foam bitumen agra seminar paper

8/4/2019 Foam Bitumen Agra Seminar Paper

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Foam Bitumen Mixes for Base Layers-Laboratory and Field Study

Dr. Sunil Bose, Head Flexible Pavements Division, CRRI-New DelhiShri Arun Gaur, Lecturer Civil Engineering Deportment, MNIT-Jaipur

G Narendra Goud, Student M.Tech Transportation Engineering MNIT-Jaipur

AbstractIn the dense populated cities like Delhi, where environmental pollution and Land fill

problems are of prime concerns in the recent years. In rapid developing countries like India,

where conservation and optimum utilization of the road building materials specially petroleumand mineral products are an important issue. There is an immediate attention requirement

towards the development and implementation of Eco-friendly and cost effective pavementconstruction technologies. Through application of these technologies the efficient use of existing

and waste materials can be made with out creating problems to the environment and at the sametime meeting the quality requirements of the pavements.

Advances in technology and techniques in the in recent years have made cold recycling anincreasingly popular and cost-effective pavement construction and maintenance technique. In thepresent study an effort is made to study the laboratory and field behavior of recycled cold mixes

with binder as foamed bitumen. The Marshall specimens were cast using foamed bitumen incombination with cement. The specimens were tested for Density, Indirect Tensile Strength,

Resilient modulus and dynamic creep. Benkelman Beam deflection study was carried out on thepavement constructed with recycled foamed bituminous mix after a period of three months from

construction and field cores were cut from the pavement and were investigated in the Laboratory.It was found that the pavement constructed with foamed bitumen treated RAP was structurally

sound and cores cut from that pavement have shown higher ITS and MR values when comparedwith Laboratory cast cores but they shown less creep stiffness and densities.

1.0 IntroductionIn the dense populated cities like Delhi, where environmental pollution and Land fill

problems are of prime concerns in the recent years. In rapid developing countries like India,

where conservation and optimum utilization of the road building materials specially petroleumand mineral products and energy are an important issues. The rehabilitation and up gradation of

existing badly distressed Pavements due to rapidly growing heavy vehicular traffic are attractingthe concentration. There is an immediate attention requirement towards the development and

implementation of Eco-friendly pavement construction technologies. Through application ofthese technologies the efficient use of existing and waste materials can be made with out creating

problems to the environment and at the same time meeting the quality requirements of thepavements.

Advances in technology and techniques in the in recent years have made cold recycling anincreasingly popular and cost-effective pavement construction and maintenance technique. It has

been proved in abroad that cold recycling with foamed bitumen is one of the best alternatives tobe considered as a rehabilitation option. Cold recycling technology can be an option which has

the potential to address the above mentioned issues.In the present study an effort is made to study the laboratory and field behaviour of

recycled cold mixes with binder as foamed bitumen. The Marshall specimens were cast usingfoamed bitumen in combination with cement. The specimens were tested for density, Indirect


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Tensile Strength, Resilient modulus and dynamic creep. Benkelman Beam deflection study was

carried out on the pavement constructed with recycled foamed bituminous mix after a period ofthree months from construction and field cores were cut from the pavement and were investigated

in the Laboratory.

2.0 Literature review

2.1 Foam bitumenIn order to mix bitumen with road-building aggregates, you first need to considerably

reduce the viscosity of the cold hard binder. Traditionally, this was done by heating the bitumenand mixing it with heated aggregates to produce hot mix asphalt. Other methods of reducing the

bitumen viscosity include dissolving the bitumen in solvents and emulsification. Prof. Csanyicame up with the idea of introducing moisture into a stream of hot bitumen, which effects a

spontaneous foaming of the bitumen (similar to spilling water into hot oil). The potential offoamed bitumen for use as a binder was first realised in 1956 by Dr. Ladis H. Csanyi, at the

Engineering Experiment Station in Iowa State University. Since then, foamed asphalt technologyhas been used successfully in many countries, with corresponding evolution of the original

bitumen foaming process as experience was gained in its use.

Figure 1: schematic diagram of foamed bitumen production

The foamed bitumen, or expanded bitumen, is produced by a process in which pressurized waterand compressed air is injected into the hot bitumen (155-180

0c), resulting in spontaneous

foaming. The physical properties of the bitumen are temporarily altered when the injected water,on contact with the hot bitumen, is turned into vapour which is trapped in thousands of tiny

bitumen bubbles. In the foam state the bitumen has a very large surface area and extremely lowviscosity making it ideal for mixing with aggregates however the foam dissipates in less than a

minute and the bitumen resumes its original properties. In order to produce foamed asphalt mix,the bitumen has to be incorporated into the aggregates while still in its foamed state. A distinct

difference between foamed asphalt mixes and conventional asphalt stabilised mixes is the way inwhich the bitumen is dispersed through the aggregate. In the later case the bitumen tends to coat

all particles whilst in the foamed mixes the larger particles are not fully coated. The foamedbitumen disperses itself among the finer particles forming a mortar which binds the mix together.

2.2 Characterization of Foam bitumenFoamed bitumen is characterized by two primary properties:


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1. Expansion Ratio that is a measure of the viscosity of the foam and will determine howwell it will disperse in the mix. It is calculated as the ratio of the maximum volume offoam relative to its original volume

2. Half-Life is a measure of the stability of the foam and provides an indication of the rateof collapse of the foam. It is calculated as the time taken in seconds for the foam to

collapse to half of its maximum volume.The best foam is generally considered to be the one that optimizes both expansion and half-life.

Figure 2: Bitumen Foam characterization

2.3 Action of FoamixUnlike hot-mix asphalt, material stabilised with foamed bitumen does not appear black.

This result from the coarser particles of aggregate not was being coated with bitumen. When

foamed bitumen comes into contact with aggregate, the bitumen bubbles burst into millions oftiny bitumen droplets that seek out and adhere to the fine particles, specifically the fraction

smaller than 0.075 mm. The bitumen droplets can exchange heat only with the filler fraction andstill have sufficiently low viscosity to coat the particles. The foamed mix results in a bitumen-

bound filler that acts as a mortar between the coarse particles, as shown in Figure 3. There istherefore only a slight darkening in the color of the material after treatment. The addition of

cement, lime or other such fine cementitious material (100 % passing the 0.075 mm sieve) assiststhe bitumen to disperse, in particular where the recycled material is deficient in fines.


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Figure 3: Foamed bitumen dispersion and binding in the treated mix

2.4 Material suitability for foamed bitumen treatment

The foamed bitumen process is suitable for treating a wide range of materials, rangingfrom sands, through weathered gravels to crushed stone and RAP. Aggregates of sound and

marginal quality, from both virgin and recycled sources have been successfully utilized in theprocess in the past. As depicted in Figure 4, the minimum requirement is 5% passing the 0.075

mm (No. 200) sieve. When a material has insufficient fines, the foamed bitumen does notdisperse properly and tends to form what are known as stringers (bitumen rich agglomerations

of fine material) throughout the recycled material. These stringers vary in size according to thefines deficiency, a large deficiency will result in many large stringers which will tend to act as a

lubricant in the mix and lead to a reduction in strength and stability.

Figure 4: Material gradation envelops

Material that is deficient in fines can be improved by the addition of cement, lime or other suchmaterial with 100 % passing the 0.075 mm sieve. However, the use of cement in excess of 1.5 %

by mass should be avoided due to the negative effect on the flexibility of the stabilised layer. Theenvelopes provided in Figure 4 are broad and can be refined by targeting a grading that provides

the lowest voids in the mineral aggregate. This produces foamed bitumen mixes with the mostdesirable mix properties. A unique relationship for achieving the minimum voids, with an

allowance for variation in the filler content, is shown in equation. This relationship is useful as itprovides flexibility with the filler content of a mixture. A value of n = 0.45 is utilised to achieve

the minimum voids.

Where: d = selected sieve size (mm)

P = percentage by mass passing a sieve of size d (mm)D = maximum aggregate size (mm)


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F = percentage filler content (inert and active)

n = variable dependent on aggregate packing characteristics (0.45)Achieving a continuous grading on the fraction less than 2 mm is important for the proper

dispersion of the foamed bitumen and easier compaction, thereby reducing voids and thematerials susceptibility to water ingress. Where necessary, therefore, consideration should be

given to blending two materials to improve the critical grading characteristics.Moisture Conditions: The moisture content during mixing and compaction is considered by many

researchers to be the most important mix design criteria for foamed asphalt mixes. Moisture isrequired to soften and breakdown agglomerations in the aggregates, to aid in bitumen dispersion

during mixing and for field compaction. Insufficient water reduces the workability of the mix andresults in inadequate dispersion of the binder, while too much water lengthens the curing time,

reduces the strength and density of the compacted mix and may reduce the coating of theaggregates. The optimum moisture content (OMC) varies, depending on the mix property that is

being optimized (strength, density, water absorption, swelling). However, since moisture iscritical for mixing and compaction, these operations should be considered when optimizing the

moisture content. The optimum mixing moisture content occurs in the range of 65 - 85 per cent ofthe modified AASHTO OMC for the aggregates.

Curing Conditions: Studies have shown that foamed asphalt mixes do not develop their fullstrength after compaction until a large percentage of the mixing moisture is lost. This process is

termed curing. Curing is the process whereby the foamed asphalt gradually gains strength overtime accompanied by a reduction in the moisture content. A laboratory mix design procedure

would need to simulate the field curing process in order to correlate the properties of laboratory-prepared mixes with those of field mixes. Since the curing of foamed asphalt mixes in the field

occurs over several months, it is impractical to reproduce actual field curing conditions in thelaboratory. Most of the previous investigations have adopted the laboratory curing procedure

proposed by Bowering (1970), i.e. 3 days oven curing at a temperature of 60 C. This procedureresults in the moisture content stabilizing at about 0 to 4 per cent, which represents the driest state

achievable in the field. In the present study the specimen are cured for 72 hours at 400C

temperature only.

3.0 Laboratory and Field studies3.1 Material evaluation

Representative sample of pulverized and air dried Reclaimed Asphalt Product (RAP)and Crusher stone dust were collected from stock piles and then sieved through a set of sieves for

gradation. The details of sieve analysis are presented in tables 1 and 2. Bitumen content andmoisture content of air dried RAP found to be 5.2% and 0.12% respectively. Moisture content

and specific gravity of air dried Stone Dust found to be 0.40% and 2.68 respectively. Based onpulverized RAP and stone dust gradation their proportions were fixed (RAP:Stone

dust::55%:45%) to meet the gradation requirements for Foamed bitumen treatment. Figure 5

shows the gradation envelops.


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0

20

40

60

80

100

0.01 0.1 1 10 100sieve size, mm (log scale)

Percenta

gepassing

lowerlimit

upperlimit

combined achieved

RAP

stone dust

Figure 5: Gradation envelops

Table 1: Sieve analysis of pulverized and air-dried RAPsieve size, mm 37.5 26.5 19 13.2 9.5 6.7 4.75 2.36 1.18 0.6 0.425 0.3 0.075 pan

cumulative % passing 100.0 99.2 95.0 74.7 52.1 39.1 29.1 16.6 7.5 5.3 3.4 2.0 0.2 0.0

Table 2: Sieve analysis of Stone Dustsieve size, mm 6.7 4.75 2.36 1.18 0.6 0.425 0.3 0.075 pan

cumulative % passing 100.00 93.40 72.00 50.60 43.60 35.80 26.20 9.00 0.00

OMC Determination for Foamed Bitumen Treatment: The pulverized and air dried RAP is

separated in to three different fractions (i.e. P-19mm & R-13.2mm, P-13.2mm & R4.75mm andP-4.75). The proportioned and un-treated material was used to find Optimum Moisture Content

with modified Proctor compaction effort for foamed bitumen treatment. The Optimum MoistureContent found to be 8.75% with a Maximum Dry Density of 2.09 g/cc. The mixing moisture

content of proportioned material was decided based on optimum moisture content and air driedfield sample moisture content to prepare foamix.

Foamed Bitumen Characterization: The Study of foamed bitumen and its characterization waiscarried out using Wirtgen Foam bitumen Laboratory plant, WLB-10. The Foamability and the

variation of foam characteristics viz. expansion ratio and half life time were observed at differentair pressures, temperatures and Bitumen water contents. The bitumen used was of 80/100

penetration grade. The figure xx shows variation of Half life time and Expansion ratio withBitumen water at 4.5 bars air pressure and 165

oC bitumen temperature. Optimum foam

producing bitumen water found to be 3.3% by weight of bitumen.

3

4

5

67

8

9

10

11

12

2.0 2.5 3.0 3.5 4.0 4.5Bitumen water content, %

Expansion

ratio

0

1

2

34

5

6

7

8

9

Halflife

,seconds

exp ratio

half life

Figure 5: Bitumen water content Influence on expansion ratio and half life time of Foamed

bitumen


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3.2 Foamix preparation and specimens castingThe graded material and filler cement was mixed using pug-mill type mixer Initially dry mixing of

proportioned material was carried out for 10 to 15 seconds then additional water was added and then in to

that mix foamed bitumen was sprayed using WLB-10, after setting the calculated and determined

parameters on the laboratory plant. Foam bitumen quantity varied from 2 to 5% with 1% interval and

cement varied from 0 to 3% with 1% interval. The Marshall Specimens were cast with the mixture,

the number of blows applied were 75 on each side.

3.3 Specimens conditioning and testingThe Marshall specimen prepared with formulated material have been tested for Bulk

Density, Resilient modulus (MR) and Indirect Tensile Strength (ITS) after a curing period of 24hours at room temperature in mold and 72 hours at 40

0C after taken out of mold. And testing was

carried out at room temperature only. Duplicate samples were tested for soaked Indirect TensileStrength after a soaking period of 24 hours in water bath at ambient temperature. Indirect Tension

Test for Resilient Modulus was carried out at a repetitive load 100 N, frequency 0.1 Hertz and ata temperature of 25

0C. The test results of bulk density, indirect tensile strength and Indirect

Tension test for Resilient Modulus are presented in table 3. Field cores cut from the Foamedbitumen treated recycled pavement layer were tested for Bulk Density, Resilient modulus (MR),

Indirect Tensile Strength (soaked and un-soaked) and dynamic creep resistance. Some Laboratorycast specimens were also tested for dynamic creep resistance since the uniaxial unconfined creep

test is effective in identifying the sensitivity of asphalt mixtures to permanent deformation orrutting. Dynamic creep test was conducted under unconfined conditions at a temperature of 400C. The Specimens were placed in the temperature control cabinet for a minimum period of two

hours for conditioning the specimen to achieve test temperature before testing. The contact stress

of 3 kPa was applied for 0.1 second and rest period of 0.9 second at a frequency of 1 Hz. Theload was applied for a maximum of 3600 cycles. The results of Dynamic creep test on lab and

field cores presented below in table 4.The values of Resilient modulus were plotted in graphs (Figure 6) and then linear trend

lines were drawn to observe the variation in MR with foam bitumen and active filler. It wasobserved from the graphs that the increase in foam bitumen and increase in cement increased the

MR but at higher cement contents and at higher foam bitumen contents increase in MR was notmuch significant. The optimum cement content ranges from 1 to 2% and optimum foam bitumen

content ranges from 3 to 4%. The maximum MR values observed was 2372 MPa at 1% cementand 5% foam bitumen and 2350 MPa at 3% cement and 3% foam bitumen.

The ITS values were increased and then decreased with increase in foam bitumen. Theaddition of cement increased the ITS values significantly. Maximum ITS observed was 510 kPa

at 3% cement and 4% foam bitumen (Figure 7). The specimens with cement were observed to bevery less susceptible to moisture as it was observed from soaked ITS of the specimens.

Table 3: Test results of Marshall Specimens of Foamix

ITS, kPaMold

ID

Filler

type

Filler,

%

Foamed

Bitumen, %

Bulk

Density,

g/cc

Average

Bulk

Density, g/cc

Resilient

Modulus,

MPa

Mean Resilient

Modulus, MPaDry Soaked

TSR,

%

0/2/1 2.107 1211 316.74

0/2/22

2.0632.085

14251318

183.4158

0/3/1 2.114 2090 353.89

0/3/2

0%

32.182

2.148800

1445259.87

73


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0/4/1 2.134 1845 372.66

0/4/24

2.1322.133

15281687

322.4187

0/5/1 2.129 2544 402.01

0/5/25

2.1312.130

17652155

318.3179

1c/2/1 Cement 2.340 2519 329.83

1c/2/2 Cement2

1.9642.152

15172018

292.9489

1c/3/1 Cement 2.188 2585 390.23

1c/3/2 Cement3

2.1272.158

22502417

405.37104

1c/4/1 Cement 2.126 2132 437.23

1c/4/2 Cement4

2.1252.125

23622247

387.0489

1c/5/1 Cement 2.148 2335 450.46

1c/5/2 Cement

1%

52.074

2.1112464

2399343.44

76

2c/2/1 Cement 2.144 2094 435.79

2c/2/2 Cement2

2.1402.142

22442169

305.2370

2c/3/1 Cement 2.161 2188 448.34

2c/3/2 Cement3

2.1392.150

22012195

403.7690

2c/4/1 Cement 2.152 2278 519.35

2c/4/2 Cement

4

2.155

2.153

2286

2282

376.00

72

2c/5/1 Cement 2.126 2300 359.33

2c/5/2 Cement

2%

52.077

2.1012253

2277301.16

84

3c/2/1 Cement 2.163 1957 484.19

3c/2/2 Cement2

2.1202.141

20281993

433.8390

3c/3/1 Cement 2.117 2494 494.21

3c/3/2 Cement3

2.1212.119

18022148

426.5786

3c/4/1 Cement 2.114 2058 512.92

3c/4/2 Cement4

2.1182.116

22872173

402.8279

3c/5/1 Cement 2.110 2258 500.38

3c/5/2 Cement

3%

52.095

2.1022390

2324382.34

76

Field cores

1 Cement 1.5% 3.5% 2.110 3350 525.8072

2 Cement 1.5% 3.5% 2.090 2374 403.3839

3 Cement 1.5% 3.5% 2.108 3416 342.1538

4 Cement 1.5% 3.5% 2.035

2.090

2302

2861

258.0461

155

Table 4: Dynamic creep Test results of Foamix

S.NO Mold description

Creep

stiffness,

MPa

Total accumulated axial

strain at 1 hour of

loading, %

Remarks

1 1.5% Cement, 3.5% Foamed bitumen 464.7 0.015 No failure

2Field core of 1.5% cement, 3.5% Foamed

bitumen30.5 0.222

No failure


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Variation of MR with Foamed Bitumen and Cement

500

750

1000

1250

1500

1750

2000

2250

2500

2750

3000

3250

3500

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

Foamed bitumen, %

Resilientmodulus,MPa

0% Filler

1% Cement

2% Cement

3% Cement

Figure 6: variation of Resilient modulus with foamed bitumen and cement

Variation of Dry ITS with Foamed bitumen and cement

0

50

100

150

200

250

300

350

400

450

500

550

1.5 2 2.5 3 3.5 4 4.5 5 5.5Foamed bitumen, %

DryITS,KPa

0% Filler

1% Cement

2% Cement

3% Cement

Figure 7: variation of ITS with foamed bitumen and cement

3.4 BBD study on RAP Foamix pavementBenkelman beam deflection study has been carried out on the pavement constructed with

Recycled mix of Foamed bitumen in Kumbalgodu industrial area, Bangalore after three monthsof construction i.e. in the month of March 2006. The interval of deflection measurement points

was selected as 30 meters and initial point was marked at a distance of 10 meters from the zeroChainage of the Road (i.e. SH-17 Junction). The pavement temperature observed was 37

0C, The

PI value and moisture content of sub-grade soil found to be 14% and 17% respectively. Thetemperature correction factor and moisture correction factor applied were -0.02 and 1.1

respectively. The average characteristic rebound deflection of the pavement found to be 1.17mm.

Table 5: Deflection data (LHS, towards Karnataka cold Storage Pvt. ltd)Chainage, km & m 00+010 00+040 00+070 00+100 00+130 00+160 00+190 00+220 00+250 00+280 00+310

Distance, m 10 40 70 100 130 160 190 220 250 280 310

Corrected Rebound

Deflection, mm0.89 0.66 1.18 0.37 0.62 0.65 0.31 0.62 0.37 1.03 1.31

Table 6: Deflection data (RHS, towards Karnataka cold Storage Pvt. ltd)Chainage, km & m 00+010 00+040 00+070 00+100 00+130 00+160 00+190 00+220 00+250 00+280 00+310

Distance, m 10 40 70 100 130 160 190 220 250 280 310

Corrected Rebound

Deflection, mm1.2 0.99 1.01 1.16 0.33 0.62 1.06 1.32 1.23 1.14 0.57


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4.0 ConclusionsThe following conclusions were drawn based on the studies performed on foamed

bitumen treated RAP in laboratory and Field.

When recycling with foam bitumen mixing moisture content should be around

60% of OMC as per Wirtgen Cold Recycling Manual, however observing the material

it can be varied from 50 to 65% to reduce problems in compacting the mixLoss of strength on soaking is very less with foamed bitumen and cement treated

material, in most of the cases the tensile strength ratio ranges from 70 to 100% and it

is 155% in case of field cores

Cores cut from the foamed bitumen treated pavement have shown higher ITS and MR

values in comparison with laboratory cast cores

Dynamic creep stiffness of Cores from the field was very less in comparison with

laboratory cast cores but they were comparable to HMA cores, which needs to be

further examined before any conclusions are drawn.

Benkelman beam deflection study on foamed bitumen treated pavement shows that it

was structurally sound with an average characteristic rebound deflection of 1.17mm

and no functional failure was observed even in the absence of surface course

Foam bitumen treated mixes can be one of the considerable options for base courses

in a flexible pavement structure since it requires a surface course

AcknowledgementsThe authors are grateful to the director for granting permission to publish this paper. Thanks are

also due to M/S Wirtgen India Pvt. Ltd. For supporting during foamix study and NagarjunaConstruction Company for the help rendered during field study.

ReferencesWebsites

www.asphalt.csir.co.za www.arra.org www.infratech.com www.wirtgen.com www.betterroads.com www.asphaltwa.com/wapa www.trb.orgReports and papers


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