Construction and Building Materials 26 (2012) 13–20

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Construction and Building Materials

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Review

Analysis of use of natural fibers and asphalt rubber binder in discontinuousasphalt mixtures

Sandra Oda a,⇑, José Leomar Fernandes Jr. b, Jesner Sereni Ildefonso c

a University Federal of Rio de Janeiro, Department of Civil Engineering, Rio de Janeiro, RJ, Brazilb University of Sao Paulo, Department of Transportation, Sao Carlos, SP, Brazilc State University of Maringá, Maringá, PR, Brazil

a r t i c l e i n f o a b s t r a c t

Article history:Received 26 July 2010Received in revised form 28 May 2011Accepted 18 June 2011Available online 26 July 2011

Keywords:FiberDiscontinuousMixtureStone matrix asphalt

0950-0618/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2011.06.030

⇑ Corresponding author.E-mail address: odasandra@gmail.com (S. Oda).

The growth of traffic requires more pavements with high durability and security to users. One of the solu-tions adopted in developed countries is a mixture with discontinuous graduation of type SMA (stonematrix asphalt), which requires a higher content of protecting the asphalt pavement of damage by form-ing a thicker film around the aggregate, which holds up oxidation, dampness penetration and crackingand separation of aggregates. Due to the higher content of asphalt it is necessary to add fiber to avoiddrain down the binder. Bahia was the first state in northeastern Brazil to build an urban stretch withSMA, but without fibers. Despite not meeting the technical recommendations, the pavement did notshow any defect in terms of the absence of fiber. The mixture was produced with asphalt–rubber binderwhich, because of its viscosity, allowed the use of a higher content of asphalt, even without fiber. Theobjective of this paper is analysis the use of natural fibers in mixture of type SMA. The fiber standard(for example, DER-SP) and usually recommended for using in SMA are imported and expensive, resultingin a higher final cost. To reduce the cost and meet standards we intend to use residues available in theregion (coconut and sisal), since Bahia is one of the largest producers of coconut and sisal in Braziland, consequently, of coconut shells and sisal fibers. In this work, there was produced asphalt mixtureswith four fibers: coconut, sisal, cellulose and polyester. The results of mechanical tests (tensile strengthand modulus of resilience) demonstrate that blends with natural fibers showed high resistance, whilepreventing the asphalt to drain down.

� 2011 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142. Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.1. Aggregates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.2. Binder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.3. Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.3.1. Wastes from coconut bark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152.3.2. Sisal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.4. Asphalt mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.4.1. Dosage of asphalt mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3. Analysis of results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.1. Drain down of binder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.2. Volumetric parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.3. Mechanical parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.3.1. Resilient modulus and tensile strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.3.2. Fatigue test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

ll rights reserved.

Fm

14 S. Oda et al. / Construction and Building Materials 26 (2012) 13–20

4. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

1. Introduction

Brazil, like most countries, depends on the highways to trans-port load and passengers. The necessity of a road network able tomeet the production and passengers drainage grows with the in-crease of vehicle fleet and traffic demand [1]. Due to the growthin traffic volume and specially to technological development thatallows trucks to move with higher axle loads, it must be takensome care during the stages of design, construction and mainte-nance of pavements.

The pavement is a layered structure, built on the sub-grade andthat should support loads from traffic, providing users with safety,comfort, and economy, strictly related to the state of the pavementsurface. The loads applied by traffic are most of it supported by theaggregate of pavement surface, which must meet minimum qualityrequirements. Moreover, the ranking of the aggregates also affectsthe service performance. Depending on the size of aggregates, as-phalt mixtures can be: discontinuous open (open-graded), discon-tinuous dense (gap-graded) or dense solid.

One of the functions of the pavement surface is to provide secu-rity for users and contribute for reducing the accident rate, thatcritical in wet surface, when there is a decrease in adhesion (fric-tion) and visibility (reflection of light and water spray).

Unfortunately, we can see that too many pavements present onits surface different types of defects, such as cracks, holes anddeformities, causing discomfort, reducing costs, and increasingsafety for users. Aiming to meet user’s expectations, in a more eco-nomic and faster way, they have been implementing emergencyservices in order to correct the pavement surface. Many road agen-cies, enterprises and Brazilian town halls have been performingmaintenance activities and pavements rehabilitation alongsidethe technical recommendations, because of lack of technicalinvestments and of poor management preparation, lack of exper-tise and despondency of the technical teams [2].

The development of new technologies, which makes possiblethe construction of highways with a longer useful life, giving achance to postpone some rehabilitation intervention and a de-crease in the frequency of maintenance activities, becomes essen-tial. Trying to improve the quality of asphalt pavements, it hasbeen used asphalts such as asphalt–rubber. The advantage ofapplying this kind of product is that, due to its higher viscosity,the mixture provides greater resistance to some failures, such aspermanent deformities and cracks caused by fatigue. The best re-

ig. 1. Structure of aggregates of mixture SMA and structure of conventional hotix asphalt [3 apud 1].

sults are obtained when you apply asphalt–rubber indiscontinuous mixtures, where usually there is some increase oftensile strength, reduction of traffic noise and an increase in fric-tion, providing a safe and comfortable floor to users and reducingcosts of maintenance and rehabilitation of pavements.

Discontinuous asphalt mixtures tend to have better perfor-mance in terms of resistance to permanent deformation (due tothe size of aggregates), the onset of fatigue cracking and wear (be-cause of the greater thickness of the asphalt), when compared toconventional asphalt mixtures [1]. Discontinuous asphalt mixturesare composed of about 70% of coarse aggregate, leading thereforeto a higher stone–stone contact. Because of that it is recommendedthe use of crushed aggregates with high quality, good micro-tex-ture and always virgin, in other words, it cannot be made of recy-cled pavement.

In most of European countries it required the use of 100% ofcrushed aggregates. To ensure the stability of the mixture, thereis an amount of fillers that varies between 8% and 13% (a littlebit higher than conventional asphalt concrete). Due to the highcontent of fines in discontinuous mixtures, the asphalt contenttends to be higher than that of dense mixtures (asphalt concrete)in about 1–1.5%. Fig. 1 shows the difference between the stoneskeleton of a mixture of stone matrix asphalt, SMA, with the masticinvolving aggregates, compared to conventional hot mix asphalt,an asphalt concrete, AC.

Due to a higher content of asphalt mixtures in the SMA, there is atendency for occurring some drip of the binder. Therefore fibers areadded in order to inhibit this [4]. Among various kinds of fiber (cellu-lose, minerals, etc.), cellulose have been used frequently and haveshown good results, although they present the drawback of a highcost.

This study aims to evaluate the use of asphalt rubber binder andnatural fibers (sisal and coconut) in discontinuous asphalt mix-tures (SMA). To do that, it will be done a comparison betweenthe performance with mixtures without fibers and polyester fibersand cellulose.

2. Materials

2.1. Aggregates

The aggregates were selected according to their properties, specially resis-tance to wear by Los Angeles abrasion, since the specification for discontinuousmixtures requires it to be less than 30%, while for dense mixtures the specifiedvalue is 50% [5]. Aggregates (gravel 5/800 and gravel 3/800) were obtained fromValério Quarry and the stone powder was obtained from Omacio Quarry, locatedin the metropolitan area of Salvador, Bahia. The filler used was limestone dust.Table 1 presents the results of the characterization of aggregates and the grada-tion obtained is presented in Table 2.

2.2. Binder

The binders used were: CAPFLEX B (Brazilian commercial asphalt rubber,composed of 20% ground tire rubber) and AC 50–70. The characteristics are pre-sented in Tables 3 and 4, respectively.

2.3. Fibers

To avoid draining down asphalt material, American and European standards [4]recommend to add fiber, in order to enable a higher binder content and hence athicker film around the aggregate, delaying oxidation, moisture penetration andcracking and separation of aggregates. These advantages serve to protect the as-phalt concrete wear [1].

Fig. 3. Cellulose fiber.

Table 2Gradation of aggregates (% passing).

Sieve Opening (mm) Gravel 5/800 Gravel 3/800 Stone powder Filler

3=400 19.1 100.0 100.0 100.0 100.0

½00 12.7 86.2 100.0 100.0 100.03/800 9.52 38.2 98.9 99.1 100.0# 4 4.76 17.6 47.0 86.6 100.0# 8 2.38 6.2 19.3 58.1 100.0# 16 1.19 2.2 9.1 33.2 100.0# 30 0.60 2.2 9.1 33.2 100.0# 50 0.297 1.7 6.4 21.9 100.0# 200 0.075 1.4 3.2 4.9 98.0

Table 3Properties of asphalt rubber binder.

Test Asphaltrubber

Method

Penetration (100 g, 25 �C, 5 seg) (dmm) 55.0 ASTM D 5Softening point (�C) 62.0 ASTM D 36Elastic recovery (%) 62.5 ASTM D 6084Brookfield viscosity, sp 31, 6 rpm (cP)

175 �C4.000 ASTM D 4402

Density (g/cm3) 1.030 DNIT ME 193

Fig. 2. Polyester fiber.

Table 1Characterization of the aggregates.

Tests Result Specification Method

Wear by Los Angeles abrasion (%) 20 Max 30% DNIT ME 035Bulk specific gravity, Gsb (g/cm3) 2.737 – DNIT ME 043Effective specific gravity, Gse (g/cm3) 2.747 – ASTM D2041

S. Oda et al. / Construction and Building Materials 26 (2012) 13–20 15

In the process of producing an asphalt mixture, the fibers are added to hotaggregates before adding the asphalt binder. By placing the binder and the startof the mixing process, the fibers are spread throughout the mixture. The determina-tion of fiber content is based on the experience, and several publications suggest thelevel of 0.3–0.5%. There are tests that check if the fibers are enough to inhibit thedrain down of the binder, such as AASHTO T-305 [6].

In Rio Grande do Sul, 3200 km from Salvador, Bahia, a polyester fiber is pro-duced (Fig. 2) from vehicle tires. However, the cost of transport turns the use of thisproduct in pavements in the Northeast uneconomical.

In South and Southeast regions, cellulose fibers are used in SMA mixtures(Fig. 3). Those fibers are similar to pellets (beans) because they are wrapped in as-phalt (for example, with 66% fiber and 34% asphalt). The cellulose fibers are chem-ically inert, resistant to dilute acids and alkalis and totally innocuous in terms ofphysiologic and toxicological [1].

2.3.1. Wastes from coconut barkConsumption of green coconut water in any season is growing and getting

attention as a promising product in Brazilian market, introducing an increase ofconsumption estimated at 20% per annum. Nowadays, Brazil is the world leaderin the production of coconut, with an area of approximately 57,000 ha. Conse-quently, consumption of fruit generates a large amount of waste coconut bark(Fig. 4).

Table 4Results of characterization tests of AC 50–70.

Characteristics Limi

Saybolt furol viscosity (s) 135 �C 110163 �C175 �C

Softening point (�C) –Penetration, 100 g, 5s, 25 �C, 1/10 mm 50–7Flash point (�C) 235Density (g/cm3) –Thermal susceptibility index �1.5

* Thermal susceptibility index = ð500Þðlog PENÞþð20Þðt �CÞ�1951120�ð50Þðlog PENÞþðt� CÞ , where (t �C) = softening point.

It is estimated that only in Rio de Janeiro, over 400 tons of coconut barks aredeposited in landfills and dumps. In northeastern Brazil, it represents almost 70%of waste generated on the beaches. The coconut bark is a material of difficultdecomposition (8–12 years), and 80–85% of the gross weight of the coconut are dis-carded as waste [7,8].

The coconut is made up of several parts, among them there is the exocarp, thatis a very thin layer covering the fibrous mesocarp. These elements form the bark ofcoconut (about 5 mm thick, depending on the species). Underneath this layer liesthe woody endocarp, which is very hard. The mesocarp fiber becomes fiber integralfull or made of residual of wiring, and it is used to make mattresses, brooms, drain-age tubes and screens against erosion, resin, coal, cement, and plaster. A mesh madeof coconut fiber hardly rots and is being used in European countries to containslopes. In the automobile industry, the residual fiber is already being used to makeparts for automobiles and banks. The coconut fiber integral can also replace thefiberglass, for example, in a parasol [10].

The use of wastes from coconut bark is very frequent due to the low ash contentand the ease of being acquired in northeastern Brazil. Results obtained by [11,12]showed the feasibility of using coconut mesocarp for adsorption of oil and grease

ts AC 50–70 Method

min 174 ABNT NBR 14950573059 ABNT NBR 6560

0 50 ABNT NBR 6576min 302 ABNT NBR 11341

1043 ABNT NBR-6296a + 1,0 0.79 *

Fig. 4. Coconut barks [9].

Fig. 5. Coconut fibers in different processing steps.

Fig. 6. Sisal processing steps.

Fig. 7. Sisal fiber after processing.

Table 5Physical and mechanical properties of plant fibers [18–21].

Properties Coconut Sisal Malva Polypropylene Cellulose

Apparent specificgravity (g/cm3)

1.177 1.370 1.409 0.913 1.609

Volume of voidspermeable (%)

56.6 60.9 74.2 – –

Absortionmaximum (%)

93.8 110.0 182.2 – 643

Elongation at break(%)

23.9 a51.4

4.9 a5.4

5.2 22.3 a 26.0 –

Tensile strength(MPa)

95 a118

347 a378

160 250 700

Modulus ofelasticity (GPa)

2.8 15.2 17.4 2.0 10–40

16 S. Oda et al. / Construction and Building Materials 26 (2012) 13–20

present in the effluent of oil. Before being used in the experiments, the coconutbarks are dried, crushed and sieved to obtain particle size suitable to be studied[13].

The material is washed with water to remove unwanted materials such asleaves, sticks and other impurities. Then the material is dried at room temperatureand stored in plastic bags until use. Of mesocarp it can be extracted fibers of variouslengths (Fig. 5). After the processing steps, the final product may, for example, beused in the manufacture of seats and benches for the automotive industry, replac-ing petroleum-based products such as polyurethane foam [9].

2.3.2. SisalSisal was brought from Mexico in 1903 and introduced in the states of Paraíba,

Bahia and Rio Grande do Norte, due to favorable weather conditions. It is a plantthat requires warm weather and great light. Suitable for semi-arid regions, sisal,for being highly resistant to prolonged dry weather, with peculiar structures of de-fense against arid conditions [14,15].

Bahia is the largest producer of sisal from Brazil, accounting for 95.6% of alldomestic production and relying on 200,000 ha, which places Brazil as the world’slargest producer. The United States is the largest importer of Brazilian productsbenefited from sisal, specially strings and wires. China also purchases the benefitedfiber for manufacturing sandals. In Bahia, the area involved covers three

Table 6Value in the market (U$/t) and the amount of available waste (t/year) [22].

Fiber Mainproduct

Name Value(U$/t)

Quantity(t/year)

Malva Gross fiber clean Fiber type 4 340.00 1180Coconut Medium and long

fibersShort fiber (10–30 mm)

270.00 3000

Cellulose Paper production Reject 15.00 17.000(Aracruz, ES)

Sisal Green fiber Green fiber Null 30.000 (Apaeb,BA)

Wires and cords White fiber 180.00 25 (Crispim)Carpets Scraps of yarn Null 54 (Cosibra)

Table 7Gradation of the mixture evaluated.

Sieve Opening (mm) SMA AASHTO 9.5 mm

3=400 19.1 100.0

1/200 12.7 97.83/800 9.52 93.6# 4 4.76 45.1# 8 2.38 24.0# 16 1.19 19.0# 30 0.60 15.9# 50 0.297 14.1# 200 0.075 9.2

Mixture SMA - AASHTO 9,5 mm

0102030405060708090

100

0,0 0,1 1,0 10,0 100,0Sieve (mm)

% P

assi

ng

MinimumMaximumProject

Fig. 8. The curve of asphalt mixture evaluated.

Table 8Results of drain down test.

Type of fiber Content (%) Drain down (%)

Without fibers 0.0 0.42Polyester 0.3 0.21

0.5 0.03Sisal 0.3 0.21

0.5 0.05Coconut 0.3 0.18

0.5 0.03Cellulose 0.3 0.11

0.5 0.07

Table 9Volumetric parameters.

Parameters Values

Content of AC (%) 6.8Bulk specific gravity, Gmb (g/cm3) 2.367Maximum specific gravity, Gmm (g/cm3) 2.468Air voids, Va (%) 4.1Voids in mineral aggregate, VMA (%) 19.8Voids filled with asphalt, VFA (%) 78.9

Table 10Volumetric parameters of the SMA mixtures with 0.3% of fibers.

Parameters Withoutfibers

Coconut Sisal Polyester Cellulose

Content of AC (%) 6.8 6.8 6.8 6.8 6.8Bulk specific gravity,

Gmb (g/cm3)2.342 2.352 2.339 2.335 2.365

Maximum specificgravity, Gmm (g/cm3)

2.470 2.470 2.470 2.470 2.470

Air voids, Va (%) 4.6 4.2 4.7 4.9 3.7Voids in mineral

aggregate, VMA(%)

20.4 20.1 20.5 20.7 19.7

Voids filled withasphalt, VFA (%)

77.5 79.3 77.0 76.6 81.4

Table 11Volumetric parameters of the SMA mixtures with 0.5% of fibers.

Parameters Withoutfibers

Coconut Sisal Polyester Cellulose

Content of AC (%) 6.8 6.8 6.8 6.8 6.8Bulk specific gravity,

Gmb (g/cm3)2.349 2.353 2.347 2.329 2.357

Maximum specificgravity, Gmm (g/cm3)

2.455 2.455 2.455 2.455 2.455

Air voids, Va (%) 4.3 4.1 4.4 5.1 4.0Voids in mineral

aggregate, VMA(%)

20.2 20.0 20.2 20.8 19.9

Voids filled withasphalt, VFA (%)

78.6 79.6 78.4 76.3 81.3

Table 12Mechanical parameters of mixtures evaluated.

Mixtures SMA MR (MPa) RT (MPa)

CAPFLEX B, without fiber 3.077 1.1AC 50–70, without fiber 7.306 0.9AC 50–70, with cellulose fiber 6.417 1.1AC 50–70, with coconut fiber 7.948 1.1AC 50–70, with sisal fiber 7.193 1.0AC 50–70, with polyester fiber 5.629 0.8

S. Oda et al. / Construction and Building Materials 26 (2012) 13–20 17

micro-regions: Northeast, Piemonte da Diamantina and Paraguaçu, with a geo-graphic extension of 398,599 km2, which includes over 150 municipalities and pop-ulation of nearly 3 million inhabitants [15,16].

The leaves of the sisal produce a highly resistant fiber that can be used in theproduction of brooms, bags, hats, twine, rope, mats, carpets, cellulose for the pro-duction of kraft paper (high resistance) and other kinds of fine paper (for cigarettefilters, sanitary napkins, diapers, etc.). Besides these applications, it is possible touse the fiber in the automotive industry, and also in the furniture and geotextilesindustries (protection of hillsides, agriculture, and road surfacing), and in the mix-ture of polypropylene to replace fiberglass and construction [14].

The shredding of sisal is the major post-harvest stage. Ut consists in the processof pulp elimination which involves the fiber of leaves through a mechanical scrap-ing. The leaf of sisal, while passing through the refining process, produces the fiber(a product which is 4% of the leaf) and residue (96%), composed of mucilage prod-ucts (15%), juice (80%), and bushing (1%), which can be separated using a rotatingsieve [14]. After shredding, the fiber must be washed in water tanks, where it is im-mersed overnight (8–12 h). By morning, the fibers are placed on the wires, poles, todry in the sun. The next step is the beating, which consists in removing dust thatsurrounds the sisal fiber [17]. From the beating, in addition to fiber, it results onby-products, bushing and dust. The bushing is used to make rope and blanket(for protection of slopes in agriculture). The powder is used in mixture with cornfor the preparation of animal feed.

Mixtures SMA

0

1.000

2.000

3.000

4.000

5.000

6.000

7.000

8.000

A-B, withoutfiber

AC 50-70,without fiber

AC 50-70, withfiber of

cellulose

AC 50-70, withfiber of coconut

AC 50-70, withfiber of sisal

AC 50-70, withfiber of

polyester

Res

ilient

Mod

ulus

(MPa

)

Fig. 9. Results of the resilient modulus.

Mixtures SMA

0,0

0,5

1,0

1,5

A-B, withoutfiber

AC 50-70,without fiber

AC 50-70, withfiber of

cellulose

AC 50-70, withfiber of coconut

AC 50-70, withfiber of sisal

AC 50-70, withfiber of

polyester

Tens

ile S

treng

th (M

Pa)

Fig. 10. Test results of tensile strength by diametrical compression.

Table 13Results of fatigue test of the SMA mixtures with different types of fibers.

Mixture Height (cm) Loading level (%) Load (N) N rt (MPa) Dr (MPa) ei

Without fiber 1 5.64 22.07 1850 19.903 0.2041 0.8165 2.79E�05Without fiber 2 6.17 30.43 2780 12.854 0.2815 1.1260 3.85E�05Without fiber 3 6.11 40.58 3700 4442 0.3754 1.5015 5.14E�05Cellulose 1 6.19 20.07 2250 4835 0.2262 0.9048 3.53E�05Cellulose 2 6.04 30.90 3380 1213 0.3482 1.3930 5.43E�05Cellulose 3 6.28 39.58 4510 1316 0.4460 1.7842 6.95E�05Coconut 1 6.20 20.25 2220 6187 0.2244 0.8974 2.82E�05Coconut 2 6.10 30.66 3320 1714 0.3397 1.3588 4.27E�05Coconut 3 6.25 39.69 4430 809 0.4398 1.7592 5.53E�05Sisal 1 6.18 20.06 2050 5694 0.2054 0.8217 2.86E�05Sisal 2 6.13 30.50 3070 1808 0.3123 1.2491 4.34E�05Sisal 3 6.21 40.12 4100 669 0.4109 1.6435 5.71E�05Polyester 1 6.19 19.90 1660 13.241 0.1648 0.6592 2.79E�05Polyester 2 6.16 30.11 2480 6379 0.2493 0.9973 4.22E�05Polyester 3 6.20 40.09 3310 2425 0.3319 1.3276 5.61E�05

18 S. Oda et al. / Construction and Building Materials 26 (2012) 13–20

Fig. 6 shows the sisal processing steps and Fig. 7 is a sample of the fiber afterprocessing. Table 5 presents the physical and mechanical properties of plant fibersand Table 6 presents the market value (U$/t) and the amount of available waste (t/year) of some kind of fibers.

Natural fibers analyzed in this study were obtained from companies located inSalvador, Bahia. The coconut fiber was supplied by the company POEMATEC –Comércio de Tecnologia Sustentável for the Amazon and the fiber was suppliedby Tecelagem de Sisal da Bahia – Industry, Trade, Import and Export Ltd.

Fatigue Life SMA

100

1000

10000

100000

1010,1Δσ (MPa)

N (N

umbe

r of c

ycle

s)

Without fiberCelluloseCoconutSisalPolyester

Fig. 11. Chart of fatigue test.

Table 14Fatigue models of SMA mixtures with different types offibers.

Types of fibers Fatigue models

Without fiber N = 13565.0 (1/Dr)2.4406

N = 1.71 � 10�7 (1/e)2.4406

Cellulose N = 3448.3 (1/Dr)2.0609

N = 2.82 � 10�6 (1/e)2.0609

Coconut N = 4424.5 (1/Dr)3.0294

N = 1.02 � 10�8 (1/e)3.0294

Sisal N = 3243.2 (1/Dr)3.0603

N = 7.33 � 10�11 (1/e)3.0603

Polyester N = 5292.0 (1/Dr)2.3773

N = 2.12 � 10�7 (1/e)2.3773

Table 16Results of mechanical analysis with structures 1 and 2.

Fiber MR (MPa) rt (MPa) rc (MPa) Dr (MPa) N

Structure 1Without fiber 7306.2 0.83100 �0.07880 0.9098 17.085Cellulose 6416.7 0.77780 �0.08446 0.8623 4680Coconut 7948.1 0.86610 �0.07528 0.9414 5313Sisal 7193.4 0.82450 �0.07947 0.9040 4417Polyester 5911.7 0.74500 �0.08817 0.8332 8167

Structure 2Without fiber 7306.2 1.53300 �0.10960 1.6426 4040Cellulose 6416.7 1.43700 �0.11700 1.5540 1390Coconut 7948.1 1.59800 �0.10500 1.7030 882Sisal 7193.4 1.52200 �0.11050 1.6325 724Polyester 5911.7 1.37700 �0.12180 1.4988 2022

where MR = resilient modulus obtained from laboratory test; rt = tensile stress inthe surface of the pavement obtained in the program ELSYM 5; rc = compressivestress in the surface of the pavement obtained in the program ELSYM 5; Dr = dif-ference between the strains of tension and compression (rt � rc); N = number ofcycles.

S. Oda et al. / Construction and Building Materials 26 (2012) 13–20 19

2.4. Asphalt mixtures

2.4.1. Dosage of asphalt mixturesFor dosing the mixture it was selected a discontinuous mixture of type SMA

(stone matrix asphalt), of AASHTO MP8-01 (9.5 mm). According to recommenda-tions of the specification, the dosage of the SMA was performed employing fibers.In this paper, there were produced mixtures with asphalt rubber binder without fi-bers (reference) and mixtures with AC 50–70 with fibers (coconut, sisal, polyester,and cellulose). Table 7 and Fig. 8 show the gradation curve of the mixture evaluated(SMA).

3. Analysis of results

3.1. Drain down of binder

Table 8 presents the test results of drain down, which wasaccomplished at 180 �C.

Fibers were added in two percentages (0.3% and 0.5%). FromTable 8 it can be checked that the addition of fiber reduces by atleast 50% of the drain down of binder (from 0.42% to 0.21%). Thecellulose fiber with the lowest value of drain down (0.11%) when

Table 15Hypothetical pavement structures 1 and 2.

Structure Layer Thickness (cm)

1 Surface 15Base 25Sub-base 30Subgrade Semi-infinite

2 Surface 10Base 15Sub-base 20Subgrade Semi-infinite

added to a smaller amount of fibers studied (0.3%). However, withthe increase of the content to 0.5%, the polyester and coconut fiberspresented the best results (0.03%), and the sisal fiber also showedgood results (0.05%), mainly if compared with the cellulose fiber(0.07%), which is already used in SMA mixtures.

3.2. Volumetric parameters

Table 9 presents the results of the volumetric parameters of theSMA with asphalt–rubber binder.

Tables 10 and 11 show the results of the volumetric parametersof the SMA mixtures with natural and synthetic fibers.

3.3. Mechanical parameters

The tests were conducted at Laboratory of Roads of the Depart-ment Transport of the Engineering School of Sao Carlos at the Uni-versity of Sao Paulo. In order to determine the mechanicalparameters there were used specimens (CPs) molded in the Mar-shall compactor, in the asphalt content project.

3.3.1. Resilient modulus and tensile strengthThe resilient modulus, MR, of the asphalt mixture is the rela-

tionship between the tensile applied to a specimen (SP) and theelastic deformation (recoverable) correspondent.

In this work, it was performed indirect tensile test with re-peated loading and the test temperature of 25 �C to determinethe MR, following the method DNER ME 133. The load is appliedwith a frequency of 1 Hz and the duration of 0.1 s. The resilientdeformations are measured by an electromagnetic–mechanicaltransducer type LVDT (Linear Variable Differential Transformer),which sends the information to a computer program for dataacquisition.

Coefficient of poisson MR (MPa)

0.35 Variable0.40 30000.40 20000.45 500

0.35 Variable0.40 20000.40 15000.45 500

17085

46805313

4417

8167

4040

1390 882 724

2022

0

5000

10000

15000

20000

Without fiber Cellulose Coconut Sisal Polyester

N (

cycl

es)

Structure 1

Structure 2

Fig. 12. Results of analysis of fatigue test.

20 S. Oda et al. / Construction and Building Materials 26 (2012) 13–20

The tensile strength, RT, of asphalt mixtures is obtained bydiametral compression test applied to cylindrical specimens, fol-lowing the method DNER ME 138. The test, conducted at a temper-ature of 25 �C, consists of applying the load progressively, with astrain rate of 0.8 ± 0.1 mm/s until failure.

The test results are presented in Table 12 and Figs. 9–11. It canbe verified that all the asphalt mixtures showed high tensilestrength, accompanied by a high value of modulus of resilience,showing also that the type of fiber has little influence on mechan-ical parameters.

3.3.2. Fatigue testIn the fatigue test, the specimens were subjected to diametral

loading and 25 �C of temperature.Samples have been subjected to three levels of tension and, for

each, there was determined the number of cycles required for rup-ture (displacement greater than 3.5 mm). Table 13 presents the re-sults of fatigue tests.

Charts were elaborated in the number of cycles due to stressdifference, in logarithmic scale (Fig. 11). For each graph it wasmade the regression curve of fatigue, resulting in the equation cor-responding to it (Table 14).

With the obtained results, there was made the comparison ofthe mixtures evaluated through a simulation of two hypotheticalpavement structures (Table 15). The tensional analysis was per-formed using the ELSYM 5 and the results are presented in Table16 and Fig. 12.

4. Conclusions

The results of drain down test showed that the asphalt mixtureswith natural fibers present excellent performance if compared tomixture made with polyester and cellulose fibers, which are al-ready used in discontinuous mixtures in Southern and Southeast-ern Brazil.

When subjected to the evaluation of mechanical parameters, allasphalt mixtures showed high tensile strength and high value ofresilient modulus, with little influence on the kind of fiber.

The results of fatigue analysis show that the mixture with an as-phalt modified rubber (CAPFLEX B, without fiber) had the bestbehavior and the results obtained with cellulose fibers, sisal andcoconut shells were not significantly different.

Acknowledgements

The development of this work was only possible because theyhad the support of the Foundation for Research of the State of Bahi-a (FAPESB), School of Engineering of Sao Carlos, University of SãoPaulo and the Center for Excellence in Asphalt (CEASF).

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