CHAPTER TWO
LITERATURE REVIEW
2.1
Introduction
Like other hot mix asphalt, porous asphalt consists of a mixture of aggregates, filler
and binder. Apart from binder type, the binder or asphalt content must be carefully
selected. If the asphalt content is too high, binder drainage will occur and if on the
other hand, the mix will not be durable
(Brown and Mike, 1996). Any binder used
in a porous mix should posses strong cohesion force so that a stabilized mix can be
achieved but simultaneously maintaining an open structure. According to Adnan
(1990), conventional bitumen cannot exhibits the required binding properties and
hence the use of modified bitumen was needed. The use of porous mix with additive
improved the properties of porous mix.
Shuler and Hanson (1990) observed an
increase in resistance to stripping due to water action when hydrated lime was used as
the filler.
2.2
Properties of Bitumen
Bitumen is widely used as a construction material in civil engineering but its
mechanical properties are more complex than typical civil engineering materials such
as steel, cement or concrete (Whiteoak, 1990). Bitumen can be described as a viscous
liquid, or a solid, consisting essentially of hydrocarbons and their derivatives, which is
soluble in trichloroethylene and is substantially non-volatile and softens gradually
when heated. It is black or brown in colour and possesses waterproofing and adhesive
properties. It is obtained by refinery processes from petroleum and is also found as a
5
natural deposit or as a component of naturally occurring asphalt, in which it is
associated with mineral matter BS 3690 (BSI 1989a).
2.2.1
The Ideal Binder
The most important property of bitumen when it is used in road construction is the
way its stiffness changes with temperature (Simon, 1996). Ideally a binder is required
to be stiff enough at elevated temperatures so that it can resist deformation while
flexible enough at low temperature so as to inhibit cracking.
An ideal binder must exhibit the following properties (Mustafa et al. 2000):
(a)
Sufficient rigidity in order to minimize the rutting during hot day. In
addition, it must have positive effect on the fatigue life of the bituminous
hot mixture.
(b)
Flexible enough (during cold temperature) in order to avoid thermal cracks.
(c)
It must make the pumping process of the liquid binder faster and hardness
(or viscosity) should be decreased to facilitate mixing and compaction of
the hot bituminous mixtures.
2.2.2
Rubberised Bitumen
Rubber has been blended with bitumen to improve its properties. The benefits of
blending rubber with bitumen are well documented (Summers, 2003). Among others,
it increases its elasticity and increases its softening point. These benefits will be
passed on to the bituminous mix that incorporates the rubberised bitumen. Rubberised
bitumen has been mainly used for the wearing course with a fair degree of success for
over 30 years.
Its action in a bituminous mix is similar to that of synthetic
6
thermoplastic rubbers.
According to Summers (2000), the original trial work
involving rubber in bituminous mixes was conducted in Leicestershire in conjunction
with the then Transport Road Research Laboratory and rubber companies.
In Malaysia, rubberised bitumen is equally used for resurfacing jobs for roads and
airports. The use of rubberised bitumen for road pavement has increased substantially
in the last several years. According to Mustafa and Sufian (1997), rubber additives for
road construction had been used in this country since the 1940’s but there has not been
any recorded evidence of such practices. The evidence available indicated that rubber
was used in the early 1980’s. However, these works were also not monitored and as a
consequence there were no published reports on it. The Public Work Department
(PWD) started monitoring and reporting the use of rubber additives for its road
construction since the late 1980’s.
The first recorded trial was in 1988 for the
rehabilitation of Jalan Vantooran in Kelang. Subsequently, several more field trials
were constructed under a collaborative agreement between the PWD and Rubber
Research Institute of Malaysia (RRIM). The trials used varying forms and techniques
of incorporating rubber. Some examples of field trials involving rubberised bitumen is
shown in Table 2.1.
Table 2.1 Field Trial Sites Involving Rubberised Bitumen in Malaysia
(Mustafa and Sufian, 1997)
Trials Sections
Date of
Construction
Rembau-Tampin
December 1993
Sungai Buloh
December 1997
Kuantan - Gambang
2002
Types of Rubber Additives
Rejected glove rubber powder,
tyre shaving and latex
Tyre shaving
Rejected tyre-rubber powder
7
Generally, based on research done by Fernando and Guirguis (1984), Anderten (1992),
Mustafa and Sufian (1997), the addition of rubber has the following effects on the base
binder:
(a)
Increase in high temperature viscosity
(b)
Reduce temperature susceptibility
(c)
Improve in ageing resistance by reducing the oxidation process
(d)
Increase flexibility of the mix
(e)
Increase stiffness modulus
(f)
Increase resistance to rutting
2.2.3
Rubberised Mixes
A type of rubber that has been extensively used to modify bitumen is crumb rubber
obtained from used vehicle tyres and which is indeed a waste material.
These
modified materials, popularly described as crumb rubber modified (CRM) bituminous
materials, have the added environmental benefit of recycling scrap tyres that would
otherwise be stockpiled or used in landfills. The use of recycled scrap tyres in asphalt
mixture applications is not a recent development with reclaimed tyre crumb being used
in the asphalt industry for over 30 years (Airey et al. 2004).
Reclaimed tyre crumb can be incorporated into asphalt mixtures using two different
methods, referred to as the wet and dry process. In the wet process, rubber and
bitumen are digested together at high temperature to produce a crumb rubber binder.
The crumb rubber binder is added to aggregate in a mixing plant in the same way as
any other binder. In the dry process, however, dry rubber particles are added to
aggregate and bitumen in a pugmill or drum mixer at the asphalt mixing plant. The
8
rubber is usually mixed with the aggregate prior to bitumen addition but is still
considered part of the binder. According to Oliver (2000), the wet process has the
advantage that the binder properties are better controlled, while the dry process is
easier in terms of the logistics for marketing.
2.2.4
Polymer Modified Bitumen
According to Summer (2002), the term “polymer” does not automatically mean a
synthetic material. It basically means a combination of a large number of similar
small molecules or “monomers” into large molecules or “polymers”. The polymer has
different properties to the monomer. There are a large number of naturally occurring
polymers which can be organic or mineral substances. Such natural examples of
polymers include hair, rubber, diamonds and sulphur.
Even bitumen could be
regarded as a polymer because of the long-chain nature of some of the organic
molecules that are the constituent parts of bitumen.
The way the polymer usually influences the bitumen characteristics is by dissolving
into certain component fractions of the bitumen itself, spreading out its long chain
polymer molecules to create an inter-connecting matrix of the polymer through the
bitumen. It is this matrix of the long chain molecules of the added polymer that
modifies the physical properties of the bitumen. Due to the thermoplastic nature of the
polymers, some polymers will actually break up into their constituent molecular
blocks at high temperatures, during mixing and laying and recombine into their
polymer chains at lower temperatures (Summer, 2002).
9
2.3
Drain Asphalt Modified Additive
Drain Asphalt Modified Additive (DAMA) is a type of additive which was developed
by Darintech, Korea for use in a wide range of highway and airfield paving
applications especially open mixes. The constituent materials of DAMA are fine
elastomer powder, fine crumb rubber modifier and other substance that asserts
outstanding capability in manufacturing of polymer modified asphalt mixtures.
Thermoplastic epoxy is dissolved in 140oC or higher to merge with asphalt that it
clearly improves the physical properties.
Ecological asphalt (Ecophalt) pavement is a type of porous asphalt using DAMA
which was developed by Darintech. This asphalt mixture has about 20% air voids.
The effects of using DAMA is to reduce permanent deformation especially at elevated
temperatures and heavy duty load, increase dynamic elasticity under low temperature
and to slow down the process of ageing. The advantages of porous asphalt using
DAMA was confirmed by ecophalt pavement laboratory and field investigations
which include a 50% to 80% noise reduction, improved skid resistance and reduce
aquaplaning potential (Ecophalt Pavement, 2000). Other materials added are meant to
prevent the aging of asphalt and subsequently increase the durability of pavement.
2.3.1
Aggregate Material
In Korea, Ecophalt is made up of 19 mm and 13 mm granite aggregate while sand is
the fine aggregate fraction used. The basic aggregate properties are summarised in
Table 2.2.
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Table 2.2 The Properties of Aggregate Material (Ecophalt, 2001)
Test
Code
KSF
2503
Test Items
Specific
Gravity
Water
Absorption
(%)
Abrasion loss
(%)
Specification
19mm
13mm
Sand
Filler
>2.45
2.603
2.584
2.616
2.700
KSF
2503
<3.0
1.302
1.295
0.752
-
KSF
2508
<35
13.317
12.977
-
-
The aggregate gradation, which is a combination of 19 mm, 13 mm, sand and filler is
shown in Table 2.3.
Table 2.3 Aggregate Gradation (Ecophalt, 2001)
26.5 mm
Maximum Particle
Size  13mm
-
Maximum Particle Size 
19mm
100
19 mm
100
95-100
13.2 mm
92-100
53-78
9.5 mm
62-81
35-62
Sieve Size
2.3.2
4.75 mm
10-31
2.36 mm
10-21
300 
3-12
75 
2-7
The Composition of DAMA
DAMA is a type of polymer modified additive that was formulated to enhance
the quality of the asphalt mixture.
DAMA is a minute particle composites of
petroleum thermoplasticity resin, rubber particles obtained from high quality worn-out
tyres and other materials. The characteristic feature of this additive is the relative ease
in which it can be incorporated into an asphalt mixture by mixing the thermoplasticity
11
vinyl additive in the mixer at a regular asphalt plant. When this additive is used in
drain asphalt concrete pavement, it can greatly improve the bonding between
aggregate and bitumen in pavement. The rubber particles chipped from worn out tyres
have protective characteristics from ultraviolet rays and anti-oxidation.
These
properties greatly enhanced the durability of porous pavement so as to be used in high
performance road pavements.
2.3.3
Production of Mixture
The two most important factors that must be taken into consideration in the production
of the Ecophalt paving mixture are mix temperature and mixing time. The critical
values are described in Tables 2.4 and 2.5.
Table 2.4 Standard for Temperature Management for Ecophalt Paving Mixture (ºC)
(Ecophalt, 2001)
Temperature Regime
Standard
Heating Temperature of Aggregate
190 ± 5
Heating Temperature of Bitumen
170 ± 5
Temperature of Discharge Mixture
180 ± 5
Table 2.5 Mixing Time (Ecophalt, 2001)
Factors
Mixing Time (sec)
Supply of Aggregate
4-5
Dry Mixing
5-7
Wet Mixing
40 or more
Discharge, etc.
6-8
Total
55-60
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The supply of DAMA should begin just after the initialization of the asphalt injection.
In dry process of Ecophalt mixes, the selection of temperature must be right since the
mixes contain small quantity of fine aggregate. The quality standard of the Ecophalt
paving mixture is described in Table 2.6.
Table 2.6 Quality Standard of Ecophalt Paving Mixture (Ecophalt, 2001)
Items
Quality Standard
Maximum Particle Size Maximum Particle Size
of Aggregate  13 mm
of Aggregate  19 mm
Void Fraction (%)
20 or more
20 or more
Marshall Stability (kg)
500
350
Flow (1/100 cm)
20-40
20-40
Residual Stability (%)
75
75
Blows (Double-sided)
50
50
2.3.4
Laboratory Test Results
From results conducted in Korea, the hot mix asphalt (HMA) design was used to
determine the optimum binder content of HMA. The test results of drain graded 13
mm and 19 mm mixes with varying percentage of DAMA 0%. 0.5% and 1% of the
bituminous mixture are shown in Table 2.7 and 2.8, respectively. Table 2.7 shows the
porosity and binder content of each HMA.
Table 2.8 exhibits coefficient of
permeability and abrasion loss ratio of drain graded 13 mm and 19 mm.
The abrasion loss decreases as the quantity of DAMA increases and this indicates the
effectiveness of DAMA to improve resistance to disintegration. The porosity slightly
decreased with increasing amount of DAMA content.
13
Table 2.7 Porosity and Asphalt Binder Content (Darin Tech, 2001)
Type of
HMA
Drain
graded
13 mm
Drain
graded
19 mm
DAMA 0%
Design
Porosity
Binder
(%)
Content
DAMA 0.5%
Design
Porosity
Binder
(%)
Content
DAMA 1%
Design
Porosity
Binder
(%)
Content
20.17
5.0%
19.78
5.0%
19.37
5.0%
19.45
4.8%
20.8
4.8%
18.77
4.8%
Table 2.8 Coefficient of Permeability and Abrasion Loss Ratio (Darin Tech, 2001)
Type of HMA
Drain Graded
13mm
Drain Graded
19mm
2.4
DAMA (%)
Coefficient of
Permeability (cm/sec)
Abrasion Loss
Ratio (%)
0
7.06 × 10-2
41.96
0.5
6.85 × 10-2
28.65
1
7.35 ×10-2
17.06
0
6.95 ×10-2
36
0.5
7.43 ×10-2
24.79
1
8.76 ×10-2
15.73
Global Application of Porous Asphalt
Historically, porous asphalt was developed to mitigate road accidents but now the
prime mover, especially in Europe on grounds of traffic noise reduction. The United
States of America has some of the earliest initial experience with open mixes. Opengraded friction course (OGFC) has been used since 1950 in different parts of the
United States to improve the surface frictional resistance of asphalt pavements
(Mallick et. al. 2000). OGFC improves wet weather driving conditions by allowing
the water to drain through its porous structure away from the roadway.
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In early November 1991, one of the first commercial porous asphalt contracts in the
United Kingdom took place in Dorset on a stretch of the A351 Wareham Bypass
(Shell Bitumen, 1992). Hampshire County Council had two trial sites on the A31.
One short length between Winchester and Airesford and a longer section laid in 1995
on the Bently by-pass (Rushmoor, 1998). Following the use of this material on the
center section of the A331 Blackwater Valley Relief Road by Surrey County Council,
excellent noise reduction qualities and markedly less spray in wet weather compared
to conventional surfacing were noted.
After years of experience and research, Heijmans Civil engineering at Rosmalen
developed double layer porous asphalt to mitigate clogging and further improve noise
reduction. The double layer porous asphalt appears to be the latest technology of
porous asphalt.
Test sections of this construction have been in use since 1990
(Bochove, 1996). In 1996, the town of Breda has approximately 50,000 m2 of this
type of surface course. The new concept consists of a double-layered porous asphalt
construction, made up of a bottom layer of coarse porous asphalt and a top layer of
fine-graded porous asphalt.
The first application of porous asphalt in Spain was in 1980 on four
experimental road sections on one of the northern highways prone to frequent rainfall.
Initially, the objective was to use these mixtures in rainy areas in order to improve
traffic safety and comfort on wet surfaces. The favorable results obtained from these
mixtures have promoted the construction of new experimental pavements and small
projects to be carried out in the next few years. By 1986, this material started to be
used extensively. Now, the purpose for using this material has changed. It is not only
15
used to improve driving conditions in the rain, but also to provide a durable surface,
with a smooth, safe and quiet ride in any type of weather. In 1990, Spain has 3 million
m2 of porous asphalt roads. Porous asphalt is being used for all types of traffic
conditions and for any type of roads and highways. According to Ruiz et. al. (1990)
the most notable projects are the 44 km (500,000 m2) on Highway N-VI.
The
highways were between Las Rozas and Villalba carrying some 20,000 vehicles per
day per carriageway and 2,000 of which were trucks (13 ton axle load). The 70 km
highway (about 800,00 m2) on the toll road between Bilbao and Behobia, with about
9,000 vehicles per carriageway of which 1,200 were trucks and the 33 km (400,000
m2) in ACESA toll roads with traffic varying between 800 and 1,800 trucks per day.
According to Darin Tech (2004), roads in Korea have been paved with latest porous
asphalt paving technology since the late 1960’s. Nevertheless, after more than 3
decades, the inherent problems with the asphalt concrete pavement, which were the
deterioration of the structural elements at high temperature and cracking at low
temperature, have not been solved satisfactorily. The road pavement in the city and
important highways, where heavy vehicles pass through, were subjected to
deformation or rutting especially due to high temperature in the hot day and low
temperature cracking due to repetitive loading especially in cold temperature. In order
to overcome these problems, improved mix hot mix asphalt (HMA) design procedure
and using lower penetration binder have been tried in the past and has met with some
improvements. Nowadays, new additive materials have been developed to improve
the physical and chemical properties of asphalt binder.
16
Systematic investigation has been performed on construction material and material
mixtures, which had been used for the construction of the Federal Motorway A2 in
Lower Saxony Germany, in order to develop criteria for the optimization of porous
asphalt (Renken, 1998). This new generation of porous asphalt surface course is
already used for more than 4 years in different sections of the Federal Motorway A2.
Many European countries have carried out experiments on the use of porous asphalt in
an attempt to reduce noise levels.
In Denmark, Raaberg et. al. (2000) reported that the use of porous asphalt as wearing
course was suspended for a number of years due to the high number of accidents in
winter conditions in the 1970’s. In 1998, Denmark participated in a joint Nordic
project regarding an examination of Low Noise Road Surfaces and at that point it was
again considered to lay porous asphalt as wearing course.
2.5
Overview of Current Practice of Porous Asphalt in Highway Application
The first porous asphalt application on roads took place in the 1960’s (Reichert and
Bonnot, 1993). However, after about ten years, the use of porous asphalt has grown
rapidly in some countries where the material is used for a large part in road surface
maintenance works on highly trafficked roads. Some countries even impose the use of
porous asphalt on motorways beyond a certain level of traffic.
In the Netherlands, the policy since the end of the nineteen eighties is to apply porous
asphalt as a wearing course material on motorways especially to reduce traffic noise,
splash and spray.
Voskuilen et al. (2004) noted 60% of the Dutch motorways
incorporate a porous asphalt wearing course and their policy is to approach 100 % by
17
2010.
In 2001, the statistics of porous asphalt application in various European
countries is shown in Table 2.9.
Table 2.9 The Statistics of Porous Asphalt Laid in European Countries
2001)
Countries
Area of Porous Asphalt Laid
Netherlands
48 million m2
France
43 million m2
Italy
13 million m2
Germany
2.5 million m2
(EAPA,
In efforts to reduce traffic accidents, porous asphalts were tried in Malaysia. Several
porous pavements were constructed more than a decade ago on expressways and
federal roads in accordance with European specifications.
However, pores were
clogged shortly after in service and ponding water took place. Then, it was decided to
carry out a pilot study using the Japanese technology developed under temperate
climate.
This technology has been successfully modified and applied under
Malaysia’s tropical monsoon climate (IDI-Japan, 2003).
2.6
Laboratory Tests on Porous Asphalt
2.6.1
Marshall Stability
The principal purpose of the Marshall Test was to establish the optimum binder
content required for each of the different binders of dense asphalt. The Marshall
method of optimum binder content determination for porous asphalt is not applicable
because the stability and flow values are insensitive to changes in binder content
(Smith et al. 1974). In porous asphalt, the source of stability is from aggregate
18
interlock enhanced by the stone to stone contact (Edwards, 1973). Typically, Marshall
stability values for porous asphalt are significantly lower than that of dense asphalts.
2.6.2
Rutting
With the exception of a few specific cases (for example the construction of underlying
cross drains in porous mix, in Austria) no permanent deformation of the rut type can
be noted regardless of the mix type used (binder, mix design, etc.), even under the
most severe traffic loads (Lefebvre, 1993). This is due to the small thickness of the
surfacing and to the self-locking characteristic of the granular skeleton of the mix.
This satisfactory behaviour mitigates the results of laboratory rutting tests which, in
some cases, reveal the presence of ruts. Lefebvre (1993) also noted despite its high
voids, porous asphalt exhibits a high resistance to permanent deformation.
Huet et al. (1990) carried out comparative tests on porous asphalt made with pure
asphalt cement, SBS modified asphalt and pure asphalt cement with mineral fibers on
a test track. Overall rut depth after 600,000 cycles is about 5 mm with a slight
advantage going to the SBS modified binders sections. This could result from the high
ring and ball softening point of this binder. From the results of the laboratory wheel
tracking tests at a temperature of 60oC carried out by Jimenez and Gordillo (1990),
mixes fabricated using 4.0% and 4.5% EVA were more resistant to plastic deformation
than mixes prepared using ordinary bitumen. Average rut depths after 1 hour on
unmodified and modified mixes were 5.6 mm and 1.7 mm, respectively.
From
practical observation from field measurements in the Netherlands, an average rut depth
growth of 1.5 mm/year was measured on similar structures with conventional surfaces
(Van der Zwan et al. 1990). In 1984, fifteen trial section of porous asphalt surfacings
19
were laid on A38 Burton, the first measurements were made in 1986, forming a
baseline for subsequent test. Generally porous asphalt does not deform excessively
and the total deformation values from 1986 to 1990 confirmed this. All the surfacings
deformed at overall rates of less than 0.5 mm/year (Colwill et al. 1992). Gerardu et al.
(1985) recorded after 10 years in service a maximum rut depth of 6 mm. Mallick et al.
(2000) conducted tests on the four specimens prepared at design asphalt contents, all
of the rut depths are less than 5 mm after 8000 cycles.
2.7
Summary
This chapter presents an overall literature review of porous asphalt. The main reason
for considering the application of this particular type of road surfacing is the drainage
characteristics of the surface layer.
The drainage is made possible by the large
percentage of voids up to 20% and that are interconnected, allowing water and air to
flow towards the road shoulder.
The use of porous asphalt offers a number of
advantages such as reduce aquaplaning potential, improve skid resistance at high
speed, reduce glare particularly on wet roads and an overall improvement in traffic
safety. On the other hand, the disadvantages of porous asphalt compared to traditional
road surfacings includes short design life, high cost in terms of construction,
maintenance and repair. However, porous asphalt has been applied in increasing
quantities in European countries such as the Netherlands, France, Italy and Germany.
20