Reclaimed Asphalt Pavement.pdf

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Abstract — The volume of heavy good vehicles is multiplying

year by year. This has led to various distresses in the pavement.

The ageing of bitumen binder is yet another problem causing

deterioration of pavements. The method commonly preferred to

protect the road system is overlaying the distressed pavements

with virgin courses. But this leads to thickening of pavement

layers, depletion of natural ingredients, and use of non-

renewable resources and emissions of harmful gases.

Reclaimed asphalt pavement (RAP) technology is one of the

rehabilitation methods used in many of the developed countries.

In developing countries like India, this method is in its initialstages. Depletion of natural resources and increase in road

elevation due to continuous overlaying, necessitate the adoption of

reclaimed asphalt pavement technology. This technique is a

promising and cost effective technology for rehabilitating

distressed and aged pavements. Recycling in place of overlaying

of asphalt pavements contributes to various ecological and

economic advantages. The use of RAP in asphalt mixes is a mean

to recycle the existing roadway and use that material in a limited

amount in the construction of new pavements.

This report discusses about various methods of recycling.

The advantages of Reclaimed asphalt pavement technology over

conventional method are discussed. An integrated mix design

approach for hot recycled mix from RAP samples was also

studied.

I ndex Terms — depletion, recycling, sustainable

I. I NTRODUCTION

ue to the steady increase in traffic, more and more roads

are deteriorating. The proper strengthening and

maintenance of the road network is urgently required.

Effective, timely and speedy maintenance is the only way to

protect the erosion of huge capital investments which are

linked to the road system. Overlaying the distressed

pavements with virgin courses had been adopted and continuesto be the preferred method for restoration of aged pavements.

The continuous application of overlays increases the pavement

Manuscript received December 10, 2010.

Dr. R. Sathikumar, Dean(U.G. Studies), College of Engineering ,

Trivandrum ( e-mail: [email protected]).

Nivedya M.K., M.Tech Student, Traffic and Transportation Division,

Department of Civil Engineering, College of Engineering, Trivandrum

(e-mail: [email protected]).

thickness and approaches the curb line. The conventional

methods are responsible for 22 percent of the global energy

consumption 25 percent of fossil fuel burning across the world

and 30 percent of global air pollution and greenhouse gasses.

Recycling, in place of conventional method of overlaying

of asphalt pavements has made a rapid advancement in the

developed countries. The availability of proven and efficient

recycling technology favoured the adoption of Reclaimed

Asphalt Pavement (RAP) Technology in many countries. This

method of strengthening and repairing roads was based on

their durability rather than their initial cost.The concept of RAP lies in restoring the physico-

chemical properties of the aged bitumen to its original and the

same time to enhance the mechanical properties and strength

of the aged binder. The various ecological and economic

advantages which contributed to enhancement of recycling

processes throughout the world are conservation of aggregates

and binders, reduced cost of transportation, preservation of

existing pavement geometrics, preservation of environment,

conservation of energy and labour, decrease in pavement

thickness/height.

With the development of RAP technology, asphalt

pavement rehabilitation costs would significantly decrease.The effective use of RAP solves a larger societal problem

because it does not occupy landfill space. In addition to the

economic benefits of using RAP , rehabilitation options that

create RAP may have substantial engineering benefits. For

example, the ability to mill and remove old, distressed

pavements allows for more effective rehabilitation techniques.

Severely cracked or rutted layers can be removed so that their

damage is not reflected through a new surface layer.

A. Need for the Study

The developed countries are using RAP technology to a

very large extent where as developing countries like India, it isstill in the very initial stage. In this method the same pavement

can be recycled over and over again, thereby conserving the

aggregates and binders. The energy and labour is also

preserved. But there is no widely accepted reclaimed and mix

design methodology. It’s high time that the recycling process

need to be implemented owing to their major advantages over

overlaying process. This highlights the need for the study.

Reclaimed Asphalt Pavement (RAP)

Technology for a Sustainable Pavement

Dr. R. Sathikumar and Nivedya M. K.

D

National Technological Congress, Kerala - 2011

College of Engineering Trivandrum, January 28-29, 2011

NATCON 2011 41





eliminate existing wheel ruts, restore crown and

slope, and eliminate pot holes, irregularities and

rough areas. Pavement- widening operations can also

be accommodated in the process. A uniform

pavement structure is obtained by this process.

3. It can eliminate alligator, transverse, longitudinal and

reflection cracking. Ride quality can be improved.

4. The production cost is low, and only a thin overlay is

required.

5. Engineering costs are low

6. Materials and energy are conserved and air quality

problems resulting from dust, fumes and smoke are

eliminated. The process is environmentally desirable,

since the disposal problem is avoided.

Full depth Reclamation is used for pavements with deep

rutting, load associated cracks, non- load associated cracks,

reflection cracks. it is particularly recommended for pavementshaving a base or subgrade problem. Modern equipment is

available with the option of using water, emulsion, foamed

asphalt or cement slurry as the recycling agent.

Hot Mix Recycling

It is a method in which RAP is combined with new

aggregates and an asphalt cement or recycling agent to

produce HMA. The RAP may be obtained by paving milling

with a rotary drum cold milling machine or from a ripping or

crushing operation. RAP from different sources and containing

different asphalt contents and aggregates with different

gradations should be stockpiled separately. The RAP cannot

be processed in normal drum mix plant since excessive blue

smoke is produced when the RAP comes in contact with the

burner flame. Most of the smoke problem is caused by the

light oils in soft grades of asphalt binder used to rejuvenate the

aged asphalt in the RAP. The smoke problem could be solved

by various processes such as lowering the HMA plant’s

production rate, decreasing the moisture content of the RAP,

lowering the discharge temperature of the recycled mix,

introducing additional combustion air, and decreasing the

percentage of RAP.

III. EXPERIMENTAL I NVESTIGATION

A. Mix Design [2]

A study [2] showed that the use of RAP in the surface

course of airfield pavement had a good resistance to rutting for

RAP containing HMA mixes. From another study[1] the mix

design for recycled mix was done to ascertain its in-service performance. Basic requirements of mix design was given as

The quantity of old aggregates and new aggregates was

to be adjusted in such a way that the resultant

gradation of aggregates conforms to the specified

gradation.

The quantity of the aged asphalt binder, virgin asphalt

binder and the rejuvenator, if any, was to be adjusted

in such a way that the resultant viscosity becomes

equal to the desirable viscosity at operating

temperature. Some other parameter (for example

complex shear modulus etc.) may be chosen insteadof viscosity.

The total quantity of asphalt binder should be adjusted

in such a way that it satisfies the desired asphalt

binder quantity of the target mix.

The other volumetric and strength parameters of the

mix should also be satisfied.

The step-by-step laboratory procedure followed in a work

done on RAP samples reported [1] is described below.

Representative samples (say 2 samples) from in-service

pavement (i.e. RAP) were procured and was cleaned for

deleterious matters. These materials were identified as Sample

1 and Sample 2.The RAP samples were proportioned, and mixed with virgin

asphalt binder and new aggregates, for various target bitumen

contents. Standard Marshall testing was conducted for

estimation of the possible optimal binder content. Further,

creep and fatigue tests were performed on the recycled

samples in order to assess their performance. The same tests

were conducted for virgin mixes, with same specification, to

have a comparative idea of mix performance. It was reported

that recoverable strain in recycled mix was comparable to that

of virgin mix and at lower strain levels; the fatigue lives of the

recycled mixes were better or similar to that of virgin mix.

However, at higher strain level, the opposite trend was

observed.

B. Constituent Properties[2]

The physical properties of the individual components of

the collected RAP samples were determined. Aged asphalt

binder and old aggregates were separated from the RAP

samples using Centrifuge Bitumen Extractor (CBE). The basic

objective of the recycled mix design is to know the best

constituent proportions between the RAP, virgin binder and

new aggregates. The total binder content of the recycled mix

Fig. 2. Hot in place Recycling



NATCON 2011 43



was found out by some preliminary estimation and iterative

mix design process done. The average asphalt binder content

of the RAP and the gradation of the old aggregates present in

RAP were found out. The virgin and extracted (aged) binders

were tested for their physical properties. The test results are

given in Table 1. The gradation of RAP aggregates is

presented in Fig 3

TableI: Properties of extracted and virgin asphalt binder

TestSpecific

ations

Bitumen type

80/100

gradeSample 1 Sample 2

DuctilityISI 1208:

197867 11 10

SofteningP

oint (OC)

ISI

1205:196949.5 69.5 78.5

SpecificGravity

ISI1202:1978

1.007 1.003 1.209

Flash PointIS

1448:1969280 255 260

PenetrationIS

1203:197887.5 26 18.7

Dynamic

Viscosity at

100OC(mPa

s)

ASTM

D 4402-021140 6240 4750

Source: Aravind et al.(2007)

Fig. 3 Gradation of RAP aggregates

Source: Aravind et al. (2007)

In this study, the minimum rolling temperature 100 0C, as

specified by MORT&H guidelines was chosen as the reference

temperature. The target viscosity was chosen as 2320 MPas.

This was basically the viscosity value observed in 60/70

penetration grade of binder at the target temperature. It means

the target of the present mix design problem is to achieve a

viscosity of the recycled mix (at reference temperature) similar

to that of 60/70 grade of bitumen, by using 80/100 grade of

bitumen as the recycling agent. The proportion between the

aged and virgin binder ( pob : pnb), percentage of binder presentin RAP ( P b

RAP ) and the percentage of total binder demand of

the recycled mix( P Rb) were known. From this percentage of

virgin bitumen ( P Rnb) and RAP (PR RAP) to be added to obtain

the recycled mix was estimated. Once the percentages of two

constituents (i.e, P Rnb and P R RAP ) are known, the quantity of the

third constituent (i.e., percentage of new aggregates in

recycled mix, ( P Rna)) was automatically known. The aggregate

gradation of the recycled mix was suitably adjusted by using a

desirable gradation of the new aggregates. The final form of

the derived formulae for proportion calculation, satisfying the

requirements of recycled mix design is presented in Table 2.

Where,

pnb - proportion of virgin binder

P Rb - percentage of total binder demand of the recycled

mix

pob - proportion of aged binder

P Rb - percentage of total binder demand of the recycled

mix P b

RAP - percentage of binder present in RAP

P R RAP - percentage of RAP

P Rnb - percentage of virgin bitumen

The constituent proportions calculated from the equations

were numerically identical to that of calculated as per Asphalt

Institute, (Aravind et al. (2007). Using the above equations an

illustration is shown below

Proportion of virgin binder( pnb ) 60%

Percentage of total binder demand of the

recycled mix( P

R

b )

4

Proportion of aged binder( pob ) 40%

Percentage of binder present in RAP( P b RAP ) 3.5

Substituting ,

Percentage of virgin binder = pnb x P Rb = (60X4)/100

= 2.4

Percentage of RAP = pob X P Rb X 100/ ( P b RAP )

= 40 X 4 X 100/(3.5)

Percentage of virgin binder = pnb X P Rb

Percentage of RAP = pob X P Rb X 100/ ( P b RAP )

Pecentage of new aggregates = 100-( P R RAP + P Rnb)



NATCON 2011 44



= 45.7

Pecentage of new aggregates =100-( P R RAP + P Rnb)

= 100-(45.7+2.4)

= 51.9

It is seen that nearly 50% percentage aggregates are

replaced by adding RAP.

C. Mix Preparation[2]

Mainly two processes were adopted to prepare the samples.They are type 1 and type 2 processes.

(i) Type 1 Process:

First, aged binder and old aggregates were separated from

the RAP using CBE equipment. Then, precalculated quantity

of virgin binder was added to the extracted binder to produce a

homogeneous mixture of binder of required viscosity. This

binder mix was then added to a hot mix of old and new

aggregates to produce the recycled mix.

(ii) Type 2 Process:

Collected RAP was broken into pieces using hammer. While breaking, aggregates should not be crushed due to impact of

hammer. This broken material was added to new aggregates

and then heated to higher temperature. To this mixture, known

amount of hot virgin binder was added. This mixture was

mixed well to produce the recycled mix.

In the study [1], four possible mix combinations were

obtained .Tests were conducted for the virgin mix, using the

mid-point gradation of the Semi-Dense Bituminous Macadam

(SDBC) mix as specified by MORT&H. The common zone of

binder content for which all the Marshall parameters satisfied

was found to be ranging between 5.0 % and 6.4 %. Binder

content within the feasible zone was adopted as design value.

The construction cost of asphalt layer, made up of recycled

mix and virgin mix, for a 7 m wide and 1 km long stretch was

compared [1]. It was estimated that cost of construction with

recycled mix was economical compared to virgin mix and

percentage saving in the construction cost varied between 12

% and 54 % for different mixes. The variation in the material

cost was due to differences of design thickness and mutual

constituent proportions [1].

IV. CONCLUSION

The majority of old asphalt pavements are recycled at

central processing plants, asphalt pavements may be

pulverized in place and incorporated into granular or stabilized

base courses using a self-propelled pulverizing machine. Hot

in-place and cold in-place recycling processes have evolved

into continuous train operations that include partial depth

removal of the pavement surface, mixing the reclaimed

material with additives (such as virgin aggregate, binder and

softening or rejuvenating agents to improve binder properties),

and placing and compacting the resultant mix in a single pass.

From the studies it was found that the resilient

modulus and Marshall Stability values were higher for the

virgin mixtures than the RAP mixtures. From the studies it was

concluded that at current time, there was no specific test

available that would accurately determine the presence and

quantity of RAP in hot-mix asphalt.

The cost of construction using recycled mix was

economical compared to virgin mix. Percentage saving in the

material cost was found to be varying in different mixes due tothe variation in the thickness and constituent proportions. The

economic benefits of using RAP, rehabilitation options that

create RAP have substantial engineering benefits. The ability

to mill and remove old, distressed pavements allows for more

effective rehabilitation techniques. Severely cracked or rutted

layers can be removed so that their damage is not reflected

through a new surface layer multiple studies that the structural

performance of recycled mixes is equal and in some instances

better than that of the conventional mixes. A sustainable

development is a development that meets the needs of the

present without compromising the ability of future generations

to meet their own needs. Recycling of pavements by re-usingthe existing materials will protect natural resources for future

generation. Thus RAP is a sustainable pavement construction

for the environment.

ACKNOWLEDGMENT

I express my sincere thanks to Dr. M. Satyakumar,

Traffic and Transportation Division Head, Department of Civil

Engineering, College of Engineering, Trivandrum and Dr.

Rajib B. Mallick, Associate Professor, Department of Civil

and Environmental Engineering, Worcestor Polytechnic

Institute, USA for their kind co-operation during this work .

R EFERENCES

[1] Aravind, K. and Animesh Das, “Pavement design with central plant

hot-mix recycled asphalt mixes”, ASCE Journal of Transportation

Engineering, Vol. 21 , 2007, pp 928 – 936

[2] Elie, Y. Hajj, Peter, E. Sebaaly and Pratheepan Kandiah, “ Evaluation of

the use of reclaimed asphalt pavement in airfields HMA”, ASCE

Journal of Transportation Engineering, Vol. 35, 2009, pp 163-169

[3] Rajib B. Mallick and Tahar El-Korchi, “Pavement engineering-

principles and practice,” CRC Press, London, 2009, pp. 405–413.



NATCON 2011 45

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