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Paper No. 535
RUTTING IN FLEXIBLE PAVEMENTS A CASE STUDY
V.K. SINHA*, H.N. SINGH** & SAURAVSHEKHAR***
ABSTRACT
Flexible pavements are generaly adopted for construction of roads in India. Bitumen as a binder is known to be highly
sensitive to high temperatures. Distresses in the form of ruts, cracking, ageing etc. are common on Flexible pavements.
These are still observed on pavements constructed presently with thick layers of binder courses at high cost. Rutting one of
the commonly observed permanent nature distress is the subject matter of this case study. The effect of high pavement
temperature on the stability of mix in conjunction with lower softening point of bitumen has been studied in the context of
prevail ing high temperature in top pavement layers. Study brings out the inadequacies in existing specifications and
suggests some follow up actions to improve the existing specifications. Use of modifiers in the top binder courses like DBM
to enhance the thermal dependent characteristics of the bituminous mixes is one of the recommendations. Adoption of
catalogue type performance based specifications covering different climatic regions of the country are also suggested.
1. INTRODUCTION
Flexible pavements have been traditionally provided
on most of the important highways of the country. Thick
bituminous pavement layer broadly comprising of a DBM
layer of 160 to 180 mm topped with 50 mm bituminous
concrete are being provided presently by way of
strengthening. The bitumen used in the design of mixes
for SDBC, PC, DBM and BM is typically of 60/70 grade.
However, in few cases wearing course, having
bituminous concrete 50 mm thick is also being provided
with modified bitumen. Modifiers in such cases are either
CRMB or PMB. Use of modifiers, however, is not
common. The design of mixes are being done as perMarshall method with normal 75 blows for all locations
without considering the effects of climatic, traffic
variations etc.
Despite the construction of thicker pavement, such
bituminous pavements suffer from rutting frequently in
quite early age. Such deformations in the form of rutting
are more pronounced at locations of intersections, curves
and in stretches where heavy traffic operates with low
speed and is subject to frequent stop/start condition. Such
early rutting of the flexible pavements should concern
all highway engineers. This is particularly so, whenconstructing long performing pavements is the moto of
all highway agencies in view of huge investment being
made on the construction of such highways.
The Paper is based on a case study representing a
typical rutted stretch of a four-lane road which has been
* Secretary General, IRC } E-mail: [email protected]
** Executive Engineer (Retd.) PWD Bihar, Material Engineer, Quest Consultants Pvt. Ltd.
*** Director, SA Infrastructure Consultants Pvt. Ltd.
Written comments on this Paper are invited and will be received upto 31st December, 2007
widened and strengthened recently with thick bituminous
pavement layers. The effect of high temperature ofpavement layers on in-service behaviour of compacted
bituminous mixes is the key objective of this case study.
2. STUDY STRETCH
The stretch considered is about 250 m long, suffering
substantial rutting to a maximum depth upto 35 mm. This
stretch is near an intersection. Heavy trucks with high
axle loads in large number (about of 4500 trucks per
day) are operating on this stretch, at a relatively low
speed with frequent stop/start condition. The crust
composition of this stretch is given in Table 1.
S.No. Type of layer Thickness
(mm)
1. Bituminous Concrete (BC with CRMB 60) 5 0
2. Dense Bitumen Macadam (DBM Layer II) 8 0
3. Dense Bitumen Macadam (DBM Layer I) 8 0
4. Wet Mix Macadam (WMM) 250
5. Granular Sub-Base (GSB) 260
The study stretch comprises both types of surfaces
(i) Exposed DBM surface without BC and (ii) DBM
layer covered with BC surface in adjoining length. Same
traffic is operating on both these surfaces. Time lag
between laying of DBM and laying of BC on the DBM
is on average about six months plus.
TABLE 1. CRUSTCOMPOSITION ATTHESTUDYSTRETCH
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3. RUT DEPTH MEASUREMENT
The rut depth measurements has been done in the
field using a string line across the carriageway. The details
of rut depth with assumed chainages are furnished in
Table 2. Fig 1 depicts the general appearance of therutted portion.
Cores were taken from both rutted and fair locations.
At rutted locations, the top layer of DBM (Layer II)
was observed to have undergone deformations, whereas
TABLE2. DETAILSOFRUTDEPTH
Off-set from Kerb edge (m)
Chainage 1 2 3 4 5 6 7
102.300 14 16 11 7 3 2 1
102.250 22 21 18 15 14 11 2
102.200 8 9 10 9 9 8 4
102.150 12 12 11 11 5 4 2
102.100 12 9 6 6 2 1 -2
102.050 12 1 9 0 5 0 1
102.000 21 15 15 4 5 2 2
101.950 12 2 1 0 1 -4 -2
101.900 23 10 18 10 6 2 2
101.850 28 5 14 - 4 - 2 - 1 - 2
101.800 32 Junction Crossing
101.770 33 12 19 2 14 8
101.750 26 4 21 -5 10 4 8
101.720 22 8 21 6 5 6 8
101.700 10 2 17 6 5 6 8
101.650 12 9 15 10 18 14 8
101.600 9 2 4 3 5 9 9
Fig 1. Showing the Rutted Portion of the Pavement
(Not to Scale)
BC layer, in general, was not found significantly
disturbed. Subsidence under the wheel paths was
observed to be due to the deformation of top layer of
DBM. The above observations reveal that the actual
rutting is due to permanent deformation in the DBM
(Layer II), immediately underneath the BC layer.
Both the bituminous mix material as taken from the
cores at rutted locations and at fair locations, were tested
in the laboratory for the engineering properties. Tables 3
and 4 give the test details for the BC portion at rutted
and fair locations respectively. It is seen that the density
of the mix are same for both locations. Marginally higher
bitumen content has been noted in the rutted portion.
Optimum Bitumen Content (OBC) under job-mix formula
(JMF) was 5.0 per cent with permissible variation of
0.3 per cent. Such marginal variations could be due to
migration of bitumen during formation of the rut, due to
movement of aggregates from rutted portion and due to
some aggregate particles being cut partly through cutting
of the cores. Some reduction in air voids is also noticed.
These factors might contribute marginally to the process
of rutting or may even have arisen due to rutting. The
variations are, however, insignificant.
4. INVESTIGATION DONE
The methodology of investigation is based on the
TABLE
3. ENGINEERING
PROPERTIES
OF
RUTTED
PORTION
OF
BC
Core Density Bitumen FI + Air
No. (gm/cc) content EI Voids
(%) (%) (%)
01 R 2.511 5.475 3.09
02 R 2.497 5.551 32.70 3.63
03 R 2.508 5.520 3.20
TABLE 4. ENGINEERINGPROPERTIES OFFAIRPORTION OFBC
Core Density Bitumen FI + Air
No. (gm/cc) content EI Voids
(%) (%) (%)
01 S 2.5 5.080 3.9
02 S 2.496 5.137 29.34 3.67
03 S 2.486 5.105 4.05
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process of elimination of lesser or insignificant causes
to enable focusing on the main cause. Rutting in
bituminous pavement can occur due to variety of causes.
Some of the common causes for rutting could be as given
below.
Inappropriate mix design
Incorrect grading
Excessive Binder content
Excessive fines like sand/clay
Round aggregates with smooth texture
Inadequate initial field compaction and density
Effects of hot weather temperature on
pavement
Effects of heavy traffic loads
Effect of slow speed (frequent stop/start or
stationary condition)
Effect of secondary compaction
4.1. Inappropriate Mix Design
Initial mix design was done by Marshall method with
75 blows. Grading of aggregates followed in actual
execution are broadly as prescribed under Job-Mix
Formula (JMF). The Design Bitumen Content (OBC)
has been arrived as per Marshall test.
Tables 5, 6 & 7 give the details of the gradation and
other engineering properties of BC mix with CRMB 60,
as used in actual construction of the rutted portion. Tables
8, 9 &10 give similar details for DBM (Layer II)
underneath BC. From the perusal of the tables it will be
seen that actual execution has been done in accordance
with MOSRT&H Specifications and as per JMF. Some
marginal variations in gradation determined by extraction
of bitumen and from dry aggregates taken from Hot
Bins are just natural and are not significant. Binder content
also appears to be as per JMF and MOSRT&H
Specifications. Natural sand has not been used. Similarly,
rounded aggregates are also not used as is evident from
Photo 1.
Sieve Sizes 26.5 19.0 13.2 9.5 4.75 2.36 1.18 0.60 0.30 0.15 0.075
(Percent Passing)
Range as per 100 90 - 59 - 52 - 35 - 28 - 20 - 15 - 10 - 5 - 2 - 8
MOSRT& H 100 79 72 55 44 34 27 20 13
Specifications
As per approved 100 94 74 63 46 35 25 19 13 9 6
JMF
Permissible 7 7 6 6 5 4 4 4 3 3 1.5
Variation for JMF
Date Sample Gradation as per samples taken at the time of laying mix at rutted locations
No.
18.4.05 BC/33 100 93.45 73.17 64.57 46.55 34.26 25.86 18.08 12.14 8.15 6
BC/34 100 94.11 75.19 63.59 46.19 35.12 24.14 18.16 11.56 8.26 7
26.4.05 BC/35 100 95.4 73.21 66.09 45.68 34.17 26.11 18.16 12.09 8.11 5
BC/36 100 93.74 72.55 65.84 45.1 34.82 25.16 18.72 12.1 8.7 6
TABLE5. SUMMARYOFAGGREGATEGRADATIONFORBC (CRMB 60)
(GRADATIONAFTEREXTRACTIONOFBINDER)
Photo 1.
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180 SINHA, SINGH& SHEKHARON
TABLE 7. SUMMARY OFACTUAL BITUMENCONTENTVS DESIGNBITUMENCONTENT
Properties Binder Bulk Air VMA VFB Stability Retained Flow Stability AIV FI & Average
Measured content Density Voids (%) (%) (kg.) Stability (mm) / Flow (%) EI Core
(%) (gm/cc) (%) (%) (kg/mm) (%) Density
(gm/cc)
Properties as per 5.00 2.480 4.28 16.05 71.0 1240 95.17 3.2 987.5 15.23 24.85
approved JMFSpecified Limit Min Not 3 - 5 Min 14 65 - 75 Min 90 2.5 - 250 Max Max
as per MOSRTH 5.0 specific to 16 1200 Min 4.0 - 500 30 30
Specifications
Date Sample As per actual samples taken at the time of laying mix at rutted locations
No.
18.4.05 BC/33 5.010 2.474 4.48 15.44 71.0 1358.8 96.6 2.87 473.45 16.14 26.8 99.56
BC/34 5.002 2.473 4.52 15.46 70.76 1375.17 2.90 474.2 15.57 26.3
26.4.05 BC/35 5.020 2.472 4.52 15.5 70.8 1418.7 96.9 2.93 484.2 15.5 27.6 99.35
BC/36 5.011 2.472 4.52 15.5 70.8 1386.0 2.93 473.04 15.8 27.9
Sieve Sizes (Percent 45.0 37.5 26.5 13.2 4.75 2.36 0.30 0.075
Passing)
Range as per MOSRT&H 100 95-100 63-93 55-75 38-54 28-42 7-21 2-8
Specifications
As per approved JMF 100 100 85 63 45 34 13 4
Permissible Variation for 8 8 8 7 6 5 4 2
JMF
TABLE8. SUMMARYOFMEASUREDAND CALCULATED PROPERTIES OFDENSEBITUMINOUSMACADAM (DBM) (60/70)(GRADATIONAFTEREXTRACTIONOFBINDER)
Sieve Sizes 26.5 19.0 13.2 9.5 4.75 2.36 1.18 0.60 0.30 0.15 0.075
(Percent Passing)
Range as per 100 90 - 59 - 52 - 35 - 28 - 20 - 15 - 10 - 5 - 2 - 8
MOSRT&H 100 79 72 55 44 34 27 20 13
Specifications
As per approved 100 94 74 65 46 35 25 19 13 9 6
JMF
Permissible 7 7 6 6 5 4 4 4 3 3 1.5
Variation for JMF
Date Sample Gradation as per samples taken at the time of laying mix at rutted locations
No.
18.4.05 BC/33 100 93.9 73.22 63.2 44.66 33.68 24.75 17.25 10.10 7.87 6
BC/34 100 93.2 72.55 64.33 43.99 33.61 24.81 18.56 12.93 9.79 726.4.05 BC/35 100 94.5 76.2 67.11 44.71 36.13 24.68 20.07 14.17 8.89 5
BC/36 100 92.8 73.2 66.7 46.38 36.08 28.2 22.22 15.72 8.90 6
TABLE6. SUMMARYOFAGGREGATEGRADATIONOFDRYAGGREGATESFORBC (CRMB 60)
(GRADATIONDETERMIND FROMDRYAGGREGATES FROMHOTBINS)
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Date Sample No. Gradation as per samples taken at the time of laying mix at rutted locations
2.8.04 DBM/272 100 100 85.08 63.65 46.21 34.24 13.68 4.48
DBM/ 273 100 100 84.84 63.42 45.98 33.45 13.04 4.57
3.8.04 DBM/274 100 100 84.34 62.14 44.27 34.60 12.12 4.20
DBM/ 275 100 100 86.52 63.53 46.47 35.49 14.48 4.55
4.2. Compaction and Density
Details of Table 7 for BC and Table 10 for DBM
suggest that there is no significant problem due to lack
of compaction and inadequate density of the rutted portion
at the time of execution. The compaction density does
not appear to be a significant cause of rutting from the
specifications point of view.
4.3. Effect of High Pavement Temperature on
Performance of BC and DBM Layer
The key objective of the case study was to assess
the likely effect of high temperature on the performance
of top bituminous layers in a flexible pavement. It is a
common knowledge that bitumen as a material is quite
sensitive to high temperature. Stability aspects of bitumen
TABLE 10. SUMMARYOFMEASURED AND CALCULATED PROPERTIES OFDENSEBITUMINOUSMACADAM (DBM) (60/70)
(ASPERLABTESTSRESULTOFRUTTEDSAMPLES)
Properties Measured Binder Bulk Air VMA VFB Stability Flow FI & AIV Average
content Density Voids (%) (%) (kg.) (mm) EI (%) (%) Core(%) (gm/ (%) Density
cc) (gm/cc)
Properties as per JMF 4.580 2.43 4.20 14.90 71.74 1120 2.82 26.84 13.1 98%
Specified Limits as per Min 4.0 Not 3 - 6 Min 66.75 Min. 990 2 - 4 < 30 < 30
MOSRT&H specified 12 to
Specifications 14
Date Sample No. As per actual samples taken at the time of laying mix at rutted locations
2.8.04 DBM/272 4.59 2.481 4.39 14.97 70.67 1321.1 2.33 26.86 16.77 98.99
DBM/273 4.60 2.470 4.82 15.36 68.62 1152.3 2.50 27.99 17.20
3.8.04 DBM/274 4.57 2.479 4.32 15.62 71.24 1272.2 2.40 25.85 17.44 98.95
DBM/275 4.58 2.477 4.40 15.10 70.86 1137.6 2.40 27.36 16.97
TABLE9. SUMMARYOFMEASUREDAND CALCULATED PROPERTIES OFDENSEBITUMINOUSMACADAM (DBM) (60/70)
(GRADATIONDETERMINEDFROMDRYAGGREGATESTAKENFROMHOTBINS)
Sieve Sizes (Percent 45.0 37.5 26.5 13.2 4.75 2.36 0.30 0.075
Passing)
Range as per MOSRT&H 100 95-100 63-93 55-75 38-54 28-42 7-21 2-8
Specifications
As per approved JMF 100 100 85 63 45 34 13 4
Permissible Variation for 8 8 8 7 6 5 4 2
JMFDate Sample No. Gradation as per samples taken at the time of laying mix at rutted locations
2.8.04 DBM/272 100 97.50 82.65 63.09 43.9 32.93 13.61 4.48
DBM/ 273 100 98.56 85.76 62.45 44.55 35.46 15.51 5.98
3.8.04 DBM/274 100 100 84.34 62.14 44.27 34.60 12.12 4.20
DBM/ 275 100 100 86.52 63.53 46.47 35.49 14.48 4.55
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mix for both top BC layer and underneath DBM layer
were accordingly investigated.
4.3.1.Measurement of pavement temperature:
Two different types of thermometers were used for
recording the temperature.One was electronicallycontrolled digital thermometer and the other was ordinary
glass mercury thermometer. These were duly calibrated
before the measurement. The ambient air temperature
on the day of measurement was 48 oC layer-wise
pavement temperature was measured during the peak
summer hour of 2.30 P.M. in the month of June 2007.
The temperature measurement was done on the
rutted portion of the pavement at number of locations.
The temperature was measured at different locations
depth-wise in increment of 20 mm. The first measurement
was done at 20 mm below the top of BC surface and
thereafter it was measured broadly at the interface of
BC and underlying DBM layer. The measurement in
DBM layer continued thereafter at interval depth of every
20 mm. The layer-wise pavement temperature was
measured for both locations i.e. covered with 50 mm
BC wearing course as well as at locations where top
surface of DBM was not covered with BC. The
corresponding layer-wise temperatures as measured are
furnished in Table 11. Fig 2 again shows these
temperatures layerwise. Fig 3 shows the equipment
used for making the temperature measurement.
From the perusal of the Table 11, it will be seen that
TABLE11. LAYERWISERECORDINGOFTEMPERATUREDATED7.6.07 AT2.30 PM
DBM Layers Exposed to Sun (Partial Construction) DBM Layer Covered with BC CRMB-60 (Completed
Cosntruction)
Location of Temperature Temperature Location of Temperature Temperature
recorded in Digital in Glass recorded in Digital in Glass
temperature Thermometer Thermometer temperature Thermometer Thermometer
in (oC) in (oC) in (oC) at particular in (oC) in (oC) in (oC)
place near
chowk
Top surface 68.2 67 Top surface 60.2 59
of DBM (at the of BC (at the
depth of 20 mm depth of 20
from top) mm from top)
Below 20 mm 63.7 63 Below 50 mm 57.3 56
(from above) BC (at the inter
-face of BC and
DBM layer)
Below 40 mm 58.8 58 Below 20 mm 55 54
(from DBM Top
surface)
Below 60 mm 56 54 Below 40 mm 54.2 53
(from DBM Top
surface)
Below 80 mm 53.9 52 Below 60 mm 52.7 51
(from DBM Top
surface)
Below 100 mm 53.9 52 Below 80 mm 51.3 50
(from DBM Top
surface)
Below 100 mm 50.2 49
from DBM Top
surface)
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the pavement temperature in top BC layer was observed
to be 60oCand at the interface of DBM and BC layer it
was 57oC. Against this, the pavement temperature in
the top DBM layer (where BC has not been laid) was
68.2oC. The difference of 8 oC is due to better
characteristic of CRMB modifier with respect to specific
heat and other associated thermal attributes. It is furtherobserved that the temperature gradient also, is less steep
at locations covered with CRMB 60 than the locations
where top layer was DBM without BC. The advantage
of modifiers like CRMB in this respect needs to be noted.
4.3.2. Softening point of bitumen used: The
bitumen of 60/70 grade was procured from Panipat and
Halida refineries. As per the test results done by the oil
companies, the softening point was 49oC (Panipat) and
47oC (Haldia). The softening point for CRMB as per
Panipat refinery test was 61oC. The softening point of
60/70 grade bitumen used, when compared with thepavement temperature in DBM layer (vide Table 11) is
much lower than the temperature of corresponding
pavement layers.
The summer temperature, broadly of this or still
higher range, normally occurs in the plains of India for
at least three months. During these months the
bituminous mixes of the pavement layers are obviously
in a very soft state of cohesion. The heavy traffic
operating during these months actually subject the mix
Fig. 3. Temperature Measured under the different Layers
of Pavement
Fig. 2. (a) Layer-wise Temperatures of Location having
DBM with BC (CRMB 60) (Not to scale)
BC (CRMB) 60 (50 mm) 60oC
57oC
DBM (Layer II) with 60/70 grade bitumen
Thickness - 80 mm
54oC
52oC
51oC
DBM (Layer I) with 60/70 grade bitumen
Thickness - 80 mm 50oC
WMM
Thickness 250 mm
GSB
Thickness 260 mm
55oC
Fig. 2. (b) Layer-wise Temperatures of Location having
DBM without BC (Not to scale)
DBM (Layer II) with 60/70 grade bitumen
exposed to Sun 68.2oC
63.7oC
Thickness 80 mm 58.8oC
56oC
DBM (Layer I) with 60/70 grade bitumen
53.9oC
Thickness 80 mm
WMM
Thickness 250 mm
GSB
Thickness 260 mm
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184 SINHA, SINGH& SHEKHARON
of top DBM layers into a kneading action. The
determination of stability by applying blows as per
Marshall, therefore deserves reconsideration. Hveem
method is more suitable under such situations.
Specifications should look into this aspect, because
according to authors the temperature of the mix higherthan softening point may be a significant factor to the
occurrence of rutting in flexible pavements in our country.
According to Australian Asphalt Pavement Association
(AAPA) Asphalt guide (Table 3.2 of the guide), pavement
temperatures as reproduced in Table 12 are to be rated
as high to medium temperature category, deserving
special consideration for the selection of bitumen type,
including mix design.
Temperature Category Maximum Pavement
Temperature
High > 58oC
Medium 52oC - 58oC
Low < 52oC
4.3.3.Stability loss study:Stability of the mix is
one of the key design consideration in the Marshall
method of design. IRC:SP:53-2002 prescribes
requirements of mix prepared with modified bitumen.
This is reproduced in Table 13. It will be observed that
minimum Marshall stability (75 blows) at 60oC is 1200
kg. It also prescribes the requirement of minimum
retained stability of 90 per cent after 24 hours in water
bath at 60oC. For high rainfall areas it is 100 per cent.
Minimum Marshall stability for both BC and DBM with
60/70 grade bitumen as prescribed in MOSRT&H
Specifications (Fourth Revision 2001) is 900 kg only. No
criteria for retained stability has been prescribed in
MOSRT&H Specifications for BC and DBM with 60/
70 grade bitumen. Prescribing same stability for BC and
DBM (900 kg) and not prescribing any minimum
percentage for retained stability in normal 60/70 gradebitumen is a gap in the specifications. It needs to be
addressed.
The tests for Retained Stability is done as per ASTM
D-1075. ASTM D-1075 basically prescribe the
procedure to evaluate the effect of hot weather
temperature on cohesion of compacted bituminous mixes.
For this purpose, the procedure prescribes conducting
(Source: IRC:SP:53-2002)
(Source: AAPA, Asphalt Guide 2002)
TABLE 12. PAVEMENTTEMPERATURE
TABLE13. REQUIREMENTSOFMIXPREPAREDWITHMODIFIEDBITUMEN
Sl.No. Properties Requirement Method of Test
Hot Climate Cold Climate High Rainfall
1. Marshall Stability 1200 1000 1200 ASTM:D:1559-
(75 blows)at 60oC, 1979
kg, Minimum
2. Marshall Flow at 2.5 -4.0 3.5-5.0 3.0-4.5 ASTM:D:1559-
60oC, mm 1979
3. Marshall Quotient 250-500 Stability /flow
kg/mm
4. Voids in 3.0-5.0
compacted mix, %
5. Requirement of 90 95 100 ASTM:D:1075-
retained stability 1979
after, 24 hours in
water at 60oC, %
Minimum
6. Coating with 95 95 100 AASHTO T 182
aggregate, %
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TABLE14. RETAINEDSTABILITYOFBC MIXAFTER24 HOURSATDIFFERENTTEMPERATURES
Retained Stability = 24 hours stability * 100
at 650C 30 minute stability
= 1161.2 *100 = 93.40%
1243.3
Compaction 75 blows Date- 3/7/07 to 4/7/07
Binder CRMB-60
STABILITY AFTER 24 HOURS IN WATER BATH @65
0
CSl. No Volume of Proving Ring Calibration factor Volume CORRECTED FLOW IN
marshall Reading of Proving Ring Correction VALUE (Kg) (mm)
specimen (cc)
(A) (B) (C) (D)* E = BxCxD
1 486.5 385 2.767 1.09 1161.2 4.4
2. 483.5 390 2.767 1.09 1176.3 4.5
3. 484.0 380 2.767 1.09 1146.1 4.3
1161.2 4.40
STABILITY AFTER 30 MINUTES IN WATER BATH @600C
Sl. No Volume of Proving Ring Calibration factor Volume CORRECTED FLOW IN
marshall Reading of Proving Ring Correction VALUE (Kg) (mm)
specimen
(in cc)
1 486.0 415 2.767 1.09 1251.7 2.9
2. 480.5 400 2.767 1.14 1261.7 3.3
3. 485.5 410 2.767 1.09 1236.6 3.2
4. 484.0 405 2.767 1.09 1221.5 3.4
5. 483.5 415 2.767 1.09 1251.7 3.0
6. 487.0 410 2.767 1.09 1236.6 3.1
1243.4 3.15
Sl. No Volume of Proving Ring Calibration factor Volume CORRECTED FLOW IN
marshall Reading of Proving Ring Correction VALUE (Kg) (mm)
specimen
(in cc)
1 486.5 395 2.767 1.09 1191.3 3.6
2. 484.5 405 2.767 1.09 1221.5 3.4
3. 485.0 395 2.767 1.09 1191.3 3.6
1201.4 3.53
STABILITY AFTER 24 HOURS IN WATER BATH @600C
Retained Stability = 24 hours stability * 100
at 600C 30 minute stability
= 1201.4 *100 = 96.63%
1243.3
* D is corelated to A
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186 SINHA, SINGH& SHEKHARON
STABILITY AFTER 30 MINUTES IN WATERT BATH @600C
Retained Stability = 24 hours stability * 100at 650C 30 minute stability
= 995.3 *100 = 82.50%
1206.4
Compaction 75 blows
Binder 60/70 bitumen
STABILITY AFTER 24 HOURS IN WATER BATH @ 600C
TABLE15. RETAINEDSTABILITYOFBC MIXAFTER24 HOURSATDIFFERENTTEMPERATURES
Compaction 75 blows Date- 4/7/07 to 5/7/07
Binder 60/70 Bitumen without CRMB
STABILITY AFTER 24 HOURS IN WATER BATH @650C
Sl. No Volume of Proving Ring Calibration factor Volume CORRECTED FLOW IN
marshall Reading of Proving Ring Correction VALUE (Kg) (mm)
specimen(cc)
(A) (B) (C) (D)* E = BxCxD
1 487.5 320 2.767 1.09 965.1 4.6
2. 483.5 330 2.767 1.09 995.3 4.9
3. 486.5 340 2.767 1.09 1025.5 4.7
995.3 4.73
Retained Stability = 24 hours stability * 100
at 600C 30 minute stability
= 1110.9 *100 = 92.08%
1206.4
Sl. No Volume of Proving Ring Calibration factor Volume CORRECTED FLOW IN
marshall Reading of Proving Ring Correction VALUE (Kg) (mm)specimen
(in cc)
1 485.5 400 2.767 1.09 1206.4 2.8
2. 481.5 395 2.767 1.14 1191.3 2.9
3. 486.0 400 2.767 1.09 1206.4 3.1
4. 484.5 390 2.767 1.09 1176.3 3.0
5. 484.0 410 2.767 1.09 1236.6 3.2
6. 487.0 405 2.767 1.09 1221.5 3.3
1206.4 3.05 mm
* D is corelated to A
Sl. No Volume of Proving Ring Calibration factor Volume CORRECTED FLOW IN
marshall Reading of Proving Ring Correction VALUE (Kg) (mm)
specimen
(in cc)
1 484.5 360 2.767 1.09 1085.8 3.8
2. 486.0 375 2.767 1.09 1131.0 3.7
3. 483.5 370 2.767 1.09 1115.9 3.8
1110.9 3.77 mm
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TABLE16. RETAINEDSTABILITYOFDBM MIXAFTER24 HOURSATDIFFERENTTEMPERATURES
Compaction 75 blows Date-7/7/07 to 9/7/07
Binder 60/70 Bitumen
STABILITY AFTER 24 HOURS IN WATER BATH @550C
Retained Stability = 24 hours stability * 100
at 550C 30 minute stability
= 1095.8 *100 = 91.71%
1194.9
Binder 60/70 bitumen
STABILITY AFTER 24 HOURS IN WATER BATH @600C
STABILITY AFTER 30 MINUTES IN WATER BATH 600C
Sl. No Volume of Proving Ring Calibration factor Volume CORRECTED FLOW IN
marshall Reading of Proving Ring Correction VALUE (Kg) (mm)
specimen
(in cc)
1 486.5 330 2.767 1.09 995.3 3.8
2. 484.0 345 2.767 1.09 1040.5 4
3. 487.0 330 2.767 1.09 995.3 3.7
1010.4 3.8
Retained Stability = 24 hours stability * 100
at 600C 30 minute stability
= 1010.4 *100 = 84.56%
1194.9
Sl. No Volume of Proving Ring Calibration factor Volume CORRECTED FLOW IN
marshall Reading of Proving Ring Correction VALUE (Kg) (mm)
specimen(cc)
(A) (B) (C) (D)* E = BxCxD
1 486.5 370 2.767 1.09 1115.9 3.3
2. 488.5 365 2.767 1.09 1100.9 3.2
3. 484.5 355 2.767 1.09 1070.7 3.0
1095.8 3.2
Sl. No Volume of Proving Ring Calibration factor Volume CORRECTED FLOW IN
marshall Reading of Proving Ring Correction VALUE (Kg) (mm)
specimen
(in cc)
1 486.5 390 2.767 1.09 1176.3 2.9
2. 487.5 395 2.767 1.09 1191.3 2.7
3. 481.5 410 2.767 1.14 1293.3 3.1
4. 484.5 360 2.767 1.09 1085.5 3.7
5. 480.0 400 2.767 1.14 1261.8 34
6. 483.5 385 2.767 1.09 1161.2 3.3
1194.9 3.18
* D is corelated to A
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TABLE17. RETAINEDSTABILITYOFDBM MIXAFTER24 HOURSATDIFFERENTTEMPERATURES
Compaction 75 blows Date-30/6/07 to 2/7/07
Binder 60/70 Bitumen
STABILITY AFTER 24 HOURS IN WATER BATH @600C
Retained Stability = 24 hours stability * 100
at 600C 30 minute stability
= 990.3 *100 = 81.58%
1213.9
Compaction 75 blows
Binder 60/70 bitumen
STABILITY AFTER 24 HOURS IN WATER BATH @650C
STABILITY AFTER 30 MINUTES IN WATER BATH @600C
Sl. No Volume of Proving Ring Calibration factor Volume CORRECTED FLOW IN
marshall Reading of Proving Ring Correction VALUE (Kg) (mm)
specimen
(in cc)
1 497.5 405 2.767 1.04 1165.5 3.2
2. 486.5 395 2.767 1.09 1191.3 3.1
3. 484.5 415 2.767 1.09 1251.7 2.9
4. 480.0 400 2.767 1.14 1261.8 3.0
5. 485.0 390 2.767 1.09 1176.3 2.8
6. 487.5 410 2.767 1.09 1236.6 2.6
1213.9 2.93
Retained Stability = 24 hours stability * 100
at 650C 30 minute stability
= 774.6 *100 = 63.81%
1213.9
Sl. No Volume of Proving Ring Calibration factor Volume CORRECTED FLOW IN
marshall Reading of Proving Ring Correction VALUE (Kg) (mm)
specimen
(in cc)
1 498.5 265 2.767 1.04 762.6 5.5
2. 496.5 270 2.767 1.04 777.0 6.3
3. 488.0 260 2.767 1.09 784.2 3.3
774.6 5.0
Sl. No Volume of Proving Ring Calibration factor Volume CORRECTED FLOW IN
marshall Reading of Proving Ring Correction VALUE (Kg) (mm)
specimen(cc)
(A) (B) (C) (D)* E = BxCxD
1 486.5 335 2.767 1.09 1010.4 3.6
2. 483.5 330 2.767 1.09 995.3 3.7
3. 487.0 320 2.767 1.09 965.1 3.3
990.3 3.5
* D is corelated to A
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the tests at a temperature of 60oC 1oC. These tests
are done in a bath tub at 60oC by keeping the samples
both for 30 minutes and for 24 hours. The stability after
30 minutes and after 24 hours is compared and the ratio
of the stability values gives the retained stability (per
cent basis) at the temperature of 60 oC. This loss of
stability with temperature is a measure of stable
performance of the bituminous mixes at high temperature.
Ten number of samples have been tested in the
laboratory to study the effect of high temperature in terms
of the retained stability. These samples have been taken
for different types of bitumen mixes i.e. BC with CRMB
60, BC with 60/70 grade, bitumen (without CRMB),
DBM with 60/70 grade bitumen (without CRMB). The
samples have been taken directly from batch mix plant
producing these mixtures as per the JMF and as used in
the construction of the rutted portion of the road project,
comprising the study stretch for this case study.
Details of these tests are furnished in Tables 14 to
17. The JMF for this stretch prescribes a retained stability
of 95 per cent for BC (CRMB 60) layer. Fig 4 shows in
a graphical form the retained stability (per cent basis) of
different mixes at temperatures 650C & 600C after 24
hours as compared to stability value at 600C after 30
minutes. Fig 5 shows, in the form of a histogram, the
stability values of these mixes at the temperatures of
600C and 650C. The typical values presented in the
Tables and Figures as above, indicate the likely loss of
stability at high temperature. This is interesting when
compared with the lower softening points of these mixes.
It is observed that loss of stability is substantial at a higher
temperature, particularly in case of DBM mixes. The
behaviour of BC mixes with modifiers like CRMB is
much better as compared to those without a modifier.
4.3.4. Retained stability for BC mix: Retained
stability of BC mix with CRMB after 24 hours at 60 oC
is 96.63 per cent which is well above 90 per cent
prescribed in IRC:SP:53-2002. The retained stability of
the BC mix of 60/70 bitumen without CRMB at 65oC,however is 82.50 per cent against 93.40 per cent with
CRMB at 65oC. It is 92.08 per cent without CRMB as
against 96.63 per cent with CRMB at 60oC. The effect
of modifier like CRMB or PMB in preventing the stability
loss at higher temperature is thus quite vivid.
4.3.5. Retained stability for DBM mix: The
retained stability for top layer of DBM at 60oC is about
82 per cent. The retained stability at 650C for DBM is
far low, around 63 per cent. The stability loss in case of
DBM at higher temperatures deserves early
consideration for up-gradation and updation of our
specifications of top layers of flexible pavement. The
test results obliquely suggest that perhaps we cannot
have flexible pavements in our country lasting for 20 to
30 years with the use of 60/70 grade bitumen without
modifiers. Performance grade bitumen with superpave
type specifications needs to be evolved. We should
otherwise consider providing composite or even rigid
pavements as an alternative considering the expected
long-term pavement life of 20 years plus.
Fig. 5. Histogram Showing Stability (kg) of different mix
at 600C (30 min), 600C (24 hours) & 650C (24 hours)
Fig. 4. Layer-wise retained stability of pavement materials
Vs various temperatures
ASTMD 1075-1979
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190 SINHA, SINGH& SHEKHARON
4.4. Effect of Heavy Traffic Loading Moving at
Slow Speed
Literature suggests that permanent deformation like
rutting gets further accentuated at high pavement
bituminous pavements are inadequate and need early
updation. Rutting observed in the case study obviously,
had the compound effect of both the high pavement layer
temperature and slow moving/stationary vehicles.
temperature, when the heavy truck traffic operates at a
slow speed with frequent stop/start condition as is the
case in the study stretch. This is a typical situation on
most of heavily trafficked corridors in India, particularly
near intersections, roundabouts and adjoining Toll Plazas
and other control booths like Check posts, Octroi booths
etc. Australian Asphalt Pavement Association (AAPA)
gives a table indicating damaging effect of slow moving
vehicles. This is reproduced in Table 18.
Superpave mix design recommends for additional
requirements in the selection of bitumen grade etc. to
account for the vehicles moving at a slow speed and for
conditions of standing load applications. According to
superpave recommendations for slow moving design
loads, the binder would be selected one high temperature
grade higher, such as a PG-64 instead of a PG-58. For
standing design loads, the binder would be selected two
high temperature grades higher, such as a PG-70 instead
of PG-58. For extraordinary high numbers of heavy
traffic loads (between 10,000,000 to 30,000,000 ESAL)
the engineer is encouraged to consider one high
temperature binder grade higher than the selection based
on climate. These recommendations do suggest the
additionality of adverse effect due to slow moving
vehicles on the performance of flexible pavement. These
are over and above the effects due to the hot climatic
region. This also speak loudly that our specifications for
TABLE 18. TRAFFIC LOADING
Indicative Traffic Volume
Traffic category Heavy vehicle/lane/day Structural design level (MSA) Traffic speed
Very heavy > 1000 2 x 107 Generally > 25 Km/hr
> 500 5 x 106 Stop/start Generally
< 25 Km/hr
Heavy 500 to 1000 5 x 106to 2 x 107 Generally > 25 Km/hr
100 to 500 5 x 105to 5 x 106 Stop/start Generally
< 25 Km/hr
Medium 100 to 500 5 x 105
to 5 x 106
Generally > 25 km/h< 100 < 5 x 105 Sop/Start, climbing lanes
or generally < 25 km/h
Light < 100 < 5 x 105 Generally > 25 km/h
(Source: AAPA, Asphalt Guide 2002)
4.5. Effect of Secondary Compaction
One of the known cause of rutting in flexible
pavement is the secondary compaction by the plying
vehicles over the time. Compaction of bitumen mixes at
refusal density while maintaining a minimum air voids of
3 per cent is being suggested in the literature. Bitumen
mixes used in study stretch had been tested for 300 blows,
while broadly maintaining air voids at 2.75 per cent and
VMA and VFB as per specifications. As the study stretch
has been opened to traffic only about a year back, effect
of the secondary compaction was not considered in the
case study.
CONCLUSIONS & RECOMMENDATIONS
The present case study is a limited study. It has
attempted to examine the adverse effects of high
temperature in the top layers of binder course on theoverall performance of flexible pavements. It
demonstrates that existing pavement design method
followed in India requires an early review and up-
gradation to meet the different (specific) site conditions.
The generic nature of specifications as prescribed at
present cannot cater to the need of constructing flexible
pavements for design life of 20 to 30 years. At least
some catalogue type specifications covering different
regions of the country need to be evolved on the pattern
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of performance based specifications like Superpave of
USA. The results of the limited case study undertaken
are only indicative. More elaborate studies are required
to ensure wider understanding of the problems of the
flexible pavement. Some of the recommendations areas below:-
Needs for instrumentation to study the behaviour of
temperature on the performance of the bituminous
mixes is required to be taken up to enforce
development of mechanistic design based on
indigenous database.
Data bank needs to be created, maintained andanalyzed to study the variations and variability in
material characterization.
Specifications should be evolved considering the
need to construct long-term performing pavements.
Higher standards in respect of bitumen binder is
required to be set. The present standards for
viscosity, stability, loss of stability at higher
temperature etc. are either inadequately provided
or are missing in the existing specifications.
Generic nature specifications, as followed today
need to be discarded in favour of performance based
specifications as highlighted above.
Special provisions to account the adverse effect ofslow moving/stationary vehicles is to be provided
rather presuming transient loads in our design.
Specifications need to provide against stability loss
at higher temperature. For top DBM layers stability
loss at 60oC should preferably be kept around 97
per cent.
Use of modifiers to enhance thermal related
characteristics of bitumen should be made
mandatory in top DBM layer. General paving
bitumen as being used in the DBM layers may not
serve.
Composite construction including Whitetopping in
top layers should be tried on pilot basis to safeguard
bituminous roads against deformations at high
temperature.
Cement is relatively much better binder compared
to bitumen. In heavy traffic corridor with high
temperature, cement concrete roads may be
considered as a viable alternative on long-term
performance considerations, based upon life cycle
cost.
REFERENCES
1. Superpave Mix Design Vol. I & Vol. II, Superpave series
No.1 & 2 (SP1 & SP2), Asphalt Institute, Lexington.
2. Specifications for Road and Bridge Works, MOSRT&H
(Fourth Revision 2001), IRC.
3. IRC:SP:53-2002 (First Revision) Guidelines on Use of
Polymer and Rubber Modified Bitumen in Road
Construction.
4. Asphalt Guide, Australian Asphalt Pavement Association(AAPA) AUSTROADS Sydney 2002.
5. Highway Research Record No. 189 Design Performance
and Surface Properties of Pavement (9 Reports) 1967.
6. The Properties of Asphaltic Bitumen , Edited by J.PH.
Pffiffer, Elsevier Publishing Company, Inc. New York
Amsterdam, London Brussels.
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