ECG504 – HIGHWAY AND TRAFFIC ENGINEERING LABORATORY 1.0 INTRODUCTION Skidding, i.e. loss of adhesion between a vehicle's tyres and the road surface, occurs in many road accidents whether or not it is the actual cause of the accident. Over the years, tyre manufacturers have done a lot of research into different types of rubber and tread patterns to improve the safety of motor vehicles. Governments have introduced regulations concerning the tread depth and general condition of the tyres. Highway engineers have also researched ways to improve the skid resistance of road surfaces. The impetus for this research came from the Transport and Road Research Laboratory (TRRL) of UK. One of the first things they did was to devise the Pendulum Skid Tester which, being portable, can be taken to the site or used in laboratory experiments. This device simulates the skid resistance offered by a road surface to a motor car travelling at 50 km/h. It gives a number, being a percentage, somewhat akin to a coefficient of friction. Subsequently, they devised the Sideways Force Coefficient Routine Investigation Machine (SCRIM). This is a lorry with a fifth wheel set at an angle to the direction of travel and the lateral force on this wheel is measured and recorded. The lorry travels at 50 km/h and continually monitors the Sideways Force Coefficient (SFC). Other devices include braking force trailer and the meter. These can be used at the high speeds required for testing airport runways. With devices to measure skidding resistance, researchers then monitored changes during the life of road pavements. It was found that skid resistance falls rapidly after a road is opened to traffic but the rate of deterioration slows down, eventually settling to a constant value. This latter value is dependent on the surface texture, rock type and traffic volume.
Figure 1 : A Portable Pendulum Skid Resistance Tester Faculty Of Civil Engineering UiTM shah Alam | 1
ECG504 – HIGHWAY AND TRAFFIC ENGINEERING LABORATORY 2.0 OBJECTIVE The objective of this test is to determine the skid resistance value (SRV), microtexture of road pavement surface. 3.0 APPARATUS i. ii. iii. iv. v. vi.
Portable Pendulum Skid Resistance Tester Rubber slider Scale ruler Brush Water container Thermometer
4.0 PROCEDURE i.
Clean the road surface selected for test with a brush from debris, dust, and any fine granular particles ii. Set up a skid resistance tester so that the center column is vertical (this is done by adjusting the three levelling screws at the base of the skid resistance tester) iii. Adjust the height of the pivot so that the arms swing freely through its arc without touching road surface (check that it swings freely right through to the zero on the scale) iv. The lower the pivot height so that the pendulum rubber slide is in contact with the surface between 124 and 127 mm by the contact path gauge (thin scale ruler), which is placed alongside for measuring contact path length. v. Raise the slider by lifting handle of the pendulum arm so that it is moved to right top right hand side and the starting locked ring is positioned. Then a drag pointer is set to zero. The pendulum is released by pressing the release button, allowing its rubber slider to make contact with the test surface prior to engaging it the retaining catch. vi. The direct mean skid resistance value for the dry pavement surface is indicated by the drag pointers as results of at least five swings of the pendulum are made for each test dry surface. vii. Water the road surface (wet condition) where the readings of skid resistance value are to be taken. viii. Repeat step number 5 ix. After it has swung through, catch the arm to prevent a back swing which could affect the related reading.Note and record the readings on the scale x. Repeat the above steps to obtain a minimum of three readings in order to get the average skid resistance value. 5.0 RECOMMENDATION
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ECG504 – HIGHWAY AND TRAFFIC ENGINEERING LABORATORY The stiffness of the rubber slider varies with temperature. Hence, it is recommended to measure the surrounding temperature during the test, and apply the reading of the pendulum tester with its correlated correction value, as below:
Figure 1: Skid resistance/ temperature correction relationship (TRRL, 1969)
The test was conducted at the same spot of pavement, thus the readings obtained might not differ much from each other. Hence, it is recommended to change the spot due to possible difference in surface texture. It is suggested that the pendulum arm is lowered gently so that the rubber slider barely touch the road surface. This will gives minimum value for maximum safety, since most vehicles that skid are usually driven at high speed. When conducting the test, we found out that the surface resistance lessen once it is wetted with water. However, in realistic condition during heavy rain, the water always flow (which in wetted condition the water will probably flow out or into the texture) hence the depth of water may be greater thus reducing much more road resistance to skidding. If applicable, the test might be deepened using flowing water if considered important.
6.0 RESULT Faculty Of Civil Engineering UiTM shah Alam | 3
ECG504 – HIGHWAY AND TRAFFIC ENGINEERING LABORATORY
Location
1 (concrete)
2 (Brick)
3 (Road)
Surface Texture and Condition
Smooth
Medium
Rough
Reading on Skid Resistance Tester Wet Dry 25
24
27
24
25
23
24
27
28
26
29
27
45
34
45
34
45
32
Average wet dry 26
24
41
27
45
33
7.0 DISCUSSION
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ECG504 – HIGHWAY AND TRAFFIC ENGINEERING LABORATORY The desired texture on concrete pavements is obtained by treating the surface of the fresh concrete. A properly constructed concrete pavement usually does not exhibit any unevenness. This will make the microtexture of the concrete in smooth condition. The skid resistance of concrete in dry condition is 24 mm of sliding length and 26mm sliding length in wet condition. This is because of the smooth surface of the concrete provide a small resistance to the rubber. The brick which in medium rough is providing a 27mm sliding length in dry condition and 41 mm in wet condition which give us an medium resistance between the other two material. Brick microtexture which is brittle give small unevenness and give us a resistance slightly higher than concrete skid value. The difference between wet and dry condition is 14mm is to large. That mean the resistance is decrease greatly when the material is wet. Then, for our third material which is road that have rough macrotexture and even microtexture surface give us the highest skid resistance compare to the other material which is 45 in wet condition and 33 in dry condition. The difference is also acceptable when in wet with 12mm sliding value. This is proved that road is texture is suitable for use as transport material. 8.0 CONCLUSION Base on the result of skid resistance of the material, its is proved that the road is best material to be used as surfacing material which have the highest value of skid resistance which is 33mm in dry condition and 45mm in wet condition because of its rough microtexture at the surface material and have the best effective contact area. The road also have acceptable drop in skid resistance when in wet condition which is give balance between optimum contact area and water effective water dispersion.
9.0 REFERENCES i.
BSI (1990). British Standard BS 812:Part 114:1989 Testing aggregates -Method for determination of the polished-stone value. British Standards Institution, London. Faculty Of Civil Engineering UiTM shah Alam | 5
ECG504 – HIGHWAY AND TRAFFIC ENGINEERING LABORATORY ii. iii. iv. v. vi.
10.0
Hosking, R. (1992). Road aggregate and skidding. Transport Research Laboratory State-of-the-art Review 4, HMSO. TRRL (1969). Instructions for Using the Portable Skid Resistance Tester. Road Note 27, Transport and Road Research Laboratory HMSO. FKA, Laboratory Manual. University Teknologi Mara , Shah Alam . February 2013. Muniandy R., Radin Umar Radin Sohadi. Highway Materials, A Guide Book For Beginners.University Putra Malaysia: Penerbit Universiti Putra Malaysia; 2010. Standard Road Skid Resistance; B.S.I., 1990; British Standards Institution; 1990.
APPENDIX
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ECG504 – HIGHWAY AND TRAFFIC ENGINEERING LABORATORY
A portable skid resistance tester
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ECG504 – HIGHWAY AND TRAFFIC ENGINEERING LABORATORY
Set up the apparatus
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ECG504 – HIGHWAY AND TRAFFIC ENGINEERING LABORATORY
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