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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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