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

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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

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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 Types of Rubber Additives

Rembau-Tampin December 1993 Rejected glove rubber powder, tyre shaving and latex

Sungai Buloh December 1997 Tyre shaving

Kuantan - Gambang 2002 Rejected tyre-rubber powder

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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

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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).

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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 Items Test Code Specification 19mm 13mm Sand Filler

Specific Gravity

KSF 2503 >2.45 2.603 2.584 2.616 2.700

Water Absorption

(%)

KSF 2503 <3.0 1.302 1.295 0.752 -

Abrasion loss (%)

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)

Sieve Size Maximum Particle Size 13mm

Maximum Particle Size 19mm

26.5 mm - 100

19 mm 100 95-100

13.2 mm 92-100 53-78

9.5 mm 62-81 35-62

4.75 mm 10-31

2.36 mm 10-21

300 3-12

75 2-7

2.3.2 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

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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)

ItemsQuality Standard

Maximum Particle Size of Aggregate 13 mm

Maximum Particle Size 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.

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Table 2.7 Porosity and Asphalt Binder Content (Darin Tech, 2001)

Type of HMA

DAMA 0% DAMA 0.5% DAMA 1%

Porosity(%)

Design Binder Content

Porosity(%)

Design Binder Content

Porosity(%)

Design Binder Content

Drain graded 13 mm

20.17 5.0% 19.78 5.0% 19.37 5.0%

Drain graded 19 mm

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 DAMA (%) Coefficient of Permeability (cm/sec)

Abrasion LossRatio (%)

Drain Graded 13mm

0 7.06 × 10-2 41.96

0.5 6.85 × 10-2 28.65

1 7.35 ×10-2 17.06

Drain Graded 19mm

0 6.95 ×10-2 36

0.5 7.43 ×10-2 24.79

1 8.76 ×10-2 15.73

2.4 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. Open-

graded 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

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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.

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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

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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 (EAPA, 2001)

Countries Area of Porous Asphalt Laid

Netherlands 48 million m2

France 43 million m2

Italy 13 million m2

Germany 2.5 million m2

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

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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

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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.

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