to the processing of the rubber in the tire making equipment. By using organo-lithium compound in this case, it was possible to maintain a vinyl content not greater than 18, but to produce a polybutadiene styrene copolymer that has random block styrene and without the use of polar modifiers, which normally will increase the 1,2 content. This copolymer, when compounded in the tread recipe, as shown in the Table XVI, gave properties that are actually equivalent to that of emulsion SBR and in some cases even better. This is particularly true in the properties of the Young modulus index, which showed between -38 to -54 C the Stanley London Skid Resistant, in which the control is 100, shows that 110-115 was obtained. 

The International Friction Index (IFI) is similar to the SRI discussed above and was developed in the PIARC international experiment to compare and harmonise texture and skid resistance measurements. The index allows for the harmonising of friction measurements with different devices that use smooth tread test tyres to a common calibrated index. The procedure for determining the IFI is covered in ASTM E 1960 (2011). 

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