LABORATORY 4 ROAD SKIN RESISTANCE
1.0 INTRODUCTION
One of the surface requirements for road pavement is that it should posses adequate skid resistance. Skid resistance is important for road safety. With skid resistance it allows for better ‘grip’ between tire and road surfaces. Most road surfaces have adequate skid resistance in the dry as compared during wet condition. The presence of water between tire and road surface reduce the contact are which are needed to create the ‘grip’. This method describes the procedure for determining the frictional properties (skid resistance value) of a pavement surface using a Portable Skid Resistance Tester. The instrument, which gives direct reading, gives a measure of the friction between a skidding tire and dry/wet road surface in low speed situation ( <50km/h). It provides the highway engineer with a practical means of obtaining reliable scientific evidence on which to take appropriate measures to reduce skidding.
2.0 OBJECTIVE To determine the skid resistance value of road pavement surface.
3.0 APPARATUS A Portable Pendulum Skid Resistance Tester, a rubber slide, a scale ruler, brush, water container and thermometer.
Portable pendulum skid resistance tester
Scale rule
Brush
4.0 PROCEDURE
I. The skid resistance tester was set up so that center column is vertical by adjusting the leveling screws. II. The height of the pivot was adjusted so that the arms swing freely without touching the road surface. The pivot was checked to swing freely right through to the zero on the scale. III. The pivot height was lowered so that the friction foot is in contact with the road surface over the precise distance (150mm) as shown by the gauge (scale rule) which is placed alongside. IV. The pendulum arm was raised to the starting position and the retaining catch was engaged. V. The road surface was wetted with water where the readings of skid resistance will be taken. VI. The maximum swing indicator was checked to be set to the vertical position. VII. The pendulum arm was released. VIII. The pendulum arm was caught after it swings through to prevent back swing which could disturb reading. IX. The reading on the scale was recorded. X. The test was repeated to obtain a minimum of three readings.
5.0 RESULT OF OBSERVATIONS
Location
1
2
3
Surface Texture and Condition Rough surface Road pavement (tar)
Medium rough surface Concrete pavement
Smooth surface Tiles
Reading on Skid Resistance Tester Wet Dry 53
85
49
90
53
87
45
74
44
74
42
72
43
70
39
66
35
69
Average Reading Wet
Dry
51.67
87.33
43.67
73.33
39.00
68.33
6.0 SAMPLE OF CALCULATION
Location
Reading on Skid Resistance Tester Wet Dry
Surface Texture and Condition Rough texture Road pavement (tar)
1
53
85
49
90
53
87
AVERAGE READING ON SKID RESISTANCE TESTER
Location 1: Rough surface
WET Average
=
Reading 1 + Reading 2 + Reading 3 3
Average
=
53 + 49 + 53 3
=
51.67
=
Reading 1 + Reading 2 + Reading 3
DRY Average
3
Average
=
=
85 + 90 + 87 3 87.33
Average Reading Wet
Dry
51.67
87.33
7.0 DISCUSSION
Skid resistance is the force developed when a tire is prevented from rotating slides along the pavement surface (Highway Research Board, 1972). Skid resistance is an important pavement evaluation parameter because inadequate skid resistance will lead to higher incidences of skid related accidents.
Based on the result of the experiment, the differences between Skid Resistance Value (SVR) for each type of surface are obviously varied, depending on its surface texture and also its condition, either wet or dry.
The surface which turned out to have the highest Skid Resistance Value (SVR) is the road pavement; with the average wet SVR of 51.67 and dry SVR of 87.33. Tiles surface which represent smooth texture is having wet SVR of 39.00 and dry SVR of 68.33. The concrete pavement, which is classified as medium rough texture is having wet SVR of 43.67 and dry SVR of 73.33. Based on the value, the readings of the skid resistance value are decreasing as the surface texture changing from rough texture to the smoother texture. It is because the SVR is depends on the pavement surface’s microtexture. Microtexture refers to the small-scale texture of the pavement aggregate component. Rougher surface will have larger microtextures which produce larger force to prevent rotating slides along the pavement. With the presence of water, the SVR value will be reduced since water is an element which reduces the friction between two interfaces.
The experiment is implemented in highway engineering in order to evaluate the surface friction between the road and vehicles’ tires, which enable more research to be made to maximized road safety, primarily during the rain. Most roads are designed with a convex camber to provide sufficient drainage gradient, thereby allowing surface water to drain out of the road. Storm drains may be installed at regular intervals and modern paving materials are designed to provide high friction in most conditions. Permeable paving allows water to soak through the paving material, reducing slipperiness in very adverse conditions.
8.0 CONCLUSION
Surface with rougher texture will have higher friction value compared to smoother surface texture. The skid resistance test is important in highway engineering since inadequate skid resistance will lead to higher incidences of skid related accidents. Besides, skid resistance measurements can be used to evaluate various types of materials and construction practices of highway and road. Meanwhile, the skid resistance test with wetted surface was done to illustrate the road condition during rain, where it is dangerous for any vehicle to travel in high speed.
In general, the friction resistance of most dry pavements is relatively high; wet pavements are the problem. The numbers of accidents on wet pavements are twice as high as dry pavements, including other factors such as visibility in addition to the skid resistance value.
9.0 APPENDIX
Skid resistance test on road pavement (tar)
Skid resistance test on concrete pavement
10.0
REFERENCE
Interactive Training Guides, University of Washington. (2005). Skid Resistance. Retrieved October 30, 2011 from http://training.ce.washington.edu/
Nanyang Technological University. (2009). Skid Resistance Test. Retrieved September 28, 2011 from www3.ntu.edu.sg/cts/tlab/006.pdf
The Idiots’ Guide to Highway Maintenance. (2008). Skid Resistance and High Friction Surfacing. Retrieved October 30, 2011 from http://www.highwaysmaintenance.com/skidtext.htm
Wikipedia, the free encyclopedia. (2008).Road slipperiness. Retrieved September 30, 2009 from http://en.wikipedia.org/wiki/Road_slipperiness
