Rutting in Flexible Pavements – A Case Study (1)

7/22/2019 Rutting in Flexible Pavements A Case Study (1)

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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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178 SINHA, SINGH& SHEKHARON

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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HIGHLIGHTSOFTHE178THCOUNCILMEETING 179 RUTTINGINFLEXIBLEPAVEMENTS- A CASESTUDY

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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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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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


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



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



= 1201.4 *100 = 96.63%

1243.3

* D is corelated to A


10/15


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




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



= 1110.9 *100 = 92.08%

1206.4


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




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




= 1095.8 *100 = 91.71%

1194.9



STABILITY AFTER 30 MINUTES IN WATER BATH 600C



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



= 1010.4 *100 = 84.56%

1194.9



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



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



12/15


TABLE17. RETAINEDSTABILITYOFDBM MIXAFTER24 HOURSATDIFFERENTTEMPERATURES

Compaction 75 blows Date-30/6/07 to 2/7/07

Binder 60/70 Bitumen




= 990.3 *100 = 81.58%

1213.9

Compaction 75 blows



STABILITY AFTER 30 MINUTES IN WATER BATH @600C



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



= 774.6 *100 = 63.81%

1213.9



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



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



13/15


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


14/15


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


15/15


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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Rutting in Flexible Pavements – A Case Study (1)

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