Recyled Tyre Rubber.PDF

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182 R. Maharaj et al

asphalt and the bitumen which are the only deformable components in the mixture.Both these systems have thermal susceptibilities and often experience lowtemperature cracking in cold environments as most bitumen have been shown toexhibit an apparent glass temperature near zero degrees Celsius and hence its physicalbehaviour moves from ductile to brittle, (Kortschot et al., 1984). The crackingphenomenon is attributed to thermal shrinkage stresses and further damage occurs dueto weathering, moisture damage, frost heave, heavy traffic or embrittlement due to thechemical oxidation of functional groups within the asphalt. Engineers are required toalso develop asphalt mixes that provide pavement stability during the hightemperature periods to avoid creep and distortion of the material. These limitationscan be overcome and the properties significantly modified by blending a polymericmaterial with asphalt and bitumen for improving the viscoelastic behavior while

maintaining their own advantages, (Fawcett et al., 2002, Masson et al., 2001, Blancoet al., 1995, Wen et al., 2001, Lu et al., 2000, Singh et al., 2003). Research has shownthat asphalt rubber blends are a good alternative to pure bitumen and has beenextensively studied, (PIARC, 1999).

The addition of scrap tyre rubber in asphalt has been known to improve asphaltsdurability as a result of the increased resistance to cracking, reduced temperaturesusceptibility, improved oxidation and aging resistance as well as an improvedresistance to permanent deformation. Asphalt Rubber (AR) pavements can be used atapproximately half the thickness of conventional pavements, it results in less noisepollution at the road tyre interface, helps reduce tyre waste, helps road paint to standout more and AR pavements can be successfully recycled with either microwave

technology or conventional mix technology, (Douglas and Carlson, 1999; Way, 1999;Crockford et al., 1995).

Most developing countries struggle to properly manage their levels of solid wastedue to inadequate service coverage, limited utilization of recycling activities andinadequate landfill disposal, (Zurbrugg, 2003; OECD, 1999). In Trinidad and Tobagoresidential solid waste is collected and taken to landfills. The total rubber contentcontained in landfills in Trinidad is approximately 4.6%, (SWMCOL, 1995). Sincewaste tires are known to act as a breeding ground for vermin and mosquitoes, inaddition to wasting valuable landfill space because they contain approximately 75%void space then it can be said that land-filling is not a good disposal technique forwaste tires, (Scrap Tire Management Council, 1999).

The most famous natural deposit of lake asphalt is the Trinidad Lake Asphalt(TLA), which occurs naturally in the form of a 100 acre lake located on the island ofTrinidad in the West Indies. The material basically comprises a mixture of bitumen,water and very fine mineral matter. TLA is well known for its consistent properties,stability and durability, and is widely used for bridge and airport applications wherehigh stability surfaces are required. TLA is a well established commercial product andtypically, a 50:50 blend of TLA and bitumen is adopted in the production of TLAmodified mastic asphalt, (Widyatmoko, 2008).

There exists a clear relationship between the differences in the quality of asphalt(different compositions) from different sources and the resulting performancequalities is well known, (Oyenkunle, 2006; 2007, Andersen, 2001, Trejo, et al., 2004).


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The Influence of Recycled Tyre Rubber 183

Asphalts conformation with the same specifications can often produce pavements ofvarying physical properties, performance and serviceability. Consequently bitumenand asphalt materials may interact with additives differently. Research investigatingthe influence of polymeric materials on the mechanical properties of Trinidad LakeAsphalt and Trinidad Petroleum Bitumen is limited.

This study intends to investigate the influence of scrap tyre rubber on therheological properties of TLA and TPB and hence its potential use as a recyclingoption in Trinidad and Tobago.

ExperimentalMaterials and preparation of samples

A scrap tyre was obtained and shredded. The steel was removed and the pieces ofrubber were then immersed in liquid nitrogen before grounding. The resulting CrumRubber (CR) of various particle sizes was then dried and sieved. The CR of diameter400m was then blended in TLA (Lake Asphalt of Trinidad and Tobago Limited) anda 60/70 penetration refinery bitumen, TPB (Petroleum Company of Trinidad andTobago Limited).

Aluminium cans of approximately 500cm3 were filled with 250260 g of asphaltand put in a thermoelectric heater Thermo Scientific Precision (Model 6555) wherethe temperature was raised to 200 C. A digital IKA (Model RW20D) high shearmixer was then immersed in the can and set to 3000 rpm. The CR was addedgradually (5 g/min) while the system was kept at a temperature of 2001 C. Each

TLA-Rubber blend was formed from 0, 2, 5 and 10% of CR by weight and each TPB-Rubber blend was formed from 0, 10, 15, 25 and 30% of CR by weight.At the end ofmixing, the material was split into different cans and transferred to an oven at 200 C,under static conditions and in an oxygen-free environment. After the desired period ofcuring, the cans were taken out and the molten mixtures were then cast into a ringstamp with 25 mm diameter and 1 mm thickness for subsequent rheological testing.Before testing, the samples were cooled at room temperature and stored in a FisherIsotemp freezer at 20 C.

Rheological Measurements

The rheological characterization of the various asphalt blends were studied using an

oscillatory dynamic shear rheometer (ATS RheoSystems) operated within the lineardomain under strain control. The test geometries were plateplate (diameters 25mmand 1mm gap). Viscosity measurements were conducted in the temperature range20 C 140 C and frequency range was 0.1 15.91 Hz. The maximum strain was keptbelow the limit of the linear viscoelastic region.

Results and DiscussionRheology is that part of science that is interested in the description of the mechanicalproperties of different materials under various deformation conditions when they

simultaneously perform the capability to flow and accumulate recoverable


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deformation; in this case, the rheological properties of bituminous blends aremeasured using the DSR and variations in the complex modulus and phase angleswere observed. The Complex modulus represents stiffness, whilst phase angle isnormally used to demonstrate the viscoelastic response of bituminous materials.Higher values of phase angle indicate a tendency towards more viscous behaviour,whilst lower values indicate more elastic response. The elastic behaviour (lower phaseangle) is generally associated with high stiffness and increased brittleness; while theviscous response (higher phase angle) reflects high ductility and low stiffness.

Figures 1 and 2 show the variation of the phase angle and G* with frequency atdifferent temperatures for TPB and TLA respectively.

Figure 1: Variation of G* and Phase angle with Frequency at different temperaturesfor Bitumen.


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Figure 2: Variation of G* and Phase angle with frequency at different temperaturesfor TLA.

TLA exhibited lower phase angles and higher G* values than TPB over thetemperature range. At 333K and at a frequency of 4.0 Hz, TPB was almost completelyviscous (phase angle 88.4 degrees) whereas the phase angle for TLA was 54.2degrees. At these conditions of temperature and frequency, G* for TLA wasapproximately 2000 times that of TPB. These observations are consistent with thesuperior physical properties of TLA as the material was significantly stiffer and more

elastic material than TPB. As expected the phase angles for TPB and TLA increasedand the values of G* decreased with increasing temperature. For example at a loadfrequency of 15.9Hz the phase angle for TPB increased from between 18 to 86.4 andthe G* values decreased 36 times as the temperature moved from 293K to 333Kwhereas for TLA it increased from between 35.5 to 79.4 and the G* values decreased50 times as the temperature increased from 333K to 383K. The materials moved fromexhibiting an elastic response to an almost viscous liquid. The effect of the loadfrequency was more pronounced at lower temperatures and affected the phase angleand G* as the response tended to be more elastic and stiffer with increased loadfrequency.


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Incorporating rubber particles in TLA had a significant effect on the viscoelasticproperties of the material.

Figure 3 shows that the addition of CR to TLA resulted in a significant increase inthe values of G* which corresponds to an increase in the stiffness of TLA blends. Theincrease appeared to plateau at around 5%. This thickening effect can be associatedwith the reaction between the TLA and the CR at high temperatures during theblending process. The CR crosslinks with the TLA and absorbs some of the asphaltmolecules resulting in the swelling and thickening the mixture, (Navarro et al., 2002;Worsak, 2005). The increase in stiffness increased as the load frequency decreased.Adding 5% CR to TLA at a load frequency of 15.9Hz resulted in a twenty five foldincrease in the complex modulus whereas the increase was approximately twohundred times at a load frequency of 0.1Hz.

Figure 3: The effect of increasing CR% on Complex Modulus for differentfrequencies at 80C.

Figure 4 shows the effect of the CR on the phase angle of the TLA blends. Theeffect of the addition of CR to TLA on the phase angle produced interesting results.The viscosity of the material increased (higher phase angle) with the addition of 2%CR and further addition of CR resulted in a decrease of the viscoelastic response(lower phase angle). The effect on phase angle on CR became more pronounced asthe frequency increased. Adding 5% CR to TLA at a load frequency of 15.9Hz


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resulted in a decrease of more than fifty percent in the phase angle whereas thedecrease was twenty six percent at a load frequency of 0.1Hz.

Figure 4: The effect of increasing CR% on Phase Angle over a temperature range of80C to 140C.

The influence of the addition of CR on TPB resulted in an increase in the complexmodulus of the material, maxima being observed at 5% crum rubber. It was alsoobserved that the maxima which occurred at 5% increased with increasingtemperature, (see Figure 5). Adding 5% CR to TPB at 20C resulted in a two foldincrease in G* whereas the increase was ninety one times at 120C.

Adding 5% CR to TPB resulted in a significant decrease in the phase angle, theextent of which increased with increasing temperatures. A decrease of seventy one

percent was observed at 120C compared to twenty nine percent at 20C. Theviscosity recovered with 10% CR addition and fyrther addition of CR resulted in agradual decrease in viscosityof the blends. The temperature dependence of theviscoelastic response produced a sporadic response especially at lower temperatures.This was also observed by Lesueur (2008) and was attributed to the potential lack ofpolymer/bitumen compatibility. Since the dispersion of the polymer molecules withinthe bitumen is dependent on the absorption of the maltene component of the material,it follows that chemical composition of an asphalt determines its polymercompatibility. For TLA, the ratio of naphthene aromatic: polar aromatic : asphalteneis approximately equal to one, unlike the other asphalts, which generally have a lowproportion of asphaltenes compared with aromatics (Chattergoon et al., 1992).


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Figure 5: The effect of increasing CR% on Complex Modulus of Bitumen-RubberBlends for different frequencies at 80C.

Figure 6: The effect of increasing CR% on Phase Angle of the Bitumen-RubberBlends over a temperature range of 80C to 120C.


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The effect of the CR on the viscoelastic properties of the blends is illustrated bythe Black Curves in Figure 7 and 8. For practical purposes it is possible to producea stiffer but more viscous TLA based material by the addition of 2% CR. BlendingTLA with CR > 2% produces a material that is significantly stiffer and more elastic.However increasing the CR concentration in TPB produces a marginal increase instiffness and a significant increase in elasticity.

Figure 7: Graph Showing Complex Modulus vs. Phase Angle for TLA-RubberBlends.

Figure 8: Graph Showing Complex Modulus vs. Phase Angle for TPB-RubberBlends.


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ConclusionThe addition of CR in TLA and TPB resulted in changes in the rheological propertiesof the materials and confirmed previous findings that the rheology of asphalticmaterials is composition dependent.

The addition of CR to TLA resulted in a significant increase in the values of G*.This increase appeared to plateau at approximately 5% CR. The effect of the additionof CR to TLA on the phase angle resulted in an increase in the viscosity of thematerial (higher phase angle) with the addition of 2% CR and further addition of CRresulted in a decrease of the viscoelastic response (lower phase angle).

The addition of CR to TPB resulted in an increase in the values of G*, with amaximum occurring at approximately 5% CR. The effect of the addition of CR toTPB on the phase angle resulted in a general n increase in the viscosity of the material

(higher phase angle) except at 5% CR concentration where a significant decrease ofthe viscoelastic response was observed (lower phase angle).

Variations of the rheological properties reflect variations in the mechanicalproperties of the various blends. Blends with relatively lower G* and higher phaseangles are more ductile and flexible resulting in a more crack resistant materialwhereas blends with relatively higher G* and lower phase angles are more elastic anddeformation resistant.

The results therefore confirm waste tyre rubber has enormous potential to be usedas a modifier of TLA and TPB. The abundance of waste tyre rubber in Trinidadrenders the material environmentally attractive for improving the use of asphalt.

References

[1] Blanco, R., Rodrguez, R., Garca-Garduno, M., Castano, V. M. J ApplPolym Sci 1995, 56, 57.

[2] Chattergoon, L., Whiting, R., Smith, C., 1992. Improved Methods forSeparation and Chromatographic Analysis of Natural Asphalts. Analyst, 1992,117, 1869

[3] Crockford, W.W., Makunike, D., Davison, R.R., Scullion, T. and Billiter, T.C.(1995). Recycling Crumb Rubber Modified Asphalt Pavements. ReportFHWA/TX-95/1333-1F.

[4] Zurbrugg, C. (2003). Solid Waste Management in Developing Countries.Retrieved on 17th January, 2009, from www.eawag.com.

[5] Douglas, D. and Carlson, H. Z. (1999).Asphalt-Rubber: An Anchor to CrumbRubber Markets. Paper presented at the Third Joint UNCTAD/IRSGWorkshop on Rubber and the Environment. Veracruz, Mexico. Retrieved 25thNovember 2008. Website: www.asphaltrubber.org

[6] Fawcett, A. H.; McNally, T. M.; McNally, G., 2002. Adv Polym Technol,2002, 21, 275.

[7] Kortschot, M. and Woodhams, R.T., 1984. Polymer Engineering Science Vol24 no. 4 252-256.


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[8] Lesueur, D. (2008). The colloidal structure of bitumen: Consequences on therheology and on the mechanisms of bitumen modification. Advances inColloid and Interface Science , 42-82.

[9] Lu, X.; Isacsson, U. J., 2000. Appl Polym Sci 2000, 76, 1811.[10] Masson, J.-F.; Pelletier, L.; Collins, P. J., 2001. Appl Polym Sci 2001, 79,

1034.[11] Navarro, F.J., Partal, P., Valencia, V., Gallegos, C. and Martinez-Boza, F.

(2002). Rheological characteristics of ground tyre rubber-modified bitumens.Chemical Engineering Journal , 53-61.

[12] PIARC, Modified binders, binders with additives and special bitumen,Roads (PIARC Journal), No. 303, 1999, p. 88-91 and 106-107.

[13] OECD (1999). Relationship between global MSW, global population andglobal GDP[14] Oyenkunle, O. L., 2006. Certain relationships between Chemical Compositionand Properties of Petroleum Asphalts from Different Origin. Oil and GasScience and Technology Vol 61 No. 3 pp 433-441.

[15] Oyenkunle, O. L., 2007. Influence of Chemical Composition on the PhysicalProperties of Paving Asphalts. Petroleum Science and Technology, 25:1401-1414.

[16] Scrap Tyre Management Council. (1999). The Many Uses of Crumb Rubber.Paper presented at Texas Natural Resource Consevation Commission, Austin,Texas. Retrieved on the 19th November, 2008. Website: www.tceq.state.tx.us

[17] Singh, B., Tarannum, H., Gupta, M. J., 2003. Appl Polym Sci 2003, 90, 1365.[18] SWMCOL (1995). Report on the Waste Quantification and Characterizationexercise Beetham Landfill, Guannapo Landfill and Forres Park Landfil.[19] Trejo, F., Centeno, G., Ancheyta, J., 2004. Precipitation, fractionation and

characterization of asphaltenes from heavy and light crude oils. Fuel 83:2169-2175

[20] Way, G.B. (1999). Flagstaff I-40 Asphalt Rubber Overlay Project, Nine Yearsof Success Arizona Department of Transportation.

[21] Wen, G., Zhang, Y., Zhang, Y., Sun, K., Chen, Z. J., 2001. Appl Polym Sci2001, 82, 989.

[22] Widyatmoko, I. and Elliott, R., 2008. Characteristics of elastomeric andplastomeric binders in contact with natural asphalts. Construction and

Building Materials, 22, pp 239249.[23] Worsak, Kanok-Nukulchai.(2005). Rubber Modifed Asphalt for Better Road

Pavement. Asain Institute of Technology, Bangkok. Retrived on 3rd April2009 from www.doh.go.th/


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