The permeability and indirect tensile strength characteristics of porous asphalt mixes

1. INTERNATIONAL JOURNAL OF CIVIL ENGINEERING
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online), Volume 5, Issue 8, August (2014), pp. 62-67 © IAEME
AND TECHNOLOGY (IJCIET)
ISSN 0976 – 6308 (Print)
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Volume 5, Issue 8, August (2014), pp. 62-67
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IJCIET
©IAEME
THE PERMEABILITY AND INDIRECT TENSILE STRENGTH
CHARACTERISTICS OF POROUS ASPHALT MIXES
Harish.L
(Asst. Professor, Department of Civil Engineering, REVA ITM, Bengaluru)
ABSTRACT
Porous Asphalt is a bituminous mix with very low fines content resulting in high voids ratio.
It is promoted as being effective in enhancing traffic safety in rainy weather,reducing hydroplaning
tendencies and having good skid resistance properties at higher speed oftraffic. The use of Porous
Asphalt tends also to reduce noise and glare at night. In this researchaggregate gradation proposed by
the National Asphalt Pavement Association is adopted.
The porous asphalt mix is designed to have air voids content in the range of 18-22%.Hence
the mixes are compacted at 50, 65, 75 and90 blows of compaction of Marshall rammer on each face
to obtain the voids content in thedesired range. The Cantabro abrasion test was performed to obtain
resistance of the mix toravelling. The rest results indicated that the abrasion loss reduced as the
binder content increasedand also the air voids content decreased with increase in compaction level.
The permeability measurements indicated that the Constant head technique provides strong
correlation to air voidsand bulk density than compared to that of Falling head technique. The
moisture susceptibility asmeasured by tensile strength ratio (TSR) indicated that with increase in
compaction the strength increases, however itwas found to be very much lower than that of the dense
graded mixes.
Keywords: Porous Asphalt, Marshall Mix Design, Abrasion Test, Permeability, Indirect Tensile
Strength.
1. INTRODUCTION
The roadway design has focused on providing a strong, durable and safe pavement for
themotoring public. However increase in traffic noise, reduced visibility during rain, splash andspray
of water on the pavement are becoming important factors to be considered for thepavement selection.
Experience and evidence is mounting to show that these can be better andmore economically
controlled at the source by designing quieter pavement surfaces.

2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online), Volume 5, Issue 8, August (2014), pp. 62-67 © IAEME
63
1.1 Advantages of porous asphalt
1. Porous asphalt can absorb a greater amount of runoff on the pavement surface.
2. The porous asphalt surface is said to have a ‘negative texture’ which does not excite tyre treads
to the same extent as conventional positively textured road surfaces and hence produces low
levels of tyre noise.
3. Rutting is reduced because there is no visco-elastic flow in the compacted layer.
4. Reduction in glare on the pavement surface during night riding is a significant advantage of
porous asphalt mix.
5. Safety during wet weather condition and night driving is increased due to better visibility of the
road and road markings.
1.2 Objectives of the present study
1. To assess the properties of aggregates and binder by conducting laboratory tests.
2. To determine the optimum binder content for the selected gradation using the stipulated design
method.
3. To determine the volumetric properties of the mix prepared at optimum binder contentfor
varying air voids content.
3. To determine the permeability of the mix by adopting Constant head and Falling
headtechniques.
4. To determine the Indirect tensile strength of the mix at varying voids content.
2. DESIGN METHODS FOR POROUS ASPHALT
The mixture design of the porous asphalt is less structured than traditional Marshallmethod of
mix design or new Superpave method of mix designs. However the approach hasseveral features
similar to dense graded mixture design.
2.1 The main components in design include
1. Characterisation and selection of materials.
2. Fixing the aggregate gradation and compaction method.
3. Binder optimisation by determining the air voids, drain down of asphalt and abrasion
resistance.
2.2 Design steps
1. Selection of aggregate gradation for the mix.
2. Preparing Marshall specimens with trial bitumen contents based on expected optimum binder
content.
3. Determining the Percentage Air voids, Voids in coarse aggregates in the compacted mix.
4. Determining the abrasion loss by conducting the Cantabro abrasion test.
2.3 The optimum binder content is decided for
1. A design air voids content of 20%.
2. Maximum abrasion loss of 20%.
3. Drain down mass not exceeding 0.3% by weight of mix.

3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online), Volume 5, Issue 8, August (2014), pp. 62-67 © IAEME
64
3. PRESENT INVESTIGATIONS
3.1 Aggregates
In the present investigation aggregates of strong and durable nature were used. The
aggregates were tested for their physical properties and the results are presented in Table below.
Table 3.1: Physical properties and requirements of Aggregates
Sl. No Description of Tests Test Result
Requirements as per
MoRTH
1 Aggregate Crushing Value (%) 22.07 ----------
2 Aggregate Impact Value 22.71 Max 24%
3 Combined Index (%) 29.30 Max 30%
4 Water absorption 0.10 Max 2%
5
Aggregate specific gravity
Coarse aggregates 2.688 ----------
Fine aggregates 2.72 ------------
3.2 Aggregate Gradation
The gap graded aggregate gradation for the porous aspalt proposed by National
AsphaltPavement Association (NAPA) was adopted for the study. The adopted gradation is
presented in Table below
Table 3.2: Adopted aggregate gradation of Porous asphalt mix
Sieve size, mm
Gradation proposed by
NAPA
Adopted gradation,
% Retained
19 100 0
13.2 85-100 7.5
9.5 55-75 28.5
4.75 10-25 48.5
2.36 5-10 11
.075 2-4 4.5
3.3 Binder
The binder used for the study was neat 60/70 penetration grade bitumen. The binder
wastested for penetration, ductility, softening point, specific gravity test and flash point standards.
Theproperties and requirements are presented in Table 3.3.
Table 3.3: Physical properties and requirements of Binder
Description of Test Test Results Requirements as
per IS 73:2002
Penetration at 25°C, in 1/10th of mm 66 60-70
Softening Point, °C 53.5 45-55
Ductility at 27°C, cm 79 Minimum 75
Specific gravity at 27°C 1.02
Flash point, °C 262 Minimum 175

4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online), Volume 5, Issue 8, August (2014), pp. 62-67 © IAEME
65
3.4 Cantabro Abrasion Test
The Cantabro abrasion test was conducted and the percentage losses inabrasion were
calculated. The results are shown in Table 3.4.
Table 3.4: Results of Cantabro Abrasion Loss of Marshall Specimens
Binder
Content, %
Bulk
density, g/cc
Theoretical
density, g/cc
Volumetric Properties Cantabro
abrasion
% voids % VMA %VFB loss
3.5 1.985 2.552 22.21 28.99 23.39 28.67
4 2.015 2.534 20.485 28.345 27.74 24.49
4.5 2.038 2.517 19.01 27.96 32.01 21.71
5 2.055 2.499 17.655 27.69 36.25 16.78
3.5 Selection of Optimum Binder Content
A graph is plotted with % voids and Cantabro abrasion loss on Y axis and binder content on
X axis. The binder content corresponding to 20% air voids and 20% abrasion loss is taken to be the
optimum binder content for the porous asphalt mix. The Graph is shown in fig. 3.1.
Binder content corresponding to 20% voids = 4.2%
Binder content corresponding to 20% abrasion loss = 4.7%
Optimum binder content = (4.2+4.7)/2 = 4.45%
Figure 3.1: Selection of OBC for porous asphalt mix
3.6 Permeability Tests
Constant head and Falling head technique were used to determine the coefficient of
permeability porous asphalt mix. The results are presented in Table 3.5.
The use of constant head or falling head technique for measuring permeability is assessed by
regression method. From Fig. 3.2 3.3 it is seen that by Constant head technique there is high
correlation between permeability and % voids (R2 = 0.962) whereas the falling head technique has
low correlation between permeability and % voids (R2 = 0.767).

5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online), Volume 5, Issue 8, August (2014), pp. 62-67 © IAEME
66
Table 3.5: Permeability of Porous asphalt mix by Constant and Falling head technique
Compaction
Level
Bulk Density
g/cc
% Voids
Coefficient of Permeability, m/day
Constant Head Falling Head
50 1.912 24.07 9.14 9.25
65 1.966 21.90 7.2 7.17
75 1.982 21.27 5.68 6.99
90 2.036 19.14 4.33 6.83
Figure 3.2: Variation of Permeability with % voids measured by Constant head technique
Figure 3.3: Variation of Permeability with % voids measured by Falling head technique

6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online), Volume 5, Issue 8, August (2014), pp. 62-67 © IAEME
67
3.7 Indirect Tensile Strength Test
The Marshall specimens of the porous asphalt mix were prepared at OBC, conditioned in water
bath at 25°C for 2 hours prior to testing. The test specimens were then placed in the loading frame
and load was applied to cylindrical strips at rate of 50mm/minute. The ultimate load to failure was
recorded. The results are presented in Table 3.6.
Table 3.6: Results of Indirect Tensile Strength of porous asphalt mixes
Compaction
Level
Bulk Density
g/cc
% Voids
Indirect Tensile Strength
N/mm2
50 1.912 24.07 0.175
65 1.966 21.90 0.215
75 1.982 21.27 0.320
90 2.036 19.14 0.371
4. CONCLUSIONS
1. From Table 3.2 it is observed that the mix is gap graded with 83.5% coarse aggregates and
16.5% fine aggregates.
2. From Table 3.4 it is observed that with the increase in binder content from 3.5% to 5% the
abrasion loss reduces from 28.67% to 16.78%.
3. From Table 3.4 it is observed that with increase in binder content from 3.5% to 5%, the bulk
density marginally increases from 1.985 g/cc to 2.055g/cc and air voids content reduces from
22.21% to 17.66%.
4. From Table 3.4 it is observed that as compaction increases from 50 to 90 blows the bulk
density increases by 6.1% and air voids decreases by 20.5%.
5. The Coefficient of permeability can be measured by Constant and Falling head methods. The
Constant head method has higher correlation coefficient than Falling head technique and hence
Constant head method is more suitable for measurement of permeability of porous asphalt
mixes.
6. From Table 3.6 it is seen that as compaction increases from 50 to 90 blows the Indirect Tensile
Strength increases by 53%.
5. REFERENCES
1. Kunnaweekamitpong, Robert Schmidt, Hussainbahla, Jeffrey Russell Comparison of
laboratory and field permeability of HMA mixtures TRB 83 annual meeting.
2. G.W. Maupin Jr, “Investigation of test methods, pavements and laboratory design related to
asphalt permeability” Virginia transportation research council, June 2000.
3. L. Allen Cooley Jr. E. Ray Brown SaeedMaghsoodloo “Development of critical and pavement
density values for coarse graded pavements” NCAT report, Sep 2001.
4. Qing lu, Sang lau, John T Harvey “Compaction of noise reducing asphalt mixtures in the
laboratory” TRB 89 annual meeting.
5. Rebecca S. McDaniel, William D. Thornton, Jorge Gomez Dominguez “Field evaluation of
porous asphalt pavement” The Institute for Safe, Quiet and Durable Highways, May 2004.
6. Dr. Talal H. Fadhil, Salah S. Jasim, Dr. Kahlil E. Aziz and Ahmed S. Ahmed, “Influence of
using White Cement Kiln Dust as a Mineral Filler on Hot Asphalt Concrete Mixture
Properties”, International Journal of Civil Engineering Technology (IJCIET), Volume 4,
Issue 1, 2013, pp. 87 - 96, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.