IRC:117-2015

GUIDELINES FOR THE STRUCTURAL

EVALUATION OF RIGID PAVEMENT
BY FALLING WEIGHT DEFLECTOMETER

INDIAN ROADS CONGRESS

2015
 IRC:117-2015

GUIDELINES FOR THE STRUCTURAL

EVALUATION OF RIGID PAVEMENT
BY FALLING WEIGHT DEFLECTOMETER

Published by:
INDIAN ROADS CONGRESS
Kama Koti Marg,
Sector-6, R.K. Puram,
New Delhi-110 022
January, 2015

Price : 7 300/-
(Plus Packing & Postage)
 IRC:117-2015

PERSONNEL OF THE HIGHWAYS SPECIFICATIONS

AND STANDARDS COMMITTEE
(As on 9” August, 2014)

1. Das, S.N. Director General (Road Development), Ministry of Road

(Convenor) Transport & Highways, New Delhi.
2. Varkeyachan. K.C. Addl. Director General, Ministry of Road
(Co-Convenor) Transport & Highways, New Delhi.
3. Chief Engineer (R) S,R&T (Rep. by Shri S.K. Nirmal), Ministry of Road
(Member-Secretary) Transport & Highways, New Delhi

Nem6ers
4. Basu, S.B. Chief Engineer (Retd.), MORTH, New Delhi
5. Bongirwar, P.L. Advisor, L & T, Mumbai
6. Bose, Dr. Sunil Head, FPC Divn. CRRI (Retd.), Faridabad
7. Duhsaka, Vanlal Chief Engineer, PWD (Highways), Aizwal (Mizoram)
8. Gangopadhyay, Dr. S. Director, Central Road Research Institute, New Delhi
9. Gupta, D.P. DG (RD) & AS (Retd.), MORTH, New Delhi
10. Jain, R.K. Chief Engineer (Retd.), Haryana PWD, Sonipat
11. Jain, N.S. Chief Engineer (Retd.), MORTH, New Delhi
12 Jain, Dr. S.S. Professor & Coordinator, Centre of Transportation
Engg., Dept. of Civil Engg., IIT Roorke, Roorkee
13. Kadiyali, Dr. L.R. Chief Executive, L.R. Kadiyali & Associates, New Delhi
14. Kumar, Ashok Chief Engineer (Retd.), MORTH, New Delhi
15. Kurian, Jose Chief Engineer, DTTDC Ltd., New Delhi
16. Kumar, Mahesh Engineer-in-Chief, Haryana PWD, Chandigarh
17. Kumar, Satander Ex-Scientist, CRRI, New Delhi
1B. Lal, Chaman Director (Projects-III), NRRDA (Ministry of Rural
Development). New Delhi
19. Manchanda, R.K. Consultant, Intercontinental Consultants and
Technocrats Pvt. Ltd., New Delhi
20. Marwah, S.K. Addl. Director General (Retd.), MORTH, New Delhi
24. Pandey, R.K. Chief Engfneer (Planning), MORTH, New Delhi
22. Pateriya, Dr. I.K. Director (Tech.), NRRDA, (Ministry of Rural
Development), New Delhi
23. Pradhan, B.C. Chief Engineer, National Highways, PWD, Bhubaneshwar
24. Prasad, D.N. Chief Engineer (NH), RCD, Patna
25. Rao, P.J. Consulting Engineer, H.No. 399, Sector 19, Faridabad
IRC:117-2015

26. Raju, G.V.S. Dr. Engineer-in-Chief (R&B), Rural Roads, Director

Research and Consultancy, Hyderabad, Andhra Pradesh
27. Representative of BRO (Shri B.B. Lal) ADGBR, HQ DGBR, New Delhi
28. Sarkar, Dr. P.K. Professor, Deptt. of Transport Planning, School of
Planning & Architecture, New Delhi
29. Sharma, Arun Kumar CEO (Highways), GMR Highways Limited, Bangalore
30. Sharma, M.P. Member (Technical), NHAi, New Delhi
31. Sharma, S,C. DG (RD) & AS (Retd.), MORTH. New Delhi
32. Sinha, A.V. DG (RD) & SS (Retd.), MORTH, New Delhi
33. Singh, B.N. Member (Projects), NHAI, New Delhi
34. Singh, Nirmal Jit DG (RD) & SS (Retd.), MORTH, New Delhi
35. Vasava, S.B. Chief Engineer & Addl. Secretary (Panchayat) Roads
& Building Dept., Gandhinagar
36. Yadav, Dr. V.K. Addl. Director General (Retd.), DGBR, New Delhi
37. The Chief Engineer (Mech.) (Shri Kaushik Basu), MORTH, New Delhi

Correspon¢fing hfembers
1. Bhattacharya, C.C. DG (RD) & AS (Retd.), MORTH, New Delhi
2. Das, Dr. Animesh Professor, IIT, Kanpur
3. Justo, Dr. C.E.G. Emeritus Fellow, g34, 14" Main, 25t’ Cross,
Banashankari 2’d Stage, Bangalore
4. Momin, S.S. Former Secretary, PWD Maharashtra. Mumbai
5. Pandey, Prof. B.B. Advisor, UT Kharagpur, Kharagpur

Ex-Off?cio femders
1. President, (Bhowmik, Sunil), Engineer-in-Chief,
Indian Roads Congress PWD (R&B) Govt. of Tripura
2. Honorary Treasurer, (Das, S.N.), Director General (Road Development),
Indian Roads Congress Ministry of Road Transport & Highways
3. Secretary General,
Indian Roads Congress
 IRC:117-2015

GUIDELINES FOR THE STRUCTURAL EVALUATION

OF RIGID PAVEMENT
BY FALLING WEIGHT DEFLECTOMETER

INTRODUCTION

1.1 A large number of cement concrète parements have been constructed in India on
all categories of roads in order to have durable maintenance free roads even under adverse
moisture and heavy traffic conditions. The moduli of subgrade reaction (k) are usually adopted
from their correlation with CBR values recommended in Portland Cement Association
(PCA) Manuat of USA. A still subbase of DLC covered with a plastic sheet has a very high
modules of subgrade reaction not found in any international guideline. The modulus of
subgrade reaction (k) over the layer recommended in IRC:5&2011 has been computed
based on a theoretical approach given in AASHTO Guide for Design of pavement structures,
1993. Its yalidity is yet to be established. The pavement might be over designed or under
designed. lt is necessary to determine the actual pavement design parameters such as
strength of concrète and modulus of subgrade reaction by back calculation from field tests
after the construction and reassess actual life of the pavement. Properties of different layers
also can be determined by using analytical tools. One of the most difficult exercices for a
pavement engineer is analyzing deflection data collected with a faTling weight deflectometer
though FWDs dave Deen in use for over 30 years, the methods to process the data are far
from perfect. Engineers, based on the deftection, their experience and judgement, can take
appropriate measures to prevent continuing damage to concrète pavements.
The draft “Guidelines for the Structural Evaluation of Rigid Pavement by Falling Weight
DeflectometeL’ was prepared by the Sub-group comprising Shri R.K. Jain, Shri Satander
Kumar, Dr. B.B. Pandey and Col. V.K. Ganju. The Committee deliberated on the draft
documenl in a series of meetings. The H-3 Committee finally approved the draft document
in its meeting held on 19th June, 2014 and authorized the Convenor, H-3 Committee to send
the final draft for placing before the HSS Committee.
The composition of the Rigid Pavement Committee (H-3) is given below:
Jain, R.K. Convenor
Kumar, Satander Co-Convenor
Kumar, Raman Member Secretary

/tfemöers
Bongirwar, P.L. Pandey, Dr. B.B.
Ganju, Col. V.K. Prasad, Bageshwar
Gautam, Ashutosh Sachdeva, Dr. S.N.
Gupta, K.K. Seehra, Dr. S.S.
Jain, A.K. Sengupta, J.B.
Jain, L.K. Sharma, R.N.

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IRC:117-2015

Joseph, Isaac V. Singla, B.S.

Kadiyali, Dr. L.R. Sitaramanjaneyulu, K.
Krishna, Prabhat Tipnis, Col. Manoj
Kumar, Ashok Venkatesha, M.C.
Kurian, Jose Rep. of CMA (Avtar, Ram)
Maiti, Dr. S.C. Rep. E-in-C Branch
Corresponding Members
De, D.C. Nakra, Brig. Vinod
Justo, Dr. C.E.G. Reddi S.A.
Madan, Rajesh Thombre, Vishal
Ex-OfJ'/cio Members
President, (Bhowmick, Sunil}, Engineer-in-Chief,
Indian Roads Congress PWD (R&B), Govt. of Tripura
Honorary Treasurer, (Das, S.N.), Director General
Indian Roads Congress (Road Development)
Ministry of Road Transport &
Highways
Secretary General,
Indian Roads Congress
The Highways Specifications & Standards Committee (HSS) approved the draft document
in its meeting held on 9th August, 2014. The Executive Committee in its meeting held on
18th August, 2014 approved the same document for placing it before the Council. The IRC
Council in its 203* meeting held at New Delhi on 19” and 20th August, 2014 approved the
draft document for publishing.
1.2 A good number of panels of concrete pavements display cracks at corners and
along longitudinal and transverse joints within five years of their construction (Photos 1
and 2) though the thicknesses were large enough to prevent flexural cracking caused by
combined effect of stresses due to heavy axle loads and temperature gradients. A major
cause of damage to a concrete pavement is due to the permanent deformation caused to
granular layers and the subgrade due to the heavy vehicles operating on highways. The
location of voids below the pavement caused by the settlement of the lower layers must
be found out and filled up as early as possible. Conditions of dowel bars at the transverse
joints and tie bars at longitudinal and shoulder joints should be evaluated from time to time
to determine the load transfer efficiency of joints by FWD, so that retrofitting of the dowel and
tie bars can be done before the pavement slabs are damaged.
1.3 It is desirable to carry out theoretical analysis of multi layer rigid pavements by
finite element method to determine pressure on the subgrade soils and estimate the extent
of voids formation below the concrete pavements due to heavy loads. Since, a Dry Lean
Concrete cannot be treated like Winkler’s foundation, a more refined method considering a
concrete pavement and DLC resting on Winkler foundation is more appropriate for checking
the safety of the pavement.
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 IRC:117-2015

Photo 1 Longitudinal Cracks Photo 2 Corner Cracks

2 SCOPE
2.1 These guidelines are meant for evaluating the structural condition of in-service
rigid pavements using Falling Weight Deflectometer and for estimating the strength of the
pavement concrete as well as the modulus of the subgrade reaction so that the capacity
of the pavement to withstand future traffic loading i.e. balance life of the pavement, can be
determined using cumulative fatigue damage principle as laid down in IRC:58-2011.
2.2 Structural evaluation exercise should include load transfer at the transverse
and longitudinal joints so that necessary measures may ‘be taken to retrofit dowel and tie
bars before extensive damage occurs. The deflection data can be used to detect voids at
transverse joints, longitudinal joints, interiors as well as at the corners so that actions can be
taken to fill up the voids by grouting to prevent large scale damage to pavements.
2.3 Method for filling of voids detected by FWD testing or by any other means like
GPR etc. by cement grouting and for retrofitting of dowel bars/tie bars has been described in
Appendix-I.
2.4 These guidelines may require revision from time-to-time in the light of experience
and developments in the field. Towards this end, it is suggested that to all the organizations
using the guidelines should keep a detailed record of periodical measurements, performance,
traffic, climatic condition, etc. and provide feedback to the Indian Roads Congress for further
revision.

3 CONSTRUCTION HISTORY
Before the evaluation process begins, following types of data are to be collected:
i) Month and the year of construction
ii) Traffic considered in pavement design
iii) Thickness and strength of pavement concrete
iv) Thickness and strength of dry lean concrete subbase
v) CBR of subgrade
vi) Modulus of subgrade reaction considered in design
vii) Temperature differential of pavement concrete

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IRC:117-2015

4 TRAFFIC
Traffic data for the highway under consideration should be collected since its characteristics
may change after the completion of the project.
4.1 Axle Load Survey
Pattern of commercial vehicles has undergone a sea change during the last decade. Number
of tandem and tridem axles on major highways have increased considerably while share of
single axle load with dual wheel has decreased. The legal axle load limits in India are fixed as
10.2, 18 and 24 tonnes for single axles, tandem axles and tridem axles respectively. Each of the
axles have dual wheels on either side. A large number of axles operating on National Highways
carry much higher loads than the legal limits. Data on axle load distribution of the commercial
vehicles is required to compute the number of repetitions of single, tandem and tridem axles
carrying different loads. Axle load survey may be conducted for 48 hours both in day as well as in
night hours, covering a minimum sample size of 10 percent in both the directions as laid down in
IRC:58-2011. Heavy axle loads induce very high flexural stresses in the pavement slab resulting
in large consumption of fatigue resistance of concrete. They also transmit very high pressure
on the subgrade and subbase causing permanent deformation in the granular and subgrade
soils.

4.2 Axle Load Spectrum

Spectrum of ax)e load should be determined for single, tandem, tridem and multi-axle loads
for the evaluation of safety of pavement from cracking and evaluation of the remaining life
of a concrete pavement from the consideration of cumulative fatigue damage. The following
load intervals for each class of axle load, as prescribed in Clause 5.2 of IRC:58-2011 should
be as follows:
Single axle 10 kN
Tandem axle --- 20 kN
Tridem axle 30 kN
After the collection of axle load data, they may be tabulated as per the format shown in
Table 1 for the computation of fatigue damage till the time of the test and the remaining life
of the pavement. Additional columns have to be added for including the fatigue damage
analysis for each category of axle loads,
Table 1 Spectrum of Axle Load
Single Class Cumulative Tandem Class Cumulative Tridem Class Cumulative
Axle Load Mark No. of Axles Axles Mark No of Axles Axle Load Mark No of Axles
Interval kN Load kN Interval kN
kN interval kN
kN
195-205 200 - 390-410 400 585-615 600 -
185-195 190 - 370-390 380 555-585 570
175-185 1B0 - 330-350 340 525-555 540
165-175 170 - 330-350 340 495-525 510
155-165 160 - 310-330 320 465-495 480
145-155 150 - 290-310 300 435-465 450 -

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 IRC:117-2015

The buses and light vehicles like pickups will not contribute to fatigue damage and hence
they be ignored in the analysis.
The cumulative number of repetitions of axles at the time of structural evaluation of the
pavement may be computed from the following formula:
5 A ((l r) - 1
1

Where,
C Cumulative number of axles, for estimating fatigue damage at the time
of FWD test. C can be determined for different values of n to determine
the remaining life. C has to be further classified into repetitions of axle
loads based on their weight as shown in Table 1.
Initial number of axles per day in the year when the road is opefational.
Annual rate of growth of commercial traffic (expressed in decimals) from
actual data collected after the construction.
n Period in years after the construction.
Expected number of applications of different axle load groups at the time of evaluation can
be estimated from the axle load spectrum.

5 FALLING WEIGHT DEFLECTOMETER

5.1 Falling Weight Deflectometer (FWD) is an impulse-loading device in which a
transient load is applied to the pavement and the deflected shape of the pavement surface
is measured. The working principle of a typical FWD is illustrated in Fig. 1. D0, D1, D2
and D3 mentioned in Fig. 1 are surface deflections required at radial distances of 0 mm,
300 mm, 600 mm and 900 mm for determination of pavement design parameters. Impulse
load is applied by means of a falling mass, which is allowed to drop vertically on a system of
springs placed over a circular loading plate. The deflections are measured using displacement
sensors as shown in Fig 1. Trailer mounted as well as vehicle mounted FWD models are
available commercially. The working principle of all these FWD models is essentially the
same. A mass of weights is dropped from a pre-determined height onto a series of springs/
buffers placed on top of a loading plate. The corresponding peak load and peak vertical
surface deflections at different radial locations are measured and recorded.

Fig. 1 Working Principle of Falling Weight Deflectometer

IRC:117-2015

5.2 Different magnitudes of impulse load can be obtained by selection of a suitable

mass and an appropriate height of fall. Under the application of the impulse load, the
pavement deflects. Velocity transducers are placed on the pavement surface at different
radial locations to measure surface deflections. Geophones or seismometers are used as
displacement transducers. Load and deflection data are acquired with the help of a data
acquisition system.
5.3 A typical Falling Weight Deflectometers (FWD) include a circular loading plate of
300 to 450 mm diameter. 300 mm diameter load plate is recommended in these guidelines
for evaluation of rigid pavements. A rubber pad of 5 mm minimum thickness is glued to the
bottom of the loading plate for uniform distribution of load.
5.4 A falling mass in the range of 50 to 350 kg is dropped from a height of fall in the
range of 100 to 600 mm to produce load pulses of desired peak load and duration. Heavier
models use falling mass in the range of 200 to 700 kg. The target peak load in the range of
40 kN to 60 kN or higher may be applied on concrete pavements to get a reasonable deflection
of the order of 0.15 mm since pavements of major highways in India consisting of 150 mm
DLC and 300 mm PQC are very stiff and a higher load may be required to get a deflection of
about 0.15 mm.
5.5 Calibration of the FWD: For producing reproducible results, the FWD should be
calibrated. The calibration procedure has been described in details in the IRC:115-2014.

6 PAVEMENT EVALUATION PROCESS

6.1 Pavement condition survey of the entire project length shall precede the actual
deflection test by FWD. A suggested format for Pavement Condition Survey is given in
Appendix-II. It will consist of visual observations of cracking and faulting if any. Ground
Penetrating Radar (GPR) may be used to determine the thickness of pavements in a short
time and to locate approximately the areas where voids may have formed below the pavement
slab which can be confirmed by FWD deflection tests at a later stage. FWD deflection data
may be collected at interiors, corners, transverse joints and longitudinal joints in the outer
lane at intervals of 500 m. Heavy loads travel mostly in outer lanes and very often greater
distresses also are found in the outer lanes. If there are distresses in the inner lanes also,
FWD test should be done in those lanes also, The loading positions are shown in Fig. 2.
Load position for transverse and
longitudinal shoulder joints

1 nner lane

1oad posit n for corner Median

and Interior loading
Fig. 2 Load Positions for Corner, Interior, Transverse and Longitudinal Shoulder Joints

6
 IRC:117-2015

For two way two lane roads, both lanes have to be tested for corner, edge, interior, transverse
and longitudinal joint loading. Single lane roads are usually provided on low volume roads and
FWD test on such pavements are not necessary. Spacing for tests can be lower depending
upon the condition of pavements. For the evaluation of the modulus of subgrade reaction
as well as strength of pavement concrete, it is necessary that the test be carried out at the
interior when the temperature gradient is zero or negative when top surface is cooler than
the bottom and the central portion of the pavement slab is in full contact with the foundation.
During the day time, the surface is hotter than the bottom and the slab will curl up forming a
convex surface with raised central region as shown in Fig. 3(a). The test in the raised part
will show high deflection. The edges will be resting on the foundation. Similarly, edges will get
raised during the night and test at the edge will give large deflections as shown in Fig. 3(b).
These factors should be considered while carrying out the test.

Ja} Convex top surface during day

(b) Concave top surface during night

Fig. 3 Shape of Top Surfaces of a Concrete Slab During Day and Night
For two lane roads without concrete shoulder, test should be carried out at the corner, interior
and edge positions. When there are no dowel bars, tests at the transverse joints should be
carried out in the morning hours to determine the load transfer due to aggregate interlock
when the joint opening will be higher because of contraction of slabs at lower temperatures.

6.2 Surface Temperature Measurement

Ideally, the pavement temperature will be recorded directly from temperature holes at each
test location as the FWD test is being performed. While this is the preferred approach for
research projects, it is not practical for production level testing (network level or maintenance
and rehabilitation projects). Therefore, for production level testing the economic and practical
approach is by measuring the surface temperature at each test location. This can be easily
done using an infrared thermometer. The FWD can automatically measure and record the
pavement surface temperature to the FWD file. If the FWD is not equipped with an infrared
thermometer, then the FWD operator can use a hand held thermometer and record the
temperature to a file. By measuring and monitoring the surface temperature during testing,
the FWD operator can suspend testing if the pavement becomes too hot (>40°C).
6.3 Evaluation of Subgrade Modulus, Elastic Modulus of Concrete and Strength
of Pavement Concrete
Step by step procedure:
1. FWD test should be done and deflection at 0 mm, 300 mm, 600 mm and
900 mm radial distances from the centre of loading point should be measured.

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IRC:117-2015

2. The area parameter of deflection basin should be calculated using following

formulae-
Dl D2 D3
A = 6 1+ 2 +2 + ...2
D0 DO DO
Where,
A Area parameter of the deflection basin
D0 Deflection at centre of the loading plate in mm
D1 Deflection in mm at 300 mm from centre of the loading plate
D2 Deflection in mm at 600 mm inch from centre of the loading plate
D3 - Deflection in mm at 900 mm from centre of the loading plate
The value of A is about 11.8 for a single layer elastic half space (pavement
and soil has the same elastic modulus) while for an extremely rigid layer
with a very high elastic modu)us {D0=D1=D2=D3),the value ofA is 36. For a
concrete pavement, A will be less than 36.
3. From area of deflection basin, Radius of relative stiffness (I) can be evaluated
from the charts given in References 1 and 2. The excel sheet provided with
the guidelines uses the chart in equation form and it gives directly the value
of /. (Snap shot of excel sheet is shown in Appendix-V)
4. After finding the Radius of relative stiffness, normalised deflections (d,)
are calculated using various equations formed from the charts given in
References 1 and 2. (Snap shot of excel sheet is shown in Appendix-V). The
excel sheet directly gives the values of the normalised deflections.
5. Subgrade modulus value can be found by following formulae for different normalised
deflections and average of all should be taken as subgrade modulus.
Pd,
k, —- ... 3
1° D,
Where,
1, 2, 3, 4
Radius of relative stiffness, mm
Load in kN
Measured deflections in mm at various radial distance
Normalised deflections in mm at various radial distances
k value for pavement design should be 50% of that determined by FWD
since only static modulus of subgrade reaction is to be used for
pavement design(2).
6. Elastic Modulus (MPa) of concrete can be found by using the formulae

E _ 12(1— q,.)k / ...4

' l000/t 3

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 IRC:117-2015

Poisson’s Ratio of Concrete.

h Thickness of concrete layer in mm.
radius of relative stiffness in mm
modulus of subgrade reaction in MPa/m
E Elastic modulus of concrete, MPa
Strength of concrete can be determined from the value of E from the
following relation
/t = (E /5000)0 50

Flexural strength (/„„) can be determined from the of the concrete slab as given below:
-— 0.7 )0 ’ 0 ... 6

The entire computation process is illustrated in the programmed excel sheet attached with
the guidelines. A solved example is given in Appendix-III.
JVote: The concrete properties (E„ f), {„,) estimated are for the age of concrete at the time of FWD
test. The strength› values obtained from the computed elastic modulus are based on stat/sfica/
cormlation from laboratory tests and they are approximate. Exact values of strength of concrete
may be determined from cores for verification.

6.4 Fatigue Behaviour of Cement Concrete

IRC:58-2011 gives the fatigue equations (Clause 5.8.d) that should be used for the evaluation
of fatigue life. Computed values for modulus of rupture and modulus of subgrade reaction are
to be used in fatigue damage analysis.
The relation between fatigue life (N) and stress ratio is given as:
N = unlimited for SR < 0.45
4.2577 ’'6'
N —- when 0.45 ¿ SR 0.55 .. 7
SP —11.4325

0.971 8 — SR
Log N ——
0.0825
for SR 0.55 : 8
Where,
SR ratio of load stress and modulus of rupture of concrete
Cumulative Fatigue Damage (CFD) during the design period can be expressed as

CFD = Z (10 A.M to 4 P.M) + Z (0 A.M to 6 A.M) + Z (Remaining hours) ... 9

The computation indicates that contribution to CFD for bottom up cracking is significant only
during 10 A.M te 4 P.M because of higher stresses due to simultaneous action of wheel load
and positive temperature gradient. For the top down cracking, only the CFD during the period

9
IRC:117-2015

between 0 A.M to 6 A.M is important. Various locations may have different behaviour and
designers may examine this aspect.
Stress ratio can be obtained from the ratio of axle load stress and the computed modulus
of rupture from the FWD test as illustrated in the Appendix-I. Excel Sheet format given in
IRC'58-2011 can be used for the evaluation of the fatigue life consumed till the date of the
test and the remaining life of the pavement can easily be estimated. Sum of the fatigue lives
consumed for bottom up cracking as well as for top down cracking should be less than 1.0 to
ensure that the estimation of the pavement life is more conservative since cracks appearing
on the surface could have started from the top or from the bottom.

7 CAUSES OF EARLY CRACKING OF CONCRETE PAVEMENTS

7.1 Single axle loads cause higher bending stresses in pavement slabs while tandem
and tridem axles carrying double and triple load of that carried out by singe axle cause lower
bending stresses due to superposition of positive and negative bending moments. But vertical
stresses on the granular and the subgrade soil are very large due to heavily loaded multi-axle
vehicles. Tandem axles weighing as much as 400 kN (legal limit = 19 tons i.e. 186.2 kN) and
tridem axles far above the legal limits are common on heavy duty corridors. The pavement
slabs designed as per IRC:58-2011 are safe for cracking due to flexural tensile stresses
against overloaded trucks since this is considered in the fatigue damage analysis.
Heavy axle loads, cause high vertical stresses on the granular layer and the subgrade resulting
in accumulation of permanent deformation with time forming voids below the slabs. The voids
can be at the corner edge, transverse and longitudinal joints or in the interior of cement
concrete slab. The stresses can be very high when a part of the slab is unsupported near a
void. More water can accumulate in the voids and fast moving heavy loads may cause high
pressure in the confined water causing serious erosion of soil and granular material which
will increase the size of the voids further. Cracks will appear in those places due to repeated
bending of unsupported slab causing early damage to pavement slabs. It is necessary to
detect the voids early and grout it with cement mortar to fill up the voids. If GPR is available,
locations identified by GPR can be tested with FWD to confirm the existence of voids since
interpretation of GPR data may not be very precise.

8 DETECTION OF VOIDS UNDERNEATH THE RIGID PAVEMENT

Detection of voids below a pavement slab can easily be done bya Falling Weight Deflectometer.
Deflections are measured along the wheel path and a plot of central deflection vs distance
has to be made.
The locations where the deflections are much higher {Fig. 4) than the normal may indicate
presence of voids. Drilling and grouting with cement-mortar slurry may make the pavement
safe.

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 iRC:117-2015

“ U.I+'4

' • - -•'.”-’'’-’.-.-'-
’f % 34 # 7 g’1O’ 2:13. 415 16 1 ’’1 1?302 2# 23

Fig. 4 Deflection Data Along a Highway

FWD Tests should be done during the period when the pavements are nol in curled conditions.
In winter, time available for test may be longer. Conditions in India vary markedly with
geographical locations and local experience should be the guiding principle for tests. If FWD
tests are done on a pavement slab over a void and a slab without any void at different load
levels such as 40 kN, 50 kN, 60 kN and 70 kN or 80 kN and the results may appear as shown
in Fig. S. The Y-axis shows the maximum deflections under different loads. This is another
way to differentiate Pavement slabs with and without voids below it.
Deflections, mmx10

Test on area with

est on area without voids

Load, kN
Fig. 5 FWD Test on Area with and Without Void

9 EVALUATION OF LOAD TRANSFER EFFICIENCY OF JOINTS

Transverse as well as longitudinal joints deteriorate with traffic due to continuous loading.
The proper load transfer at joints has to be maintained for a good functioning of pavements.
For a new pavement, the joint efficiency is nearly 100 percent since the deflections on
either side of joint under a wheel load are almost equal and the ratio decreases as the joints
deteriorate under repeated loading. Photo 3 shows loading plate of an FWD stationed close
to a longitudinal joint near the shoulder of a four lane highway in India.
When deflection sensors are at the either .side of a joint with deflections D1 and D2 on the
loaded and unloaded sides as shown in Fig. 6, the Load Transfer Efficiency (LTE) is defined
as:
LTE = 100 (D /D,) .. 10
IRC:117-2015

Fig. 6 Deflections on the Loaded Photo 3 FWD Test at a Concrete

and Unloaded Side at a Joint Shoulder Joint
Condition of joints
For a new pavement, D, = D2 but D becomes less and less as the joints deteriorate.
If Dy/D1 < 0.5 transverse joints in critical condition
If D2/D1 < 0.4 longitudinal joints in critical condition
Where,
D1 is the deflection on the loaded side of the slab
& D2 is the deflection on the unloaded side of the slab
If the above conditions are reached, retrofitting of dowel and tie bars are recommended, as
prescribed in ARC:SP:83. The above deflections can be measured by FWD.
If the deflection sensors are 300 mm apart during the FWD tests as shown in Fig.7, the Load
Transfer Efficiency is determined from equation given as:
LTE = 100 B (D2/D1) 11
Where,
B lies between 1.05 and 1.15. A typical value of 1.05 may be adopted (2). If the
LTE values are too low, retrofitting of dowel bar and tie bars are recommended
before large scale deterioration occurs. Tests should be carried out across the
cracks also to examine the load transfer across them. This will help in establishing
whether the cracks extended to full depth.
Do weI bar

Fig. 7 Deflection Measurements at a Joint by FWD with Sensors 300 mm apart

Extract of Typical test results of FWD testing for load transfer efficiency of transverse joints
conducted by Central Road Research Institute (CRRI) on NH-2 are given in Appendix-IV.
Similar format can be used for recording data.
10 FREQUENCY OF TEST
Tests for structural evaluation should be repeated between three and five years for assessing
the health of the rigid pavements so that appropriate action is taken timely to prevent
distress.

12
 IRC:117-2015

Appendix-I
{Refer C/ause y,3

1. Filling of Voids in Rigid Pavement

1.1 General: A major cause of damage to the concrete pavement is due to the
permanent settlement/deformation caused to granular layers and the subgrade due to
heavy vehicles operating on highways within 3 to 5 years of its construction. Although the
design thickness of pavement can withstand the combined effect of stresses due to heavy
axle loads and temperature gradient, but the voids created due to permanent settlement
of the lower layers and curling of pavement create additional stresses causing longitudinal
transverse cracking during day time and corner cracking during the night time. It is therefore
recommended that detection of voids underneath the Rigid Pavement is done as described
in Section 8 on a regular interval of 3 to 5 years or when such longitudinal/transverse/corner
cracks start appearing on the rigid pavement.

1.2 Grouting Process

i) Holes of 12 to 15 mm dia are drilled up to the bottom of the DLC at 1 m
square interval over the whole area of voids to be filled under the slab.
ii) Compressed air is blown into the holes to remove loose debris and water
etc.
iii) The holes are temporarily plugged and the slab surface is swept to clean.
iv) Grout material is injected in each hole at a pressure of 0.35 N/mm2 until the
voids accept no more grout or flow up through an adjacent hole.
v) For early and fast flow of grout and to minimise air beneath the PQC two
holes are drilled, vacuum pump may be used for sucking air from second
hole.
vi) Sides of injection holes are roughened and cleaned and filled with
polymerized fine concrete or epoxy mortar.
vii) Traffic is opened only after minimum appropriate curing time for the grout.

2. Retrofit of Dowel/Tie Bars

This has been described in Chapter: 11. Special Technique for Rehabilitation of Rigid
Pavement in IRC:SP:83-2008.

13
Note:

Chainage
Crack

Panel No.
Mapping

ChainagePaneS
shoua

Length (m)
ldlsobe

Width (m)

l ize
donoen the road plan

Composition

Condition (Fair/Poor/
Failed)

Speed (km/h)

Quality (G/F/P/VP)

Transverse Cracks
less than 1.5 m Appendix-II
W:eather

Transverse Cracks
more than 1.’5 m

Longitudinal Cracks
Full Depth

Pothole

Corner Cracks

Settlement

Pavement Edge
Pop out (mm)

Condition of Joints

Road Side Drain

(NE/PF/F)

Remarks

Sf02-£fL.OH
 IRC:117-2015

Appendix-III
(Refer Clause 6.3)
Example: An FWD test was conducted on a 300 mm thick concrete pavement. The radius of
FWD plate is 150 mm and recorded maximum load is 50 kN. Sensors were located at 0, 300,
600 and 900 mm and corresponding deflections recorded are 0.080, 0.075, 0.065, 0.055 mm.
It is assumed that concrete has Poisson’s ratio of 0.15. Determine subgrade modulus and
elastic modulus of concrete when subgrade is considered as liquid (Winkler) foundation.
Solution: Changing the following values in excel sheet specified for subgrade modulus
calculation we can easily get the subgrade and elastic modulus of concrete:
Radius of loading plate (a), mm 150
Load (P),kN 50
Poisson ratio for concrete (g,) 0.15
Poisson ratio for subgrade (r,) 0.45
Thickness of the concrete slab h (mm) 300
Deflection measured at 0 mm distance from the center of the load area 0.08 mm
Deflection measured at 300 mm distance from the center of the load area 0.075 mm
Deflection measured at 600 mm distance from the center of the load area 0.065 mm
Deflection measured at 900 mm distance from the center of the load area = 0.056 mm
Using excel sheet.
The modulus of Subgrade reaction - 78 MPa/m
K value for design is to be taken as 50% of 78 MPa/m as per the AASHTO 93 since only static
k value is to be used or design, k = 39 MPa/m
Elastic modulus of concrete in MPa 32908 MPa
Compressive strength of concrete (cube) 43.32 MPa
Flexural strength
- 4.d1 MPa
A excel sheet have been programmed for carrying out all the computations instantly

15
IRC:117-2015

Appendix-IV
(Refer Clause 9)
Sample Data-Load Transfer Efficiency
The Load Transfer Efficiency (LTE) of transverse joints was measured by Central Road Research
Institute (CRRI) on Delhi-Mathura Road (NH-2) with three different target impact loads of 5500 kg,
7600 kg and 11000 kg. The dia of loading plate of FWD was 300 mm and sensors measuring
deflections of loaded and unloaded slab across the joint were 200 mm apart. The pavement layers
consisted of 150 mm thick Dry Lean Concrete (DLC) over compacted subgrade and 300 mm thick
Pavement Quality Concrete (PQC) of M40 Grade. The drop weights, deflection of loaded and unloaded
slabs and LTE are given in Table 2 to 4.
Table 2 Joint Load Transfer Efficiency (Target Impact Load - 5500 kg)
Joint hlo. Drop Weight, kg Loaded Slab Deflection, pm Unloaded Slab Deflection, ym LTE, %
5634 170 167 98.23
1 5559 165 161 97.57
5575 165 161 97.57
5671 106 105 99.05
5591 105 10:3 98.09
5612 106 104 98.11
5614 163 161 98.77
3 5662 163 159 97.54
5578 162 161 99.38
Avg. = 145 pm or 0.145 mm Avg. = 98.25
Table 3 Joint Load Transfer Efficiency (Targét Impact Load - 7600 kg)
Joint No. Drop Weight, kg Loaded Slab Deflection, pm Unloaded Slab Deflection, ym LTE, °/
7679 218 215 98.g2
1 7537 213 210 98.59
7663 216 141 99.29
7657 142 141 99.29
2 7621 142 141 99.29
7663 143 140 97.90
7599 219 214 97.71
7607 220 213 96.81
7603 216 212 98.14
Avg. = 192 km or 0.192 mm Avg. = 98.40

Table 4 Joint Load Yransfer Efficiency (Target Impact Load - 11000 kg)
Joint No. Drop Weight, kg Loaded Slab Deflection, pm Unloaded Slab Defiection, ym LTE, %
10924 2g3 285 97.26
1 10971 294 286 97.27
10921 293 285 97.26
10881 292 289 98.97
2 10985 294 2B9 98.29
10971 295 291 98.64
11301 214 212 99.06
3 11178 210 210 100
11082 211 210 99.52
Avg. = 266 km or 0.266 mm Avg. = 98.47

Note : The load transfer efficiency of all the joints tested are very high and hence they are in good
condition.

16
 IRC:117-2015

Appendix-V
(Refer Clause 6.3)
Evaluation of strength of pavement slab and modulus of
subgrade reaction of foundation from FWD test
Evaluation of foundation properties as well as strength of concrete using Falling weight deflectometer both winkler as well
as solid elastic foundations are considered in the analysis. the inputs are (1) defelctions at radial distances of 0, 300, 600,
900 mrri (2) applied load and the radius of the loading plate (3) Thickness of the pavement slab. The poisson ratio of the
slab and the foundation are taken as D.15 and 0.45 respectively. The outputs are modulus of subgrade reaction elastic
modulus of the concrete slab and flexural strength of the concrete.In case of solid elastic foUndation the outputs are elastic
modulus of the foundation and the concrete and the flexural strength of the concrete.
Inputs
Type of foundation (Liquid - 1 ; Solid - 2] 1
Rad/us of loading plate (a), mm in Col F 5.905511811 150
Load (P), hN in Col f 11227.5 50
Poisson ratio for concrete (y,) 0.15 D.15
Poisson ratio tor subgrade (p,) 0.45 0.45
Thickness of the concrete slab h (mm) in Col F 11.81102362 300

Deflection measured at O mm distance from’the center of the load area D.003149606 0.08
(wk) ,Col F
Deflection measured at 300 mm distance from the center of the load area 0.002952756 0.075
(w,),CoI F
Deflection measured at 600 mm distance from the center of the load area 0.002559055 0.065
(wp),CoI F
Def\ection measured at 900 mm distance from the center of the load area 0.002204724 0.056
(w,),CoI F
Result
Area of deflection basin (Sq mm),CoI F 31.2 20128.992
Radius of relative stiffness, I (mm),Col F 39.054 991.968
Normalised deflection, d, (mm),CoI F 0.124 3.137
Normalised deflection, d, (mm),Col F 0.]16 2.94't
Normalised deflection, d (mm),CoI F 0.101 2.578
Normalised deflection, d, (mm).Col F 0.085 2.150

Modulus of subgrade reaction k (MPa/m) for Winkler foundation/Elastic 287.9829711 78.130

modulus of foundation E, {MPa) [for solid foundation], Col F

Elastic modulus of concrete E, (MPa),CoI F 4769344.766 32908.479

Cubestrengh strenght of concrete f„ (MPa) 43 :32

Ftexural s\rength, Mpa 4 61

The k value shown in F27 is to be determined in different seasons for It\ree to five years to determine the long
term modulus for design In the interim period 50% of F27 may be considered for design as per AASHTO 93

17
IRC:117-2015

11 REFERENCES

1. lonnides, A.M., E.J. Barenberg, and J.A. Lary (1989), ‘Interpretations of Falling
Weight Deflectometer Results Using Principles of Dimensional Analysis' Proc. 4th
Int. Conf. on Concrete Pavement Design and Rehabilitation, pp. 231-247.
2. AASHTO (1993), ’AASHTO Guide for Design of Pavement Structures’, American
Association of State Highway and Transport Officials, Washington D,C.
3. IRC:115-2014, ‘Guidelines for the Structural Evaluation and Strengthening of
Flexible Road Pavements using Falling Weight Deflectometer (FWD) Technique.
4. IRC:58-2011, 'Guidelines for the Design of Plain Jointed Rigid Pavements for
Highways’.
5. Maitra, Swati Roy, ’Numerical and Experimental Investigation on Jointed Concrete
Pavements’, Ph.D. Thesis, LIT Kharagpur, 2011.
6. Huang, V.H., ‘Pavement Analysis and Design’ Pearson Education Inc,
2nd Ed, 2004.

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