Comparative study of the effect of treated coir fiber and natural rubber modified bitumen on open graded friction course mixes

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online), Volume 6, Issue 1, January (2015), pp. 54-66 © IAEME
54
COMPARATIVE STUDY OF THE EFFECT OF TREATED
COIR FIBER AND NATURAL RUBBER MODIFIED
BITUMEN ON OPEN GRADED FRICTION COURSE
MIXES
Loui T R 1
Satyakumar2
Chandrabose T .A 3
1
Assistant Professor, Dept, of Civil Engineering College of Engineering, Trivandrum
2
Professor, Dept, of Civil Engineering College of Engineering, Trivandrum
3
PG Student, Dept.Of Transportation Engineering College of Engineering, Trivandrum
ABSTRACT
Open Graded Friction Course (OGFC) is a porous, gap-graded asphaltic concrete mixture that
contains a high percentage of interconnected air voids. These types of mixtures are also referred to as
Permeable Friction Course (PFC). Generally, the OGFC pavement reduces hydroplaning, splash and
spray, and improves roadway visibility and the skid resistance of pavement surface under wet
weather conditions. This research gives the results of a study focusing on four different OGFC mixes
prepared with PG 60/70 bitumen, PG 60/70 & coir fiber, Natural Rubber Modified Bitumen
(NRMB) and NRMB & coir fiber. Surface treatment process was done on the coir fiber to improve
the properties like durability and temperature stability. Coir fiber was mainly used in this study to
reduce the drain down loss of OGFC mix. Natural Rubber Modified Bitumen is widely used in south
Kerala and a few studies were conducted on mixes prepared with it. Mix designs were performed
according to the design procedure proposed by the National Center of Asphalt Technology (NCAT)
for a range of 4.5 – 6.0 % bitumen content and 0.3% fibre dosage. The optimum mix was compacted
by three different compaction levels: 35 blows/face, 50 blows/face and 75 blows/face. Several
laboratory tests were carried out in this study to evaluate OGFC mix properties. Marshall test, Drain
down test, Cantabro abrasion loss test and permeability test were used to evaluate the performance of
OGFC mixes. The mix prepared with NRMB and coir fiber was selected as optimum mix which
provides adequate strength and adequate air void in order to drain the rain water quickly. 50
blows/face was selected as optimum compaction level to satisfy maximum stability and minimum
percentage air void in the OGFC mix.
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING
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ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 6, Issue 1, January (2015), pp. 54-66
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55
Keywords: Open graded Friction Course, Coir fibre, Natural Rubber Modified Bitumen &
Compaction effort.
I. INTRODUCTION
Open-graded friction course (OGFC) mixture is a special purpose mixture that is being
increasingly used in pavement surfacing around the world. OGFC is characterized by the use,
predominantly, of narrowly graded crushed coarse aggregate without a significant proportion of
fines. This results in sufficient interconnected voids to provide high permeability for subsurface
drainage. Asphalt content is slightly higher than dense mixes of the same maximum aggregate size to
enhance the durability of the mix.
Porous asphalt, as it is called in Europe, is designed to have interconnected voids, which
provides high permeability. Water easily enters the pavement and is removed from the surface; hence
wet weather friction and visibility are enhanced. The macrotexture of the porous mix is higher than
dense mixture. This increased macrotexture increases surface roughness and enhances the surface
friction. Permeability might decrease as the OGFC layer ages and, therefore, its ability to transmit
water through decreases. Debris clogging in the surface pores plugs the mix. Traffic densification
(loss of voids) can also contribute to reduced permeability. This would require additional
maintenance and cost.
Mix design approaches have evolved since the first generation of OGFC. It started with
specifying the percentage of asphalt needed based on the drain down test. New design techniques
still use this test. In addition, voids are measured and the compacted specimens are artificially aged.
Durability and moisture sensitivity are also evaluated. Moreover, modified and fibre asphalts are
being used to counter the problems of drain down. OGFC pavements typically fail by ravelling.
More specifically, the pavement fails when the asphalt binder ages and becomes brittle. Drain down,
a separation of asphalt mastic from the course skeleton, can occur during storage or transport which
would result in a thin binder coating that is inadequate to prevent particles from being dislodged by
traffic. The thin binder film can also age more rapidly, aggravating the ravelling problem.
Sometimes, the failure occurs when the pavement is only six to eight years old. Such a short life is
difficult to accept.
Use of modified binders, fibres and mineral fillers can solve the potential problems
associated with OGFC. Advantages of using natural fibre over man-made fibres include low density,
low cost, recyclability and biodegradability. These benchmark properties make natural fibre a
potential replacement for synthetic fibres in composite materials opening up further industrial
possibilities. However, high level of moisture absorption by the fibre leads to poor wettability and
insufficient adhesion within the matrix (interfacial adhesion) resulting degradation of composite
properties. In order to expand the use of natural fibres as successful reinforcement in composites the
fibre surface needs to be modified to enhance fibre-matrix adhesion.
The selection of compaction method and compactive efforts should be carefully made for the
OGFC mixes. Uniformly graded coarser aggregate skeleton in the OGFC mixes under higher
compactive efforts results in the aggregate degradation. The different agencies have adopted various
means of compaction and compactive efforts.
1. 1 Need for the Study
In India, OGFCs are yet to be experimented by highway agencies, and specifications for the
same do not exist. In order to develop design method for OGFC, the present investigation was
focused on the use of two binders (PG 60/70 & NRMB) used in the country, for the paving of
highways and rural roads and the use of natural fibre (coir fibre) in the mix. India’s Ministry of Road
Transport and Highways (MoRTH) has expressed an interest in evaluating such mixtures for national

56
highway projects in parts of hilly sections in India as some benefits can be obtained from the
enhanced surface friction of these mixtures (Punith et al., 2012)[8]
. In high rain fall area, there is a
need for an OGFC mix for providing good skid resistance and to drain the water quickly. There is a
need for a mix design such that the OGFC mix should provide good strength & stability and satisfy
adequate air void to provide good permeability property.
1.2 Objectives
• To design an optimum mix for OGFC to provide adequate strength and permeability to drain
water quickly
• To study the effect of NRMB on the different performance parameters of OGFC mix.
• To study the effect of surface treated coir fibre on the different performance parameters of
OGFC mix.
2. LITERATURE REVIEW
Kandhal et al. (1998)[4]
conducted a survey in USA to determine where OGFCS have been
used, why they are used in some places and not others, mix design and construction practices,
OGFC’s performance history, and problems encountered. The survey showed that significant
improvements have been observed in the performance of open graded courses (OGFC) since their
introduction in the 1950s.
Mallick et al. (2000)[5]
conducted a study to evaluate the performance of OGFC in the
laboratory with different gradations and types of additives, and recommended a rational mix design
procedure for the new-generation OGFC mixes. Additionally, the construction and performance of
six OGFC pavements (constructed prior to this study) are discussed. These mixes generally meet the
requirements for gradation band and Cantabro abrasion recommended in the new mix design system.
Based upon the evaluation of six OGFC field pavements, it has also been shown that OGFC mixes
meeting the new mix design requirements are constructible and have exhibited good performance.
Mallick et al. conducted studies on new generation porous asphalt mixtures by using the superpave
gyratory compactor (SGC) and Marshall hammer. A study was conducted to determine the required
number of gyrations. Three samples of each were compacted with 100 gyrations of the SGC and 50
blows/face of Marshall hammer. It was determined that about 50 gyrations with SGC and 50
blows/face with the Marshall hammer produce about 18 percent air voids generally found in the
field.
Hassan et al. (2005)[1]
conducted a research project to investigate four different OGFC mixes
containing no additives, cellulose fibers, styrene butadiene rubber (SBR) polymer, and a combination
of both fibers and SBR polymer. Mix designs were performed according to the design procedure
proposed by the National Center of Asphalt Technology for a range of 4.5–6.5% asphalt content. The
mixture containing fibers and SBR polymer was selected as an acceptable mix design with an
optimum asphalt content of 6.5%.
Kandhal et al. (2008)[6]
conducted a critical review of bituminous paving mixes used in India
in accordance with the MORTH Specifications (2001) has been made keeping in perspective the
fundamentals of mix selection based on their intended functions in different courses within the
flexible pavement.
Suresha et al. (2008)[7]
carried out a laboratory investigation on the effect of various binders
on the performance and durability of porous friction course (PFC) mixes. The performance was
evaluated in terms of stone-on-stone contact condition, air voids, and hydraulic-conductivity of
compacted PFC mixes. The structural durability was investigated based on aged abrasion loss and
moisture susceptibility. The findings provide a better understanding of the effect of each binder type
on the performance and durability of PFC mixes.

57
Punith et al. (2012)[9]
conducted a study focusing on the use and properties of OGFC
mixtures containing reclaimed polyethylene modified binder (RPEB), crumb rubber modified binder
(CRMB), and neat 60/70-grade binder with cellulose fibers. Drain down test, Cantabro stone loss
test, permeability test, indirect tensile strength test, resilient modulus test, rutting test, and skid
resistance test were used to evaluate the performance of OGFC mixtures. The addition of fiber
stabilizers and polymerized asphalt significantly reduced the potential for drain down in OGFC
mixtures.
Kabir et al. (2011)[2]
carried out a study to investigate the effects of natural fibre surface on
composite properties are discussed. Several fibre surface modification methods are reported and their
effects on composite properties are analysed. These properties constitute the prime area of research
in developing green fibre polymer composite technologies.
3. MATERIAL CHARACTERIZATION
3.1. Bitumen
The most widely used Penetration Grade 60/70 bitumen and Natural Rubber Modified Bitumen
(NRMB) are used as the binder.
3.2 Coir fibre
Chemical composition: Water soluble- 5.25%, Pectin and related compound- 3.00%,
Hemicelluloses- 0.25%, Lignin- 45.84%, Cellulose- 43.44%, Ash- 2.22%
Average Length in inches- 6-8, Density (g/cc) - 1.2, Elongation (%) - 30, Tensile strength
(MPa) – 593, Elastic Modulus (GPa) – 4-6, Swelling in water (diameter) - 5%
Surface Treatment of the Extracted Coir fibre: The surface treatment process adopted in this work
was the sodium hydroxide treatment [2]. Known weights of extracted coir fibres were soaked in
prepared known volume of 5% NaOH solution for 2 hours. The products were removed and washed
with distilled water and dried at 60 0 C and stored in specimen bag ready for use.
4. METHODOLOGY
4.1 Experimental Program
The following tests were carried out in OGFC mixtures: Marshall mix design using 50
blows/face, the drain down test, resistance to abrasion loss by the Cantabro Abrasion test and the
cross plane permeability test
4.2 Check for stone-on-stone contact criteria
Stone-on-stone contact for the OGFC mix is defined as the point at which the voids in coarse
aggregate (VCA) of the compacted OGFC mixture (5.5% binder) (AASHTO T166) is less than the
VCA of the coarse aggregate alone in the dry rodded test (AASHTO T19).
Voids in coarse aggregate in the dry rodded condition (VCAd) is calculated by:
VCAd= (Gcaγw– γs) / Gcaγw (1)
Voids in coarse aggregate in the compacted mix (VCAm) is calculated by:
VCAm = 100 – ( * Pca) (2)

58
Where: γw -Density of water, γs - bulk density of the coarse aggregate fraction in the dry rodded
condition, Gca - bulk specific gravity of coarse aggregate, Gmb- bulk specific gravity of compacted
mix and Pca- % of coarse aggregate in the total mixture.
The stone-on-stone contact condition was confirmed when the ratio of VCAm to VCAd was
found to be less than unity.
4.3 Drain down test
AASHTO T305 drain down test method was used in this study. In this method, known mass
of loose sample is placed in a wire basket which is positioned on a plate & placed in a temperature
controlled oven for one hour at 170 0
C. At the end of one hour, the basket containing the sample is
removed from the oven along with the plate and the mass of the plate or container is determined. The
amount of drain down is then calculated by:
Drain down = ((Initial sample mass – Final sample mass) / Initial sample mass) x 100
A maximum drain down of 0.3 percent by weight of total mix is recommended.
4.4 Cantabro Abrasion test (Unaged)
The resistance to compacted porous asphalt mixtures to abrasion loss was analyzed by means
of the Cantabro test. This is an abrasion and impact test carried out in the Los Angeles Abrasion
machine (ASTM Method C131). An OGFC specimen compacted with 50 blows on each side is used.
The mass of the specimen is determined to the nearest 0.1 gram (P1). The test specimen is then
placed in the Los Angeles Rattler without the charge of steel balls (25±5 0
C). The machine is
operated for 300 revolutions at a speed of 30 to 33 rpm. The test specimen is then removed and its
mass determined to the nearest 0.1 gm (P2) and the percentage abrasion loss is calculated.
The percentage abrasion loss = 100 x (P1 – P2) / P1
The recommended maximum permitted abrasion loss value for freshly compacted specimens is 20
percent.
4.5 Permeability tests
A compaction permeameter under falling head condition was used for permeability testing. It
is cylindrical in shape with internal diameter same as that of Marshall mould (10.16cm) and bottom
of the mould is perforated. The aggregates and bitumen are well mixed at a temperature about 1500
C.
Inside of the mould is oiled. Then the mix was filled in the permeameter set up and compacted by
giving 100 blows using manual pedestal compactor. After 24 hrs, this compacted mix saturated for
24 hrs. Calculate coefficient of permeability (Ψ) using the equation (as per ASTM)
Ψ = ln ( ) (3)
Where: a = πd2
/ 4 = cross-sectional test area of specimen, mm2
, L = thickness of the specimen, mm,
A = πd2
/ 4 = cross-sectional area of stand pipe above specimen, t = time for head to drop from h0 to
h1, sec, h0 = initial head and h1 = final head
Minimum recommended coefficient of permeability for OGFC as per ASTM is 100 m/day.

59
5 RESULTS AND DISCUSSIONS
5.1 Mix Design
Mix design was performed according to the design procedure proposed by National Centre of
Asphalt Technology (NCAT)[5]
. The mix design involves selecting an aggregate gradation, mixing
the aggregate with the asphalt with or without the fibres. The mixed specimen are evaluated for air
voids, drain down, unaged abrasion and permeability. The optimum mixture is selected based on the
limits proposed by NCAT.
To establish a gradation for the OGFC mix, three gradations were considered (Table 4). The
selection of OGFC gradation was based on evaluation of stone-on-stone contact with consideration
of air voids. Stone contact is an essential criterion for which the mix is tested. It is a method of
ensuring the stability of the mix. The criterion is checked by comparing the voids in the coarse
aggregate (VCA)(retained on a 4.75 mm sieve) in the mixed and compacted sample with the voids in
the same coarse aggregate in a dry-rodded condition (VCAd) based on AASHTO T19 test. The stone
contact exists when VCA is less or equal to VCAd.
To evaluate the three gradations and obtain the VCA, trial mixes were made at 5.5 % asphalt
cement content, by total weight of the mix. The VCAdwas performed on coarse fraction of the
gradation. Table 4 shows the result obtained on two samples for the three gradations. The result
indicate the condition of stone-on-stone contact was only achieved for the trial 1 gradation (coarse
gradation). Therefore, the trial 1 was adopted for the mix design trials presented in the following
sections.
Four types of mixes were selected for determining the effect of modified bitumen (NRMB) &
surface treated coir fibre on the performance of OGFC and for determining the optimum mix. The
four types of mixes selected were: Mix prepared with PG 60/70 (MP), Mix prepared with PG 60/70
and coir fibre (MP-F), Mix prepared with NRMB (MN) and Mix prepared with NRMB and coir fibre
(MN-F). The fibre dosage was fixed as 0.3% [5]
. The OBC for four types of mixes were found out
from Marshall tests by varying the bitumen content from 4.5% to 6% with 0.5% increments. Unaged
abrasion test, drain down test and permeability test are carried out by varying the bitumen content
from 4.5% to 6% with 0.5% increments. The values of Abrasion loss, Percentage drain down and
Coefficient. of permeability at OBC (from Marshall test) were found out for all mixes from the test
results. The values of Abrasion loss, Percentage drain down and Coefficient of permeability at OBC
of all mixes were checked with the limits proposed by NCAT and found out the optimum mix which
satisfies all the requirements suggested by NCAT.
The Marshall mix design trials used asphalt content in the range of 4.5-6%, by total weight of
the mix excluding the weight of the fibres, with 0.5% increments. Specimens were compacted using
the Marshall hammer using 50 blows on each side. The optimum bitumen content (OBC) was
calculated by considering the following criteria: Maximum stability value, maximum bulk density
and bitumen content corresponding to 20 % air voids.
The bitumen content corresponding to above three criteria were selected and optimum
bitumen content was calculated as average of three values. The optimum bitumen content (OBC)
obtained from Marshall tests were 5.5, 5.62, 5.4 and 5.53% for specimens prepared with neat
bitumen (PG 60/70), neat bitumen (PG 60/70) with surface treated coir fibre, NRMB and NRMB
with surface treated coir fibre respectively.
5.2 Unaged Abrasion Test
The binder content in the OGFC mixture significantly influenced the abrasion loss; at lower
binder contents, the abrasion loss observed was higher. Fig. 1 shows that the percent abrasion
loss generally decreases with the increase in asphalt content.

60
5.3 Drain down test
Fig. 2 illustrates that the drain down percent increases with the increase in asphalt content for
mixtures with and without surface treated coir fibers. The test results illustrate the advantage of
adding surface treated coir fibers in preventing the binder runoff from the aggregate due to stiffening
of the mixture.
5.4 Permeability Test
The test results indicated that with the increase in binder content, a reduction in permeability
of the porous asphalt mixtures occurs. The permeability of all the 4 mixes were found to be between
90 and 143 m/day, as shown in Fig. 3.
5.5 Determination of Optimum OGFC mix
The summary of the all test results of OGFC properties of different mixtures at their optimum
binder content was given in Table 8. The important conditions taken for finding the optimum mix
were: Maximum stability, Air void in the range 18 to 22%, Percentage Abrasion loss should be
below 20% (unaged specimens), Percentage drain down should be below 0.3% and Coefficient of
permeability should be greater than 100 m/day.
The OGFC mix prepared with NRMB and coir fibre satisfies all requirements proposed by
NCAT and that was selected as optimum mix.
5.6 Effect of compaction effort on OGFC parameters of the optimum mix
The optimum mix (MN-F) was compacted by three different compaction levels: 35
blows/face, 50 blows/face and 75 blows/face. The effect of compaction effort on percentage air void,
Marshall stability and coefficient of permeability were found out and the results are shown in Fig. 4.
The percentage air void values were found to be in the range of 24.25 to 12.45%, when the
compaction effort increased from 35 to 75 blows/face. As per the standard requirements of NCAT,
OGFC mixes should have a minimum air void of 18%. The percentage air void corresponding to 35
and 50 blows/face satisfied this requirement. However, in the mixes tested for 75 blows, the
percentage air void failed to satisfy the minimum air void requirement. The reduction in the
percentage air void due to change in the compaction level from 50 blows to 75 blows was found to
be 38%. Similarly, change in compaction level from 50 to 35 blows, resulted in an increase of 22%.
When the compaction increased from 35 (light compaction) to 50 blows/face (medium compaction),
the stability value was increased due to the densification of mix that resulted in the reduction of air
voids content and when the compaction further increased to 75 blows/face (heavy compaction),
stability value was decreased due to the degradation of aggregates.
The ASTM D 7064 suggests a minimum K of 100 m/day. The K values of mix compacted
with 50 blows or compacted with 35 blows, were found to satisfy this requirement. The mix
compacted with a compaction efforts of 75 blows, had K value lesser than 50 m/day. For mix
compacted with 35 blows, the K value were higher by a factor of 60% as compared to mix
compacted with 50 blows. In the case of mixes compacted with an effort of 75 blows, the mean K
values were reduced by a factor of 58% as compared to mix compacted with 50 blows. So 50
blows/face was selected as optimum compaction level to satisfy maximum stability and minimum
percentage air void in the OGFC mix.

61
6. FIGURES AND TABLES
Figure 1: Variation in Unaged Abrasion loss with bitumen content
Figure 2: Variation in Percentage drain down loss with bitumen content
Figure 3: Variation in Coef. of Permeability with bitumen content

62
Table I. Physical Properties of Binders
Property
PG 60/70
(Grade requirement)
NRMB 70
(Grade requirement
Penetration (250
C)(mm) 66(60-70) 69(50-90)
Softening point (ring & ball) (0
C) 51(45-55) 53(min 50)
Ductility (cm) 86(>75) 98(min 50)
Specific Gravity (g/cc) 1.01(.97-1.02) 1.02(Not specified)
Viscosity at 1500
C, minimum (poise) 2.6 (3.5 poise@1350
c) 2.2(2 - 6 poise @ 1500
C)
Table 2. Properties of Aggregates
Property Test Requirement Test method Test Results
Particle shape Combined Flakiness and
Elongation Indices
Max. 35% IS: 2386 Part 1 30%
Strength Los Angeles Abrasion Value
Aggregate Impact Value
Aggregate Crushing Value
Max. 40%
Max. 30%
Max. 30%
IS: 2386 Part IV
IS: 2386 Part IV
IS: 2386 Part IV
21%
26%
27%
Water
absorption
Water absorption Max. 2% IS: 2386 Part III 0.25%
Stripping Coating and Stripping of
Bitumen Aggregate
Mini. Retained
Coating 95 %
IS: 6241 100%
774.5
1105
916
0
200
400
600
800
1000
1200
30 35 40 45 50 55 60 65 70 75 80
Stability,kg
Compaction effort,Blows/face
Marshall Stability (kg)
Marshall
Stability
(kg)
24.25
19.8
12.45
0
5
10
15
20
25
30
25 30 35 40 45 50 55 60 65 70 75 80
PercentageAirvoids,%
Compaction effort,Blows/face
Air voids (% )
Air voids…
165.5
103
43.5
0
50
100
150
200
25 30 35 40 45 50 55 60 65 70 75 80
Coef.ofPermeability,m/day
Compactioneffort,Blows/face
Coef. of Permeability (m/day)
Coef. Of…

63
Table 3. Gradation Used for the Study (NCAT)[5]
Grading Band Trial 1 Trial 2 Trial 3
IS sieve size
(mm)
Cumulative % by weight of total aggregate passing
19 100 100 100 100
12.5 85-100 88 93 97
9.5 55-75 58 65 72
4.75 10-25 11 17.5 24
2.36 5-10 6 7.5 9
0.075 2-4 3 3 3
Table 4. Stone-On-Stone Contact Verification
Property
Trial Gradations
Trial 1 Trial 2 Trial 3
Percentage retained on 4.75 mm
sieve (%)
89 82.5 76
Bulk Specific gravity of compacted
mix, Gmb (g/cc)
1.889 1.96 2.03
Bulk Specific gravity of coarse
aggregate, Gca (g/cc)
2.7 2.7 2.7
Voids in the coarse aggregate,
VCAm (%)
40.2 42.13 43.77
Voids in the coarse aggregate in a
dry rodded condition, VCAd (%)
42.1 39.94 39.85
VCAm / VCAd 0.957 < 1 1.05 >1 1.09 > 1
Max. Specific gravity of loose mix,
Gmm (g/cc)
2.34 2.33 2.32
Percent Air voids (%) 21.62 18.67 15.77
Table 5. Unaged Abrasion Test Results
Bitumen
content
Abrasion loss (%)
PG 60/70
PG 60/70 with coir
fibre
NRMB
NRMB with coir
fibre
4.5 30.45 27.1 26.56 23.8
5 28.3 23.6 24.3 19.5
5.5 26.5 18.5 19.7 16.1
6 21.4 15.3 16.3 12.4
Table 6. Drain down Test Results
Bitumen
Content (%)
Percentage Drain down (%)
PG 60/70
PG 60/70
with Coir
fibre
NRMB NRMB with Coir fibre
4.5 0.26 0.13 0.27 0.16
5 0.32 0.16 0.4 0.21
5.5 0.61 0.21 0.93 0.28
6 1.86 0.32 2.05 0.38

64
Table 7. Permeability Test Results
Bitumen Content
(%)
Coef. Of Permeability (m/day)
PG 60/70
PG 60/70 with Coir
fibre
NRMB
NRMB with Coir
fibre
Bitumen Content
(%)
Coef. Of
Permeability
(m/day)
Bitumen Content
(%)
Coef. Of
Permeability
(m/day)
Bitumen Content
(%)
PG 60/70 PG 60/70
Bitumen Content
(%)
Coef. Of
Permeability
(m/day)
Bitumen Content
(%)
Coef. Of
Permeability
(m/day)
Bitumen Content
(%)
PG 60/70 PG 60/70
Table 8. Summary of the Mix OGFC Properties at OBC
MixType
OBCfrom
Marshalltest(%)
OGFC Properties at OBC
Stability(kg)
PercentageAir
Void(%)
AbrasionLoss
(%)
Percentage
Draindown
(%)
Coef.of
Permeability
(m/day)
PG 60/70 5.5 1002 20 23.5 0.61 112
PG 60/70 with
coir fibre
5.62 1010 20.2 18 0.225 112
NRMB 5.4 1125 20 21 0.8 105
NRMB with
coir fibre
5.53 1205 19.8 16 0.28 104
Table 9. Effect of Compaction Effort
Type of Compaction
Properties
Marshall Stability (kg) Air voids (%) Coef. of Permeability (m/day)
35 blows/face
765 24.2 160
784 24.3 171
774.5 24.25 165.5
50 blows/face
1105 19.8 103
1105 19.8 103
1105 19.8 103
75 blows/face
908 12.4 46
924 12.5 41
916 12.45 43.5

65
7. CONCLUSIONS
• The gradation with lowest percentage passing through 4.75 mm sieve (Trial 1) satisfies the
stone-on-stone contact criteria and selected as design gradation.
• OBC increased with the addition of coir fibre in both PG 60/70 and NRMB samples.
• Maximum stability value of NRMB sample was found higher than that of PG 60/70 sample
and percentage increase in stability value is 12 %
• There was an increase in maximum stability value observed in both PG 60/70 and NRMB
sample with the addition of coir fibre. Percentage increase in PG 60/70 with coir fibre sample
was 0.9 % and percentage increase in NRMB with coir fibre sample was 6.78%.
• There was no considerable change in percentage air void observed with the addition of coir
fibre in both PG60/70 and NRMB samples.
• Unaged abrasion loss decreased with increase in bitumen content in all mixtures. NRMB
samples shows good abrasion resistance than PG 60/70 samples
• Unaged abrasion loss decreased with the addition of coir fibre in both PG 60/70 and NRMB
samples.
• Percentage drain down increases with increase in bitumen content in all mixes. NRMB
samples shows higher drain down loss as compared to PG 60/70 samples.
• Percentage drain down decreased with the addition of coir fibre in both PG 60/70 and NRMB
samples.
• Coefficient. of permeability decreases with increase in bitumen content in all mixes.
• There was no considerable change in coefficient. of permeability is observed with the
addition of coir fibre in both PG 60/70 and NRMB samples.
• The OGFC mix prepared with NRMB and surface treated coir fibre was selected as optimum
mix from the four mixes.
• The compaction effort play a significant role in air voids contents, permeability and stability
of OGFC mix.
• When the compaction increased from 35 (light compaction) to 50 blows/face (medium
compaction), the stability value was increased due to the densification of mix that resulted in
the reduction of air voids content and when the compaction further increased to 75
blows/face (heavy compaction), stability value was decreased due to the degradation of
aggregates.
• The percentage air void corresponding to 35 and 50 blows/face satisfied the NCAT
requirement. However, in the mixes tested for 75 blows, the percentage air void failed to
satisfy the minimum air void requirement.
• The coef. of permeability values of mix compacted with 50 blows or compacted with 35
blows, were found to satisfy the ASTM requirement (100 m/day). The mix compacted with a
compaction efforts of 75 blows, had coef. of permeability value lesser than 50 m/day.
• 50 blows/face was selected as optimum compaction level to satisfy maximum stability and
minimum percentage air void in the optimum OGFC mix.
8. ACKNOWLEDGEMENT
This study was the part of research work carried out with financial support from Transportation
research centre (TRC) Government of Kerala

66
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