Friction Tests on Contaminated Surfaces

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brian
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Friction Tests on Contaminated Surfaces

Post by brian »

2006 TRL Limited report on friction tests on contaminated surfaces: “Friction Tests on Contaminated Road Surfaces”, Lambourn & Viner.
The following are portions of the various sections:
Executive Summary:
  • The presence of containments in the tyre/road interface can reduce the friction generated between the tyre and the road. The sudden reduction in this friction experienced by the driver of a vehicle who traverses an area of road surface subject to contamination could potentially contribute to a loss of control of the vehicle and thus could pose a serious hazard. The objective of the study was to test various selected contaminants to identify the contaminants which, on a typical road surface, cause the greatest loss of friction and to provide guidance as to the importance of this effect.
Summary:
  • The results show that, for the skid cars, the reduction in friction observed with the contaminants, as compared to the dry and wet conditions, is clear but modest. The lowest figures, of 0.41 for oil on asphalt and 0.44 for diesel on the concrete, are lower than the corresponding measurements on these surfaces when wet, but comparable with figures which may be found on other road surfaces that are wet. These figures may be surprising in view of the commonly held belief that spilt diesel fuel will make a road dangerously slippery, and that engine oil might make it more slippery still.
    TRL_friction_tests.jpg
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    Unlike the results with the cars, the friction coefficients recorded with the PFT(Pavement Friction tester, see below) in the presence of contaminants are below the range of values expected from road surfaces in wet conditions and in the worst case, are virtually zero. The comparison of the PFT results with those from the skid cards provides an indication of the relative influence of tyre condition and surface texture.
CONCLUSIONS:
The following are some of the conclusions drawn from this study:
  1. For small or medium sized cars with tyres in good condition, skidding on a surface with good skid resistance and moderate or high texture depth, friction coefficients above 0.4 could be expected for all the contaminants tested, even when spread copiously or in a thick layer. This performance is no worse than might be expected on many road surfaces when wet.
  2. The tyre tread is critically important to delivering this performance and, with s11100th tyres , friction coefficients of practically zero can be observed in some circumstances. This worstcase scenario may apply even when the underlying surface is highly skid resistant and with a good texture depth.
  3. Other than the tyre tread, the important parameters influencing the result seem to be the viscosity of the liquid contaminants followed by the surface texture (with the engine oil – the most viscous contaminant - a virtually zero friction coefficient was recorded on a surface with good underlying surface texture).
  4. The performance of the proprietary absorbent material in clearing up the contamination was superior to that of sand.
The main implication of this work for highway authorities is that, given the worst-case scenario it is clearly important to avoid contamination or clear it up as quickly and effectively as possible. For areas where contamination may occur regularly, such as agricultural accesses or entrances to refuse disposal facilities, it is recommended that a regime of regular inspection and decontamination of the road surface be enforced. Where spillage of liquid contaminants is involved, it is recommended that a proprietary absorbent product is used to remove the contamination in preference to the use of sand for this purpose. Consideration should also be given to whether the risks to road users as a result of the presence of contamination could be mitigated by the use of warning signs or speed restriction

PFT=Pavement Friction Tester which is a locked-wheel friction tester consisting of a towing vehicle and purpose built test trailer fitted, for this study, with ASTM standard smooth tyres (ASTM E524-88). This equipment is common in the United States and is used in England by the Highways Agency for research.
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