EXPERIMENTAL INVESTIGATION OF GEOTEXTILES IN ASPHALT CONCRETE

PAVEMENT

Adnan Qadir, Professor, Department of Urban and Infrastructure Engineering, NED University of

Engineering and Technology, University Road Karachi, Pakistan

E Mail: adnan@neduet.edu.pk

June 1, 2013

uc11081

6/1/2013

Adnan Qadir 1

.

ABSTRACT

The asphalt pavement roadways networks in Pakistan experience severe distresses in the form of

rutting (permanent deformation) and fatigue cracking. The prime reason behind such a pathetic

conditions are attributed to many factors such as incorporation of inferior quality construction

materials, hypothetically designed layer thicknesses, misconstrued traffic loadings and Spartan

temperature differences to name few. The ultimate result is therefore premature failure of pavement

before completing its envisioned design life. It is therefore become imperative to either improve the

quality of construction materials and/or fit in reinforcement materials in asphalt pavements for

strengthening its response. The presented study is thus an attempt to investigate the effectiveness of

integrating geotextile in asphalt concrete pavement. The geotextile was introduced as a sandwiched

layer between old and new asphalt concrete layers and were subjected to rutting in wheel tracking

device. The controlled samples (without geotextile material) were also made and tested to draw the

comparison. It was found that the introduction of geotextiles resulted in 40% less rut depth as of

control samples, making them more appealing to be investigated further.

Key Words: Rutting, Geotextile, Overlay

Adnan Qadir 2

INTRODUCTION

High quality roads are very important for the development of a country. Road transportation can be

rightly regarded as the most important mode of transportation as it complements all the other modes.

Owing to the importance of roads, attempts are made constantly to come up with measures to make

the roads durable and effective. There are a number of challenges which need to be completed in

order to provide safe, smooth, rapid, efficient, environmental friendly and economic roads. One of the

main challenges in the flexible pavement is pavement distresses. These distresses affect the properties

of roads in terms of bad riding quality, energy losses, safety issues and economic losses. The severity

of these distresses changes with different factors like soil condition, weather, loading etc. One of the

common distresses in the pavement is rutting. Rutting is defined as the accumulation of small

amounts of unrecoverable strains resulting from applied loads to the pavement. This deformation is

caused by the consolidation, a lateral movement of the HMA under traffic, or both. Shear failure

(lateral movement) of the HMA courses generally occurs in the top 100 mm of the pavement surface

[1]. The factors causing rutting are poor mix design, poor construction procedure, excessive loading,

and inadequate drainage system. Pakistan has 260,000 km of roadways network with an estimated

asset value of over 2500 billion Rupees [2]. This network widely carries 91% passenger traffic and

almost 96% of the freight traffic [2]. The majority of the roads in Pakistan are in poor condition. The

distresses like permanent deformation in the wheel path (rutting) and fatigue cracking degraded the

condition of the roadways network making them unsafe for the daily users and affecting the country’s

economy. Pavement condition survey in 2010[3,4] suggested that 41% of the National Highway

(NHA) lost its structural integrity and load carrying capacity. The survey data showed that 58% of

the NHA network suffers from some sort of rutting that affect mobility and users

safety. Approximately 27% of the NHA network poses a serious safety hazard where wheel path ruts

more than 25mm as shown in Figure 1[5]. This is primarily due to under-designed layer thickness,

under-estimated truck loading, severe temperature variation and/or construction faults. While

increasing the pavement structure layer thickness is a viable solution to those distresses, the cost

associated with such alternative is dramatically high. Unfortunately, the gap between the funds

required and available for maintenance and rehabilitation activities has never been bridged since

1999[6]. In this scenario it is crucial to research for materials that could be incorporated in pavements

for making them more resistant to distresses, durable and last longer. Such pavements will have

greater service life than the conventional pavements and will, therefore, require lesser maintenance.

FIGURE 1 Rutting in Kashmir and Islamabad Highway (Khan, 2008)

Conventional material utilized in construction of the pavement in the past to curb rutting have not

been successful to-date and the focus has now been shifted to use the materials that are smart enough

to increase the resistance in pavement and make it durable against excessive loading and temperature

condition to address rutting. The incorporation of Geotextiles in flexible pavements is a very

common occurrence and numbers of research deliberations are available at various forums justifying

its presence in a pavement. In Pakistan, unfortunately little or no work has been undertaken to study

the application of geotextiles in the pavement especially during overlaying the pavement. The

presented study is thus an effort to highlights the importance of geotextiles in the pavement

application.

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OBJECTIVES AND SCOPE The proposed study was aimed to ascertain the effectiveness of using Geotextile in asphalt concrete of

pavement so as to increase its service life by meeting the following objectives:

Evaluate the effectiveness of geotextile against mix-rutting in HMA samples by incorporation of

geotextile , sandwiched between two layers (a rutted layer and a new layer) of a sample and

testing in wheel tracking device at standard load and maximum temperature available in the

machine

Draw comparisons for rutting susceptibility tests on samples with and without geotextile

material.

The scope of this project included the preparation of samples for rutting tests with and without

geotextile material. Samples without geotextile material were referred as control samples. The

Optimum Asphalt Content OAC was determined using the Marshall Mix Design Method. The rutting

test was conducted at temperature of 60°C, 10,000 load passes and application of a default load of 700

N in Wheel Tracking Device. The scope of this research was limited to investigation of mix rutting

only and placement of geotextile in the center of the prepared sample for rutting test.

LITERATURE REVIEW

From the perspective of the American society for testing and materials, geosynthetic materials are a

planar product that are mass-produced from polymer material and can be used as a reinforcement in

any civil engineering structure or system. geosynthetics are a non woven textile fabrics with wide

range of application in building, geotechnical, highways and rail infrastructure. Such type of

geosynthteic are also commonly known as geotextile. Geotextile plays a significant part in modern

pavement especially to control rutting. Geotextile are also known to extend the service life of roads

as well as to increase the load carrying capacity. This is because of the fact that the addition of

geotextile increases the overall elasticity of the pavement that helps in reducing the accumulation of

tensile strains by relieving the stresses. The description available [7] about application of geogrids in

asphalt layer claims that concluded that with the of appropriate geotextile material has the capability

to interrelate with the asphalt concrete layer to enhance its ductility, restraining strains and

eventually reduces the crack being developed even if the crack appears it is kept to its minimum

value. The manufacturer also claims that the geotextile s reduces superficial rutting normally

attributes to asphalt mixes having low stiffness’s.

The placement of geotextile in asphalt concrete is a serious matter and is being investigated by many

researchers. A study was undertaken by [8] to optimize the location of geotextile material in asphalt

concrete to minimize rutting. Three point beam bending and shearing test were performed on

reinforced (with geotextile) and non reinforced beam specimens at different locations within the

beam. Their test result suggests that geotextile must be located below the center of asphaltic concrete.

A research on the use of geotextile material [9] found that the rutting are dependent upon the elasticity

of asphalt concrete as well as the viscosity of asphalt binder used. The research was based on the plate

load test applied to specially constructed test section of roads in the city of Vilnius (Lithuania). The

research also concludes that the rutting depth is also influenced by the type of geosynthtic material.

The author recommend that use of geogrids (geo composite) will help in reducing the shear strains

and rutting. A study reported by [10] for assessment of geogrids in railways and asphalt application

shows that the use of geogrids are instrumental in reducing the accumulated permanent strains in the

asphalt concrete. The study finds that the introduction of geogrid raises the stiffness of the asphalt

pavement that eventually impedes production further tensile strain and consequently helps in keeping

rut depth to minimum. The author concluded these results on the basis of performance of fatigue test,

wheel tracking device test and using pavement testing facilities (large wheel application) on control

and modified samples. The experimental work consists of three cross section of asphalt pavement

subjected to repeated loading. The first cross section was unreinforced, the second section was

reinforced from the base, and the third cross section was reinforced from the mid depth. The result

shows that the cross section which is not being reinforced exhibit both cracking and rutting. The

second section which is reinforced from the base prevents fatigue cracking and rutting. This

investigation has concluded that with the use of geotextile one could prevent both rutting and fatigue

cracking. The researcher studied that with the use of geotextile pavement life extend to a factor of 2.5-

3 as compared to the section which haven’t used geotextile.

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EXPERIMENTAL DESIGN

Studies like the one presented here needs careful estimation of the samples needed to be prepared so

that the adequate amount of material is procured and the investigation are completed well in time. The

experimental design adopted in this study is illustrated in the form of flow chart as illustrated in

Figure 2.

FIGURE 2 Experimental setup

MATERIAL SELECTED

Material play vital role in any experiment. Experimental result changes with the change in properties

of the material. In this study three types of material were used (aggregates, asphalt and geotextile

material). Aggregates were obtained from local quarries and were tested for its basic properties like

Loss Angeles abrasion and specific gravities. Penetration graded asphalt 60-70 was used in this study

to follow the recommendation for the region by the local highway authoriy. The aggregate and

asphalt properties are illustrated in TABLE 1.

TABLE 1 Properties of Aggregate and Asphalt Aggregates Asphalt

Description Value Description Value

Aggregate type Limestone Penetration, mm 63

L A Abrasion, % 23 Specific gravity 1.03

Bulk Specific gravity 2.620 Flash Point , F 178

Bulk Specific gravity, SSD 2.632 Fire Point, F 232

Apparent Specific gravity 2.653 Softening Point, C 44

Average absorption, % 0.500 Ductility, mm 85

The aggregates gradations termed as class B locally were used for the preparation of asphalt concrete

mix according to local standards, and is being illustrated graphically in figure 3.

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FIGURE 3 Aggregate gradation in the study.

The geotextile material used in this study is technically known as Geocomposite, which actually is a

combination of a geotextile and a geogrid. This type of geotextile is a non-woven mat 2 mm thick,

consisting of planar mesh having fiberglass yarn as a base that is adequately crusted with modified

asphalt. It can be simulated as knitted warp having orientated structure that provides adequate yarn

strength and enhances the mechanical properties such as tensile, tearing and creep-resistant strengths.

The manufacture also claims that the geogrid has admirable compliance for accommodating

temperature changes and is proven to have insignificant stretch values combined with sound alkali

resistance[11]. It is because of this property it can be recommended to be used for reinforcement of

old asphalt roads. The geogrid used in the study is being illustrated in figure 4.

FIGURE 4 Geotextile used in the study

RESEARCH METHODOLOGY AND PREPARATION OF SAMPLES

The methodology adopted in this study is actually an attempt to introduce reinforcement between two

layers of asphalt pavement so that it can act monolithically and the load transfer from the overlaid

layer to the old layer is gradual. Another thing important before overlay is the way the existing

Adnan Qadir 6

depressions are leveled, the study did not tried to mill the surface of the rutted sample since the

milling machines are not very economical as well as readily available in the region hence it is easy to

apply the leveling course rather to mill the surface before overlaying. One more novel approach

adopted in the study is the application of the tack coat material that is normally recommended for

normal overlay and no special material was used to glue the geotextile to the asphalt concrete.

The experimental work consisted of preparation of rutting samples namely control and

modified (in which geotextile material was used) but before that it was pertinent to keep air void

content same for each type of rutting samples. This was required because the rutting is also affected

by varying the air void content and since the objective of the research was limited to one variable

(geotextile addition) only and hence it was important to keep the air void constant in the mixes

prepared for testing.

Marshall Mix design methodology was adopted to calculate the optimum asphalt content for a

sample preparation at target 5 percent air voids. The optimum asphalt content was found to be 4.7%.

Further replicates samples were also prepared to confirm the control of air voids obtained

theoretically. Later on the bulk density measurement of the replicated samples helped in determining

the quantity of material required to be mixed and obtain desirable compacted sample for testing

against rut resistance.

The study actually prepared rutting samples in two phases, in the first phase eight control

samples of two (2) inch thickness were prepared. After compaction the HMA sample was taken out

from the mound and placed carefully on an even surface to cool and harden. The sample was left

undisturbed for at least a day to allow for sufficient aging. After 24 hours elapsed the sample was

placed again in the mould. The mould was then placed in the wheel tracking device. These samples

were then tested in the rutting machine at 60°C temperature and for 10,000 passes (5000 load cycles).

In the second phase samples were transferred into 4 inch mould, the depression was filled and tack

coat applied. Geotextile were placed in four of the samples and then the mix material was spread over

the geotextile and sample was compacted in the vibratory compactor. Four more samples were also

prepared in the same manner but without geotextile between it. Hence a total of sixteen samples were

mixed, compacted and tested for rutting. The Compacted samples are illustrated in figure 5 while the

rutted sample is shown in figure 6.

FIGURE 5 Compacted samples.

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FIGURE 6 Sample after rutting test.

RESULTS AND DISCUSSION

Figure 7 shows the average result of rutting test of three controlled and modified samples and from

the figures it is clearly observed that rutting depth is less in modified sample as compared to

controlled samples meaning that geo-composites are effective in controlling rutting. The reasons for

such behavior is expected and also found consistent with the available literature [9]. This is because of

the ability of geotextile to act as reinforcement and to control the critical tensile strain in the asphalt

concrete.

The reduction in rutting is also may also be due to the fact that the presence of geo-composite has

increased the overall modulus of elasticity resulting in more ductile behavior. The cause of reduction

in the values of rutting as against control sample is also because of the viscoelastic behavior of asphalt

that become soft at higher temperature and ultimately lose control of aggregate in binding, the

presence of geo-composite is thus become valuable in keeping the particles intact. Moreover the geo-

composite also reduces the shear strains in asphalt concrete layers consequently keeping rutting to

minimum. Also the fabric present in the geotextile enthralls asphalt from the bond and performed as a

stress respite membrane. The fabric also acts as a barricade to support the deterrence of water

inflowing to the pavement underneath level.

FIGURE 7 Rutting performances of controlled and modified samples.

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6 7 8 9 10

Ru

t D

epth

(m

m)

Number of Passes (Thousands)

Modified sample Controlled sample

Adnan Qadir 8

Another interesting finding of this study is the way geotextile has helped in controlling the rutting

from recurrence. The average rutting of 50 mm sample was found to be 9.17 mm whereas after

overlaying with control material it was curtailed to 4.5 m while the modified samples kept the rutting

to below 4 mm, hence the rutting were minimized to nearly 60% by using the geotextile

reinforcement(Figure 8).

FIGURE 8 Average Rutting in 2 inch and 4 inch samples.

CONCLUSIONS

The study was conducted in order to know what advantages can be obtained by inserting a geotextile

material before laying an overlay on the pavement. Accordingly samples were rutted first in a wheel

tracking device and leveled, tack coated, layer inserted and one more layer was compacted and then

tested again for rutting. It must be noted that though both samples have a rut depth less than 10mm

which is the maximum recommended by the Asphalt institute [12] but since the samples were tested

at 10000 passes, it is envisaged that with more number of load passes the controlled sample will fail

much earlier as compared to modified samples. This is evident from the observation summarized in

Table 2, which elaborate following facts in the study.

1. Rut depth of modified sample on 5000 passes was 30% less as compare to control sample.

2. Rut depth of modified samples on 10000 passes was 40% less as compare to control sample

3. Geotextile was found to be 40% more effective in control of rutting in long life as compare to

control sample.

TABLE 2 Effective Rut Depths on Difference Passes No. of Passes Modified Control % Effective

5000 2.31 3.76 30

10000 3.09 6.28 40

RECOMMENDATIONS

It is recommended that future study may consider of the effect of following on rutting behavior of

asphalt concrete.

The study has considered only one variable, however the effect of other variables like

different temperature and different load condition must be evaluated before the material is

recommended

Though the study conducted used the center depth criteria, a complete optimization of

position of geosynthetic material is needed to get better results.

Adnan Qadir 9

ACKNOWLEDGEMENT

The author would like to acknowledge the efforts made by the final year student of Civil Engineering

department for their laborious work to make study presentable at some forum.

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