10TH AAPA INTERNATIONAL FLEXIBLE PAVEMENTS CONFERENCE

SESSION 2 - INNOVATION

The Use of Crumb Rubber in Slurry and Microsurfacing and Chip Seals

Cilynn Holleran,

Vice President,

Valley Slurry Seal Company, USA

Jeffrey R. Reed,

President,

Valley Slurry Seal Company, USA

Jack Van Kirk,

Director Of Asphalt Technology,

Basic Resources Inc, USA.

OIAI'" Flexible FlAtlAl"'e - Pc\VeW\e�ts fol'" the 21 st Ce�tlAl"'y

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USE OF CRUMB RUBBER IN SLURRY AND MICROSURFACING AND CHIPSEALS

Glynn Holleran, Vice President, Valley Slurry Seal Company, USA Jeffrey R. Reed, President, Valley Slurry Seal Company, USA

Jack Van Kirk, Director Of Asphalt Technology, Basic Resources Inc, USA.

ABSTRACT

The problem of disposal of tyre rubber is well known. In USA alone 282 million tyres a year are discarded. The stockpile currently is about 1-2 billion tyres (NAPA 1993). Many methods of disposal have been used including burning, burying, and recycling to other rubber products. In some countries, tyre rubber has been used in road applications to enhance performance or as a means of disposal, with the road serving as a sort of horizontal land fill.

The increase in popularity of emulsions in many countries, for environmental and energy reasons has meant that the traditional hot applied methods using rubber have become a less attractive method of using tyre rubber and emulsion alternatives are required.

The application of crumb rubber in emulsions has been somewhat limited. This is not because rubber cannot be emulsified but because the other components in crumb rubber and the crosslinked nature of the tyre rubber have meant that even the best wet process blends are distinctly two phase. This makes creation of a stabilized emulsion difficult. The solution has been to add the rubber into dry aggregate mixes with emulsion or create a dispersion in a suitable diluent . One such process is the subject of this paper.

In this paper the properties and manufacturing methods of emulsions using a dispersed crumb rubber is discussed. The properties of the emulsion are discussed in terms of stability and general properties; the application and performance are discussed in the areas of slurry and microsurfacing and chip sealing.

Laboratory mix design methods indicate that the use of crumb rubber can reduce deformation in slurry and microsurfacing, increase allowable asphalt content without bleeding, increase flexibility and abrasion resistance. The combination with latex additives appears to give even greater improvements . Adhesion too is improved and this may be partly attributable to the oil fraction used in the product manufacture. This was checked using different solvents and it was found that solvent has a significant effect. This would be attributed to enhanced wetting. Resistance to reflective cracking also appears to be improved.

In chip seals stone retention is improved.

1. INTRODUCTION

Scrap rubber, crumb rubber, reclaimed rubber are all terms describing rubber recycled from other uses, principally car tyres. It is not a pure polymer but a blend. However most car tyres in USA are mainly vulcanized, ie. crosslinked SBR or polyisoprene and carbon black, which acts as a reinforcing agent. The tyre compounds can also include other polymers as well as other fillers and chemicals additives. The principal polymer components have been used as additives to asphalt in many places . Natural rubber has been used with success in Malaysia and in the Middle East, SBR has long been used in USA and carbon black has been used as a stabilizing agent for asphalt . Ground tyre rubber is thus a good additive for property modification.

The rubber in the tyre rubber systems however has been crosslinked or vulcanized. This, in fact, gives the rubber its high elasticity and thus ability to rebound as well as imparting some physical strength. (In SBR or natural latex systems the rubber is added in as a latex usually and any crosslinking that occurs is due to heat and or aging). This vulcanization in tyre rubber reduces significantly the dispersion capability of the rubber molecules and reduces stability. When mixed with asphalt, a two phase system is created. For these reasons, the morphology and physical properties are quire different from simple SBR addition. Also the actual sizing of the ground rubber particles is important, not just for the time they take to disperse, but also because this has a large effect on the degree of "reaction" that occurs and the morphology of the blend.

Ground tyre rubber has been used in road applications for many years in Australia and USA in sealing applications such as SAM and SAMI, as well as in crack sealing and joint filling. However, with the availability of synthetic polymers of known composition and performance and moderate cost there seems to be no particular economic benefit in using Ground tyre rubber. Difficulties of handling related to high viscosity build up (Bahai 1995) and poor storage characteristics have created further problems. On site blending (Cano 1997) has been extensively and successfully used in the Western States of USA (Van Kirk 1997). Processes for steric stabilization (Harbinson 1995) have also been developed which employ chemical additives and extender oils.

The problems of emissions, stone retention (especially where diluents such as kerosene and diesel fuel are banned) have not been successfully countered. In California, a hood extraction system has been patented (Corcoran 1995) but this is limited in use.

In hotmix, the California Department of Transportation (Caltrans) has successfully used dense, open graded, and gap graded asphalt rubber overlays on concrete and asphalt concrete freeways and as rehabilitation treatment with SAMls (Van Kirk 1992). In fact, the methodology is now allowing layer thickness reductions (Van Kirk 1997) in the state of California.

In pavement maintenance treatments the use of crumb rubber has been limited to chip seals applied hot, this can also be as the base layer of a Cape Seal treatment. Such systems have been very successful, often extending pavement life by 7-10 years on jobs that would have otherwise required reconstruction (Cano 1997).

2. METHODS OF USE

2.1 Hot Applications

There are two basic systems for using scrap rubber in hot applications.

1. Wet Process 2. Dry process

Each begins with scrap rubber in a convenient form. This may be with buffings from a retreading operation or from a tyre processing plant. This may also be ground rubber and such materials may be ground at ambient temperature or cryogenically. The advantage of ground rubber is that it may be digested or mixed faster than larger particles. It was found, in work carried out at the Australian Road Research Board in the 1980s (Oliver 1989) that the morphology of the rubber influenced the physical properties of the final binder. The ambient ground rubber appeared to give better results, as it has a roughened surface morphology.

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a) Wet Process (Epps 1992).

The loading rate of rubber is 15-20%.

The rubber is mixed and digested in the asphalt by either low or high shear mixing. The rubber undergoes a specific interaction with the asphalt. This is often referred to as a reaction. It is rather a physiochemical reaction rather than simply a chemical one. The rubber swells in components of the asphalt to produce a composite. In the wet process this is aided by the use of added aromatic oils (extender oils).

The particle size and shape has a large effect on this digestion rate along with the temperature. Digestion is achieved by a range of on site mixing systems that use auger and propeller mixers. The presence of particulate rubber dispersed through the asphalt matrix is key to the success. It has been conjectured that the mechanism of crack blunting is due to strain alleviation of a crack tip by these rubber particles.

The wet process is used mostly in Australia, South Africa and USA (RTA 1995), (Polgeiter 1989).

Variations on the process have been developed in California using a so-called type II rubber that contains a second recycled rubber component which is substantially natural rubber. This is often tennis ball rubber or mat rubber.

A new, performance based, specification has been in development by Caltrans for some time (Reese 1995) . This is based on SHRP methodology and, while it is not as yet validated, points towards a future approach that may allow the specification to become non material specific.

The addition of scrap rubber should:

• Reduce thermal cracking

• Reduce rutting

• Reduce reflective cracking • Aging resistance

• Chip Retention.

The type II system with natural rubber addition improves stone retention and resistance to fatigue and reflective cracking. This is used in California mostly and is specified in the recipe specifications issued by that state.

How well properties are achieved depends on asphalt! rubber compatibility, the mixing time and method, the size of the ground rubber particles, the mix design and the application parameters such as compaction and laying temperature.

b) Dry process (Epps 1992)

This is sometimes called the "rubber aggregate" process. This is a mixture of asphalt, mineral aggregate and granulated rubber. The aggregate grading is gap graded to allow for space for the 3% of rubber that is added. The time at "reaction" temperature is limited by limiting mixing time and the rubber retains its integrity. The surface only interacts with the asphalt creating a durable bond.

A percentage of the rubber granulate will be fine and can affect the asphalt as in the wet process.

A new variation on this process has been recently trialed in Southern California. This uses only the finer rubber addition and maintains the aggregate grading as for the wet process. In this the

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solid rubber particles are conveyed into the pug mill during weigh up. The theory is that the rubber particles will partially digest and fill voids.

The drawback with both systems is that mixing uniformly is difficult and often the result is significant segregation of rubber, leading to areas of raveling and bleeding (Van Kirk 1997b).

The system should produce:

• Reduction in reflective cracking

• Ice disbonding

• Raveling (increase)

• Flushing

• Flexibility

• Improved surface texture.

The surface texture produces better draining, skid resistance and noise reduction.

This has not been a very successful system mostly due to problems in ensuring a homogeneous mix.

2.2 Emulsion Addition

Polymer emulsions have been used to a great extent in chip sealing and slurry/microsurfacing (Holleran 1996, 1996). The polymers generally are pre-blended with the asphalt, co-milled as latex either by direct injection into the soap or pre mixed with the soap, or post added.

Ground tyre rubber usually can not be added so simply.

Pre-blended crumb, if completely digested, or with very small particulate size rubber, might be able to be emulsified . But crumb rubber systems in asphalt are generally two phase and the vulcanized nature and presence of additives make emulsification into a stable dispersion very difficult.

The methods by which tyre rubber may be incorporated in emulsion are thus largely confined to post addition approaches.

Ground solid crumb rubber has been added into slurry mixes as a dry ingredient, similar to the method mentioned above. In such a case, the rubber becomes a part of the aggregate phase and acts mainly as a filler. Such processes are in general use in USA.

However, to create much of a change in elasticity, increase in cohesion, and other desirable properties, the rubber needs to be fully or partially digested so that it may coat particles. This is the basis of the process to be discussed.

The increase in cohesion should improve properties such as deformation resistance (in rut filling), surface abrasion resistance, crack resistance and allow increased binder films without flushing.

2.3 Solvent Dispersion

The process referred to as the wet process may be adapted for use with emulsions. If a suitable solvent can be used that allows dispersion in the emulsion water phase, then a material capable of being post added may be produced. The solvent type is of obvious importance as it must not

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create an environmental hazard, nor degrade either the asphalt properties or those of the rubber. On the other hand, if the solvent is able to swell or soften the rubber, then it may improve wetting and adhesion.

A range of solvents has been used to optimize the dispersion and other additives such as wetting agents and carbon black. In general terms, an oil additive is preferable with a high aliphatic content and a boiling range that meets emission requirements but also allows swelling of the rubber. The material will be referred to by its deSignation of RG-1.

3. Emulsion Properties and RG-1

RG-1 is a semi swelled dispersion of crumb rubber (40-50%) in a petroleum solvent. It is supplied as a free running high viscosity material that can be readily poured and pumped.

RG-1 is used by post addition into the emulsion with simple mixing (Figure 1 shows some properties). As may be seen the emulsion is not greatly affected by addition of RG-1 except that the sedimentation rate is high. This is not surprising as the RG-1 is a separate phase and so the emulsion must be thoroughly mixed before use. There is no obvious breaking caused by the presence of the RG-1 and this is true to concentrations in excess of 20%.

Figure 1 Emulsion Properties

Emulsion %RG-1 Viscosity

Settlement Residue

Break (

Type (3 day) AS1160) CRS-2 5 120 3 67 <3min CRS-2 10 160 5 68 <3min CRS-2 20 210 10 69 <3min

PMCRS-2 10 170 6 69 nfa CQS-1h 10 39 7 60 nfa

LMCQS-1 10 65 9 61 nfa

h Micro 10 70 7 61 nfa

The residual properties of the binder were similar to that expected for about 2.5-10% residual crumb rubber. That is, torsional recovery results were up to 10% and viscosity increased. This is indicative of the recovery method and the digestion of the rubber into the asphalt due to the application of heat (Figure 2). It is interesting that the penetration actually increased, this may have been due to retained solvent. It is not unusual with elastomer systems that viscosity increases, but penetration indicates increased softness.

Figure 2 Residual Properties.

Emulsion Torsional Viscosity After

Addition pen 25C RTFOT RBSP Type Recovery p 60C

Viscositv CRS-2 0 0 1 21 764 1 21 9 40

1 0 3 1 81 1 377 2600 45 1 5 5 1 95 48 20 9 21 0 50

CaS-1 h 0 0 60 1 700 3200 40 5 4 68 2500 4500 45

1 0 5 82 49 1 5 7 95 52

Micro 0 0 60 40 5 5 68 47

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This indicates that the rheological type of the binder has changed and hence the physical properties such as thermal susceptibility have been improved.

Dynamic Shear Rheometer (DSR) measurement is difficult with two phase systems, particularly with recovered emulsion samples, but indications are that the binder has lower stiffness at low temperatures and higher stiffness at higher temperatures than the base asphalt and hence improved crack and rut resistance. This is shown approximately in Figure 3. These results are consistent with increases in elasticity as indicated by the torsional recovery and increases in ring and ball softening point with viscosity increase.

1 0,000

1 ,000

1 00

1 0

vss

Figure 3 Modulus of Residual Binders

-55 pen

-SBR

• RG-1

& RG-1 with latex

1 0 20 30 40 50

Temperature ('C)

Aging does not seem to be affected.

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To gauge the effect on the application requires testing of the final product.

Note that although the effect on cationic emulsions is reported here, the RG-1 was able to be mixed with anionic emulsions as easily and seemed to exhibit similar stability.

Emulsions based on slow set emulsifiers such as Vinsol, Indulin SAL (Westvaco) and alpha olefin sulphonate quick setting anionic systems would appear to be satisfactory. The viscosity increase due to the addition is in general greater for the anionics than the cationics. It was noted for some cationic systems that viscosity did tend to decrease with storage. This is probably due to some coarsening of the asphalt emulsion as the initial effect is to increase viscosity. The anionics tested experience some increases over time, this may indicate some swelling or gelling effects in the water phase and is likely to be surfactant based compared to cationic. Figure 4 shows this effect for cationic and anionic systems.

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Figure 4 Effect On Viscosity with Time.

400 Viscosity cst 77F

350 �-'-"

HFE 5%

--- ........ ------

300 CRS-25%

�'l 200 1 HFE

150 0 5 10

Time (hrs)

15 20 25

The dispersion of the ground rubber within the final binder was examined visually by curing samples of materials in trays. It is evident that the asphalt breaks around the rubber particles but by no means could digestion be considered to occur. This is a reinforced asphalt binder coating the particles.

Simulation, in an emulsion form, of the properties of a hot crumb rubber blend binder is thus not being achieved. To achieve this will require a emulsification of a pre-blended binder and this is the subject of current research.

In fact, this can be achieved with the use of a heat exchanger system on the emulsion mill, a high binder temperature and the use of specialty emulsifiers. The results of this development will be available for field trials in the future.

4. Slurry Seal and Micro Surfacing

4.1 Laboratory Method

International Slurry Surfacing Association (SI) guidelines were followed exactly with the RG-1 mixed in the emulsion with hand stirring.

Two aggregate sources were chosen, a granite and a volcanic basalt. To gauge the effect of the rubber a 5% by weight (based on the binder solids) rubber level was chosen to compare the tests. To put this in perspective, the results were compared to similar mixes with different polymers. To ensure that a comparison could be made, the emulsion content was equalised as optimum for the asphalt design. This was about 8% asphalt or 13.5% emulsion on the type II rock. The RG-1 was added at 5% residual as recommended and the other polymers were at 2.5% residual for the latex and 3% for the SBS. In the RG-1+ case this was 3% latex with the rubber added.

Mixing times were different for the RG-1 modified systems, and retarder levels needed to be increased significantly compared to asphalt emulsion from 0.25% to 1.0%. Water levels too were increased by around 25-30%.

For flex testing, samples were prepared according to ISSA 146. However, as the ISSA device was not available, a method was devised where the strips of metal with the slurry covering were bent in a continuous rate of about 5cm per minute and the onset of visible cracks observed. The lateral distance that the strip was bent from the horizontal was measured and the difference noted. This is obviously very operator dependent but appeared to be as reproducible

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as the ISSA 146 test. The results may only be taken as an indication however and more work is required.

All mixes met both the requirements for microsurfacing and slurry seal.

4.2 Results

a) Wet Track testing (figure 5)

Wet Track showed that the rubber additive gave improved resistance to stone loss under this test compared to asphalt. This may give the opportunity to reduce binder levels.

In combination with latex the results were further improved. This showed less improvement than with latex alone. This is probably due to the presence of particles of rubber in the surface that are taken out by the abrasion head. This is not an unexpected result. It should not be interpreted in terms of insufficient binder however.

The general increase in resistance to abrasion does indicate that binder levels may be increased for these systems by at least 1 %. This will have the effect of increasing durability, as film thickness is the determining factor for this property (Holleran 1996).

Figure 5 WET TRACK ABRASION LOSS

50

40

30

20

1 0

0 ASPHALT

vss

SBR SBS NEOPRENE/AT LATEX RG-1+ RG-1

lliD 1 HOUR

.6 DAY

b) Loaded Wheel Test ( Figure 6)

Mixes with RG-1 showed improvement in resistance to deformation relative to asphalt. The improvements were but not as large as those for polymer modification. When combined with latex, the results for the RG-1 mixes were improved significantly. These results show the effect of increased viscosity and modulus. Shear resistance cannot be gauged by this test but the results are consistent with improvements in rut resistance and indicate an application for this type of material.

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1 6

14

12

1 0

8 6

4

2

Figure 6 LOADED WHEEL TEST

DISPLACEMENT (%)

o ASPHALT SBR SBS NEOPRENE EVA NAT LATEXRG·1+ RG·1

TYPE (3%) VSS

c) Cohesion (Figure 7)

The setting of the slurry /microsurfacing was not compromised by the addition of the rubber, in fact it was improved marginally. The polymer materials were better still.

25

20

15

10

5

0

Figure 7 MICROSURFACING

COHESION COHESION

ASPHALT SBR SBS NEOPRENE NAT LATEX RG-1+ RG-1

TYPE

1030 MINUTES .60 MINUTES

This is a result of a higher green strength of the polymer modified system. It probably does not cure at any faster rate but the shear strength of the material is simply higher during all stages of the curing process.

Figure 8 illustrates this for Vial it plate test with these binders.

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Figure 8 Cohesion Build Up

[j!J] 1 hour Cure 100

80

60

40

20

oL-------------------------------� caS-1 h CaS-1 h 5% Micro Micro 5%

The improvements may also be in part due to improved wetting caused by the softening effect of residual solvent in the system, thus increasing adhesion.

Standard boiling tests for adhesion showed some improvement and Shulze Breuer testing showed higher compatibility, so this effect is significant to the mix performance. (All rubber modified mixes had AAA ratings and qualified as microsurfacing mixes.)

d) Flexural Strength - Crack Resistance

Figure 9 shows the test results on these mixes in flexure. Within the limitations previously indicated, the rubber modified material does appear to have better crack resistance in flexure. It should, therefore, improve resistance to traffic flexing in rut filling and allow an improvement in performance of the slurry coat of a cape seal.

4.3 Field Results

Figure 9 Flexural Test:25C, 4C

2

1.5

0.5

Polymers V RG-1 V standard slurry - type II Ratio to standard

o �----------------------------� 5% RG-1 5%RG-1 3% Latex

Type

3% latex

Field trials have been carried out using RG-1 and the long term effects are being quantified. The main trial carried out was on a residential street with moderate surface raveling, shrinkage cracking, and alligator cracking. This was divided into three sections, alligator cracking was worst in section III.

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Cracks were sealed with cold crack pour sealant in section I and this section was covered with a type II polymer modified (latex at 3.5%) slurry.

Section II was overlaid with the same type II slurry as above.

Section III was done with a 5% residual addition of RG-1.

All applications were at about 20lb/yd2•

4.3.1 Results

After 18 months section I had intermittent hairline reflection cracks. This was less than for comparable streets done with unmodified slurry seal in the same trial. Moderate raveling occurred.

Section II looked similar to section I.

Section III has been performing extremely well, even in the worst alligator cracked areas, little, if any cracking has been reflected through. Stone retention was excellent with little or no raveling.

4.3.2 Conclusions

The general conclusions on slurry and microsurfacing application to date are:

1. RG-1 was easy to blend into the emulsion using an in line blending system and ensuring that the emulsion was well mixed before use.

2. The emulsion mixed easily with the mixes and, although higher levels of retarder and water were required, laid as normal.

3. The slurry set and cured normally. 4. Long term effects of traffic and aging cannot be concluded from results to date. 5. The use of the crumb rubber product appeared to retard reflective cracking. 6. Stone retention appears to have been improved.

5. Use In Chip Sealing applications

5.1 Emulsion Properties/Stone Retention

In Figures 1 and 2 some properties of CRS-2 type emulsion were shown. It is clear that the rubber has some effect on the residual properties but the recovery method is likely to play a part in this. The effect of the binder on chip performance was examined using a modified Vialit plate test. Some of these tests were carried out by US Oil and Refining and some by VSS.

The modified test involves testing Vialit Plates after 1 hour and 12 hour curing at 90F. The effect of viscosity increase with time of storage was also examined.

Extra testing was carried out to compare the effect of other polymers on stone retention using the same method.

Figures 10 and 11 show the results. It is evident that the RG-1 has a significant effect on stone retention and that this is comparable and even superior to emulsion modified with latex. In combination with latex, the RG-1 performs even better.

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Figure10 Chip Retention

Emulsion % RG-1 1 hour cure 12 hour cure

Type

CRS-2 0 61 87

5 70 92

10 73 95

CMS-2 0 55 81

5 75 94

10 84 97

HFE90 0 66 85

5 76 97

10 91 96

This may be caused by an increase in cohesion produced by the rubber but may also be associated with improved wetting due to residual solvent.

120

100

80

60

40

20

0

Figure 11 RG-1 V Polymer

CRS-2

� 1 hour Cure

.12 Hour Cure

PMCRS-1h PMCRS-1h 10% RG-1 CRS-210% RG-1

5.2 Emulsion Properties! Viscosity Change

The viscosity of the cationic emulsions fell significantly with time as may be seen in Figure 4 and was greater as the addition rate was increased. For Anionic high float emulsions there was little change.

For emulsions already modified with latex the same trend was observed. This indicates that it may be better to add RG-1 on site.

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5.3 Seal Design and application

The rubber loading rates are significantly lower in the final binder than is usual for the hot applied systems. Design was carried out, as per Austroads application rates, for both aggregate and binder. No allowance was made for the fact of rubber being present.

The seals made across a range of jobs in residential streets and secondary roads over the last 5 years have shown good results.

There was some indication that reflective cracking was retarded in these trials.

6.0 Economics

Figure 12 shows the economics and environmental impact of using RG-1. For chip seal the cost is about 2-5c per square foot depending on the dose rate. For Slurry or Microsurfacing, the cost is 1.5-3.0c per square foot, depending on which treatment is used.

No extra equipment is needed, as the additive may be added at the plant using the transfer pumps in existence. Little change is required to laying procedures.

Figure 12 Tyres Used In Chip Seall Slurry per mile

Tyres used 500 �--------------------------------�

400 Chip

300

200 Slurry 100

O�--------------------------------� o 5 10 15 20 25

Miles

7.0 Conclusions

1. Crumb Rubber has extensive uses in road surfacings and mixes. 2. Emulsion processes are limited in method of incorporation. 3. A solvent dispersed ground rubber, partially swelled, can be easily mixed with

emulsions. 4. In slurry seal and microsurfacing mixes improvements in abrasion resistance,

deformation resistance and cohesion are observed in laboratory mixes. Flexural resistance is also improved. The binder appears to be improved in thermal susceptibility and in elasticity. In the field, reflective cracking appears to be retarded and stone retention is improved.

5. Such slurry seals and microsurfacings are easy to apply but may require extra retarder. 6. The addition of this material is an effective way to dispose of tyre rubber.

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8.0 References

1. Scrap Tyre Utilization Technologies. Washington 1993. National Asphalt Pavement Association Information Series 113

2. Bahai, H, Proc AAPT Vol 64. 1995. 3. Cano J. Proc. 3rd Annual Bitumen Asia Conference 1997. 4. Van Kirk, J.L Proc Rubber Division of A.C.S 1997 5. Harbinson, B Petersen Conference, Wyoming 1995. 6. Cocoran et al USA patent 1995. 7. Van Kirk, J.L TRB Annual Meeting 1992. 8. Oliver, J.W.H. (1989) Proc National Workshop on Polymer Modified Binders ARR183

Australian Road Research Board 9. Scrap Rubber Asphalt Guide Document TP-GDL-1 01, Sydney 1995 RTA Technology,

Vicroads, MainRoads WA. 10. Poltgieter, C.J, Botha, P, Renshaw, R.H. Uekeman O. 5th CAPSA Conference

Swaziland 1989. 11. Reese, R. Proc AAPT Vol 64 1995 12. Epps, J.A ed -Uses Of Recycled Rubber Tyres in Highways- NHCRP Synthesis of

Highway Practice No.198. 13. Van Kirk, J.L Private Communication. 1997 14. Holieran,G, Bryant J, Proc Combined ISSAIAEMA Conference Phoenix 1996 15. Holleran, G. ISSA Slurry Workshop Columbus Ohio 1996. 16. Holieran,G Proc Combined ISSAIAEMA Conference Phoenix 1996

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