Highway Cross Section Elements , Pavement surface characteristics , Friction, Pavement unevenness,

1. DEPARTMENT OF
CIVIL ENGINEERING
Highway Cross Section Elements
Pavement Surface Characteristics
Er. Ramprasad Kumwat
M.Tech

2. Pavement Surface Characteristics
• The pavement surface depends on the
pavement type. The pavement surface type is
decided based on the availability of materials
and funds, volume and composition of traffic,
sub grade, and climatic conditions,
construction facilities and cost considerations.
• The important surface characteristics of the
pavement are: (i) friction (ii) unevenness
(iii) light reflecting characteristics and
(iv) drainage of surface water.

3. (i) Friction
• The friction or 'skid resistance' between vehicle
tyre and pavement surface is one of the factors
determining the operating speed and the minimum
distance required for stopping the vehicles.
• When a vehicle negotiates a horizontal curve, the
lateral friction developed counteracts the
centrifugal force and thus governs the safe
operating speed.
• Frictional force is an important factor in the
acceleration and retardation abilities of vehicles.

4. • The coefficient of friction, or the skid
resistance offered by the pavement surface
under various driving and surface conditions is
important with reference to the safety.
• The maximum coefficient of friction comes
into play only when the braking efficiency is
high enough to partially arrest the rotation of
the wheels on application of brakes, at low
speeds.

5. • Skid' occurs when the wheels slide without
revolving or rotating or when the wheels
partially revolve.
• While a vehicle negotiates a horizontal curve,
if the centrifugal force is greater than the
counteracting forces (i.e. lateral friction and
component of gravity due to super elevation)
lateral skidding takes place.
• `Slip' occurs when a wheel revolves more than
the corresponding longitudinal movement
along the roads.

6. Factors affecting friction or skid
resistance
• The maximum friction offered by pavement
surface or the skid resistance depends upon the
following factors:
• (a) Type of pavement surface namely, cement
concrete, bituminous, WBM, earth surface etc.
• (b) Macro-texture of the pavement surface or
its relative roughness ,
• (c) Condition of pavement namely, wet or dry,
smoothened or rough, oil spilled , mud or dry
sand on pavement

7. • (d) Type and condition of tyre i.e. new with
good treads or smoothened and worn out tyre
• (e) Speed of vehicle
• (f) Extent of brake application or brake
efficiency
• (g) Load and tyre pressure
• (h) Temperature of tyre and pavement
• (i) Type of skid, if any

8. (ii) Pavement unevenness
• The longitudinal profile of the road pavement has
to be 'even' in order to provide good riding
comfort to fast moving vehicles and to minimize
the vehicle operation cost. Presence of
undulations on the pavement surface is called
'pavement unevenness‘.
• which results in: (i) increase in discomfort and
fatigue to road users, (ii) increase in fuel
consumption and tyre wear, (iii) increase in
vehicle maintenance cost, (iv) reduction in
vehicle operating speed and (v) increase in
accident rate.

9. • The unevenness of pavement surface is
commonly measured by using a simple
equipment called 'Bump Integrator' (BI), in
terms of 'unevenness index', which is the
cumulative measure of vertical undulations of
the pavement surface recorded per unit length
of the road.

10. • Internationally, the riding quality of a
pavement surface is quantified in terms of
`roughness' and is expressed as 'International
Roughness Index' (IRI) in units of m/km.
• The relation between the unevenness measured
using bump integrator in mm/km and the
International Roughness Index in m/km is as
follows: BI = 630 (IRI)^1.12

11. • The unevenness or undulations on pavement
surface may be caused due to various factors,
such as:.
• (i) inadequate or improper compaction of either
the fill, sub grade or pavement layers or
combination of these
• (ii) use of improper construction machinery
• (iii) use of inferior pavement materials
• (iv) improper surface and subsurface drainage
• (v) unscientific construction practices including
the use of boulder stones and bricks as `soling
course' over loose or weak sub grade soil
• (vi) poor maintenance practices and
• (vii) localized failures due to combination of
causes.

12. (iv) Light reflecting characteristics
• Night visibility depends upon the colour and
light reflecting characteristics of the pavement
surface.
• The glare caused by the reflection of head
lights is considerably high on wet pavement
surface than on the dry pavement.

13. • Light coloured or white pavement surface give
good visibility at night particularly during
rains; however white or light colour of
pavement surface may produces glare and eye
strain during bright sunlight.
• Black top pavement surface on the other hand
provides very poor visibility at nights,
especially when the surface is wet.

14. (iv) Drainage of surface water
• The pavement surface should be absolutely
impermeable to prevent seepage of water into
the pavement layers.
• Further, both the geometry and texture of
pavement surface should help in draining out
the water from the surface in less time.

15. • THANKS!
• Gmail: ramkumawat001@gmail.com