deliverable 2.1.1 roadtire

EU-LIFE+ Environment Policy and Governance

LIFE 09 ENV/GR/304“ROADTIRE”

“Integration of end-of-life tires in the life cycle of road construction”

ROADTIRE

Deliverable 2.1.1

“Worldwide survey on best (and worse) practices concerning rubberised asphalt mixtures implementation (number of different

cases, extent of application)”

S. Mavridou, N. Oikonomou, A. Kalofotias

Thessaloniki, December 2010

Table of Contents Page1. INTRODUCTION……………………………………………………..…. 31.1 Waste tires-composition-deposits………………………………………... 31.2 Tires disposal problem…………………………………………………… 51.3 Legislation- EC’s waste management systems……………….………….. 61.4 Treatment of EOL Tires……………………………………….…………. 71.5 Alternative applications of EOL Tires........................................................ 112. TIRE RUBBER IN ASPHALT MIXTURES…………………………….. 122.1 History of rubberized asphalt………………………………………….…. 122.2 Rubberised asphalt products....................................................................... 142.3 Production of asphalt mixtures with tire rubber- general processes........... 152.4 Properties of modified with tire rubber asphalt mixtures........................... 153. WET PROCESS (addition of rubber particles in bitumen)……………… 173.1 Preface…………………………………………………………………… 173.2 Production of rubberized asphalt………………………………………… 183.3 Specifications……………………………………………………………. 203.4 Properties of rubberized asphalt…………………………………………. 223.5 Cost and Benefits………………………………………………………… 283.6 Environmental concerns……………………………………. 304. DRY PROCESS (addition of rubber particles in aggregates)………….… 324.1 Preface…………………………………………………………………… 324.2 Properties of rubberized asphalt mixtures……………………………….. 334.3 Microstructure of rubberized asphalt mixtures…….…………………….. 355. CASE STUDIES………………………………….………………………. 365.1 USA……………………….…………………….……………………….. 365.1.1 Phoenix Arizona....................................................................................... 365.1.2 Flagstaff, Arizona on Interstate 40........................................................... 395.1.3 Odessa, Texas……………………………….………………………….. 415.1.4 Los Angeles, California………………………………………………… 425.1.5 Greenville County, north to Emporia....................................................... 425.2 EUROPE…………………………………………………………………. 475.2.1 Poland…………………………………………………………………... 485.2.2 Belgium……………………………………………………………….... 485.2.3 UK……………………………………………………………………… 485.2.4 Portugal………………………………………………………………… 495.2.5 Spain........................................................................................................ 495.2.6 Germany.................................................................................................. 505.2.7 France...................................................................................................... 515.2.8 Italy......................................................................................................... 515.2.9 Greece…………………………………………………………………. 536. CONCLUSIONS…………………………………………………………. 56REFERENCES………………………………………………………………. 59

AUT-LBM, PRESTE Deliverable 2.1.1 LIFE09ENV/GR/000304

1. INTRODUCTION 1.1 Waste tires-composition-deposits Solid waste management is one of the major environmental concerns worldwide. For the last 30 years many studies have been conducted in order to assess the feasibility of using industrial by-products and waste materials in civil engineering applications. The motive for such studies has been and still is the high cost, the continuous reduction and negative environmental impact of supplying natural aggregates, the legislation, which bans the disposal of wastes in landfills and recycling in general, which is demanded, in terms of sustainable development. Tires, which are included in the European Catalogue of waste as non-dangerous waste consist of synthetic and natural rubber, sulphur and sulphur compounds, silica, phenolic resin, oil (aromatic, napthenic, paraffinic-, fabric-polyester, nylon-, petroleum waxes, pigments-zinc oxide, titanium dioxide-, carbon black, fatty acids, inert materials and steel wires (Siddique and Naik, 2004). It should be noted that all the components are 100% recyclable.

Table 1: Materials composition of car and truck tires Material Car tire Truck tire

Rubber/elastomers 47% 45% Carbon black 21,5% 22% Metal 16,5% 25% Textile 5,5% - Zink oxide 1% 2% Suphur 1% 1% Additives 7,5% 5%

Source: End-of-Life Tyre Management: Storage Options, final report for the Ministry of Environment of New Zealand, July 2004, p. 10

Table 2: Elements inside tires Car tire Truck tire Element % wt % wt Carbon(C) 89.48 89.65 Hydrogen (Η) 7.61 7.5 Nitrogen (Ν) 0.27 0.25 Sulphur (S) 1.88 2.09 Oxygen(Ο) <0.01 <0.01 Chloride(Cl) 0.07 0.06 Ash 3.9 5.5

Source: End-of-Life Tyre Management: Storage Options, final report for the Ministry of Environment of New Zealand, July 2004, p 10

Annually, a steady stream of large volumes of waste tires is generated due to the continual increase in the number of all kinds of mobiles. Especially for the European Community (Austria, Belgium, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, Holland, Portugal, Spain, Sweden, UK), this amount is estimated at up to 250 million waste tires, while equal amounts are estimated for East Europe, North America, Latin America, Japan and Mid-East polluting the environment with approximately 1 billion of waste tires. In

Worldwide survey on practices concerning rubberised asphalt mixtures implementation 3


addition to this, enormous quantities of tires have already been stockpiled or land filled (3 billion of waste tires inside the EC and almost 1 billion in North America (www.etra-eu.org).

Table 3a. Annual deposit of End-Of-Life tires per member of the EC (www.etra-eu.org)

Country EOL TIRES

(tn/ year) Population Austria 50000 8054800 Belgium 70000 10143000 Denmark 39500 5251000 Finland 32000 6116800 France 401000 58265400 Germany 640000 81845000 Greece 58500 10474600 Ireland 32000 3591200 Italy 350000 57330500 Luxemburg 3000 412800 Holland 67500 15492800 Portugal 52000 9920800 Spain 280000 39241900 Sweden 60000 8837500 UK 435000 58684000 Total EC 2570500 372662100

Table 3b: Annual deposit of End-Of-Life tires per member of the EC (ETRMA, 2006)

Source: European Tyre and Rubber Manufacturers Association 2006. Summary by Kurt Reschner *) This figure also includes unknown means or disposal, Copyright: Kurt Reschner, Berlin, Germany



According to Table 3a, Italy has 5 times more habitants than Greece, while the annual deposit of EOL tires is ~6 times more than Greece’s. The European Tire Recycling Association (ETRA) is the only European organisation devoted exclusively to tire and rubber recycling. It was founded on 23 September 1994 with 19 members in 5 countries, while today ETRA has ±250 members in 47 countries including the 25 EU Member States. ETRA membership reflects both the public and private sectors involved in the environmentally safe disposition of post-consumer tires. Policy and decision makers as well as those charged with organising and connecting the links in the chain are represented. With a focus on both material and energy recovery, ETRA members include collectors, retreaders, manufacturers of recycling equipment, research bodies, developers, users of new technologies as well as users of the materials in an expanding number of products and applications(www.etra-eu.org). 1.2 Tires disposal problem Worldwide, the amounts of tires are often uncontrollably deposited, even because of the noticeable rapid depletion of available sites for waste disposal, causing great environmental problems.

Figure 1a,b: Stockpiles and uncontrollable deposit of EOL Tires

Water accumulation inside tires provides ideal temperature and moisture conditions for the spreading of mosquitoes, mice, rats and vermin. At the same time the quantity of oxygen that exists in the interior of the tires is enough to cause fire in appropriate conditions because of its inflammable components with the resulting negative impact on the atmosphere and on human’s health (www.earth-link.com.hk). Within the last ten years, the State of California has seen two of its largest tire stockpiles- located in Tracy and Westley- catch fire. Especially in Westley, at the west side of Stainislaus County, approximately 7 millions of scrap tires were involved in the fire, which was caused by a lightning storm (www.netfeed.com/~jhill/tirefire.htm.). These fires have raised concerns about the need to eliminate the existing stockpiles and to develop additional end uses for tires.



Figure 2: Tires on fire (Stanislaus Co. Ca Tire Fire)

1.3 Legislation- EC’s waste management systems However stockpiled tires should decrease in view of the application of the European Community Directive 31/99/CE and of relevant legislation worldwide (Presidential Decree 106/2004 for Greece and l’articolo 228 del decreto legislativo n. 152/06 for Italy). Under this CE Landfill Directive whole tires (except those above 1400mm outside diameter and bicycle tires) have already been banned from landfill while by mid-2006, all tires, including shredded ones, must have been recovered since the landfill ban took full effect. The general aim of this Directive is, by way of stringent operational and technical requirements on the waste and landfills, to provide for measures, procedures and guidance to prevent or reduce as far as possible the pollution of surface water, groundwater, soil and air, and on the global environment, including the greenhouse effect, as well as any resulting risk to human health, from land-filling of waste (www.etra.eu.com). Under this demand, many countries-members of the EC have already national structures, composed of key economic operators, from tire manufacturers, importers, retailers, to collectors and recyclers, who aim at promoting the collection and recovery of used tires, in participating in research and development activities and in acting quite naturally as the counterparts to local authorities. Some of these systems are showed in Table 4 and Figure 3. Table 4: Legislated systems responsible for the recycling, collection, storage and alternative use of EOL Tires over European countries (Blic de, 2002)

Country System Website Belgium Recytyre http://www.recytyre.be

Finland Suomen Rengaskierrätys http://www.rengaskierratys.com

France Aliapur http://www.aliapur.com Germany Gavs [email protected]

Greece Ecoelastika http://www.ecoelastika.gr Hungary Magusz http://www.magusz.hu

Italy Eco Pne Us http://www.ecopneus.it


http://www.recytyre.be/

http://www.rengaskierratys.com/

http://www.aliapur.com/

mailto:[email protected]

http://www.ecoelastika.gr/

http://www.magusz.hu/

http://www.ecopneus.it/


Holland Recybem http://www.recybem.nl Norway Dekkretur http://www.dekkretur.no Spain Nedes [email protected]

Poland Cuo http://www.utylizacjaopon.pl Portugal Valorpneu http://www.valorpneu.pt/

Roumania Eco Anvelope http://www.ecoanvelope.ro Sweden Sdab http://www.sdab.se

UK Used Tyre wg http://www.tyredisposal.co.uk

Figure 3: Associations for the alternative management of EOL Tires (Ecopneus.it) 1.4 Treatment of EOL Tires Rubber from EOL Tires (passenger cars, buses, trucks, bicycles) often after being shredded into smaller pieces can be reused in Civil Engineering applications in different shapes and sizes. Two main methods are used to grind tires to a required size: the first one is related to ambient size reduction using mechanical processes at or above room temperature and the second one is related to cryogenic size reduction by the use of liquid nitrogen or commercial agents to reduce it to a desired size.


http://www.recybem.nl/

http://www.dekkretur.no/

mailto:[email protected]

http://www.utylizacjaopon.pl/

http://www.valorpneu.pt/

http://www.ecoanvelope.ro/

http://www.sdab.se/

http://www.tyredisposal.co.uk/


Figure 4a,b: Shredding of EOL Tires

Figure 4 c.d.: Final product-rubber- of a Greek shredding plant-Karambas SA- (www.karabas.gr)

Ambient Scrap Tire Processing In this ambient grinding plant layout (Figure 5), the tires are first processed into chips of 2” (50 mm) in size in a preliminary shredder (A). The tire chips then enter a granulator (B). In this processing step the chips are reduced to a size of smaller than 3/8” (10 mm), while liberating most of the steel and fiber from the rubber granules. After exiting the granulator, steel is removed magnetically and the fiber fraction is removed by a combination of shaking screens and wind sifters (C). While there is some demand for 3/8” rubber granules, most applications call for finer mesh material, mostly in the range of 10 to 30 mesh. For this reason, most ambient grinding plants have a number of consecutive grinding steps (D). The machines most commonly used for fine grinding in ambient plants are: · Secondary granulators · High speed rotary mills · Extruders or screw presses · Cracker mills Ambient grinding can be operated safely and economically if the bulk of the rubber output needs to be relatively coarse material, i.e., down to approximately 20 mesh material (Reschner, 2008).



Figure 5: Schematic of an Ambient Scrap Tire Processing Plant (Reschner, 2008)

Cryogenic Tire Recycling This process is called “cryogenic” because whole tires or tire chips are cooled down to a temperature of below –80oC (-112 F). Below this “glass transition temperature”, rubber becomes nearly as brittle and glass and size reduction can be accomplished by crushing and breaking. This type of size reduction requires less energy and fewer pieces of machinery when compared to ambient size reduction. Another advantage of the cryogenic process is that steel and fiber liberation, is much easier, leading to a cleaner end product. The drawback, of course, is the cost for liquid nitrogen (LN2). Preliminary treatment of scrap tires (debeading, pre-shredding) is pretty much the same as in ambient plants. In the cryogenic process (Figure 6), the 2” (50 mm) tire chips are cooled in a continuously operating freezing tunnel (B) to below –120°C and then dropped into a high RPM hammer mill (C). In the hammer mill, chips are shattered into a wide range of particle sizes, while, at the same time, liberating fiber and steel. Because the rubber granules may still be very cold upon exiting the hammer mill, the material is dried (E) before classification into different particle sizes (F). Generally speaking, cryogenic scrap tire processing is more economical if clean, fine mesh rubber powder is required (Reschner, 2008).



Figure 6: Schematic of a Cryogenic Scrap Tire Processing Plant (Reschner, 2008) Table 5a: Comparison between Ambient and Cryogenic Ground Rubber (Reschner, 2008; CWC 1998)

Table 5b: Comparison between Ambient and Cryogenic Ground Rubber (Reschner, 2008, CWC 1998)



In Greece, at the moment there are 9 factories of treatment of EOL tires and 31 in Italy (http://www.aliapur.fr/media/files/actualites/2010/Synthese-etude-granulats-de-pneus-usages-en-Europe-FR.pdf). By reducing the particle size of worn tires, a separation of steel wires and textile fibres can be achieved as well as a further treatment of them so that commercial particle sizes can be created. 1.5 Alternative applications of EOL Tires Scrap tires are shredded for use in various applications, with the actual size, which ranges from >300mm to <500μm, a function of the intended use (CEN Workshop Agreement 14243, 2002). An amount of them is reused as treads, another is reclaimed for other forms of reuse of recycling or they can be used in cement kilns as an alternative fuel-due to its high calorific value as seen in Figure 7, or in the production of electricity despite the fact that the incineration of tires, which is an undesirable option, can not be achieved without pollution and contribution to climate change (Norquay K., 2004; Oikonomou and Mavridou, 2006).

Figure 7: Calorific value of alternatives fuels (Norquay K., 2004) Moreover, the Hellenic browncoal (lignite) is of even lower quality, with a heat value of around 13 GJt–1(Karagiannidis and Kasampalis, 2009).


http://www.aliapur.fr/media/files/actualites/2010/Synthese-etude-granulats-de-pneus-usages-en-Europe-FR.pdf

http://www.aliapur.fr/media/files/actualites/2010/Synthese-etude-granulats-de-pneus-usages-en-Europe-FR.pdf


Figure 8a,b: Use of EOL tires as secondary fuel in cement kilns

In addition to these general non civil engineering applications, several studies have been carried out in order to examine the feasible addition of these wastes in cement and asphalt products as well as in geotechnical works, where tires take the place of conventional construction materials such as fills or aggregates (Siddique and Naik, 2004; Huang et al. 2007; Oikonomou and Mavridou, 2008a &2008b, 2009a &2009b; Mavridou and Oikonomou, 2010). Recent trends in Europe and worldwide face tires as coatings, as a means for preventing soils from sliding, for sea embankment, as a means for inhibit erosion near sea, as artificial reefs in marine environment, for temporary and heavy load roads, as off coast breakwaters, in retaining walls, as sound barriers, in drainage culvert bed, for riverbank and coastal stabilization, as bridge abutment fill, in tram rail beds, for thermal insulation, as well as for insulation to limit frost penetration beneath roads, as porous bitumen additive as a means of absorbing seismic waves as well as for slope stabilization (www.etra.eu.com). The addition of rubber in a wide range of applications in Civil Engineering is based upon the unique characteristics of tire particles such as the lightweight, good (sound and heating) insulation properties, their high ability to transmit water, their long term durability as well as the high compressibility. In general, scrap tires and other wastes can be used successfully in road construction as long as they meet engineering standards and are cost effective. In all end uses, scrap tires must compete against locally available materials in performance and costs. The ideal recycled material for use in road construction and maintenance projects yields economic or engineering advantages and environmental benefits. Finally, reuse of tire rubber in the applications mentioned above can lead to the achievement of an environmental goal, which is the protection of the environment by recycling this kind of solid waste. At the same time the use of big volume of waste tire substituting natural aggregates (sand, gravel etc) represents a great advantage from the point of view of sustainability in construction while the tire mountain would cease to exist.

2. TIRE RUBBER IN ASPHALT MIXTURES 2.1 History of rubberized asphalt The use of recycled rubber in asphalt pavements started 170 years ago, with an experiment involving natural rubber with bitumen in the 1840s, attempting to capture the flexible nature of rubber in a longer lasting paving surface (Heitzman, 1992). The early bitumen-rubber formulae provided little or no benefit, the result being a modified asphalt pavement that cost


http://www.etra.eu.com/


more and had a shorter service life than conventional asphalt. However, more widespread successful formulation of rubberized asphalt was first developed in the late 1960s and began to be used widely in the early 1990s. By 2000, rubberized asphalt was used in 40 states (www.referenceforbusiness.com/industries/Petroleum-Refining-Related/Asphalt-Paving-Mixtures-Blocks.html#ixzz16zM4usqL). MacDonald was inspired by the problem he had when the roof of his mobile trailer cracked. He used bitumen as a quick patching material but after frequent moves and long exposure to the sunlight, the bitumen would oxidize and became brittle. The roof crack “reflected” through to the surface of each successive bitumen patch. He thought he could solve the cracking problem if he incorporated rubber in his next round of patching. Moreover, while devising methods to repair potholes on the streets of Phoenix and Arizona, MacDonald experimented with adding ground tire rubber to hot liquid bitumen. He found that after thoroughly mixing crumb rubber with bitumen and allowing it to react for periods of forty-five minutes to an hour, new material properties were obtained. During blending, the bitumen was absorbed by the rubber particles, which swelled in size at higher temperatures allowing for greater concentrations of rubberised binder (bitumen) contents in pavement mixtures, suitable for pothole repair. The patches worked so well that the city eventually tried using rubberised bitumen as the binder for chip seals (known as Surface Dressing in the UK) (WRAP, 2008). Rubberized asphalt mixture consists of asphalt, aggregates and tire rubber granules. Rubber aggregates can be used either as bitumen modifiers or as substitutes for natural aggregates. Typical tire rubber particles are showed in Figures 10 and 11.

Figure 9: Different processes and technologies in application of rubber in bituminous mixtures (WRAP, 2008).


http://www.referenceforbusiness.com/industries/Petroleum-Refining-Related/Asphalt-Paving-Mixtures-Blocks.html#ixzz16zM4usqL

http://www.referenceforbusiness.com/industries/Petroleum-Refining-Related/Asphalt-Paving-Mixtures-Blocks.html#ixzz16zM4usqL


Figure 10: Tire rubber granules of size <2mm (stereoscope x25)

(Oikonomou and Mavridou, 2009a)

Figure 11: Tire rubber granule of size <2mm (SEM)

(Oikonomou and Mavridou, 2009a) 2.2 Rubberised asphalt products Asphalt rubber is used as a binder in various types of asphalt pavement construction including surface treatments and hot mixes (HMA). It is also used in crack sealants. For hot mixes, asphalt rubber has been found to be most effective and is most commonly used in gap-graded and open-graded mixes, particularly for surface courses and for thin overlays that are 30 to 60 mm thick. It may be used in new construction or to rehabilitate an existing pavement Terminal blends have been used in dense- and gap-graded mixes. The most common spray application is a chip seal, also called a stress absorbing membrane (SAM). Chip seals are primarily used for maintenance and pavement preservation. Asphalt rubber chip seals may also be overlaid with hot mix, making them inter-layers, typically called SAMI-R. SAMIs are used primarily for pavement rehabilitation (Way, 2006). Use of asphalt rubber in hot mixes is typically limited to gap and open gradations because these are most effective with respect to performance and cost. Use of high viscosity (field blend) asphalt rubber binder is not recommended in dense-graded mixtures because there is insufficient void space to accommodate enough of the high viscosity asphalt rubber binder to significantly improve performance of the resulting pavement. However dense gradations are well suited for use with terminal blend (no agitation) binders such as CalTrans MB, and should provide similar structural capacity to conventional dense-graded HMA mixes (CalTrans, 2003).



Gap and open-graded Rubberised Asphalt Concrete (RAC) mixes are most often used as overlays for maintenance and/or rehabilitation of existing asphalt concrete and Portland cement concrete pavements. RAC is also used as surface (wearing) courses for new pavement construction, most often in areas where traffic noise is a consideration. Structural design is performed as for conventional dense-graded HMA pavements. Thickness reductions for resistance to reflective cracking may be applied when gap-graded asphalt rubber surface courses are substituted for dense-graded HMA for use as an overlay of structurally adequate pavement (http://www.rubberizedasphalt.org). 2.3 Production of asphalt mixtures with tire rubber- general processes There are mainly two ways of producing asphalt mixtures with tire rubber. In the first one, called the “wet process”, rubber particles are mixed with bitumen at elevated temperature prior to mixing with the hot aggregates, while in the second one, which is the “dry process”, rubber particles replace a small portion of the mineral aggregate in the asphalt mix before the addition of the bitumen.

Figure 12a. Production of rubberized Figure 12b. Production of rubberized Asphalt mixture by the wet process asphalt mixture by the dry process

Explanation of numbers of Figure 12a,b

1 Whole tires 5 Aggregate’s heating 2 Powder of EOL tires 6 Mixing bitumen with aggregates 3 Bitumen’s heating 7 Storage of mixtures 4 Aggregates 8 Loading and transportation to the site

According to ASTM D6114, the rubber, for both cases, should contain no visible non-ferrous metal particles and no more than 0.01 percent ferrous metal by weight of CRM, and should be free flowing and non-foaming. For use in rubberised asphalt, the fibre content should not be greater than 0.5 percent by weight of rubber; however this level is further restricted to 0.1 percent if used in spray application (WRAP, 2008). 2.4 Properties of modified with tire rubber asphalt mixtures Many studies have been conducted, examining asphalt mixtures, made with both the wet and the dry processes. Tire rubber has been used in asphalt mixtures providing rubberized asphalt with better performance towards skid resistance, thermal and mechanical cracking, durability (resistance to cracking and aging- due to the included carbon black, which is a potent antioxidant with a strong effect against aging-), versatility, resistance to rutting, improved tensile strength, toughness, longer pavement life (~20-30% more life), reduced surface maintenance costs during summer and winter compared to conventional mixtures, increased


http://www.rubberizedasphalt.org/


friction, elasticity and softening point, decreased brittle point, as well as resistance to the radiation of the sun (Roberts et al, 1989; Khosla and Trogdon, 1990; Khatib and Bayomy, 1999; Airey et al, 2004, Terrel and Walter, 1986; Takallou and Hicks, 1998; Goulias et al, 1997-1998-2001; Widyatmoko and Richard, 2008; Soon-Jae et al., 2008). All of the properties above are improved depending on many parameters such as how rubberized asphalt mixture was made (wet or dry process) and paved, to which country it was placed, on the weather conditions during paving (cold or warm) etc. Moreover, wearing layers based on rubber modified bitumen have better grip with the tires (shorter braking resistance), while modified asphalt mixtures provide more durable roads and airport bituminous surfaces compared to traditional asphalt (www.asfaltgumowy.pl/en/historia.html). They also reduce traffic noise up to 10dbA, show better performance in high temperatures, can be used in a variety of climate conditions, they are more flexible in smaller and under zero temperatures, while the width of an asphalt layer can be reduced from 50mm to 38mm (http://www.rubberizedasphalt.org). Furthermore, Rubberized Asphalt Concrete is cost effective, saving as much as $22000 per lane mile over conventional asphalt projects (http://ladpw.org/epd/tirerecycling/RAC-REAS.cfm). This market for EOL tires can consume large quantities of scrap tires in a positive manner. Also known as drainage asphalt, porous asphalt mix has a very high void content which allows rainwater to drain off at the surface, reducing splash and spray. Tires maintain contact with the paved surface under any conditions, avoiding aqua-planning at high speeds on wet roads. It also reduces rolling noise within and outside of the vehicle as well as light reflections (http://www.etra-eu.org). Modified with tire rubber asphalt mixtures, which are used in coverage is particularly are recommended in places where the traffic intensity is the highest and where there is trouble with proper surface maintenance, especially:

Road surfaces with traffic congestion Junctions and access roads To cover old destroyed and cracked concrete pavements To cover old cube stone surface Surfaces of the runways and landing paths at airports Layer pavement in areas that are exposed to large deformations, for instance mining

damage (http://www.asfaltgumowy.pl/en/historia.html). Equipment for feeding and blending may differ among rubberised bitumen types and manufacturers, but the processes are all similar. Temperature is always critical to controlling the production of rubberised bitumen, and right equipment such as temperature gauges or thermometers should be readily visible. Rubberised asphalt mixtures must be properly selected, designed, produced and laid in place to provide the desired improvements in pavement performance, given that pavement structure and drainage are also adequate. Moreover, it is believed that tire rubber can be used in asphalt mixtures after examining enough appropriate projects to limit the risk of failure and the associated costs of remediation. This report specifically presents a literature review and other relevant information related to the use of waste tire rubber in asphalt mixtures made by both the wet and the dry processes,



http://ladpw.org/epd/tirerecycling/RAC-REAS.cfm


for consideration of the potential implementation of the technology in Greece, and especially in the Region of Lamia (Sterea Ellada), where a pilot application will take place in July 2011. 3. WET PROCESS (ADDITION OF RUBBER PARTICLES IN BITUMEN) 3.1 Preface During the 1960’s, McDonald developed an asphalt rubber binder, which has been used in a surface treatment commonly known as a stress-absorbing membrane (SAM). This new was assigned because the binder provides elasticity that absorbs the stresses developed from movement of underlying cracks and helps prevent reflection cracks in the new surface. Asphalt rubber is claimed to be resistant to cracking and to provide an effective seal to prevent water damage to underlying layers and aging of the binder. This material has been used widely in many states of the US like Arizona, Phoenix, where it helped retard primary reflection cracking after 15 years (Way, 2006). The wet method has been successfully applied in many countries, especially the USA while a typical technical process is the following: “A mobile mixing unit is installed in the hot mix plant and ~20% of crumb rubber (<2mm size) is added to the bitumen and agitated for a period of time (1 to 2 hours) at 190/200oC, so that rubber reacts with bitumen, providing the “modified or rubberized asphalt”. From this moment on the modified binder can be pumped into the pipe system of the hot mix plant and mixed with the aggregates. In the USA 90% of the binders modified with crumb rubber are produced this way and the resulting hot mix fulfills perfectly the required specifications”, (Nolting 2010- http://www.no-waste-technology.de/rubber_asphalt.html). For European circumstances this method has some disadvantages, which create certain reluctance in contractors and administrations to use the rubber in asphalt modifications (Walter Artus GmbH, 2007):

1. A hot mix plant of a normal size has a production per hour of 100/150tons. As the percentage of modified binder uses to be around 5,5%, the minimum production of the mobile mixing unit for crumb rubber has to be 9tons per hour. The long reaction time, also called “digestion time”, reduces however the production per hour, a fact leading to the necessity of installing several big sized tanks, which use to disturb the normal work of the plant and occupies space which often is not available.

2. The addition of rubber to the bitumen produces a strong increase of the viscosity, which demands higher binder percentage, ranged from 5,5-7,5% or even 9%. In some cases, such as in open graded materials this high binder percentage is required, however it is not always desirable so it only leads to an increase of cost.

3. Temperature used in the production process of the hot mix is around 160oC or more. To maintain this high temperature, the production tank for the modification must work with an own independent burner, which has to maintain for each charge the mentioned temperature during 1 to 2 hours

4. The hot mix produced by this method is usually used in road’s surface courses and the material needs a special gradation, standard guides as prescribed by the different administrations cannot be used.

In Europe, rubberised asphalt has been used since 1981 in Belgium, the asphalt rubber hot mix called “Drainasphalt”, as well as in the neighbouring countries France, Austria,


http://www.no-waste-technology.de/rubber_asphalt.html


Netherlands, Italy and Germany, and more intensively since 1999 in Portugal and Spain (Sousa, 2000, 2003, 2005; Souza et al, 2005). Details are presented in the case studies section of this report. Taiwan was reported to have adopted the Arizona Department of Transportation gap-graded and open-graded rubberised asphalt mixtures for flexible pavement rehabilitation (Asphalt Rubber Usage Guide, 2006). There were concerns about moisture damage on asphalt surfacing in Taiwan since it has a relatively moderate climate i.e. generally high temperatures, no frost but with significant summer rain. The rubberised asphalt mixture, having air voids around 4%, contained 1% Portland cement as mineral filler. The overall material cost was reported to be 30% higher than that of conventional asphalt concrete. After 42 to 46 months, the rubberised asphalts were reported to have been performing well with insignificant fretting for the gap graded and some binder richness (bleeding) for the open graded mixture. However, future plans for use of these materials were reported to be subject to political decisions. It has been reported that rubberised asphalt has been trialled in Beijing and for use in new and maintenance work as part of the preparation for the 2008 Olympics in China. The material has also been used in EcoPark Project in Hong Kong. 3.2 Production of rubberized asphalt Wet process, which consists of two types-terminal blend and wet process high viscosity-, can be used to produce rubberized asphalt, with superior properties compared to the conventional one. In this process, finely ground tire rubber is mixed with the bitumen at 15-20%wt of it, prior to the mixing with the aggregates (ASTM D8-88). This modification of the bitumen is attributed to physical and compositional changes in an interaction process, where rubber particles swell in the bitumen by absorbing a percentage of the lighter fraction of it, to form a viscous gel with an increase in the viscosity of the rubberized binder (Heitzman, 1992). Moreover, this method involves less risk as the interaction between crumb rubber and bitumen can be controlled during the digestion process. The major objectives of a research of Labib et al, 1993 were to achieve proper dispersion of crumb rubber particulates into asphalt and to make crumb rubber compatible modified asphalt with improved, both in high and low temperature, properties which can lead to reduced cracking, rutting, and ravelling tendencies of the CRMA pavement. The approach of the study was to join the crumb rubber and asphalt molecules with small bifunctional molecules called compatibilizers. The crumb rubber compatible asphalt was prepared from 400 g asphalt heated at 163oC in a 600 ml beaker, followed by the addition of the compatibilizer having the epoxy ring with a glycidyl back bone (0.006-0.023 milimoles compatibilizer per g asphalt) to the asphalt with continuous stirring for 15-20 minutes. The crumb rubber (6-15%) was then dispersed into the hot asphalt compatibilizer mixture with continuous stirring and heating for 3 hours. The use of a compatibilizer can enhance the solubility of crumb rubber into asphalt and improve the rheological properties of crumb rubber modified asphalt. Modified compatible asphalt is advantageous over the virgin and its control by having a wider useful temperature range. The use of modified compatible asphalt has the potential to prevent asphaltic pavement from raveling and may increase the use of scrap tires. The amount of compatibilizer used in asphalt is dependent on the source of asphalt (Labib et al, 1993).



In California, the wet process is the most common method used to produce rubberized asphalt concrete. It can be noticed that the only additional equipment, which is required, is a special blending unit to mix the bitumen with the rubber particles. Paving can be done when ambient temperatures are at or above 13oC and the road is dry. At this temperature, the hot mix should be near the upper temperature in the range above. When the ambient temperature is at or above 18oC, there is more discretion with the hot mix temperature. In either case, however, it is essential that good paving practices and techniques are used, and that the hot bitumen with rubberized bitumen binder is rolled immediately upon its laying and not allowed to cool off before being worked. Asphalt Rubber Friction Course (ARFC) is generally used as the final wearing surface for both concrete and Hot Mix Asphalt (HMA) pavements. For concrete pavements, the joints are cleaned and resealed with Asphalt Rubber (AR). Spalled areas are cleaned and filled with HMA to level the surface (Way, 2006). ARFC is placed 12.5 mm thick and is used to improve smoothness, reduce cracking, provide adequate skid resistance, and reduce noise. On some badly cracked pavements a gap-graded Rubber Asphalt Concrete (ARAC), generally 37.5 mm to 50 mm thick, is placed to address cracking. An ARFC may be placed depending upon the traffic volume and type of highway. In reviewing numerous pavement designs over the last 15 years, rubberised bitumen pavement sections are typically thinner than those constructed with HMA. The average HMA pavement section is typically 100 to 125 mm in thickness, whereas the rubberised bitumen pavement sections are generally 37-62mm in thickness. Thus the rubberised bitumen pavement will be on the order of half or less than half the thickness of the HMA pavements without rubberised bitumen, (Figure 13).

Figure 13: Pavement with rubberised asphalt

(Way, 2006)



In the chip seal or slurry applications, rubberised bitumen needs to be maintained at between 191oC and 218oC, to ensure a viscosity thin enough for spraying. An ambient and surface temperature of at least 18oC is recommended so that the applied material doesn’t set too quickly (Way, 2006). 3.3 Specifications There are a number of existing specifications for rubberised bitumen; these include ASTM D6114-97 (2002), SABITA Manual 19 (1997), Caltrans’ Asphalt Rubber User Guide (2003), and VicRoads and APRG Report No. 19 (2001), Guidelines from Spain (WRAP.org). ASTM D6114 specifies three different types of rubberised bitumen: Type I, Type II and Type III; Table 6 refers. Each type of rubberised bitumen typically uses different grades of base bitumen:

Type I binders typically include stiffer base bitumen and are generally recommended for hot climates, such as: AC-20, AR-8000 and PG64-16.

Type II binders typically include base bitumen softer than Type I and are generally recommended for moderate climates, such as: AC-10, AR-4000 and PG58-22.

Type III binders typically include the softest grade base bitumen and are generally recommended for cold climates, such as: AC-5, AR-2000 and PG52-28.

Table 6: Summary of ASTM Specification D6114 for Rubberised Bitumen

The South African Bitumen and Tar Association (SABITA) has produced technical guidelines for specification and design of rubberised asphalt wearing course (Manual 19), allowing the use of 18 to 24 percent rubber by mass of the total binder blend. Oil extender, having more than 50 percent aromatic/unsaturated hydrocarbon and less than 25% saturates content, is specified to be added at a rate of up to 3 percent by mass of the blend. The rubber particles are specified to have the grading: 100 percent passing the 1.18mm, 50 – 70 percent passing the 0.6mm and 0 – 5 percent passing the 0.075mm sieve sizes, respectively. The guidelines specify monitoring the blending process and recording the reaction time of the blend. The reaction time is defined as “half the time required to add the entire rubber crumb to the bitumen, plus the period between the end of adding crumb and the time when there has been sufficient reaction between the bitumen and the rubber to ensure that the binder properties meet the specified requirements”. To prevent sticking of rubber particles, an addition of calcium carbonate or talc up to 4% by mass of rubber is permitted. The blending contractors are not allowed to deviate from the stated percentage of rubber by more than 1 percent and from the stated reaction time temperature by more than 10oC.



The blend when sampled within five minutes after completion of blending should meet the specification reproduced in Table 7. Storing the blend at elevated temperature for more than 72 hours is not allowed; the typical hot storage (160 – 180oC) allowance is between 3 to 5 hours. It is understood however that, at the time of writing this report, this specification is being reviewed.

Table 7: Bitumen-rubber specification (SABITA Manual 19)

P

Table 8a: Bitumen-rubber specifications (Spain-DIRECTIVE 21/2007) Characteristics Specification Unit BMAVC-

1

BMAVC-

2

BMAVC-3

Penetration, 25ºC EN 1426 0,1mm 15-30 35-50 55-70

Softening point EN 1427 ºC ≥ 75 ≥ 70 ≥ 70

Fraass point EN 12593 ºC ≤ -4 ≤ -8 ≤ -15

Tensile force

(5cm/min)

5ºC ΕΝ 13589

ΕΝ 13703

J/cm² … ≥ 2 ≥ 3

10º C ≥ 2 … …

Consistency

(Float test 60ºC)

NLT 183 S ≥ 3000

Dynamic

viscosity

135ºC EN 13302 mPa.s ≤ 7500 ≤ 5000

170ºC ≥ 2000 ≥ 1200 ≥ 800

Elastic

recovery

25ºC EN 13398 % ≥ 10 ≥ 20 ≥ 30

Storage

stability (*)

Difference

Ring &

Ball

EN 13399 ºC ≤ 5

Difference 0,1mm ≤ 20

Flash point v/a EN ISO 2592 ºC ≥ 235

Determination of resistance to hardening under the effect of heat and air EN 12607-1

Mass change EN 12607-1 % ≤ 0,8 ≤ 0,8 ≤ 1,0

Retain penetration EN 1426 %p.o. ≥ 60

Softening point’s change EN 1427 ºC Min -4 max +10 Min-5

max +12



Table 8b: High viscosity Bitumen-rubber specifications (BMAVC) (Spain-DIRECTIVE 21/2007)

Characteristics Specification Unit BMAVC-

1

BMAVC-

2

BMAVC-

3

Bitumen

Penetration, 25ºC Penetration,

25ºC

0,1mm 15-30 35-50 55-70

Softening point Softening

point

ºC ≥ 75 ≥ 70 ≥ 70

Fraass point Fraass point ºC ≤ -4 ≤ -8 ≤ -15

Tensile force

(5cm/min)

5oC ΕΝ 13589

ΕΝ 13703

J/cm² … ≥ 2 ≥ 3

10oC ≥ 2 … …

Consistency

(Float test 60ºC)

NLT 183 S ≥ 3000

Dynamic

viscosity

135ºC EN 13302 mPa.s ≤ 7500 ≤ 5000

170ºC ≥ 2000 ≥ 1200 ≥ 800

Elastic

recovery

25ºC EN 13398 % ≥ 10 ≥ 20 ≥ 30

Storage

stability (*)

Difference

Ring &

Ball

EN 13399 ºC ≤ 5

Difference

penetration

0,1mm ≤ 20

Flash point v/a EN ISO

2592

ºC ≥ 235

Determination of resistance to hardening under the effect of heat and air EN 12607-1

Mass change EN 12607-1 % ≤ 0,8 ≤ 0,8 ≤ 1,0

Retain penetration EN 1426 %p.o. ≥ 60

Softening point’s change EN 1427 ºC Min -4 max +10 Min-5

max +12

3.4 Properties of rubberized asphalt In the wet process, finely ground crumb rubber is blended with bitumen at an elevated temperature (170 to 200oC) generally in the presence of an oil extender. The interaction of bitumen-rubber in the wet process is known to be affected by the blending temperature, the duration of blending, the type and amount of mechanical blending energy, the size and texture of the rubber particles, and the aromatic component of the bitumen. The absorption of aromatic oils from the bitumen into the rubber’s polymer chains causes the polymer to swell



and soften. The type and amount of aromatic oil in the bitumen also plays a major role in determining the compatibility of bitumen-rubber blends. Bitumen modified with 15 percent rubber can increase the high temperature viscosity of the blend by a factor of 10 or more. The rate of reaction can be increased by enlarging the surface area of the rubber particles, i.e. by reducing the size of the rubber. There is also an undesirable side effect, i.e. rubber particles will require an increase in the binder content, which may lead to potential problems of flushing or bleeding, increase the paving material’s cost, and may cause tracking. The other problem was found to be the storage stability of the rubberised bituminous binder. It was reported that "the rubberised binder must be used within hours of its production" (Takallou and Sainton, 1991). However, the problem may be overcome by addition of a catalyst into the mixture. Hence, cost-effectiveness should also be considered together with the benefits that are being obtained by the use of the modifier (WRAP, 2008). South Africa and Australia started introducing bitumen-rubber as a binder for asphalt and for seals from the early 1980s and mid 1970s respectively. In South Africa, both wet and dry processes were reported to have been used successfully (Visser and Verhaege 2000). Two states in Australia (New South Wales and Victoria) adopted the wet process for limited application of rubberised asphalt, mainly as a crack resisting layer, but otherwise its usage has been predominantly for sprayed seal applications. In the case of wet process, the properties of rubberized asphalt depend on various parameters mentioned above. Preliminary production trials of these modified asphalt mixtures showed that when laid, there has been noticed a weak bonding between the components of the mixture, which had as a result loose rubber particles and distributed aggregates on the surface of the pavement. According to Laboratory tests, rubber particles retain larger proportion of the bitumen compared to the one of aggregates, suggesting an interaction between bitumen and rubber (Airey et al., 2001). Studies on dense graded rubberized asphalt mixtures, produced with this method, containing 3%-5% crumb rubber by total aggregate weight showed that such mixtures are more vulnerable to moisture damage compared to conventional ones while their stiffness reduced 30-75% depending on the crumb rubber content (Rahman et al., 2004). However, when fine rubber particles (<1mm size) are added to asphalt mixtures, as in many states like Florida, Colorado and Kansas, they produce mixtures with improved characteristics in terms of stiffness, resistance to permanent deformation and rut, while particles of such gradation are more effective than coarser ones as far as rutting resistance is concerned. Despite of that, resistance to rut should be examined for various sizes and proportions of rubber in such mixtures. Recent studies came up to the conclusion that during mixing and transportation, rubber reacts with bitumen, changing the properties of it, the shape and rigidity of the rubber and as a result the performance of the asphalt mixture (Airey et al., 2003). Studies on the effect of moisture on mechanical properties of rubberized asphalt mixtures showed that stiffness is reduced by the incorporation of rubber particles (2-8mm), and it is found to decrease in function to the percentage of rubber. This reduction was attributed to the voids created by rubber particles in the mixture and as a result more water penetrated in the matrix during saturation giving a weaker structure. Tortum et al. (2005) studied rubberized asphalt mixtures in order to determine the optimum conditions for tire rubber in them under different parameters such as tire rubber and aggregate gradation, mixing and compaction



temperature, tire rubber and binder ratio and mixing time as well. They concluded that for specific conditions, rubberized asphalt mixture perform better. Punith et al. (2002) examined the tensile strength characteristics of Dense Bituminous Macadam (DBM) mixes with crumb rubber. Results showed improved characteristics in terms of Marshall Stability and indirect tensile strength at various temperatures under soaked and unsoaked conditions. Both of these properties increased as tire rubber percentage increased. Especially for unsoaked conditions, indirect tensile strength was higher compared to those of soaked ones, while it decreased as temperature increased. Additionally, in high temperature tensile strength was almost the same for both plain and rubberized Dense Bituminous Macadam mixture. Thus such mixtures are expected to have longer life than the conventional D.B.M. A method for modifying bitumen with waste rubber powder, including a first step of mixing rubber powder with an aromatic oil in proportions of 98-60% and 2-40 % respectively, and a second step of mixing the rubber powder from the first step with bitumen in proportions of 3-30 % and 97-70 % respectively, at a temperature of 140-200°C and for a time of 5-40 minutes has been examined. The method is advantageous mainly in that the bitumen can be modified in a shorter time than with known methods, and in that the specifications of the modified bitumen can be controlled in such a way that it becomes commercially useful, thereby contributing to the solution of the environmental problem of too many tyres (www.wipo.int/pctdb/en/wo.jsp?wo=2006108887#mainContent). Moreover Wang and Zeng, 2006 examined the behaviour of two blends of rubber-modified asphalt _“Type C,” a 20% blend, and “Type E,” a 10% blend under varying temperature and confining pressure conditions. It was found that, rubber-modified asphalt had a significantly higher shear modulus under varying temperature (−10, 0, 22, 30, and 37°C) and pressure conditions (0, 138, 276, and 552 kPa) than a traditional asphalt concrete blend as rubber content increases, leading to higher stiffness. Having a higher stiffness would be attractive in terms of high-speed rail foundations, as a stiffer material would reduce the magnitude of the track deflections and the amplitude of the induced ground vibration. A stiffer foundation would also help reduce long-term rutting of the pavement. This is particularly significant for railway applications where the contact surface between the train wheels and the rail structure is especially stiff. Additionally, the rubber-modified asphalt blends more readily maintain their stiffness over larger strains than the conventional asphalt blend; this is a decided advantage of a rubber-modified asphalt blend over a conventional blend in terms of long-term durability over repeated usage. The shear modulus of the asphalt blends was highly dependent upon the temperature of the material. When the material is cooled, it gains stiffness; as it is heated, it softens. The shear moduli of the asphalt samples tested had magnitudes that fluctuate up to approximately 300,000 kPa depending upon the temperature of the material. This is a significant differential that could affect the design and performance of a high-speed railway foundation if not taken into account. The damping ratio of all the asphalt samples was highly dependent upon the temperature of the material as well. In situations of higher temperature, the damping ratio is significantly increased for all samples. Additionally, the increase in the shear stiffness as the temperature decreases is accompanied by a drop in the damping ratio; these two characteristics may effectively “cancel each other out” in terms of how effectively the material can in practice be used for vibration attenuation. Furthermore, it appears that as the confining pressure increases, the stiffness of the material decreases slightly. Rubber-modified asphalt concrete is



not a material with constant constitutive properties—rather, as seasons and temperatures change, the material will react differently to the same loading situations. Currently, the main advantage of using a rubber-modified asphalt blend appears to be in its ability to maintain significantly higher shear stiffness over a larger range of strains. Further research in taking field measurements is needed, especially in quantifying the exact nature of the temperature and loading under which the asphalt would be exposed. Once these environmental conditions are set, the effects of changing rubber content can be more definitively defined (Wang and Zeng, 2006). Tire rubber inclusions can modify a conventional hot mix asphalt in terms of flexural fatigue life, since mixtures with rubber treated with different processes (cryogenic or ambient) show greater fatigue life than the one of conventional mixtures regardless the void content, which may vary from one mixture to another for the same category of bitumen (Pais et al., 2001). During the interaction with asphalt binder, the Crumb Rubber Modifier (CRM) particles absorb a portion of the oils in asphalt binder and the particles swell; therefore increasing the viscosity and stiffness of the CRM binder. Still, the performance properties of CRM binders in hot mix asphalt (HMA) pavement are considered to be unclear due to the various interaction effects of CRM with asphalt binders, depending on the CRM percentage, source and size. Lee et al., 2008 conducted a laboratory investigation on the properties of CRM binders as a function of CRM processing method (cryogenic or ambient) and percentages (5, 10, 15 and 20%). A total of twenty-four CRM binders were produced and artificially aged through an accelerated aging process (PAV aging for 20 h at 100oC) (The Asphalt Institute; 2003). CRMs and binders were mixed in the laboratory at 177oC for 30 min by an open blade mixer at a blending speed of 700 rpm (Shen et al, 2006). Selected Superpave binder tests were conducted using rotational viscometer, DSR, and BBR to evaluate the viscosity and rutting properties at high temperature and the cracking properties at intermediate and low temperatures. According to results, higher CRM percentages for CRM binders seemed to lead to a higher viscosity, a better rutting resistance and a less chance for low temperature cracking while the ambient CRM was found to be more effective on producing the CRM binders that are more viscous and less susceptible to rutting and cracking. Study of a pilot project in Taiwan, on two test sections, the one with gap-graded design and the other with open-graded design and the incorporation of ground tire rubber showed that these mixtures can have equal or even better field density and smoothness than the conventional mixes. These mixtures still perform quite well based on field measurements and visual observations (Chui-Te, 2007). Another test project was conducted in Florida and evaluated after 10 years. Results showed that the wet process addition of crumb rubber improved crack resistance of surface mixtures, while another test project made with the dry process gave inferior results in terms of more cracked areas (Choubane et al., 1999). Projects in the late 1980s showed that asphalt rubber in dense-graded mixtures helped reduce the asphalt layer thickness by 20–50% without compromising its performance (Kirk, 1991). The thickness reduction was confirmed by accelerated load testing (ALT) at University of California Berkeley and South Africa (Hicks, 2002). Another benefit of using asphalt rubber is to prolong the pavement life.



A project in Brazil having 15% rubber in the HMA overlay binder found that cracking was developed 5–6 times slower than in conventional asphalt; also the asphalt rubber mixture outperformed in terms of surface deflection, interface strain and rut depth (Nunez et al., 2005). Similarly, binder of 15% rubber (size of 0.2/0.4/0.6 mm) was used in dense-graded asphalt in Japan. The mixture exhibited improved performance in dynamic stability, 48 h residual stability, flexural strength and strain value; and asphalt containing 0.2/0.4 mm-sized rubber showed the best laboratory results (Souza et al., 2005). Pavement performance has been routinely monitored by ADOT’s pavement management system since 1972. Over that time a general trend of cracking, rutting, ride, maintenance cost, and skid resistance have been observed. Figure 14 shows a comparison of the average percent cracking for conventional overlay/inlay projects and those projects built with an ARFC.

Figure 14: Statewide cracking performance with and without rubberised bitumen (Way, 2006)

Projects also revealed problems from the use of asphalt rubber in road surface. Bleeding and loss of coarse aggregates were observed on a Virginia SAM (stress absorbing membrane) trial section containing 20% crumb rubber in the binder, and the SAM did not hinder reflective cracking as expected (Maupin and Payne, 1997). A chip seal (or surface dressing) project in Iowa showed that the asphalt rubber compromised the friction performance (Iowa DOT, 2002). A project in Texas indicated that OGFC represented the best application for asphalt rubber in terms of cost, resistance to cracking and raveling (Tahmoressi, 2001). NCPE suggested that asphalt rubber should not be used in polymer modified bitumen (PMB), because the PMB-rubber interaction compromised the rheological properties of the aged binder and as a result, the durability of asphalt mixtures (Airey et al, 2002). Use of rubberized asphalt as a pavement material was pioneered by the city of Phoenix, Arizona on several area freeways in the 1960s because of its high durability. Since then it has garnered interest since it has the ability to reduce road noise. Studies showed a noticeable reduction in traffic noise levels, which ranged between 2-10dB related to the country and the application”.


http://en.wikipedia.org/wiki/Phoenix,_Arizona

http://en.wikipedia.org/wiki/Phoenix,_Arizona

http://en.wikipedia.org/wiki/Metropolitan_Phoenix_Freeways


Other countries, where rubberized asphalt mixtures have been used showing smaller or equal traffic noise reduction level are Canada (1991), England (1998), France (1984), Germany (1980), Austria (1988) and the Netherlands (1988) etc. As a result, many states of the USA (Arizona, Florida, California, Texas etc) and around the world continue to use such mixtures (http://www.rubberpavements.org).

Table 9: Countries Used/Using Rubberized Asphalt and Resulting Noise Reduction

(Sacramento County, 1999)

City

Year

Noise Reduction

Belgium 1981 8-10 dB (65-85%)

Canada 1991 Μείωση θορύβου

England 1998 NA

France 1984 2-3dB/3-5dB (50-75%)

Germany 1980 3dB (50%)

Austria 1988 3+ dB

Netherlands 1988 2.5dB

Table 10: Results of noise reduction of conventional and modified with tire rubber in the county of Sacramento

(Sacramento County, 1999)

Street

Pavement type

Duration after laying

Noise reduction dB

Alta Arden Expressway

Modified asphalt

1 month 16 months

6 years

-6 dB -5 dB -5 dB

Antelope Road Modified asphalt

6 month 5 year

-4 dB -3 dB

Bond Road Conventional asphalt

1 month 4 years

- 2 dB 0 dB


http://www.rubberpavements.org/


Table 11: States Using Rubberized Asphalt and Resulting Noise Reduction (Sacramento County, 1999)

3.5 Cost and Benefits The question remains whether such modified with tire rubber mixtures are cost-effective since the initial cost is considerably more than that of surface treatments using conventional binders. Generally, initial cost of modified with rubber asphalt may be increased, while the cost of the final material increases as size of rubber decreases. In general, the cost of rubberized asphalt is almost twice the cost of the conventional one. This leads to an increase of RAC (Rubberised Asphalt Concrete) per mile 30-40% compared to the one of conventional (http://www.rubberizedasphalt.org). However, after many studies it had been noticed that the cost was smaller, given the fact that rubberized asphalt layers were thicker than the conventional ones. An example is given below: For a surface layer of conventional asphalt concrete (Conventional AC) 10,16cm it is needed:

Cost per km/lane with conventional layer (AC):

1,584 tn x $55.00/ ton = $87,120

Pavement construction = $ 9,000

Total $96,120

Cost per km/lane with 5.08cm of rubberized asphalt concrete (RAC):

754 tn x $65.00/ton = $49,010

Pavement construction = + 9,000

Total $58,010

Note: Weight of RAC is 5% lower than the conventional’s (AC) one.

Cost benefit per km/ circulation lane: $96,120 - $58,010 = $38,110




Moreover, a surface layer of 5.08cm thickness contains 1308 of EOL Tires per km. That means that for a road section of 4 pales more than 5230 EOL Tires will be used providing a safer, less noisy and with longer life road. Another example comes from the USA, on the Interstate 19 project, where only a 25 mm (one inch) Asphalt Rubber Friction Course (ARFC) was placed at a cost of about $2.45 per square meter. The comparable repair strategy is to grind the concrete, that costs about $5.00 per square meter, thus the AR mix was actually less expensive to construct. The ARFC continues to provide a smooth riding, virtually crack free, good skid resistant, quiet and virtually maintenance free surface for a period as long as eighteen years. The price of AR binder reduced significantly after 1992, when the patents on AR binder ended and the price of the material dropped from about $450 per ton to about $250 per ton (Way, 2000). At present, seven companies supply AR in Arizona. ADOT monitors the price of all the products it buys and has used rubberised bitumen only when its usage appeared to be well suited to the problem and cost effective. Table 11 shows the cost of AR HMA mixes compared to dense-graded HMA made with neat bitumen binders. Rubberised bitumen is more expensive and that has often been sighted as a major disadvantage. However, AR does compete with other dense mixes and has proven to be cost effective to such a degree that ADOT has constructed over 33,333 lane-km (20.000 lane-miles) of AR mixes since 1988.

Table 12: Total Cost (Dollars Per m2 Per 25 mm thickness)

Experience reported by Arizona DOT suggests that the price of rubberised bitumen alone could be twice as high as that of unmodified bitumen, but the actual cost varies depending upon the mixture design. Way (2003) reported that in Arizona, the production cost of a gap graded rubberised asphalt is typically:

25 to 75 percent more expensive than a typical conventional asphalt; and 80 to 160 percent more expensive than typical open graded asphalt.

However, these higher material production costs do not necessarily reflect the total construction cost. For example, the use of rubberised asphalt overlay in Arizona I-40 Flagstaff project was reported to cost about $10 per square metre including the cost of the cracked and



seating, whilst the adjacent reconstruction project was built at a cost of about $25 per square metre for the paving alone, or $45 per square metre if other cost was included. Consequently, rubberised asphalt pavements have been reported to offer a whole life cost effective solution due to the extended service life and good riding quality (which results in fuel efficiency), resulting in lower maintenance cost and even a “virtually maintenance free surface for fifteen years” (Way 2003). This is illustrated in Figure 15.

Figure 15: Maintenance cost comparison in Arizona (after Way, 2006)

FHWA confirmed that the production of crumb rubber modified asphalt is normally 50–100% more expensive than producing conventional (FHWA, 1997). Practice by individual State DOT revealed a range of cost increase: 21% in Colorado (Harmelink, 1999), 50–100% in Virginia (Maupin, 1996), 25–75% for gap-graded and 80–160% for open-graded in Arizona (Way, 1998), $10–$15/tonne in Oregon (Hicks, 2002), $16/tonne in California (Caltrans, 2003), to name but a few. However, life cycle cost analysis (LCCA) was recommended by all practitioners for assessing the cost effectiveness of the use of asphalt rubber, taking an analysis period of 30–40 years including the maintenance and user cost. LCCA was conducted at ASU and OSU using the World Bank’s Highway Development and Management model (HDM-4) and the FHWA’s LCCA method (FHWA, 1998), respectively. According to their results, the use of asphalt rubber was ‘cost effective’. Meanwhile, they recognised that this is not always the case, and the results depend on many input variables which need to be studied on an individual basis (Jung et al., 2002; Hicks and Epps, 2000). In general, use of modified asphalt and asphalt mixtures can lead to a decrease of the huge stockpiles of EOL Tires, which would be deposited often uncontrollably with severe impacts on the environment. So, use of EOL Tires has many benefits, environmental, social and economical. 3.6 Environmental concerns Fume emissions have been studied extensively in a number of asphalt-rubber projects since 1993 and in all cases been determined to be below the National Institute for Occupational Safety and Health (NIOSH) recommended exposure limits (Gunkel, 1994). Table 13 is part of



a study conducted for the Michigan Department of natural Resources in 1993 comparing conventional HMA and Asphalt-Rubber Hot Mix. In this study control mix 2 contained 100% virgin aggregates and asphalt cement with a penetration of 200-250, equivalent to an AC-2.5. The rubber mix 1 (RBR1) also contained virgin aggregates and asphalt rubber binder manufactured using the “wet” process.

Table 13: Continuous Emissions Measurements and Method 18 Results (Units m/m3) Evaluation of Exhaust Gas Emissions and Worker Exposure from Asphalt Rubber Binders in Hot Mix

Asphalt Mixtures (Gunkel, 1994)

The findings of this study were significant to the asphalt-rubber industry in that many of the conventional mix materials had higher, but still acceptable, emissions in certain categories than those with rubber (Carlson and Zhu, 1999). In general, rubber does not contribute significantly to any increase in undesirable compounds, while the base asphalt and burner fuels will cause greater changes in emissions than rubber. Stout and Carlson (2003) reported that rubber crumb does not include unusual chemicals that present any new health risks. It consists mostly of various types of rubber and other hydro-carbons, carbon black, oils, and inert fillers. Most of the chemical compounds in rubber crumbs are also present in paving grade bitumen, although the proportions are likely to differ.



The Bay Area emission tests showed that measured emission rates of particulate and toxic compounds were consistently lower than the EPA AP-42 emission factors for conventional hot mix asphalt plants (Table 14).

Table 14: Particulate Emissions (after Stout and Carlson, 2003)

*determined from a baghouse filter controlling a drum mix asphalt plant production operation

4. DRY PROCESS (ADDITION OF RUBBER PARTICLES IN AGGREGATES) 4.1 Preface Rubber modified asphalt hot mixtures, produced by the dry process, were first used in Sweden in the late 1960’s in order to improve asphalt pavement skid resistance and durability. This process was patented with the name Rubit, while in the USA it was patented with the name PlusRide. In this system, mixtures are prepared by the addition of 1-3%, by weight of total mix, rubber particles as replacement of equal amounts of aggregates in gap-graded aggregate and then mixed with hot asphalt cement. These mixtures required 1.5-2% more asphalt than a conventional mix. Another system, which uses the dry process, is the generic one. This system was developed in the late 1980’s to early 1990’s and it uses rubber up to 3% by weight of fine and coarse particles to a dense-graded aggregate mixture. Experimental pavement sections have been placed in Florida, New York, Oregon and Ontario (Epps, 1994). Usually the amount of crumb rubber as well as the size of rubber is smaller than the ones in the PlusRide system. Generic is a two-component system in which the fine rubber particles act with asphalt while the coarse perform as elastic aggregate in the mixture. As well as utilisation of rubber tire waste, the dry process was also found to provide other benefits such as increased flexibility, increased fatigue life, resistance to studded tyre abrasion, reduced noise and crack reflection control. This process does not require special equipment, but it does require more labor working and it has been far less popular method because of the increased costs of having to use special graded aggregate to incorporate the reclaimed tire rubber, of constructions difficulties as well as of the poor reproducibility and premature failure of this method’s asphalt road surfacing (Hunt, 2002). Moreover, difficulties were also encountered due to the increased optimum binder content, i.e. to about 7.5 to 9.5 percent. This caused the modified mixtures to be more susceptible to mixture preparation, e.g. a tendency to produce smoke was reported during the mixing process due to the very high mixing temperature (the lowest mixing temperature is 163oC), and rutting and pickup problems were reported to occur more easily during compaction, than in conventional mixtures. As far as cost issues are concerned, economic analyses has revealed that the dry process is more economical than the wet one. At the present time, the cost of the rubberized material produced by the generic ("dry") system is minimum among all the technologies available. Additionally, this involves asphalt mixing process very much similar to that used for



conventional materials. Therefore, this system appears to have the best outlook for its widespread commercial applications (Naik et al, 1995). Finally, this process has the potential to consume larger quantities of rubber from EOL tires, which is environmentally beneficial. 4.2 Properties of rubberized asphalt mixtures The most important factor as far as production or rubberized asphalt is concerned is temperature (Kairidis, 2003). Indicative ranges are showed below:

1. Asphalt binder’s temperature >170 οC 2. Aggregates’ temperature < 160 οC 3. Minimum mixture temperature >140 οC 4. Environmental Temperature >20-25οC

Figures 16a,b: Application of modified with tire rubber asphalt mixture

Figure 17: Modified with tire rubber road

Rubber in rubberized asphalt mixtures made by the dry process increases elasticity of the mixture; it can enhance the bonding between binder and aggregates by resulting in an increase



in fatigue life and in resistance to rutting while it can lead to a reduction of thermal and reflecting cracking of these mixtures (Fernandez et al., 2002). In this process, the interaction between rubber particles and bitumen can not be easily controlled since it starts as soon as aggregates are mixed with bitumen and do not last for a long period of time. When these mixtures are constructed correctly, such pavement is better for icy road conditions (www.rubberizedasphalt.org; Khalid and Artamendi, 2002). Moreover, modified with tire rubber asphalt performs well under high temperatures, can be applied under a range of temperatures, is more flexible at low and under zero temperatures, while the thickness of the bituminous layer can be 38mm compared to the 50mm of a conventional one (http://www.rubberizedasphalt.org). Tire rubber, when used in the form of powder can act as filler which covers voids, so better compaction can be achieved leading to better mechanical performance. Moreover, as tire rubber repels water, it can be used in pavements in order to reduce water absorption. For rubberized asphalt mixtures, resistance to permanent deformation was found to decrease compared to the control ones, in terms of strain rate, because of the moisture conditioning while the presence of rubber in the mixtures resulted in an increase in fatigue performance before moisture conditioning. Therefore, rubberized asphalt mixtures perform better mechanical characteristics than the control ones in their unaged state, while this performance is getting worst under moisture conditions (Rahman et al., 2004). When rubber in the form of powder (<2mm) is added to asphalt mixtures, it improves the compactness and mechanical strength of them as rubber powder acts as filler which fills the existing voids within the granular skeleton (Kettab and Bali, 2004). Studies, on crumb rubber asphalt mixtures, showed that addition of 10-15% by weight of the bitumen, rubber caused a reduction in penetration and softening point, while viscosity increased with crumb rubber content and decreased as temperature was elevated (Khalid and Artamendi, 2002). According to Fernandez et al. (2002), laboratory study of rubberized dense asphalt mixtures showed that modified with rubber mixture had lower Marshall Stability value than the control mixture, while the flow increased with the rubber content. These mixtures did not meet the requirements of the Brazilian Standards. Rubberized asphalt mixtures presented smaller values of resilient modulus as well as tensile strength compared to conventional ones, while gradation of rubber found to have small influence on tensile strength values. Moreover the reduction in resilient modulus was higher as the size and content of rubber increased. At the same study, mixtures with fine rubber particles (0.15-1.18mm size) up to 2% by weight of the total mix showed very good performance in terms of rutting resistance. Asphalt properties of particular interest in the dry process include resilient modulus and noise reduction. Where there was a 10–20% increase of binder content as required, the resilient modulus of the rubberized asphalt was reduced implying an increase of layer thickness, compared with conventional mixtures (FHWA, 1997). Some other laboratory results showed a reduced permanent deformation (Reyes et al., 2005; Selim et al., 2005). Acoustic analysis and field measurement confirmed that rubberized asphalt paving is effective in reducing traffic noise from light-duty vehicles (Sacramento County, 1999). Leaching test






indicated that rubber in sand-based root zones (typically seen in sports and recreation fields) reduced by more than half the nitrate concentration of leachate into ground water, by replacing traditional gravel of comparable size in the drainage layer (Lisi et al., 2004). The design method for conventional mixtures can be used to design rubberized asphalt containing 1–3% of ground rubber particles. A target air void of 2–4% is the primary design factor (FHWA, 1997). The time and temperature at which the bitumen reacts with rubber particles need to be controlled with care, to retain the physical shape and rigidity required for the dry process. A project in Turkey found that when Marshall Stability, flow, VMA (voids in the mineral aggregate), unit weight and VFA (voids filled with asphalt) all were taken into consideration, the optimum technical parameters were: 0.95mm for tire rubber gradation, 10% for tire rubber ratio, 5.5% for binder ratio, 155◦C for mixing temperature, 15 min for mixing time and 135◦C for compaction temperature (Tortum et al., 2005). A study conducted in Greece, in rubber modified asphalt mixtures by the dry process, did not meet the requirements of Hellenic Standards in rubber amount higher than 1% by weight of the aggregates (Oikonomou et al., 2007). 4.3 Microstructure of asphalt mixtures Conventional and rubberized mixtures, produced with the dry process, have been examined by the use of a stereoscope (Leica Wild M10) - Figures 18-19- in the Laboratory of Building Materials of the Department of Civil Engineering at Aristotle University of Thessaloniki. As far as microstructure is concerned, it was found to be solid, while rubber particles cooperated well with aggregates with satisfactory interface (Oikonomou et al., 2007).

Figure 18: Conventional asphalt mixture

Figure 19: Modified with tire rubber asphalt mixture

Aggregate

BitumenRubber

Aggregate

Bitumen


5. CASE STUDIES

5.1 USA From 1974 until 1989, approximately 660 miles (1,100 km) of US highways were built using a Stress Absorbing Membrane (SAM) or Stress Absorbing Membrane Interlayer (SAMI) application of Asphalt Rubber. In addition to this, Arizona Department of Transportation (ADOT) and the US Federal Highway Administration (FHWA) sponsored numerous research studies, thus greatly increasing the state-of-the-knowledge concerning modified bitumen. In addition to reducing reflective cracking, it was noted early on that AR is a waterproofing membrane. Several projects were built to control sub grade moisture in order to control expansive (swelling) clays or to reduce structural pavement sections. This application proved to be very successful (Forstie et al, 1979). In 1989 ADOT documented in a research report the history, development, and performance of rubberised bitumen at ADOT (Scofield, 1989). In that report, "asphalt rubber [rubberised bitumen] has successfully been used as an encapsulating membrane to control pavement distortion due to expansive soils and to reduce reflection cracking in overlays on both rigid and flexible pavements. During the twenty years of asphalt rubber use, ADOT has evolved from using slurry applied rubberised bitumen chip seals to utilizing reacted asphalt rubber [rubberised bitumen] as a binder in open and gap graded bitumen concrete." He noted that AR could be used as a binder for Hot Mix Asphalt. Concurrent with this conclusion, it became evident that AR as a binder could provide a HMA mix suitable for addressing cracked pavements. The ADOT began to use Open Graded Friction Courses (OGFC) with conventional bitumen as early as 1954 (Morris and Scott, 1973). The primary reason for using this material was to provide a surface with good skid resistance, good ride and appearance. Over the years the gradation has changed slightly but has remained virtually the same since 1973. 5.1.1 Phoenix Arizona In 1985 ADOT began experimenting with two rubberised bitumen mixes, an open graded mix Asphalt Rubberized Friction Course (ARFC) and a gap graded mix Asphalt Rubberized Asphaltic Concrete (ARAC). ADOT had experienced cracking problems with its dense graded mixes and ravelling of its open graded mixes, Figure 20 a,b. .

Figure 20a, b: Cracked highway and ravelled pavement

(Way, 2006)



Given the good results with AR as a chip seal coat material, ADOT thought that hot mix asphalt with rubberised bitumen binder might reduce the cracking and resist ravelling. After some early and small experiments with rubberised bitumen mixes starting in 1985, ADOT built its first real AR mix project in 1988. The Gap Graded mix (ARAC) was developed by the City of Phoenix in Arizona for use as a thin overlay (25 mm) on city streets. To fully utilize AR properties two aggregate gradations that would provide a high voids in the mineral aggregate (VMA). Both gradations are shown in Figure 21, while the 25mm layer of the open-graded asphalt using rubberised bitumen concrete friction course, commonly referred to as ARFC, was placed on several miles of Interstate 19, south of Tucson, Figure 22. .

Figure 21: Gradation of ARAC and ARFC, respectively

(Way, 2006)



Figure 22: Interstate 19 before rubberised bitumen overlay

(Way, 2006) This ARFC mix contained 10.0 percent rubberised bitumen, by weight, of the mix as the binder. It was placed on top of a plain jointed concrete pavement. Since 1988, no cracks reflected through until 1996, when only a few transverse cracks appeared over the concrete joints. In 2004 the District Maintenance department reviewed this project and concluded that as before no maintenance was needed and amazingly to date, eighteen years later, no maintenance has been performed on this section, Figure 23.

Figure 23: Interstate 19 sixteen years after rubberised bitumen overlay

(Way, 2006)



From this first project, dozens of projects have been successfully built with rubberised bitumen as the binder. The AR contains approximately 20 percent ground tire crumb rubber by weight of the bitumen content and is commonly referred to as the “Arizona asphalt rubber binder”. These projects were built with the expressed purpose of controlling reflective cracks with a very thin layer of very elastic material. Rubberized asphalt cannot be applied during cold weather or very hot weather. The concrete pavement surface needs to be between 20oC and 35oC for the material to adhere properly. So rubberized asphalt can only be applied in the Spring and Fall in the Phoenix area – from March 15th to May 31st, and from September 1st to November 15th. Prior to application contractors must repair pavement cracks, chips and joints and prepare the concrete surface for the rubberized asphalt overlay. Noise Tests on Chip seal and Asphalt Rubber pavements on 7th Street by the City of Phoenix showed a decrease of about 10 decibels, or about 90% reduction in noise level. Research shows that reduction in noise levels of 50 to 75% is commonly attained. During the 1990s, the city resurfaced more than 200 miles of streets with 450,000 tons of rubberized asphalt, which used about 1.1 million old tires. The city reported that rubberized asphalt placed on Dobbins Road in 1989 has performed without maintenance for 14 years and had an estimated life span of up to 18 years. ADOT also is considered a pioneer in the use of rubberized asphalt in paving projects. More than 4.2 million tons of rubberized asphalt has been used on Arizona highways since 1988, at a cost of some $225 million. Those projects have resulted in the recycling of about 15 million old tires (http://www.azdot.gov/quietroads/what_is_rubberized_asphalt.asp). 5.1.2 Flagstaff, Arizona on Interstate 40 One of the best examples of the beneficial cost effectiveness of rubberised bitumen is a major national concrete pavement rehabilitation project conducted as part of the Strategic Highway Research Program, in Flagstaff, Arizona on Interstate 40, Figures 24 & 25. Flangstaff is a mountainous area of 2134 km elevation with an Alpine like climate. High temperatures in the summer come up to 27oC with winter time flows of -31oC. Overall rainfall is 0,7m per year and winter snows average over 2500mm per year. Interstate 40 cuts through this mountainous area and is built on soils and rock of generally poor engineering quality. The current traffic is over 20000 vehicles per day. The traffic loading has rapidly increased over the years and is quite heavy, with presently more than 35 percent large trucks (Way, 1999).



Figure 24: Concrete pavement in 1989 before rubberised bitumen overlay (Way, 1999)

Figure 25: US Interstate 40 near Flagstaff, Arizona. 4” conventional asphalt (left) and 2” asphalt

rubber overlays on Portland Concrete Cement placed in 1990, photo taken 1998 (Way, 1999) The purpose of this project was to determine whether a relatively thin overlay with AR could reduce reflecting cracking. Asphalt Rubber consisted of 80% hot paving grade asphalt and 20% ground tire. The overlay project was built on top of a very badly cracked concrete pavement, which was in need of reconstruction. The asphalt rubber overlay had performed very well. After 9 years of service the overlay was still virtually crack free, with good ride, no rutting or maintenance and good resistance. Both pavements were laid in 1990, the Figures were taken in 1998. While the conventional pavement (left image) is already severely cracked, the RMA pavement (right image) is in much better shape (Photos Courtesy of Mr. George Way, of the Arizona Department Transportation).



The average skid resistance over time has been good and there are good splash and spray characteristics, Figure 26.

Figure 26: Reduced splash and spray with open graded rubberised bitumen

(Way, 2006)

The benefits of using asphalt rubber on the project represented about 18$ million dollars in construction savings and four years less construction time. Strategic Highway Research Program SPS-6 test sections built in conjunction with the project further illustrate the very good performance of the asphalt rubber. Results have led to widespread use of asphalt rubber hot mixes through Arizona. Based upon this work over 3,333km of successfully performing asphalt rubber pavements have built since 1990.

5.1.3 Odessa, Texas The Odessa crumb rubber project was installed beginning in May 1998. The equivalent of 200,00 tires were used to produce 80,000 tons of crumb rubber modified asphalt pavement overlaid on US 385. The project included 4 lanes for 20 miles, 10 miles in each direction. The asphalt rubber hot mix used on the project helps to reduce reflective cracking, rutting, surface oxidation and road noise and lengthens the time between required maintenance. The project won a 1998 National Asphalt Pavement Association (NAPA) Quality Award. The expected additional life on the project was 3 to 4 years with little to no maintenance required. TxDOT paid a premium of approximately 363,000 to use crumb rubber modified hot mix compared to a non-rubber modified mix. This additional expense was expected to balance out by providing improved performance (Texas Natural Resource Conservation Commission and the Texas Department of Transportation, 2000).



5.1.4 Los Angeles, California Another case study occurred in the City of Los Angeles, California (Youssef, 1995). The initial placement of the asphalt rubber pavement occurred in 1982. In 1994 the pavement was milled and stockpiled at a nearby asphalt plant. The asphalt rubber grindings were added to the virgin rock and oil so that the grindings composed 15% of the final mix. At another location, the grindings were put through a microwave process where nearly 100% of the output was composed of recycled asphalt rubber. This project demonstrated that asphalt rubber can be recycled using either microwave technology or conventional mix design technology. Air sampling during paving and recycling determined that employee exposure to air contaminates were well below the Occupational Safety and Health Administration (OSHA) permissible exposure limits (PEL), and in most cases below the detection limits. 5.1.5 Greenville County, north to Emporia In 1989, the Virginia Transportation Research Council (VTRC) worked with the Suffolk District of the Virginia Department of Transportation (VDOT) in placing an asphalt rubber SAM as a modified seal surface treatment on Route 301 in Greenville County just north of Emporia (Maupin and Payne, 1997). The modified seal consisted of a layer of asphalt rubber binder, a layer of coarse aggregate, and a layer of fine aggregate. Excessive bleeding occurred on the test section, which was attributed to the combination of a bleeding condition of the existing pavement and the heavy asphalt rubber application rate of approximately 2.7 l/m2. This application rate was in the midrange of rate recommended by (International Surfacing, Inc. Specification for asphalt-rubber stress absorbing treatment (SAM or SAMI) for highways, roads, streets, and airports. Chandler, AZ). Since it was experimental, SAM was much more expensive than conventional treatments. Because of its less than satisfactory performance, no further work with this material was attempted for a few years. In 1992, test sections were installed and evaluated in VDOT’s Bristol District. The installation included a test section of asphalt-rubber SAM and two control sections: a modified seal surface treatment and a conventional surface treatment. Two types of control treatments were used because these treatments were commonly used in various locations of the state and it was desirable to know how SAM compared to both treatments. The asphalt rubber test section (SAM) and the control surface treatments using CRS-2L, which is latex modified, were evaluated by placing field test sections and observing their performance over 4 years. Construction was also observed, and data were collected on the equipment, materials, construction techniques, ambient and asphalt temperatures, and problems encountered during construction. The test and control sections were placed on Route 11 in Wythe County from 31.23 km (19.40 milepost) to 38.41 km (23.16 milepost). Both control treatments, conventional and modified single seal, are used extensively in Virginia. The conventional treatment consisted of a single layer of CRS 2L binder followed by a layer of coarse aggregate. The modified single seal consisted of a layer of CRS-2L followed by a layer of coarse aggregate, another layer of CRS-2L, and a final layer of fine aggregate (No. 9).



The quantities of asphalt and aggregate to be used on the control sections were initially estimated from past design rates for that aggregate. However, the quantities were verified with the flakiness index design test described in the 1979 asphalt emulsion manual (Payne and Mahone, 1987; The Asphalt Institute. 1964; The Asphalt Institute. 1979). During construction, the application rates for the asphalt rubber binder, CRS-2L asphalt emulsion, and aggregate were checked to ensure that the correct quantities were being applied. The rates were determined by measuring the amount of binder sprayed on 0.093 m2 metal plates placed on the pavement before the distributor and aggregate spreader passed. The application rates are shown in Table 15. The rate of application for the SAM binder was much lower than the recommended rate used on the earlier test section placed in 1989 because of the bleeding problems with that test section.

Table 15: Application Rates of Materials (Maupin and Payne, 1997)

The SAM asphalt rubber binder had 84 percent AC-20 asphalt cement from Bristol Asphalt Products, Inc., Bristol, Virginia; 15 percent ground tire rubber from Baker Rubber Co., South Bend, Indiana (see Table 16); and 1 percent ground tennis ball production waste. The styrene-butadiene latex modified emulsion, CRS-2L (2.5 percent latex), used for the conventional and modified seals was supplied by Ultrapave (see Table 2 for binder specifications). Salem Stone Co., Sylvatus, Virginia, supplied the No. 8-P aggregate and American Limestone Co. in Abingdon, Virginia, supplied the No. 9 aggregate (see Table 17 for aggregate gradations).

Table 16: Gradation of Ground Tire Rubber (Maupin and Payne, 1997)



Table 17: Aggregate Gradations (Maupin and Payne, 1997)

Table 18: VDOT CRS-2L Specifications (Maupin and Payne, 1997)

The experimental and control sections were constructed on May 11 and 12, 1992. The asphalt rubber binder was blended and applied by Able Bituminous Contractors, Inc., of Riverside, Rhode Island. The No. 8-P cover aggregate for the SAM and control sections was placed by W & L Construction and Paving Co., Chilhowie, Virginia. Although the treatments were placed in May, the air temperature was always higher than 16oC and construction never started until a surface temperature of 21oC was reached (except for one shady location where the sun never reached the pavement and the surface temperature never exceeded 13oC. A special blending unit was used by Able Bituminous Contractors, Inc., to blend the AC- 20 asphalt and the ground rubber. The heating and blending of the asphalt and rubber were done near the job site in the blending unit. The asphalt rubber binder was sprayed with a 22,800-l capacity distributor that was designed and built especially for Able Bituminous Contractors, Inc. Three distributor loads of the asphalt rubber were used for SAM.



The original application rate of the asphalt rubber was set at 0.96 l/m2 to minimize the chance of bleeding. However, the light application in the beginning did not appear satisfactory, and the application rate was raised to 1.12 l/m2. The average asphalt rubber application rate for the test section was 1.15 l/m2, which was slightly higher than the target. Application temperatures for the asphalt rubber were recommended to be between 143 and 218oC. Since the ambient temperature was cool and the contractor did not have any experience applying the material at the low application rates desired, the contractor recommended a minimum application temperature of 183oC to minimize any potential application problems. Table 19 shows the asphalt temperature of each load used.

Table 19: Application Temperature of Asphalt Rubber (Maupin and Payne, 1997)

In addition to the asphalt rubber and No. 8-P aggregate, approximately 3.0 kg/m2of No. 9 choke aggregate was spread on SAM to prevent aggregate pickup. Traffic was not allowed on SAM until after the final application of No. 9 material. This traffic control practice was also employed with the modified seal surface treatment and the conventional surface treatment. Traffic was not allowed on any section for 1 hour, and then traffic was controlled with a pilot vehicle while the adjacent lane was treated. During construction, the chip spreader always placed the No. 8-P aggregate within 30 seconds from the time the binder was sprayed to ensure that the binder did not cool too much before the aggregate was placed. A rubber tired roller followed by a steel wheel roller was used to embed the aggregate. After the No. 9 aggregate was placed, the rolling order was reversed (Maupin and Payne, 1997). Problems During and After Construction A representative of Able Bituminous Contractors, Inc, had developed a special nozzle to spray the rubberized asphalt mixture at the specified low rate. Although the nozzle was somewhat successful, clogging was a continual problem that often caused non-uniformity. As can be seen in Figure 27, severe streaking occurred when the asphalt rubber was sprayed through the small-diameter nozzles. Table 20 shows that the No. 8-P aggregate did not meet the specifications. There was also a requirement that limited the amount of 75 μm (No. 200) material to 1.5 percent as determined by washed gradation. The aggregate had a heavy dust film coating, and although a dry gradation was inadvertently performed, it would have probably failed the washed gradation requirements for 75 μm (No. 200) material. The dusty aggregate combined with the low application rate of the asphalt binder produced an opportunity for aggregate loss. A subsequent review of the literature revealed specifications that suggested pre-coating aggregate with a thin asphalt film to overcome aggregate loss (Turgeon, 1989).



When the road was released to traffic, a large number of broken windshields were reported on the SAM test section for 2 weeks. There were no problems with broken windshields on the control sections. In addition, dust was quite bad on all sections.

Figure 27. Streaking Caused by Use of Small-Diameter Nozzles

Prior to placement of the test and control sections, a pre-treatment pavement evaluation was done by VTRC personnel and Bristol District materials personnel to determine pavement distresses. The evaluation included a survey of the cracks, pavement distresses, and overall condition of the pavement. The entire section of road was severely aged, with cracks ranging in width from 6.4 mm to 16.0 mm. However, on the north end of the project where the two control sections were placed, the cracking was less frequent and not severe. Because of the overall extensive cracking, VDOT maintenance personnel attempted to patch the cracks that exceeded 6.6 mm during the week of May 4, 1992. However, because of inclement weather, many of the severe cracks were not repaired, and some failed because of poor curing conditions. The cracks on the north end were repaired successfully. It was not feasible to locate the sections in such a manner that all sections had the same types of distresses. Although this situation could be perceived as providing an unfair comparison between the test and control sections, the investigators felt that the experiment would still provide useful information about the problems experienced in the 1989 test. In addition, it provided the ultimate test for SAM since its performance was supposed to be superior to that of the control treatments. Satisfactory performance under these severe conditions would be reason for use for this material in the future. Pavement performance evaluations were conducted periodically on the test and control sections beginning in July 1992. There was no stone loss and no bleeding on the control sections. There was significant bleeding on the SAM section because of stone loss. Although the bleeding and stone loss gradually progressed as evidenced by the distress surveys, there were no further reports of broken windshields after the initial post-construction period. The final amount of cracking was approximately the same for all treatments. Since the surface on which SAM was placed had more cracking than the other sections, it was more successful at preventing the cracks from reflecting through the treatment. Although it was successful, SAM could not prevent the reflection cracks as originally hoped. Except for the appearance of stone



loss and a bleeding surface on SAM, the overall performance of the pavement structure in all sections was good. Because much of the stone was whipped off the SAM test section by traffic, the investigators decided to conduct friction tests because of potential safety problems. Problems encountered during construction were different from those associated with the earlier project in VDOT’s Suffolk District. Bleeding occurred because of excessive stone loss, not because of applying too much binder, which happened on the Suffolk project. Although bleeding occurred, the friction numbers were satisfactory. One cause of lost stone was that it was coated with excessive fines. The asphalt rubber binder is a viscous material that tends not to flow through the dust coating and form a tight bond with the large aggregate particles. The CRS-2L used on the control sections was more likely to penetrate the dust coating and coat the aggregate particles well to form a good bond. The literature (Turgeon, 1989) indicates that it may be necessary to pre-coat the aggregate with binder to ensure stone retention, which would result in higher costs. To try to prevent the bleeding that had occurred in the earlier project, the binder application rate was set lower than that recommended by industry. The lower application rate also possibly caused stone loss. The correct application rate that would result in neither bleeding nor stone loss may be hard to achieve under routine conditions. Another negative aspect of stone loss was broken windshields and inconvenience to the highway users. Phoenix, Arizona, discontinued use of SAM because of the public outcry against its use. A positive aspect of SAM was its ability to keep cracks sealed to prevent the entrance of surface water. Although many cracks of the underlying surface were evidenced by the depressed appearance, they remained sealed. The initial cost of SAM is considerably more than the initial cost of treatments currently used in Virginia. The service life of SAM would have to be much longer than that of current treatments to be cost-effective. An attempt will be made to monitor the age at which the different treatments need to be resurfaced to determine an accurate comparison of effectiveness. 5.2 EUROPE Recycled rubber’s use in asphalt is far less common in Europe, partly due to competition from polymer modifier alternatives. Moreover, both methods (wet and dry), as used in the USA, and especially the wet one are not yet accepted because of the high cost and because of the high temperature required during the long reaction time for the wet one, which leads to high energy consumption and the consequential considerable pollution, both facts which are in total disagreement with the Kioto protocol. Case studied mentioned below follow the American way. Rubberised asphalt has been used since 1981 in Belgium, as well as in the neighbouring countries France (1982), Austria (1982), Netherlands (1982), Italy (1983) and Germany (1986). In this period, the rubberised asphalt typically used 7% rubberised bitumen with 2% extender oil (WRAP, 2008).



5.2.1 Poland Asphalt mixed with rubber in Poland still has the rank of the new technology. Poland is having the same issues that many parts of the world are having, when it's cold weather and there is rain, but rubberized asphalt mixtures after two, three years, still are standing the forces very well. Hot mix asphalt mixture with tire rubber (dry process) was applied in Poznan City by Colas Company. Colsoft technology, patented by Colas Company (Dry technology) has been used to a pavement of Hetmanska Street in Poznan City. According to results, rolling noise was reduced by 3 dB(A).

5.2.2 Belgium Open graded rubberised asphalt incorporating 22% rubber with 2% extender oil was laid on the E3-Gent Ring Road in Belgium, between 1981 and 1982. However, during the same period (1980-1990), there was a significant development in bitumen modification with polymers, such as styrene butadiene styrene (SBS) and styrene butadiene rubber (SBR), which offered similar levels of performance improvement in the respective polymer modified asphalts (WRAP, 2008). This situation, coupled with lack of local specifications and expertise and the initial cost implications, has resulted in less extensive use of rubberised asphalt in Europe (Sousa, 2005). 5.2.3 UK Newcastle, England (2006) A trial project which incorporated crumb rubber and the WMA additive Sasobit® occurred in Newcastle, England, in late November of 2006. The objective of this study was to add 2.0- 2.5% of crumb rubber to the asphalt binder and achieve all of the normal asphalt specifications while keeping the fumes to a minimum. They noticed that, when mixing Rubberised Hot Mix Asphalt (RHMA) at the normal temperatures of 170-180°C, there was excessive fuming that can be hazardous and cause unsafe working conditions. This also means that the asphalt may have to be produced outside of urban areas, which can also create problems. The trial consisted of two sections. Each had 200 tons of asphalt mix with a layer thickness of 35mm. The ambient temperature at the project was recorded as being 25°C. One section of RHMA was produced at the normal operating temperature of 170°C without the addition of Sasobit®. The other section consisted of a RHMA with the additive of Sasobit® inserted into the pug mill at a rate of 1.0% of the binder content thus making it a RWMA. The production temperature was reduced to 150 °C. The fuming at the plant for both batches of asphalt was monitored and visually observed. When paving at high temperatures, and without the addition of Sasobit®, fuming was easily seen and odor was present; however paving was still possible in these conditions. When the WMA additive was added, production and paving temperatures were reduced. This, in turn, decreased the amount of fumes present without compromising the paving operations (Hicks et al, 2010). Figure 28 shows the finished mat of the rubberized warm mix asphalt (WMA) test section in Newcastle, England. The trial showed that WMA can be added to RHMA to reduce the



fuming at the plant and the paving site, as well as having no effect on the paving efficiency or performance (Sasol Wax 2010)

Figure 28: Finished RWMA Project in Newcastle, England (Sasol Wax, 2010)

It must be noted, the UK Highways Agency does not permit the use of the Dry Process in the United Kingdom (Way, 2006). 5.2.4 Portugal Portugal started to use rubberised asphalt more extensively since 2003. The mixture design is rather similar to that used in Arizona, specifically 8 to 10% rubberised bitumen without extender oil has been typically used in gap and open graded rubberised asphalt mixtures (WRAP, 2008). 5.2.5 Spain Spain’s guidelines regarding implementation of rubberised asphalt took place in July 2007, right after the publication of relevant MANUAL from CEDEX (Central Laboratory of Public Works of Spain). According to the MANUAL, more than 30 trial sections (~100km long) have been paved with asphalt mixtures modified with tire rubber (produced by both the wet and the dry process), during the last 10 years. However, Spain started to use rubberised asphalt more extensively since 2003. The mixture design is rather similar to that used in Arizona, specifically 8 to 10% rubberised bitumen without extender oil has been typically used in gap and open graded rubberised asphalt mixtures (WRAP, 2008). More than 10 trials have been applied with success on Spanish roads since 2002, being the total amount of hot mix tested 50,000tons on the following roads, with the indicated Government Agencies: -Government of Andalucia, Province of Cadiz, El Bosque-Ubrique -Government of Madrid, Province of Madrid, Valadaracete -Government of Castilla y Leon, Province of Zamora, Toro -Government of Spain, Department Valladolid, Ronda -Government of Castilla y Leon Province of Valladolid, exit from highway to Cabezon de Pisuerga -Government of Castilla y Leon Province of Leon -City of Valladolid, Avenue Juan Carlos I



-Government of Castilla y Leon, Carrizo de la Ribera -Government of Spain, Department Leon All of the trials mentioned above have been implemented using “Neumafalt” process, which is a patented modification technique within the so called wet method, based on two industrial phases:

a) Crumb rubber powder from ground tires of high cleanness and with a maximum size of 0,8mm is integrated into the bitumen, heated at a temperature of 170oC at percentages varying between 15-20% wt of the binder. The binder’s percentage ranges from 5,5 to 6,5%. The temperature needed for the mixing is between 160-170oC, while the temperature for the maintaining the modified asphalt is until getting in contact with the aggregates can be between 155-165oC. The reaction time between rubber and bitumen is 12-15minutes. Such modified bitumen has high Marshall stability, dynamic modulus as well as satisfactory performance in terms of fatigue, plastic deformation, moisture sensitivity and reflecting cracking, while the thickness of different road courses is reduced by 20-30%, compensating the cost of the bitumen’s modification.

b) Finally, tire rubber can be used not only in surface layers but in binder and base courses, so the quantity of rubber used in road construction increases heavily contributing significantly to the solution of the environmental problem of EOL Tires (Dannert, 2006).

5.2.6 Germany Germany has been placing dry process crumb rubber mixes. These dense graded dry process hot mixes typically use larger size crumb rubber as an aggregate. Unfortunately, results of the pilot applications are not presently available (Way, 2006). Stone Mastic Asphalt (SMA): A5 Appenweier - Achern Between the interchange of Appenweier and Achern, in the direction of Basel-Karlsruhe, a new road pavement was built on an existing concrete pavement by using a high elastomer "Stone Mastic Asphalt (SMA)". The total lot area was about 58,000m². The daily traffic load of about 60,000 vehicles (18% trucks) was redirected to the opposite lane (http://web.ctsag.com/). The main part of the bid was: spray adhesive, binder 0/22mm, PmB45 (8cm) and Stone Mastic Asphalt (SMA) 0/11S, PmB65 (4cm). The life expectancy of this lot was limited to about 3 to 4 years. Based on experiences and the limited useful life, the following parameters were executed:

release the concrete roadway to a scholl size of max. 50cm edge length thorough fixation of the concrete parts through a rolling apply a pressure-sensitive adhesive apply asphalt binder mixture 0/16mm by using B45 on 4.0cm minimum thickness apply stress absorbing membrane interlayer (SAMI) of about 2.5kg/m² by using

tecRoad®, a rubber modified bitumen granulate, consisting of: road bitumen, rubber powder and filler materials. TecRoad® is used as an aggregate for modifing road bitumen and asphalt, is an extremely flexible modification system that requires no or very little modification in asphalt mixing plants and can be used immediately.

sprinkle the SAMI with fine flint 8/11mm of about 15kg/m² and press with a pneumatic tyred roller. Unsed flint was removed by split sweeper.

apply SMA 0/11S with 7.0% weight tecRoad® (about 70kg/m²)



These calculations are based on the condition that the main carrying capacity is done by the underlying layers. The usage of grid reinforcement is not necessary since the asphalt binder layer was not already cracked. The use of rubber modified bitumen in the surface course on the SAMI makes the use of PmB in the binder layer redundant. The task of the binder layer consists of a balancing function and to ensure flatness (http://web.ctsag.com/). Open Graded Asphalt: A2 Hannover West - Buchholz The main content of the bid was the new construction of highway A2, section Hannover West and Buchholz, while due to high traffic load, the work could only be done on 3 weekends. The total area of the project was about 158.000 m². The process consisted of:

preparation of correct concrete road surface sealing of concrete surface with SAMI (tecRoad® 1,8kg/m² and ~5kg/m² flint 8/11) installation of asphalt binder (PmB 45A ~8cm): until the installation of OGA, the

traffic was routed over this asphalt binder sealing of asphalt binder with SAMI (tecRoad® 2,5 kg/m² and ~8kg/m² flint 8/11) installation of OGA (with tecRoad®) on 3 weekends

About 430 tons of tecRoad® were processed per weekend. For road marking, a foil was stuck down and rolled on (http://web.ctsag.com/). 5.2.7 France In France, proprietary crumb rubber mixes have been developed to reduce noise. Varying amounts of crumb rubber are used in preparing these mixes and in some cases the rubber content is less than 15 percent and/or the blending reaction process may not be utilized. These mixes all contribute to some degree to recycling waste tires, however performance of all these various crumb rubber mixes that are not rubberised bitumen is not as well documented and thus at this time cannot be fully evaluated. In 1984, an investigation was made by the French to determine hydrostatic pressure in and under Drainasphalt on City Street along the Seine River. Their findings showed a reduction of 3 to 5 dB with no trucks, and a 2 to 3 dB reduction with five percent trucks. As a result of their findings, the researcher made a proposal to overlay the Paris Loop with open graded Asphalt-Rubber (Way, 2006). 5.2.8 Italy A project in Torino was promoted and financed by the Province of Torino and technically developed by Professors Ezio Santagata and Mariachiara Zanetti of the Politecnico di Torino. Its construction began at January of 2009 and was completed in 2 phases. The chosen mix was a 3 cm Asphalt Rubber-gap graded mix 0/15 mm that replaced the originally planned porous asphalt concrete. Approximately 1.2 km (16,000 m2) on Borgaro-Venaria has been covered by the modified layer.




Figure 29a,b: Application of the modified layer

Figure 30: Application of the modified layer

Laboratory examination consisted of the characterization of the tire rubber powder, tests on modified with tire binder, evaluation of viscosity and viscoelastic properties, fatigue tests, tests on physical properties of the binder, mix design and performance characterization.

Table 20: Chemical analysis of rubber



Rubber’s specific surface has been measured at 0,020 to 0,080 m2/g, while its sulphur content ranged between 2.80 - 3.45%, with an average of 3.10%. Aggregates of different particle sizes have been used in percentages showed below: 0/5 mm particle size: 30% 5/10 mm particle size: 16% 10/15 mm particle size: 54% Modified asphalt 50/70 has been used for the production of the modified asphalt binder, by the use of wet process. Rubber of three different suppliers has been added to the binder at percentages of 0-20%wt of it.

Figure 31: Modified asphalt binder

Binder’s viscosity was influe

vestigation includes examinanced by the type and percentage of the added rubber. Future tion of binder’s properties, weaving and adhesion, regularity,

The first application of rubberized asphalt mixture made by the wet process in Greece took place in 2000 in Athens funded by the Ministry of Environment, Planning and Public Works and covered an area of 200.000m2- 3km long-. Bitumen 50/70 was mixed with tire rubber for 1 hour at 200oC. Rubber’s chemical composition is showed in Table 21, while characteristics of modified bitumen are showed in Table 22.

Table 21: Used Rubber’s chemical composition

Test ASTM D297

Projects Specs % Sample

inaccumulation of permanent deformation as well as surface state of degradation (Santagata and Zanetti, 2010). .2.9 Greece 5

Athens

Acetone 11 7,5-17,5 8-12Ash content max 18,5 6-8 8 Carbon black 20-38 26-30 28 Rubber Hydrocarbonate 30-60 48-52 50 Natural rubber 42 30-34 33



Table 22: Characteristics of rubberised asphalt

Characteristic ASTM Standards

Laboratory results

Penetration 25°C, 100g / 5s 50-100 51Penetration at 4°C, 200g / 60s 25 min. 38Apparent viscosity 5750 at 175°C, Cp 1500 - 6000 Brookfield viscosit 3000 y at 135°C, cP - Softening point, °C min 55.8 51.7 . Resilience, 25 C, % 10min 22o .Flash poin 232.2 min. 240t, °C Thin film esidue PRetention, % of original in. 79

Oven Test R enetration 75 m

Elastic re 10 cm, % - 80 covery at 10°C,Force Ductility Ratio @ 4°C - 0.47Seperatio - cceptedn after 25 hours A

Aggregates used consisted of 60% high PSV and 40% of limestone aggregates. Theirs gradation is showed in Ta

e 23: Aggregate Passing

(min-max) (%) (%)

ble 18.

Tabl gradation

Sieve

Sample (28/1/2000)

2,36mm (No 8) 100 100 2,00mm (No 10) 98-100 98 1,18mm (No 16) 50-85 63 500μm (No 30) 17 5-30300μm (No 50) 0- 8 15150μm (No 100) 0 0-1075μm (No 200) 0-1 0

Gener erized asphalt used are howed below:

al stages of the production of the rubb s

Figure 32a,b: Stockpiles of

EOL-Tires



Tire rubber was received in super bags, was loaded and weighted into the blender hopper.

Figure 33a,b: EOL-Tires for the production of rubberized asphalt

Then it was fitted into a mixer and blended at 200oC. Rubberized bitumen reacted for 60 minutes in the tank, tested as far as viscosity of the asphalt rubber binder is concerned and fed to a hot mix plant for the production of crumb rubber modified asphalt mix. The Asphalt-Rubber Hot Mix was placed using conventional paving equipment and techniques. Performance 3 years later

Very good resistance in permanent deformation Noise reduction by 6 dB(A)

No cracking on the surface Better markings reflection Increased fatigue resistance Increased elasticity under low temperatures Improved elasticity Reduced viscosity sensitivity of the binder layer in common conditions Increased συνεκτικότητα and high viscosity Higher r

near Karambas’

s by the use of mechanical process. Crumb rubber used was part of the unit’s roduction, while modified asphalt had been produced at a factory near the shredding unit.

, rubber of 0-1mm at 5% wt of asphalt binder has been used.

erized asphalt, even today shows that the performance of tisfactory, while it’s bearing capacity is

programming the implementation of a new asphalt top the Laboratory of Public works of the Region of Sterea

Better skid resistance than conventional mix

esistance of modified binder to aging (Kairidis, 2003). Region of Sterea Ellada Use of rubberised asphalt also took place in the Region of Sterea Ellada almost six years ago. Crumb rubber has been added to asphalt binder without the use of aromatic oil of Hydro Carbonate. The area covered with the modified mixture was a part of the areafactory (http://www.karabas.gr), a unit which recycles EOL Tires by shredding them into smaller piecepFor the 5cm asphalt top layer Examination of the section with rubbthe top layer, covering an area of 2000m2 is very saexcellent. The owner of the unit islayer, which will be examined by Ellada.



Figure 34. Road top layer modified with tire rubber (six years after paving)

Kastoria city Crumb rubber has been used as soil improvement for the construction of a forest road in Kastoria City. This application, as well as the increased use of tire rubber in playgrounds and athletic grounds does not comply with the project’s main issue, however it is mentioned for environmental reasons.

6. CONCLUSIONS EOL Tires can be used in road construction, providing asphalt mixtures with satisfactory properties. The story of rubberised bitumen began on or about the year 1965 with the simple goal of developing a maintenance patching material to hold old crack pavements long enough to allow for the future overlaying or reconstruction of the pavement. In the intervening 40 years its use has grown an expanded into a myriad of areas and now is a routine paving material in Arizona, California and Texas. Useful products from adding crumb rubber to pavements will continue to be developed because pavements that last longer and need less maintenance will always be in demand. Addition of tire rubber can be done by two processes, the wet and the dry one. According to the first one aggregates,

hile in the second one-“dry”-, rubber is added to the aggregates and then the binder is mixed ith them.

bility and life time, reduced cracking as well as reduced maintenance costs.

, the “wet”, rubber is added to the binder before the addition of the ww There is more bibliography on the “wet method”, especially in the USA as mentioned in the section of this process. Wet process includes the incorporation of rubber at percentages up to 20-25%wt of the binder to the mixtures. Pavement was found to perform better towards noise reduction, increased dura



As far as the “dry process” is concerned, addition of up to 3% wt of the aggregates tire rubber takes place, taking into account the limited relevant bibliography, while case studies of this process are also limited. In general, addition of tire rubber even in small percentages can lead to the reduction of huge stockpiles or EOL Tires, which usually are uncontrollably deposited.

Rubberized asphalt is a good practice, since:

it is a less expensive application when used as a thin top course over failed pavement

zona & California studies); it reduces noise as opposed to concrete pavements, and also is quieter than

(Arizona State University studies); it provides better surface road drainage when used in an Open Grade Friction Course

ssenger tires per lane-kilometre). it shows reduced thermal cracking (due to cold temperatures), while rutting (usually

ates, i.e. high temperatures in summer and severe frost in winter.

ved over with RMA or with a stress absorbing

ed traffic safety due to a better deicing property, as

en, as previously stated, generally focus on nt layer thickness due to

b rubber processing facilities in the vicinity and

ficulty in preparing mix design, the lack of rubberised

have been

n and implementation of

that would otherwise need replacement (California & Arizona studies); it is less expensive to maintain per lane-kilometre (lane-mile) in years 6 through 15 of

pavement life over conventional pavements, and the same in years 1 through 5 (Ari

bituminous pavements; rubber bitumen makes urban environments more habitable (Arizona DOT studies);

it improves wet surface traffic safety (Texas DOT studies); it creates less of a “heat island” effect than with concrete pavement at surface

(Texas & Arizona studies) it is a beneficial use for post-consumer waste tire materials, using huge amount of

them per lane-mile (about 621 waste pa

caused by hot temperatures) can be reduced with one and the same asphalt mix. Rubber Mix Asphalt (RMA) is specifically useful in areas with extreme clim

severely cracked pavements can be pamembrane interlayer (SAMI) because the more elastic properties of them significantly reduce reflective cracking.

due to lower maintenance costs and increased durability, the live cycle cost of RMA is significantly lower when compared to conventional asphalt pavements.

other advantages include increaswell as increased skid resistance.

The challenges of using rubberised bitumadditional cost if highway designers will not allow a reduced pavemethe proven properties of rubberised bitumen. Other challenges that have been mentioned include lack of availability of suitable crumthe cost of such facilities, the need for suitable blending and mixing equipment and the cost of such equipment, the degree of difbitumen binder and mix standards, the lack of trained personnel, and uncertainty and doubt about how long rubberised asphalt will last. Although all of these challengesaddressed by the rubberised asphalt industry, doubts and concerns still persist and typically only trial test sections can be built and observed to satisfy many of these doubts. Preliminary European guidelines (UK) regarding productiorubberized bitumen are listed below:

Rubber content should be not less than 15 percent and not greater than 22 percent by weight of the total binder.



Reaction time: rubberised bitumen should be maintained in the reaction tank for at least 45 minutes but no more than 4 hours, at nominally 177oC and not greater than

duced in a way that the blend viscosity at 177 C over the reaction time remains within the range of 1500 to 5000 cP. This should be

t allows the asphalt plant to switch between using the rubberised bitumen or the regular paving

berised bitumen producer should use a flow meter that

be designed in such a way that there will be no detrimental

enclosed collection point for the mixed rubberised asphalt should be used to

re

voided.

ing evaluation. A

dures must be developed and followed to ensure

ined in time.

218oC. Rubberised bitumen should be pro o

tested at least twice per day per mixing batch. For installation of a mobile rubberised bitumen mixing plant, an area of not less than

150m2 will be required, depending upon the model and make of the mobile plant (e.g. Stractco Global and CEI Enterprises manufacture a number of different plant sizes).

The mobile rubberised bitumen plant can be installed within a working day (7 – 8 hours), provided that all necessary connections and site requirements have been pre-arranged on site. The plant will have a special heavy-duty pump to transfer rubberised bitumen to either the pugmill (batch mixing plant) or the mixing zone midway down the drum (continuous mixing plant).

A two- or three-way valve should be installed in the bitumen feed line tha

grade binder, according to demand for various asphalt mix designs. For drum mix plants, the rub

interlocks the rubberised binder feed with the plant aggregate feeds. Rubberised asphalt should

effect on the properties of the loose mixed material during the period from collection, delivery to laying and compaction.

A fully isolate and minimise release of fume or odour to the surrounding environment.

Soapy water or dilute silicone may be used to prevent the material sticking on the base of haul trucks.

The use of diesel fuel or solvent based release agent must be avoided. Loose coated rubberised asphalt should be transported to site, laid and compacted

within 3 hours of production. The haul trucks should be properly insulated to ensuthat the temperature of the rubberised asphalt mixture is maintained between 149 and 163oC during the delivery period, and the temperature for completion of compaction should not be less than 143oC. This means that the ambient and pavement surface temperatures for placing gap graded rubberised asphalt mixtures should not be less than 13°C.

The use of rubber tire rollers should be avoided. Steel wheeled rollers having deadweight not less than 7.3 tonnes should be used.

Raking and handworking of rubberised asphalt mixtures should be a Successful utilization of Asphalt-Rubber in HMA requires critical engineermix design must be developed which incorporates tire rubber, aggregates and bitumen to meet expected design requirements. Layer thickness must be considered to ensure performance life of the pavement, while construction procethat the mix and structural requirement are met in the field.

t be noted, that in Greece there are no guidelines regarding implementatIt mus ion of rubberised asphalt mixtures and in terms of the ROADTIRE project, the implementation

i h will take place awh c t July of 2011 will be the first one in trial level to be exam Finally, tires can be utilised in road construction, a civil engineering application, which dominates all over world, so a huge quantity of EOL Tires can be used, eliminating the problem of their disposal, which causes the already known environmental problems.



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