USING SPECIAL EQUIPMENT TO HEAT AND REHABILITATE ROADS IS SAID,AMONG OTHER THINGS. TO OFFER COST AND ENVIRONMENTAL BENEFITS

Green ARM'S HIT0NEsyslem at w01k onNo 36 national road inSapporo, Japan

\Mhile cold recycling improves the bearing capacity ofa pavement structure, another way of processingasphalt highways is by using hot recycling.

The system uses special units to heat the surfaceto the required temperature and soften it so that arecycling machine can scarify, remove, recycle andreplace it.

According to Wirtgen, hot recycling is used for therehabilitation of damaged asphalt surfaces, so anintact pavement structure is of vital importance. Thelayers underlying the surface must fulfill all therequirements with regard to bearing capacity andresistance to frost.

Hot recycling often involves the recycling orreprocessing of reclaimed asphalt pavement (RAP)materials into hot mix asphalt in a central plant whilehot in-place recycling (HIR) is an on site, in-placemethod that rehabilitates deteriorated bituminouspavements and minimises the use of new materials.A special train is used for the process, and thesehave been deveioped by a number of companiesincluding Wirtgen, FAYAT Group, Socotherm, Martecand Green ARM.

Asphalt pavement is arguably the most recycledproduct in the United States [automobiles also claimthat statusl with ten of millions of tonnes reclaimedeach year. So as stocks of raw materials becomescarcer, and more costly, its reuse becomes moreimportant.

According to the Asphalt Recycling and ReclaimingAssociation (ARRA) the proven technology of hotrecycling provides a timely answer to the nation'sroad maintenance and rehabilitation prollems.

Reclaimed aggregates and asphaltic cements are

broken down to their original state and reused toproduce high quality asphaltic concrete, theperformance of which has been proven to equai thatof conventional mixes.

"Hot recycling can transform old, deficientpavements into good functional roadways. Problemsassociated with deterioration of asphalt andgradation can be corrected with aggregates andasphalt added to the new mix. Hot recycling can alsohelp correct and maintain vertical and horizontalgeometrics. Where curb and bridge clearances areaffected, old overlays can be milled and recycled in acost effective rehabilitation alternative," says ARRA.

Hot recycling eliminates the disposal problemsinherent in conventional methods; requires onlyminor modifications to existing equipment; can beperformed in compliance with existing air pollutioncontrol standards; and can be done repeatedly, usingthe same materials.

"Equipment now available offers a cost effectiveenhancement and allows conventional asphaltplants, which were not originally designed for usingrecycled materials, to be modified and fitted withrecycling equipment," says ARRA.

Indeed as one observer noted in a paper on thesubject: "The technology and equipment necessary todo recycling is developed and available. What makeshot recycling seem complicated sometimes is theseemingly infinite number of ways to go about it. "

The HIR process may be performed as either asingle pass (one phase) operation that monolithicallyrecombines the restored pavement with virginmaterial, or as a two pass procedure, wherein therestored material is recompacted and the applicationof the new wearing surface then follows a prescribedinterim period that separates the process into twodistinct phases, says ARRA.

"It provides a very low cost maintenance strategythat enables the public works official to effectivelyreuse existing materials. This process demonstratesthat asphalt is a rather unique construction materialin that it can be effectively and economicallyrestored. Rather than bury the deteriorated pavementwith inordinate depths of new materialconventionally applied, or lose it to the grinder,proponents of HIR encourage restoration. "

Many advantages are claimed for the process, andsays ARRA, it effectively addresses the classicsymptoms of deteriorated pavement including cracksare interrupted and fllled; aggregate stripped ofthebitumen is remixed and recoated; ruts and holes arefilled, shoves and bumps are levelled, drainage andcrowns are re-established; flexibility is restored bychemically rejuvenating the aged and brittlepavement; aggregate gradation and asphalt contentmay be modified-by some variations oi this process,

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and highway safety is enhanced through improvedskid resistance.

"ln a period of rapidly increasing costs and limitedfunding, HIR presents the opportunity to spreadavailable dollars over a much greater area. Roadwaydeterioration can be suspended, pavementspreserved and upgraded, and costly reconstructionavoided," adds ARRA.

Porous tlansformationA system that can transform or regenerate existing insitu dense asphalt pavement into porous asphaltpavement has been highlighted byJapanese companyGreen ARM.

The company says the HIT (hot in-placetransforming technology) construction method,

known as HITONE, has advanced since experimentaldemonstration work was carried out on 680m ofHighway 77 in Okinawa Perfecture, Japan, in 2005,

with HITONE the construction work using aspecial train is divided into four processes: pre-heating, milling, separating and paving, and the self-propelled machines (preheater, heater miller,separator and mixer paver) having specific functionsdrive on the road and carry out their own functions.

The concept and design for the advancedtechnology for asphalt transforming in a single passprocess was developed through a collaboration ofcreen ARM, Sumitomo, Showa, Shell, Hikari Kogyo,all of Japan, and the machine is manufactured byHitachi and Sumitomo.

"With a newly developed screening device, milledasphalt mixture collected lrom the roadsurface is screened in-place whiie thetrain is advancing, to be eventual lyconverted to porous top layer and densebottom layer," says the company.

"Separated asphalt fraction to be usedfor the upper layer is mixed in a pugmillinstalled in the separator and the rest tobe transferred to the mixer which follows,where mixing process for the lower layertakes place. This technology allowssimultaneous placement of the twodifferently graded fractions of asphalt forthe different layers.

"Utilisation of the above characteristicsprovides the HIT construction methodwith very different processes in pavingcompared to the conventionalconstruction method."

Creen ARM says that by using itsprocess the removal of milled asphalt;surface treatment after removal; andrecycling of asphalt mixture removedfrom the job site become unnecessaryand the volume of new porous asphaltmixture brought in from an outsideasphalt plant is reduced to the minimumnecessary.

"The asphalt transforming projectexecuted in okinawa in September, 2oo5shows that, with the HIT constructionmethod, it successfully reduced the totalenergy consumption by about 34/ocompared to that of the conventionalconstruction method and also realised areduction in the dump truck requirementsby 72% in that 18 trucks were required incomparison to the 64 trucks otherwiseneeded using the conventional method."

As reconstructed roads have beentransformed to porous asphalt pavement,they can effectively control suchphenomena as hydro-plane and water-spray, points out Green ARM.

Tomoyuki Wada, creen ARM'S generalmanager for administration and sales,said that since last year the HITONEtechnology had achieved some majordevelopments.

In August 2OO7, four nights of publicconstruction works on No 36 NationalRoad in Sapporo (under theadministration of the HokkaidoDevelopment Bureau of the Ministry ofLand, Infrastructure and Transport) weresuccessfully completed.

In October last year a patent for theheating process and apparatus of HITONE

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was granted in Japan, and in April this year, Caltrans(the California Department of Transportation) in theUS "appreciated HITONE and issued an official specfor HITONE for California's state highways. A tenderdocument was issued for public bidding."

Tomoyuki Wada said: "In May 2008, a processpatent was granted in Korea and we expect it to begranted in the US in the near future.

"Based on the above official specs, two pilotprojects to construct porous asphalt pavement out ofthe existing dense graded asphalt will be undertakenover 40km of Califomia state highway in August andSeptember."

Jingjintang ExpresswayIn 2OO2 cerman company Wirtgen introduced HIR, anew application for repairing damaged roadpavements in China, and since then its equipmenthas rehabilitated millions of square metres of road.

One such project was on the JingjintangExpressway, which links the port of Tianjin with thecapital, Beijing. When repaired, some 35,000vehicles./day, including 1o% ofheavy traffic, put amuch higher strain on the road than originallyplanned. The healy traffic had caused, in particular,the right-hand lane to literally fall apart.

The motorway owners decided to hot recycleseveral sections ofthe 143km long road.

According to Wirtgen, one of the benefits of thismethod was that instead of placing a new surfacecourse across the full road width, rehabilitation wasrestricted to the damaged slow lane. The option ofreplacing the entire pavement would also have beenmuch more expensive.

One section chosen for hot recycling was a 30kmstrel.ch between Caiyr.r and Dayafang.

The hot recycling method was put to the test at a

The Wirlgen hainrehabililates a sectionol the JingiintangExpressway in China

Left: A PAVIREGmachine atwork on422 Hiqhway, andright: a delail of themachine ai work

HOT REGYGTI]IG

recycling depth of 4cm and a working width ofbetween 3.8m and 4m, says wirtgen.

The heating units of the wirtgen Remixer 4500followed in the wake of a Wirtgen HM 4500 preheater.

The remixer then scarified the heated asphaltpavement material and conveyed it to the integratedtwin-shaft mixer, where the existing material wasthoroughly mixed with 8%to 10% of new mix and inaddition sprayed 0.4 - 0.5litres m' of bitumen into themix to be paved.

The recycled surfacing course material was thenplaced by the machine's integrated paving screed.The recycling train worked at an advance speed ofbetween 1.6 to 2.2m/min, and a few hours aftercompaction the road was opened, and was beingused by heavy traffic.

PAV|REC tor M2Italian motorway operator Autostrada del Brennero isusing an innovative hot recycling system to carry outrepairs to a 2km section of the A22 motorway.

Celebrating its 50th birthday next year, thecompany is said to have used 'thermal regeneration'on the route as part ofthe "huge project carried outby the company in order to keep high levels ofquality, respecting the environment. "

The PAVIREC system uses the advancedtechnology ofhot in-place recycling for deterioratedasphalt surfaces, and has been developed by theSocotherm Group, whose activities relating to infra-structures and rehabilitation are carried out bySocotherm Infraviab.

The A22 runs southwards for 314km fromBrennero in northern Italy to near Modena. With theexpansion of tourism and its related activities in theTrentino-Alto Adige region in the 1950s, problemsarose due to deficiencies ofthe existing roadstructures, which were inadequate to deal with theincrease in traffic, especially in the summer season. Itbecame evident that a new multi-lane motorway hadto be constructed.

Autostrada del Brennero was founded on 20February 1959 on the direct initiative of the localauthorities convinced of the importance of the newroad link. In 1961 the company was grantedpermission to construct and manage the A22motorway.

The first 50km section of the motorway runningthrough the Adige Valley from Bolzano to Trento,opened in December, 1968, and from Ju$, 1972 themotorway could be travelled on without interruptionfrom Brenner to Chiusa (54km) and from Bolzano toModena (228km), "representing an important link in )

HOT RECYGI.ING

the European road network." h April, 1974lhelastsection, from Chiusa to Bolzano South, wasinaugurated.

Autostrada del Brennero is the first Italian motorwavoperator to achieve the integrated certificationQuality and Environment ISO 9}ol /14OOl fro t]..e A22.

The work carried out for Autostrada del Brennerousing the 52m long PAVIREC train was on the A22'sporous asphalt pavement, and the working speedwas 2.5-3.s/min with daily production of 5,8O0m'over the working width of 3-4m.

The regeneration depth varied from 2-5cm, withthermal regeneration, a non-destroying process, usedto remove and mix the old draining pavement withadded materials.

According to Socotherm, the technique solvescompletely the problem of the disposal of productsfrom the milling of pavements because it uses 100%of the existing materials, of,fering cost savings andenvironmental benefits.

on site thermal regeneration transforms themilled material into a product, not into a waste, andreduces the withdrawal of materials from quarries,energy consumption and transportation costs. Thecompany says that a comparison with the traditionalreplacement systems shows the PAVIREC recyclingprocess requires approximately 33% lower energyconsumption.

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components in a system of melting the deterioratedasphalt by irradiation and remixing it directly over theground with a vertical mixer, avoiding the breakingof aggregates and the chemical binding substances.

Socotherm says that PAVIREC recycling requiresonly a short length of site, and compared to somerecycling systems, involves no removing,transportation or disposal of old materials; no surfacecleaning and laying of the tack coat layer (the oldone remains in place and an effective hot bonding isrealised); an 80 9Oo/o reduction in new aggregatesadded:75-8o% reduction ofthe new bitumen added,and a proportional reduction of the materials-relatedt r2n<nnrtr t inn

The work is carried out in a single operation,l0O% on site, using a mobile plant consisting ofequipment to remove the old asphalt using heat; addthe new materials; regenerate and apply the asphaltconcrete mix, and finally compaction. The road isthen opened to traffic.

Uoyager's travelsThe FAYAT Group is highlighting its Marini VoyagerHIR machine, which it says now takes full advantageof new technologies.

A descendant of the ART 22O, a mobile hot mixasphalt (HMA) plant built by Marini, with 40machines being sold worldwide (some are still in usein Venezuela, Romania, Finland and Italv), the

Voyager is a traditional parallel flow machine. It is aself-propelled travelling plant that is automated inall areas, drying and then heating the recycledmaterials to a temperature of approximately 150'C,which is compatible with good compaction.

The system it calls thermo-regeneration (alsoknown as thermo-shaping or thermo-surfacing)involves only the first few centimetres ofcarriageway: it can never become a suitablesolution for structural recycling, says the company.

However, FAYAT says that the operationaleconomies made with in-place recycling areestimated at more than 50% in comparison totraditional recycling solutions.

It also points out that the Voyager can takeadvantage ofthe appearance ofnew low-energytechnologies, such as half warm and warmsolutions.

"The two major disadvantages relating to the hotrecycling process (at 150'C) are now dispensedwith: elimination of pollutant emissions such asdust, with stoppage of drying, and increased outputto 2Ootonnes./hr in situ, instead of 1ootonnes,zhr,"says FAYAT, whose Voyager technique takes fulladvantage of the boom in half-warm emulsions andfoam bitumen.

Indeed, FAYAT says the Voyager utilises theadvantages of HIR, among which are dehydration ofthe recycled materials and perfect coating with newbitumen; it is possible lo add 2Oo/o virgin materials;milling is independent and the depth of cut can becontrolled; it is possible to bring into operationimmediately; application of a tack coat afterbrushing, and the quality is equivalent to that of atraditional hot mix plant.

FAYAT says that while traditional binders areusually bitumen, with regenerating agents, newtechnologies have opened up possibilities that areroutine for stationary plants but remain newterritory for mobile plants. These include foambitumens, emulsions, modified bitumens andsequential coating techniques.

One solution suggested is half warm emulsions,a process that involves coating asphalt aggregatesand/or aggregates heated to 90'C with highperformance emulsions. All of these solutions seekto make the viscosity of low-temperature binderscompatible with coating.

FAYAT says that the production of asphalt mixescan be schematically subdivided into fourtemperature ranges, and temperature variations inthe mixing phase have been proved to greatlyinfluence the final characteristics of the product.

Accurate studies and tests have been carried outon the benefits that can be obtained by increasingthe aggregate temperature over ambienttemperature, before mixing with foam-bitumen, orwith bitumen emulsion. I

PAVIRECrecycling requiresonly a shortlength of site,and compared tosome recyclingsystems, involvesn0 removing,transportation ordisposal of oldmaterials

Wirtgenwww.wirtgen.de

Green ARMwww.gleen-arm.com

ARRAwww.alla.olg

FAYAT Gloupwww.tayat-gloup.Gom

Socotherm Infravibwn w.socotherm.Gom

Martecwww.marteG.ca

Astec lndustries Inc

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