hma modification trb 08 reyes v3

Reyes, Figueroa, Núñez and Flintsch

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Investigation of the Effect of Recycled Polystyrene on Hot-Mix Asphalt Performance

Fredy A. Reyes Lizcano, PhD. Director, Research Group CECATA, Pontificia Universidad Javeriana Carrera 7 No 40-62 Edificio Jose Gabriel Maldonado Bogota, Colombia email: 1 Ana S. Figueroa Infante, MS. Director, Research Group INDETEC, Universidad de La Salle Carrera 2 No 10-70 Bogota, Colombia email: [email protected] Orlando Núñez Graduate Student, Center for Safe and Sustainable Infrastructure, Virginia Tech Transportation Institute. 3500 Transportation Plaza Virginia Tech, Blacksburg, VA, 24601 email: [email protected] Gerardo W. Flintsch, Ph.D.., P.E.1 Director, Center for Sustainable Transportation Infrastructure, VTTI, Associate Professor, The Charles Via, Jr. Department of Civil and Environmental Engineering 3500 Transportation Research Plaza Virginia Tech, Blacksburg, VA 24061-0105 Phone: (540) 231-9748, fax: (540) 231 15557532, email: [email protected]

Keywords: hot-mix asphalt, polymer-modified binder, dynamic modulus, fatigue, Marshall, pavement design

Submission Date: August 1, 2007 Approval Date: November 4, 2007

Submitted for Presentation at the 2008 TRB Annual Meeting and Publication in the

Transportation Research Record: Journal of the Transportation Research Board

Word Count: Abstract : 144 Text : 3,178 Figures 9 x 250 = 2,250 Tables : 3 x 250 = 750 TOTAL : 6,322 1 Corresponding author


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ABSTRACT This paper describes a research study that investigated the behavior of modified hot mix asphalt, produced with a polymer-modified binder in comparison with a standard mix currently used in Colombia. The binder was modified with polystyrene obtained from crushing icopor cups. Both static and dynamic tests were conducted in order to simulate the behavior of the mixture under the action of a 13 ton (29,120 lbs) axle load. The Marshall Mix Design procedure (currently the standard in Colombia) was used to design the asphalt mix. The mixture’s dynamic behavior was studied based on three tests: the trapezoidal fatigue test, the plastic resistance test, and the dynamic modulus test. The results show that the modification results in a high stiffness mixture, lighter that the conventional one and with enhanced rutting resistance. The effect on fatigue resistance was only partially quantified and should be further investigated.


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INTRODUCTION One common problem that pavement engineers face is the heterogeneity of the asphalt obtained from refineries. Asphalt properties vary because of changing crude sources and refining processes. This variation often affects the performance of the flexible pavements constructed with these materials. Asphalt may be found in natural deposits or produced as a by-product of the petroleum distillation process in a refinery plant. In nature, asphalt is found in a pure state or as a matrix rocks and sand. In Colombia there are natural asphalt deposits in the departments of Boyaca, Caqueta, Tolima, Meta and Casanare, among others. However, the most commonly sources of asphalt in Colombia are petroleum refineries. The entity responsible for the extraction and refinery is ECOPETROL (2). Residual asphalt was used in all the experiments discussed in this paper. Asphalt is composed of asphaltenes, resins, and oils. Asphaltenes provide the structural characteristics and stiffness of asphalt, resins provide the adhesive and cohesive properties, and oils provide consistency for the asphalt workability. Asphalt is composed a large extent of hydrocarbons of semi-solid consistency at room temperature but becomes more fluid as the temperature is increased (3). Low viscosity at high service temperatures is one of the main contributing factors for the development of pavement rutting, whereas a high viscosity at low service temperatures stiffens the asphalt making the mix more prompt to cracking (e.g., fatigue cracking). OBJECTIVE This paper describes the first stage of an investigation that considered the use of an asphalt modifier (i.e., polystyrene) as a stiffener agent for asphalt concrete to mitigate the permanent deformation (i.e., rutting) due to various factors such as: high temperature locations, static loading areas (e.g., parking lots, resting areas for trucks), and stop-and-go areas (1). The paper discusses the changes in terms of rutting, fatigue, and modulus that are induced by the addition of polystyrene to typical Colombian hot-mix asphalt (HMA). BACKGROUND Polymers There are two different types of polymers: natural and artificial. Examples of these materials include: starch, proteins, cellulose, cotton, skins, synthetic fibers, plastics, rubbers, paintings, adhesives, icopors, etc. In 1926, Herman Staundinger obtained polymers from dehydrogenation of natural rubber. Staundinger attributed the high molecular weight of these substances to the long atomic chains produced by their covalent bonds. The small units were named monomers, whereas the entire structure was named polymer. Some of the most significant development in polymers took place during World War II. It was at this time that synthetic rubber was obtained. The vulcanization of natural rubber was utilized for the fabrication of tires worldwide. However, difficulties with the process arose during the war and this prompted the development of new technologies in Germany. Contemporarily, Carothers had obtained a synthetic tire from chloroprene (2-chloro 1,2-butadiene) in the US. In 1956 Ziegler and Natta received the Chemistry Nobel Award for the elaboration of isotactic polypropylene, which nowadays has an elevated commercialization. Materials such as polyethylene, polypropylene, and polystyrene were developed soon after (1). The most common classification of polymers is summarized in Table 1.


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TABLE 1. General characteristics of asphalt modifiers

Polymer Characteristics

Thermoplastics 1. Softens with heat, may be soluble 2. They can be molded without losing any of their properties as

temperature lowers 3. Mostly linear polymers 4. Examples include polyethylene, polypropylene, polystyrene, etc.

Thermoset Polymers 1. Two-component system 2. Phenolic resins, Epoxy resins, Polyester resins, etc.

Elastomers 1. Unsaturated polymer, amorphous 2. It must be vulcanized before obtaining elastic properties 3. Examples include natural rubber, Styrene Butadiene Rubber (SBR),

and styrene-butadiene-styrene (SBS). Asphalt Modifiers The use of polymers to modify asphalt has become a standard practice worldwide. The use of modified binders provides specific asphalt characteristics that help achieve better durability and performance under traffic loads. Various modifiers help obtain better resistance to aging and water damage, better adhesion between aggregates and binder, and enhanced elastic and/or viscous properties. In particular, the use of appropriate modifiers can enhance HMA performance in terms of fatigue and rutting. Some of the most commonly used modifiers are summarized in the following sections. Asphalt modified with used tire rubber The first investigations began in 1965 with asphalt modified for asphalt interlayer applications and surface treatments (e.g., chip seals, microsurfacing, thin HMA layers with aggregate size 1/4" to 3/8"). The service life of these treatments was in some cases twice the typical life of the compared traditional systems (4). Synthetic latex and natural latex They were first used in Europe (France and Spain) in 1970 by incorporating them into emulsified asphalt to better the characteristics of emulsions used in seals. Years after, they were used in the elaboration of cold asphalt mixes and hot modified asphalt mixes (5). Styrene Butadiene Rubber (SBR) and Styrene Butadiene Styrene (SBS) polymers The impermeable materials industry has used SBR and SBS polymers to improve the performance of asphalt for more than 20 years. The percentage of SBR and SBS used is between 6 and 12%; the modified asphalts have yielded excellent results, particularly with SBS. These type of polymers have also been used in flexible pavements and resulted in reduced asphalt temperature susceptibility and enhanced performance and behavior of the mix at low temperatures (e.g., -40ºC) (6). Elseifi et al. (7) developed models to characterize the dynamic mechanical properties of elastomer-modified asphalt (SBS and styrene-ethylenebutylene-styrene (SEBS)) binders and found that polymer modification is effective in increasing rutting resistance at high temperatures and fatigue resistance at intermediate temperatures. It was also found that SBES improves the binder rutting resistance more than SBS. However, SBS was found more effective in improving the binder fatigue resistance at intermediate temperatures.


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Natural asphaltene – Gilsonite It is a triturated dust from mines that is obtained at low depths especially in the state of Utah. Their first use was in waterproof membranes and later in asphalt mixtures. This product has 70% of asphalthenes enriched with reins and oil (nitrogen bases) and when added to asphalt binder changes it physical and chemical characteristics and give greater adhesion to the HMA, major structural resistance, and durability. Hydrated lime Hydrated lime has been used with good results in materials with quartz to improve the structural capacity and adherence. However, in some problems in their mixing and contamination have been reported (8). Catalytic modifiers This European system tends to arrange the asphalt molecules when it has contact with the asphalt. These modifiers have been used with frequency in north European countries and South Africa with good results. EXPERIMENTAL PROCEDURE Methods The experiment consisted in preparing HMA mixes with and without modifying the asphalt binder with icopor crushed glasses. The testing included volumetric properties, Marshall stability and flow, fatigue resistance, and rutting potential. A typical asphalt mix (MDC-2 type) (non-modified) was used as the control. The standards and tests followed were from the Instituto Nacional de Vias (commonly used in Colombia) and ASTM. The French fatigue model, commonly used in the Laboratoire Central de Ponts et Chaussées de Francia (LCPC), was used for the investigation. The asphalt was obtained from Barranca Bermeja. The icopor glasses were crushed in order to obtain the modified asphalt. Various tests were done to investigate the optimum gradation for obtaining a good mix between the polymer and the asphalt. The best results were obtained when the all the polymer particles (crushed icopor) passed the #4 sieve. One of the main challenges faced when preparing the modified binder was achieving a uniform mix between the polymer and the asphalt. It was necessary to try different temperatures to find an “optimum” mixing temperature. The mixing tests to determine the optimum asphalt and polyestirene content as well as all the static tests were performed in the Universidad de La Salle laboratory. All the dynamic tests were conducted at the Pontificia Universidad Javeriana. Materials The granulometric distribution for the aggregates used for the how-mix asphalt was design according to the INVIAS standards as shown in Figure 1. Table 2 summarizes the results of the characterization of the original asphalt binder, polystyrene, and modified binder. The icopor glasses and the crushed icopor passing sieve #4 material that was used to modify the asphalt are shown in Figure 2(a). Figure 2(b) shows the appearance of the binder before and after the addition of the polymer.


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Test Obtained

Value Specification

Suggested Value

Aggregate specific weight (g/cm3) 2.511 INV 221 / INV 222

Los Angeles Abbrassion (max %) 28 INV 218 / INV 219 30

Elongation Index (max %) 18.2 INV 230 35

Flat Aggregate Index (max %) 31.2 INV 230 35

Fractured faces (min %) 90 INV 227 75

Sand equivalency (min %) 74 INV 133 50

FIGURE 1. Average Properties of the Aggregate used in the Experiments

TABLE 2. Characterization of Asphalt and Polysterene

Test Original Binder Specification Suggested

Value Modified Binder

Penetration 100g, 5 s to 25 °C (0,1 mm) 81 ASTM D70 80-100 70 Ductility to 25ºC (cm) +100 ASTM D118 Min 100 +37 Specific weight to 25ºC (g/cm3) 1.012 ASTM D70 - 1.2 Kinematic viscosity, 135ºC (cSt) 303.01 ASTM D5 - 296 Ignition point (ºC) 185 ASTM D92 - 180 Point of flame (ºC) 220 ASTM D92 - 220 Point of softening ring and ball (ºC) 45.20 ASTM D 36 - - Polymer Softening temperature minimum Vicat (ºC) 88.5 Flow number in minimum fusion (g/10 min) 10 Viscosity of the dissolution to 10% in minimum toluene (cP)

17.6

Max residual styrene monomer content (%) 0.2

0

10

20

30

40

50

60

70

80

90

100

0,01 0,1 1 10 100

% P

assi

ng

Aggregate size (mm)

GRANULOMETRIC CURVE


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(a)

(b)

FIGURE 2. Binder Modification: (a) Icopor glasses (intact and crushed); and (b) Binder before and after the addition of the polymer.

Marshall Mix Design The Marshall design consists in the determination of the optimum asphalt content that should be added to the HMA to achieve certain resistance properties and durability determined based on the traffic loads and expected service life of the pavement. The HMA for this study was design for high traffic loads. The unmodified mix was tested for optimum asphalt content at intervals of 0.5%. Twenty one test specimens with asphalt content between 4% and 6.5%, in weight, were tested and the optimum asphalt content determined was 6%. For the polystyrene modified mix, nine specimens were prepared with the optimum binder content and variable amount of polymer; and the amount of wet polystyrene added was 0.5, 1.0, and 1.5%. The optimum amount of polystyrene was determined to be 1%. The integration between the polystyrene and asphalt was a challenge. Due to the low solubility of the polystyrene, it was determined that using a polystyrene that passing sieve #4 and a controlled temperature of 135 ºC for mixing was the best solution. Figure 3 presents the Marshall curves for the unmodified and modified mixes. The average results of the various Marshal tests are summarized in table 4


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(a) (b)

FIGURE 3. Marshal mix design results for the (a) Unmodified and (b) modified mixes.

Unmodified Mix

0500

10001500200025003000

3.5 4 4.5 5 5.5 6 6.5 7Asphalt Content (%)

Sta

bilit

y (lb

)

Umodified Mix Flow

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

3.5 4.5 5.5 6.5 7.5

Unmodified Mix

0

5

10

15

20

25

3.5 4 4.5 5 5.5 6 6.5 7Contenido de Asfalto (%)

VM

A (

%)

Unit Weight Unmodif ied Mix

2.0802.1002.1202.1402.1602.1802.2002.2202.2402.260

3.5 4.5 5.5 6.5 7.5

Unmodified Mix

02468

101214

3.5 4 4.5 5 5.5 6 6.5 7Contenido de Asfalto (%)

VT

M (

%)

Modified Mix

0

1000

2000

3000

4000

5000

0 0.5 1 1.5 2Icopor Content (%)

Sta

bilit

y (lb

)

Modified Mix Flow

0.00

0.05

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0 0.5 1 1.5 2

Modified Mix

0

4

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0 0.5 1 1.5 2Contenido de Icopor (%)

VM

A (

%)

Modified Mix

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13

14

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0 0.5 1 1.5 2Contenido de Icopor (%)

VT

M (

%)

Unitary Weight Modif ied Mix

2.0902.1002.1102.1202.1302.1402.1502.1602.1702.180

0 0.5 1 1.5 2


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TABLE 3. Average Marshal Results for the optimal unmodified and modified HMA mixes

Test Unmmodified HMA Modified HMA Optimum Range (INVIAS)

Minimum Stability (lb) 2900 4900 >1650 Flow (mm) 3.2 3.3 2 – 3.5 Mix Voids 4.9 12.5 4 – 6%

Aggregate Voids 15.2 14.8 Min. 15% Unitary Weigth (g/cm3) 2.240 2.168 -

HMA Fatigue Life The fatigue on asphalt mixes manifests itself as the damage that occurs due to the repetitions of loads over time. The most important aspect in a fatigue analysis is the determination of the load cycles that will cause the mix to fail (9-10). The fatigue life of an HMA is determined as the number of repetition of a fixed load at which the mix fails due to cracking. The French standard NF P 98-261-1 was utilized in this study. The standard consists of applying a sinusoidal deformation of the form Z = Z0 sin (wt) in the upper end of a trapezoidal specimen as shown in Figure 5. The fatigue tests were performed at a controlled deformation of 90x10-6, 150x10-6, and 220x10-6 m at a frequency of 10 Hz and temperatures of 20, 25, and 30ºC according to the French recommendations (11).

FIGURE 4. Trapezoidal cantilever-beam fatigue fixture and specimen Rutting Potential The rutting test was performed in a rutting machine based on the LCPC methodology in accordance with the French standard NF P 98-253-1. The test was realized at 42 rpm (revolutions per minute) during which a tire with 0.662 MPa of pressure and a mass of 13 tons was used to produce permanent deformation (rutting) in a sample of 10x16x50 cm as shown in Figure 5. The temperature during the test was 60ºC, which is considered the temperature of an asphaltic mix in service. Permanent deformation readings were recorded at periodic intervals. For the unmodified mix samples, 6,700 and 3,500 cycles were applied; whereas, the modified mix was tested at 5,000 and 7,500 cycles.


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FIGURE 5. Rutting testing equipment and samples Dynamic Modulus The dynamic modulus testing was realized using a Nottingham Asphalt Tester (NAT) by the method of controlled deformation according the ASTM D 4123 standard (in an indirect tension mode). Three samples of the unmodified asphaltic mix and three samples of the modified asphaltic mix were tested. The temperatures of the tests were 15, 20, and 30ºC with frequencies of 2.5, 5, and 10 Hz. The dynamic test machine used is shown in Figure 6.

FIGURE 6. Dynamic modulus testing equipment and specimen. RESULTS The ductility of the modified binder mix decreased 63% due to the added rigidity provided by the modifier (polystyrene) gives to the mix fatigue. This acquired characteristic implies a lower thermal susceptibility of the asphalt. During the Marshall design of the mix, it was observed an increase in the stability of the modified mix with respect to the conventional (unmodified) mix. This was an interesting result; however, it was noticed that this may affect negatively the fatigue behavior of the modified mix. In contrast, the flow of the mix was not affected significantly; which favors its use in hot climates. The unit weight decreased in the modified mix because of the lighter polymer; therefore, the mix was lighter and more stable than the unmodified one. Due to the polymer modification of the asphalt, the percent voids increased, this additional space is thought to allow the rearrangement of the particles within the mix due to traffic loads in hot weather.


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The dynamic modulus results revealed that the modulus of the modified mix were higher than those of the unmodified mix at all temperatures and frequencies. Figure 7 summarizes of the averages values and the percentage of change for the modified and unmodified mixes. The modulii increased by as much as 51% for the highest temperature tested. Figure 7 shows that the highest modulus values are obtained at a temperature of 15 ºC. The dynamic modulus for the two mixes (unmodified and modified) increases as the frequency increases at all temperatures, except for the case of 15 ºC, where there is a decrease in modulus at 10 Hz. These variations could be due to the inherit variation in the samples and testing procedures.

Temperature (ºC) 15 20 30

Frequency (Hz) 2.5 5 10 2.5 5 10 2.5 5 10

Type of Mix Modulus (MPa)

Unmodified Mix 6,121 7,328 8,705 3,609 4,761 5,783 921 1219 1692

Modified Mix 7,417 10,250 9,625 4,982 5,644 7,384 1389 1814 2407

Percent Diff. 21% 40% 11% 38% 19% 28% 51% 49% 42%

Figure 7. Dynamic Modulus at different temperatures and frequencies

Fatigue performance The fatigue results are summarized in Figure 8. The modified mix showed a better performance in terms of fatigue since it can withstand a higher number of cycles than the unmodified mix for the same level of deformations. With an increase in temperature, the allowable deformation for the same number of cycles in the modified and unmodified mixes decreases.

0

2000

4000

6000

8000

10000

12000

0 2 4 6 8 10 12Frequency (Hz)

Mo

du

lus (

MP

a)

15ºC unmodified 20ºC unmodified 30ºC unmodified

15ºC modified 20ºC modified 30ºC modified


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Figure 8. Results of the laboratory fatigue tests

To quantify the change in fatigue life due to the modification, the number of allowable fatigue cycles for a 9,000 lb load (ESAL or equivalent single axle load) for two typical pavement structures was computed for the determined using the two mixes considered. The structure used for this exercise was the following:

o HMA � Thickness = 6 in, and 8 in (for structure 1 and 2, respectively). � Modulus of Elasticity = 838,753 psi (5,783 MPa) unmodified

= 1,070,959 psi (7,384 MPa) modified � Poisson’s Ratio = 0.35 � Full friction with layer underneath

o Granular Base � Thickness = 8 in. � Modulus of Elasticity (Resilient Modulus) = 35,000 psi � CBR = 60 � Poisson’s Ratio = 0.35 � Full friction with layer underneath

o Subbase � Thickness = 10 in. � Modulus of Elasticity (Resilient Modulus) = 20,000 psi � CBR = 25 � Poisson’s Ratio = 0.35 � Full friction with layer underneath

o Subgrade � Modulus of Elasticity (Resilient Modulus) = 12,000 psi � CBR = 11 � Poisson’s Ratio = 0.40


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The fatigue load cycles were calculated using the equation (1) and (2) fro the modified

and unmodified mixes, respectively. These equations were obtained from the fatigue test results displayed in Figure 8 for 20oC,

)263.0/1(

66

10188101

−

−

=x

xN tf

ε (1)

)442.0/1(

66

10419101

−

−

=x

xN tf

ε (2)

where Nf = allowable number of load cycles to fatigue, and εt = maximum tensile strain at the bottom of the HMA layer.

The resulting fatigue cycles were 8.8x106 ESAL, and 3.5x106 ESAL, for the structure 1 with modified and unmodified mix, respectively, and 2.1x108 ESAL, and 9.9x107 ESAL, for the structure 2 with modified and unmodified mix, respectively. This change in behabior is due to the crossing of the fatigue equations at a stain of approximately 550x10-6 mm/mm.

Therefore, according with the mechanistic analysis, the modified mix will perform better than the unmodified mix in term of fatigue resistance in the stronger structure but it will perform worse than the conventional mix on the weaker structure with a thinner HMA layer. This suggest that the modified mix should be used on thicker pavement structures were a stiffer mix would be beneficial but not on thinner structures in which a less stiff mix will perform better. Rutting performance The modified mix presented less permanent deformation than the unmodified mix, as can be seen in Figure 9. The samples of unmodified mix reached a rut depth of 10.9 mm and 10.6 mm, whereas the samples of modified asphalt had a rut depth of 5.6 and 4.1 mm. A comparison at 3,500 cycles reveals that rutting decreases up to 70% in the modified mix.


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Figure 9. Laboratory rutting results

FINDINGS AND RECOMMENDATIONS Following is a summary of the main findings of the study:

• The Marshall stability of the modified mix was higher than the one obtained from a conventional mix. The flow was conserved almost identical. This suggests that the mixes will provide a good level of rigidity when used in hot climates. Consistently, the modified mix has a higher dynamic modulus that the conventional mix; an increment of 11 to 51% was observed.

• The unit weight decreased in the modified mix; therefore, a lighter mix with higher stability is obtained. This suggests that the modified mix may dampen the loads transmitted to the rest of the pavement structure.

• The modified mix showed significantly lower permanent deformations, up to a 50% reduction compared with the conventional mix in the laboratory rutting test.

• Based on the limited fatigue tests conducted, it appears that the modified mix will perform better than the unmodified mix in term of fatigue resistance in the stronger structure but it will perform worse than the conventional mix on the weaker structure with a thinner HMA layer.

It is recommended to conduct additional testing in the Nottingham Asphalt Test (NAT) and the fatigue apparatus of modified mix to obtain more conclusive results on the fatigue behavior of the polystyrene modified mixture. The development of this study still needs to be completed using other tests and more data to be able to obtain a solid answer including technical and economical considerations for the inclusion or exclusion of polystyrene in asphalt mixes.

0

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0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000

Cycle s

Ru

ttin

g

(mm

)

witho ut ico po r 1witho ut ico po r 2with ic o po r 1

with ic o po r 2


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ACKNOWLEDGEMENTS The icopor study was performed under the many research projects that have been reported in the Colombian Technical Reports NTC 1524. The authors of this paper would like to express their gratitude to the aggregate plant PATRIA S.A. for their contribution with the aggregates, asphalt, and prime maters used for this study. Technicians and students of the Pontificia Universidad Javeriana and Universidad de La Salle were involved in this investigation. REFERENCES

1. Figueroa, Reyes, “Asfaltos modificados con Poliestireno”, Universidad de La Salle, Bogotá,

Colombia, 2005.

2. Ecopetrol. “Cartilla Práctica para el manejo de los Asfaltos Colombianos”. Instituto Colombiano

del Petróleo, 1999.

3. Arenas, Hugo León. “Tecnología del cemento asfáltico”. Fundación para Actividades de

Investigación y Desarrollo. Calí, 2000

4. S. K. Palit, K. Sudhakar Reddy Y B.B. Pandey. “Laboratory Evaluation of Crumb Rubber

Modified Asphalt Mixes”. Journal of Material in Civil Engineering. January/ February 2004.

5. Gallego Medina, D. Juan. “Mezclas bituminosas con betunes de alto contenido en caucho de

neumáticos: una elección por las altas prestaciones”. Universidad Politécnica de Madrid. Madrid,

2003.

6. Oda Sandra Y Fernandes Júnior José Leomar. “Viabilidad Técnica de Usar Caucho de

Neumático como Material de Pavimentación Asfáltica”. Universidad Estadual de Maringá.

Brasil. 2002.

7. Elseifi, M.A., Flintsch, G.W., and Al-Qadi, I.L. "Qualitative Effect of Elastomeric

Modification on Binder Performance at Intermediate and High Temperature," Journal of

Materials in Civil Engineering, American Society of Civil Engineering, January/February

2003, Reston, VA, pp 32-40.

8. Montejo Fonseca, Alfonso. “Ingeniería de pavimentos para carreteras”. Bogotá : Impreandes,

1998.

9. Reyes Ortiz, Oscar. “Mejoramiento de las propiedades mecánicas de una capa de asfalto con

desperdicios plásticos”. Bogotá, 1997. Trabajo de grado (Ingeniero

10. Cuellar, A. “Estudio comparativo de las leyes de fatiga de una mezcla cerrada 0/10 con y sin

adiciones de icopor”. Trabajo de Grado. Universidad Javeriana. 2003.

11. Robert Lunddtrom, Hervé Di Benedetto Y Ulf Isacsson. “Influence of Asphalt Mixture Stiffness

on Fatigue Failure”. Journal of Material in Civil Engineering. November/ December 2004.

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