ECG504
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 ofthe 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 Tester2.0
OBJECTIVE
The objective of this test is to determine the skid resistance
value (SRV), microtexture of road pavement surface.
3.0 APPARATUS
i. Portable Pendulum Skid Resistance Testerii. Rubber slideriii.
Scale ruleriv. Brushv. Water containervi. Thermometer
4.0 PROCEDURE
i. Clean the road surface selected for test with a brush from
debris, dust, and any fine granular particlesii. 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 5ix. 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
scalex. Repeat the above steps to obtain a minimum of three
readings in order to get the average skid resistance value.5.0
RECOMMENDATION
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
LocationSurface Texture and ConditionReading on Skid Resistance
TesterAverage
WetDrywetdry
1 (concrete)
Smooth25242624
2724
2523
2 (Brick)
Medium24274127
2826
2927
3 (Road)
Rough45344533
4534
4532
7.0 DISCUSSION
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.ii. Hosking, R. (1992). Road
aggregate and skidding. Transport Research Laboratory
State-of-the-art Review 4, HMSO.iii. TRRL (1969). Instructions for
Using the Portable Skid Resistance Tester. Road Note 27, Transport
and Road Research Laboratory HMSO.iv. FKA, Laboratory Manual.
University Teknologi Mara , Shah Alam . February 2013.v. Muniandy
R., Radin Umar Radin Sohadi. Highway Materials, A Guide Book For
Beginners.University Putra Malaysia: Penerbit Universiti Putra
Malaysia; 2010.vi. Standard Road Skid Resistance; B.S.I., 1990;
British Standards Institution; 1990.
10.0 APPENDIX
A portable skid resistance tester
Set up the apparatus
Faculty Of Civil Engineering UiTM shah Alam |8