Rehabilitation of Flexible Pavements.

1. Any work that is under taken to significantly extend the
service life of an existing pavement through:
Re –surfacing Restoration Reconstruction
 The periodic maintenance is carried out to preserve the
existing pavement so that it may achieve its applied loading.
 Rehabilitation is carried out to significantly increase the
functional life.
REHABILITATION

2. It is divided in to two major categories:
1. Rehabilitation methods with overlays
2. Rehabilitation methods other than overlays.
REHABILITATION

3. 1. Failure of Road Structure
 unacceptable level of service in terms of riding comfort
 unacceptable level of distress
2. Improper drainage system
3. Increase in traffic intensity
 inadequate structural capacity for expected traffic loads
4. Upgrading of geometric standards of the
existing road
Reasons of rehabilitation of road

4. 1. Road failure
Structural Failure; Sub-base or Wearing
due to excessive traffic intensity
Subgrade / foundation failure;
due to
moisture in subgrade, drainage, water logging,
salinity, and katcha shoulders

5. 2. Drainage system
Drained off surface water from the carriage way
and shoulders without allowing it to percolate in the
subgrade
Prevent the surface water, from adjoining lane,
from entering the roadway
Highest level of ground water table should be well
below the level of subgrade, preferably by at least
1.2 meters

6. 3. Increase in traffic intensity
The existing road is in good condition but due to
unexpected increase in the traffic may cause the
failure of the road at early stage or may not be able
to cater the increased traffic.
It is required to increase carriage way width and
shoulders etc.

7. 4. Upgrading the geometric standards of the road
It is possible to design and construct the pavement
in stages but it is very expensive rather difficult to
improve the geometric elements of a road in stages.
Because of the old age of the roads, the geometric
standards are also of old age.
Therefore the geometric elements should be of improved
design to enable the pavement for the smooth movement of
vehicles operating at design speed

8.  A flexible pavement with accumulated traffic loads and time in
service, may suffer one or more of the following deficiencies.
Excessive Rutting Excessive cracking
Inadequate riding Quality Inadequate skid resistance of surface
 A pavement may be adequately maintained and may not have the above listed
deficiencies, but pavement may have the following problems:
Excessive maintenance costs
Inadequate structural capacity for the expected future traffic loads.
 In all of the above cases, treating the pavement with an overlay is the most
common method for restoring, or upgrading the pavement to its desired
condition and level of serviceability
Need of Overlay

9. 1. Asphalt concrete overlay on flexible pavement
2. Conventional Portland cement concrete overlay on flexible
pavement, in which the concrete layer is placed unbounded over
the asphalt surface
3. Ultra-thin Portland Cement concrete overlay on flexible
pavement, in which a thin concrete layer of 10 cm (4 in) or less
is placed bonded over the asphalt surface.
Types of Overlay for Flexible Pavement

10. Non-Structural Overlay
• Improve ride quality.
• Correct minor surface defects.
• Improve safety characteristics
such as skid resistance and
drainage.
• Enhance appearance.
• Reduce road-tire noise.

11. 1. Component analysis design
2. Deflection –based design
3. Analytical –based design
Overlay Design Procedure

12. 1. Component analysis design
• Evaluating the condition of the components (pavement
layers) of the existing pavement
• Comparing with the thicknesses of new pavement materials
to be placed.
• The required overlay thickness is equal to he difference
between the required total thickness and equivalent
thickness of existing layer.

13. 2. Deflection based design
 Measurement of surface deflection caused by a
nondestructive test (NDT) to estimate the structural
capacity of an existing pavement.
 The design procedure is usually based on the empirical
correlations between certain NDT deflections and field
performances.

15. Evaluation of pavement performance for overlay
In designing an overlay for an existing pavement, it is imperative
to perform a thorough evaluation of the existing pavement to
determine its areas of deficiency and deterioration.
The pavement performance can be described in three main
categories as follows:
Functional Performance
Structural Performance
Safety Performance

16. Functional Performance
The most commonly used measure of function performance of
A pavement is its riding quality, which commonly quantified in
terms of Present Serviceability Index (PSI).

17. Road Roughness Indicator

19. It is the ability of a pavement to sustain the applied traffic load
without showing distress.
The FWD (Falling Weight Deflectometer) is a non-destructive
testing device that is used to complete structural testing for
pavement rehabilitation projects, research, and pavement
structure failure detection.
The FWD is a device capable of applying dynamic loads to the
pavement surface, similar in magnitude and duration to that of a
single heavy moving wheel load.
FWD generated data, combined with layer thickness, can be confidently
used to obtain the "in-situ" resilient elastic module of a pavement
structure.
Structural Performance

20. Structural Performance
FWD Load Plate and Sensors
Figure 9.15: Deflection Measurement Schematic

22. Two main concern in the evaluation of pavement safety are:
1. The skid resistance of pavement surface under wet conditions
2. The potential for hydroplaning (when vehicle tires loss
contact with the pavement surface due to the accumulation of
water on the pavement surface.
Safety Performance

23. • AASHTO, 1993 Pavement Design Guide
AASHTO procedure is based on the concept that the structural
capacity of a flexible pavement can be quantified by a SN.
The required overlay thickness is the amount that will increase
the effective SN of the existing pavement (after the necessary
milling and repair before the overlay) to the required SN to meet
the future traffic demand
SNo1 = ao1 Do1 = SNf – SNeff
Procedure for Design of AC Overlay
Do1 = SNf – SNeff
ao1
OR

24. The future structural number SNf for future traffic:
– Traffic
– Effective design subgarde resilient modulus
- Design PSI loss
– Overlay design reliability, R
- Overall standarad deviation, So

25. EP may be back calculated from deflection data measured in the
outer wheel path using a heavy –loaded deflection device (e.g.,
Falling Weight Deflectometer) and a load magnitude of approx.
9000 pounds.
( Detailed procedure is given in AASHTO 1993)
Determination of effective structural number SNeff of the
existing pavement

26. • Asphalt Institute Deflection Based Procedure
( Asphalt Overlays and Pavement Rehabilitation,
Manual Series No. 17)
The procedure is based on the concept that the structural
capacity of a flexible pavement is related to the rebound
deflection measured by a Benkleman Beam.