Pavements A CostlyNecessityThe quality of roads dictate theeconomy of a country and hencethe quality of our lives. In India,road transport handles more than60% of the freight and more than80% of the passenger traffic. Roadsare vital for the transport of goodsand passengers. Village roads arecritical for the basic minimumconnectivity for the upliftment of thesocial and economical condition ofthe rural people. Such roadsprovide access to employment,means of transporting agriculturalproduce and access to health careand social services.

Realizing the need for goodroad infrastructure, the Indiangovernment has embarked on avigorous road building effort andinvesting `1,20,000 crore perannum. In the next five years, $60billion will be invested to build35,000 km of roads. The roads that

are being built now will be readyfor maintenance and rehabilitationin the next five to ten years. Somelessons can be learnt from the UShighway system, which is a maturesystem, and most of the work inthe recent past and at present ison maintenance and rehabilitation,rather than on new construction.Because of soaring material costsand budget shortfalls, there is ahuge backlog in maintenance andrehabilitation of pavements, leadingto the issue of sustainability of themaintenance of road assets thathave been created by hugeinvestments. It should be noted thatin addition to the ongoing newconstruction, in the next five years,a significant amount of work willalso be needed for the maintenanceand rehabilitation of the newpavements. The combined work willneed (in addition to money) amassive amount of materials andenergy.

Where will all these materialsand energy come from? This articletries to present a clear picture ofthe future the challenges and thesolutions.

Impact ofInfrastructureImprovement onthe EnvironmentIt is an accepted fact that becauseof human activities and resultantglobal warming. Global meantemperature and average sea levelhave risen, whereas the snowcover both in Northern Hemisphereand the Himalayas have beenreduced. The loss of glaciers in theHimalayas is of great relevance,because of the dependence ofcrores of people on water from therivers that are fed by these glaciers.Overall, in the world transportationrepresents 10% of the worlds grossdomestc product, and has been

Sustainable Pavements in India

The Time To Start Is NowProf. Rajib Basu Mallick, Worcester Polytechnic Institute, MA, USA

Prof. A. Veeraragavan, Indian Institute of Technology, Chennai.

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reported to be responsible for 22%of the global energy consumption,25% of fossil fuel burning acrossthe world and 30% of global airpollution and greenhouse gasses.

On top of this, consider theamount of natural aggregates(mostly from quarries) that are beingused - 1,300 million tons of virginaggregates are used in the USevery year for pavementconstruction. In India, about 15,000tonnes of aggregates are requiredper kilometer of highway. A typicalproject of National HighwayDevelopment Project (NHDP) of 60km road improvement requires 20lakh ton of material. In India, inmost cases, old pavement materialsare dumped into landfills. Note thatlandfills have been identified as thelargest source of methane causedby humans .

The production of pavementmixes such as hot mix asphalt(HMA) requires a significant amountof energy, such as those neededfor production of bituminous binderfrom crude petroleum and dryingaggregates. For example,approximately 1.5 gallons of fuel isused for drying and heating oneton of aggregates consider thatfigure in terms of lakhs of tons ofaggregates that is used. Theheating of bituminous binder andHMA releases a significant amountof green house gases such ascarbon dioxide, and harmfulpollutants such as sulphur andnitrogen oxides. Constructionpeople are exposed to such gaseson a regular basis. The amount ofemission doubles for every 10oCincrease in production temperature,and increasingly, higher temperatureis actually being used for theproduction of HMA with modifiedbinders.

The scarcity of aggregates nowforces truck delivery of materialsfrom great distance the use ofdiesel for running these trucks leadsto emission of pollutants such as

particulate matter, nitrogen oxidesand sulfur dioxides. Many of thediesel engine emissions have beenidentified as carcinogenic, andharmful to the human health, evenat occupational and environmentallevels of exposure. The problem ofavailability of aggregate is acute inthe Northern Part of the country. Fora lead of 200 km (which iscommon in north India) it willrequire 180 lakh liter of diesel intransportation alone. We need toinitiate applied research on largescale to find alternate crustcomposition so that materialconsumption in road constructiongets reduced and we are able tosave diesel also. A serious attempthas to be made to improveengineering properties of traditionalconstruction material by suitableadditives so that they are able toeffectively distribute load andthereby reduce consumption.

Pavement materials have verylow thermal conductivity but relativelyhigh heat capacity. As a result, roadsand parking lots retain a hugeamount of heat, which is releasedback into the air, and which leadsto the rise in temperature, especiallyin urban areas. This phenomenonis known as urban heat islandeffect. This high temperature leadsto a greater use of pollutingequipment such as air conditioning,and increases the ozoneconcentration and air pollution. Thenet effect is more pollution andadverse health effect of theinhabitants of the urban areas.

Finally, the effect of paving onthe recharge of groundwater isdisastrous. A paved surfacesignificantly reduces the amount ofwater that infiltrates into the ground most of the water flows away asstorm water. This lowers thegroundwater level, leading toscarcity of water, pollution of water(the water now comes from levelswhich have harmful minerals), andstorm flooding.

To summarize, the total effectof paving for roads and airportsinclude depletion of naturalresources and energy, rise intemperature and air pollution andlowering of groundwater andscarcity of drinking water. Thisessentially means that we will beleaving a much less greenerenvironment, much less naturalresources and a much lesscomfortable earth for our nextgeneration than what we beganwith. Since the success or failureof a generation is not to be judgedby the people of that generation,but by future generations, are wenot failing magnimously? Thisobservation is tied to the very basicidea of sustainable development development that meets the needsof the present withoutcompromising the ability of futuregenerations to meet their ownneeds.

One important point should beremembered: pavements are for theinfrastructure and improving thequality of life, and hence the qualityof life should not be sacrificed forthe sake of pavements. Therefore,at the beginning of this Herculeantask of building a massivetransportation system in India, it isimperative that we acknowledge thefact that even though roads areneeded for developing the economyand improving the quality of ourlives, they adversely affect ourenvironment. The next step is toembrace, wholeheartedly, everyavailable green technology forpavement design and construction.The following paragraphssummarize a few suchtechnologies.

RecyclingPavement recycling, particularly, HMApavement recycling (HMA is themost widely used pavementmaterial in India) is a wellestablished proven technology. Ahost of different techniques exist

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for different situations hot mixrecycling, hot in-place recycling, coldmix and cold in-place recycling andfull depth reclamation. The past fewdecades have seen tremendousgrowth in equipment andtechniques in recycling, from millingmachines to mixing plants and in-place trains. Plants capable ofrecycling in high percentages, andmaterials that are capable ofrestoring correct asphaltenes-maltene proportions in aged asphaltare available. The literature isreplete with good practices andmanuals for effective andsuccessful recycling operations andguidelines (Table 1 givesapplications and considerations forthe different methods).

Hot Mix RecyclingHot mix recycling is accomplishedby incorporating milled andprocessed reclaimed asphaltpavement material (RAP) in new

mixes in the hot mix plant. RAP canbe added at different percentages,and depending on the percentage,a specific grade of asphalt binderor recycling agent could be used.The milled RAP needs to beregraded before combining with thenew aggregates to ensureconformity to the specified gradation.Mix design using the Marshallmethod or the Superpave methodcan be done. Various forms of drumand batch plant modifications exist,which allow the use of RAP in HMAproduction on a regular basis. Theprimary benefit of hot mix recyclingis the control of the quality of thefinished product, and the ability toprocess the milled RAP. In drumplants, the RAP is introduced inthat part which is not exposed tothe burner flame it is critical thatthe RAP is not overheated, and isheated by the superheatedaggregates.

Hot In-place RecyclingHot in-place recycling (HIR) involvesthe use of a single or morecommonly, a train of equipment thatheat the existing pavement and mill/scarify it, mix the softened RAP in-place with rejuvenating agent,compacts it in one single pass.Sometimes remixing with newmaterials and/or repaving with new

layer are also done. The selectionof the type and amount of therejuvenating agent could be doneusing mix design principles, andthe new aggregates could beselected to obtain the desiredgradation when combined with theexisting scarified mix aggregates.The benefit of this process includesthose that are related to in-placerecycling avoiding transportationand related fuel use andemissions. The end product is alsosimilar to HMA, and hence of goodquality. However, the depth to whichHIR could be conducted effectivelyis limited to about 38 mm, and theuse of large trains is only possiblein long and straight stretches ofroads.

Cold Mix Recycling andFull Depth ReclamationCold mix recycling could be doneboth in-place (cold in-placerecycling, CIR) or in the plant. InCIR, either a specialized singleequipment or a train of equipmentis utilized. The primary steps aremilling of part or all of the HMAlayer, and/or processing (forexample, to get rid of plus 50 mmparticles), mixing with emulsionand/or other additive such ascement, and compaction, andcuring. It is important to make surethat the mix is cured before thenext layer is put down, to avoidentrapment of moisture andsubsequent deterioration. CIR isgenerally used to obtain goodquality base course, with theutilization of the existing (aged andwith distresses, such as withcracks). In cold central plantrecycling, the milled RAP is mixed

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with emulsion or foamed asphalt,and transported back to the siteand laid down with a paver andcompacted. In this case, it ispossible to have a better controlover the finished product, and finescould be added to ensure theconformity to a specific gradation,such as that needed for thesuccessful use of foamed asphalt.

Full depth reclamation (FDR) issimilar to CIR, except that in thiscase, milling is extended below thedepth of the HMA layer to includepart of the granular layer. Obtaininga good base course is the objectivein this case.

Cold recycling, as discussedabove, ensures economy andbenefit to the environment byavoiding heat and energy, andemissions. In-place recycling allowsfurther economy and other benefitsby avoiding transportation. WhileCIR allows the reuse of old andaged asphalt pavements as basecourse in new pavements, FDRallows the modification to solve thebase related problems.

Low Energy MixesUse of huge amount of energy andemissions have led to thedevelopment of many types of coldand warm mix asphalt (WMA)technologies in the last decade.Cold mixes have been used for along time for various applicationssuch as full depth reclamation ofcold in-place recycling for obtainingbase courses. WMA, in variousforms, have been tried successfullyin Europe as well as in the US(See tables 2, 3 and 4 for differentmethods). The main principlebehind WMA is the use of a material

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and/or technique to lower theviscosity of the asphalt to the rangeof that required for mixing andcompaction, at lower thanconventional temperature. Thebenefits of WMA include reducedEmissions (Table 5) and fuelusage, sufficient workability at longhaul distances, improvedcompaction as well as the ability touse more recycled asphaltpavement material.

There are four competing WMAprocesses that are widely used: Atwo-component binder systemcalled WAM-Foam (Warm Asphalt

Mix Foam) that introducesa soft and hard foamedbinder at different stagesduring plant production; Theaddition of a syntheticzeolite called Aspha-Minduring mixing at the plantto create a foaming effectin the binder; The use ofthixotropic additives suchas Sasobit, a Fischer-Tropsch paraffin wax and

Asphaltan B, a low molecularweight esterified wax; Evotherm isa non-proprietary product thatincludes additives to improvecoating and workability.

There are several benefits ofthe WMA in comparison to HMA.They include reduced emissionsand worker exposure due to alowering of temperature, reducedfuel use, ability to allow longer hauldistances without losing workabilityand extension of paving seasonsin cooler climate areas.

Porous PavementsPavements with high porosity havebeen developed, that can allow asignificant amount of infiltration ofwater. Such pavements are wellsuited for parking as well a slowspeed areas. In principle, such apavement consists of an opengraded HMA course over an

uniformly graded crushed aggregatesource with approximately 40%voids over the subgrade (Figure 1).A 25 to 50 mm thick aggregate12.5 mm down size aggregate layeris used between the open gradedand the aggregate courses, and ageotextile is used between theaggregate and the subgrade layer.Test sections have proven thesuccess of such pavements, andresearch studies have shown thatmost of the pollutants are removedby filtration through the layers.

Cool PavementsAlthough different techniques couldbe adopted for reducing the surfacetemperature of pavements, the useof materials with a higher albedohas been so far the most common.Albedo, the ratio of reflected to theincident power, is different fordifferent colored materials it ismuch higher for concrete (0.5) andasphalt pavement with a whitepainted surface (0.25) compared toconventional new HMA (0.05).Specialized pavement colors areavailable for obtaining pavementswith relatively high albedo, to reducethe amount of absorbed heat, andthus to reduce the urban heat islandeffect. A good summary of theproblem as well as the different

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approaches is given by the EPA(EPA, 2005). Table 6 shows acomparison of costs of coolpavements constructed withdifferent techniques. Anotherapproach is the use of an energyharvesting system installed withina pavement to extract heat energyfor useful purposes and reduce thesurface temperature of pavements.

Critical NeedAs the above paragraphs indicate,sufficient number of greentechnologies exists for immediateadoption in India. Since everytechnology has its own niche place,sufficient opportunities exist for

practical research that couldprepare pavement designers inIndia to specify the right technologyfor the right case, that is, to answerthe question, which sustainabletechnology is best suited for everypavement construction? Suchresearch can easily be conductedby the premier institutions in India,such as the IITs, which haveexcellent facilities and brainpower.Centers of excellence forsustainable pavement constructionmust be set up to facilitate suchactivity. In addition, such centers willbecome hubs for training andtechnology transfer in future.

It is of critical importance that

Figure 1: Porous pavementSource: Soderlund, Martina. Sustainable Roadway Design- A Model For An EnvironmentalRating System. Master of Science in Civil Engineering Thesis. University of Washington,2007.

investment should be made nowon equipment and training to adoptfield-ready sustainable practices forpavement construction, andequipment and software forresearch for developing guidelinesto adopt such techniques for Indianconditions, and developingindigenous techniques. The resultsof this research must be readywithin five-ten years, when the hugeroadway network that is being builtnow, will be due for maintenanceand rehabilitation.

India cannot be, and should notbe termed as a poor country anymore as the latest computers andcell phones are available here. Indialaunches its own spaceships withsatellites. It is hoped that theleaders of this great country wouldacknowledge the greatenvironmental challenges ofpavement construction, and investwisely in technologies that wouldmake road building sustainable.The time to start this is NOW.

ReferencesInternational Road Federation.

Innovative Practices for GreenerRoads.www.irfnet.org

Soderlund, Martina. SustainableRoadway Design- A Model For AnEnvironmental Rating System.Master of Science in CivilEngineering Thesis. University ofWashington, 2007.

Sources: Moen, . Warm-Mix Asphalt

(WMA) International ScanningTour. Norwegian Public RoadsAdministration, Norway,Presentation to WMA Scan Team,May 2007.

Brosseaud, Y. Warm Asphalt-Overview in France. LCPC,France, Presentation to WMA ScanTeam, May 2007.

Andersen, E.O. WAM-Foam-AnEnvironmentally-Friendly Alternativeto Hot-Mix Asphalt. NorwegianPublic Roads Administration,Oslo, Norway, Presentation toWMA Scan Team, May 2007.

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