Surface skid resistance

The pavement surface skid resistance is directly related to the safety of the vehicles driving primarily on wet surface. 

It is known that the presence of water between the tyre and the riding surface reduces the skid resistance and that skid resistance increases as the dry contact area between the tyre and the pavement increases. The micro- and macro-texture of the pavement surface primarily contributes to the latter. 

The reduction of BFC when speed increases is more noticeable in asphalts that cannot provide an initial texture depth higher than 0.8 mm, such as asphalt concrete. 

Evidence similar to the effect of texture depth in skid resistance related to speed is given in Table 16.4. As it can be seen, skid resistance (SCRIM [Sideway-force Coefficient Routine 

Source Highways Agency, Design Manual for Roads and Bridges (DMRB), Volume 7 Pavement Design and Maintenance, 

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The values shown in the table indicate that the material compacts to the desired level with a 5-ton vibrating compactor. Surface skid resistance of the sections was measured using a California portable skid tester in accordance with California test method 342 D. The skid values are comparable with published values for fresh-open or dense-graded asphaltic concretes. The friction values increased with increasing sulfur concentration. 

Cold asphalts for slurry surfacing are commonly used worldwide for surface maintenance, for surface maintenance prevention and, above all, for the restoration of surface skid resistance of highways, city streets and airport pavements. 

Gravity fill is also used when cracking is random or patterned. The material normally used is gravity polymer covered with hard and durable sand. Epoxy resin-based materials instead of elastomer/plastomer-based materials are preferred when a longer-lasting surface skid resistance is required. However, this method of repair can be very expensive. 

The activities included in the preventive and corrective maintenance are not essentially independent of each other, except perhaps crack filling, and thus they will not be individually mentioned per case. Works for preventive and corrective maintenance include crack filling, pothole filling, patching, surface skid resistance restoration and surface evenness restoration. 

Loss of surface skid resistance is a skid hazard associated with smooth and slippery surface, which directly affects traffic safety. Unlike all other surface distresses, a smooth and slippery surface does not affect the structural deterioration of the pavement. 

Slippery surface may result from polishing and abrasion of the surface aggregate or asphalt bleeding. Both factors reduce the macro- and micro-texture of the pavement surface and the surface skid resistance provided. 

The cause for loss of surface skid resistance is exclusively the wear of the surface texture provided, the polishing of the fine aggregate and the polishing of the exposed coarse... 

Surface dressing, also known as chip seal, is one of the oldest surface treatment techniques. It is applied in many countries to restore surface skid resistance and to seal the surface inhibiting pavement disintegration. 

Bleeding or flushing of the binder results in a surface that is too rich in binder. Bleeding can cause hazardous conditions owing to loss of surface skid resistance. 

The effect of the above surface texture characteristics on the skid resistance related to vehicle speed is shown in Figure 16.5. As it can be seen, as the speed increases, the surface skid resistance decreases the decrease is more distinct when the surface lacks macro-texture (curves C and D). The best skid resistance value is provided when the surface exhibits both macro- and micro-texture (curve A) and the worst is provided when the surface lacks both macro- and micro-texture (curve D). The existence of macro-texture alone provides good skid resistance (curve C) at speeds higher than 50 km/h. 

Surface skid resistance is measured by self-powered mobile devices or towed mobile devices. Spot measurements or measurements over short road sections are usually carried out by the British pendulum or ether portable devices. 

A substantial number of mobile devices for measuring surface skid resistance have been developed globally. The majority of them have been manufactured in European Union (EU) countries. A relevant EU survey identified and reported 21 mobile devices (TYROSAFE 2008). Table 16.5 presents 19 of those devices together with their basic characteristic features. 

All devices have the ability to wet the pavement surface, creating a water film, usually approximately 0.5 mm thick, just before surface skid resistance is measured. All measurements are taken on a wet surface and readings are recorded continuously at pre-determined intervals, usually between 10 to 50 m length. 

The ASTM locked wheel skid tester or the pavement friction tester (PFT) was developed in America and is one of the first pavement surface skid resistance measuring devices. 

In order to assure road safety, countries have implemented intervention or threshold skid resistance limit values (levels) that, when reached, would require immediate action for surface skid resistance restoration. 

Texture depth directly affects the skid resistance of the pavement surface. In many countries, the minimum allowed texture depth is 0.5 mm. Pavement segments with values lower than 0.5 mm should be investigated immediately, along with skid resistance measurements, and restoration of the surface skid resistance should be programmed. 

Improvement of surface skid resistance Removal of asphalt for further recycling Surface preparation prior to asphalt laying Increased pavement efficiency... 

The milling machine is used in all recycling methods of flexible pavements, while the grinding machine is used for surface skid resistance restoration of rigid pavements. 

The repave process offers perhaps the ultimate rehabilitation/hot recycling results compared to the other two hot recycling in situ processes. In particular, its advantages over the other two in situ processes are as follows (a) complete restoration of surface skid resistance since new asphalt material is used, (b) strengthening of the pavement to a certain extent and (c) minimisation of smoke emission. 

BS 7941-2 2000 Methods for measuring the skid resistance of pavement surfaces. Test method for measurement of surface skid resistance using the GripTester braked wheel fixed shp device. 

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