Draft Guidelines for Fbm

8/12/2019 Draft Guidelines for Fbm

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GUIDELINES FOR MIX DESIGN, CONSTRUCTIONAND QUALITY CONTROL OF FOAM BITUMINOUS

MIXES

DRAFT

DECMBER 2013



ABBREVIATIONS

AASHTO - American Association of State Highway andTransportation Officials

BC - Bituminous Concrete

DBM - Dense Bituminous MacadamRAP - Recycled Asphalt PavementFB - Foamed BitumenFBS - Foamed Bituminous stablised



GUIDELINES FOR MIX DESIGN, CONSTRUCTION ANDQUALITY CONTROL OF FOAMED BITUMINOUS MIXES

1. INTRODUCTION

1.1 Pavements deteriorate with time with increased use and also due to fatigue ofthe materials. Conventionally, an overlay is provided over deteriorated

pavements to increase the structural condition of the pavements. This processrequires virgin materials viz., aggregates and binder and considering the largenetwork of roads in the country, use of virgin materials for the maintenance ofthe pavements is to be relooked. For construction of 40 mm overlay of

bituminous concrete (BC) per km of two lane road, approximately 240 cum ofaggregate and 27 tonnes of bitumen are required. Similarly for construction of

an overlay with 75 mm thick dense bituminous macadam (DBM) and 40 mmthick bituminous concrete, for a two lane road approximately 700 cum ofaggregates and 80 tons of bitumen are required, per km. By recycling of theexisting bituminous pavement layers, such huge quantities of valuable materialcan be saved and life of the pavement layers can be enhanced. Considering thematerial and construction costs alone, it is estimated that by using recycledmaterials, savings ranging from 14 to 34 % can be achieved.

1.2 Recycling of existing pavements for rehabilitation of roads has gainedconsiderable importance due to depletion of aggregates and high cost oftransportation of road construction material. Large scale rehabilitation demandshave seen the adoption of cold in place recycling as the preferred techniquewhich is both technically and financially viable. Around the world, theexperience and choice of technology for cold in place recycling varies largelydue to different pavement composition, traffic conditions, availability of virginaggregates, type of bitumen and emulsion. With the development of specialisedequipments over the last two decades and from the experience gained from fieldtrials, cold in place recycling with foamed bitumen have gained popularity overother methods of cold recycling due to less curing time, speedy construction,

stockpiling of the FB mix, energy savings and better performance.

1.3 A wide range of mix design procedures exist for foamed bituminous (FB)mixtures. Each of them differ in terms of gradations, method for determinationof percentage of foamed binder content, type and content of active filler,moisture content and the methodologies associated with size of sample, mixing,curing and compaction. The mix design procedures are also strongly dependenton the type and quality of reclaimed asphalt pavement (RAP) available. Sincedifferent countries have different pavement cross-section with the mixconstitution varying considerably, it is obvious that the mix design procedurealso varies. However it should be emphasized that the overall framework



towards the design of foamed bituminous mix remains more or less the same.The overall objective of the FB mix design procedure is to determine theappropriate quantities of foamed bitumen, RAP material, virgin aggregates,active filler, moisture content and foamed bitumen at optimum temperature and

foaming water content, such that the mix laid and compacted in the field shouldwithstand traffic load and perform over its service life for which it is designed.Most of the mix design methods for FB mixtures use indirect tensile strengthtest (ITS) in different variations.

1.4 Recycling of pavement with foamed bitumen has been adopted worldwide andis in use for over a decade. However in India, it is relatively new and very fewfield trials have been carried out. The major component of FB mixture is RAP,which is a site specific material. Different countries have evolved widelyvarying mix design procedures depending on the quality of RAP available. Forinstance, the RAP from South Africa and Australia consists mostly of naturalaggregates and cracked cement stabilised layers as they have thin bituminouswearing course whereas in United states, the RAP material have higher

percentage of aggregates coated with binder. Hence, it is expected that the samemix design procedure cannot be adopted for all regions. Very little work has

been carried out related to cold mix design procedure for Indian conditions. TheRAP material in India has a significant amount of bitumen present in it.

1.5 Since no guidelines are available for the mix design of FB mixes for Indian

conditions, a pavement engineer has an option to choose from existing mixdesign procedures followed in various countries, which may or may not suit toIndian conditions. Therefore, there is a need to formulate separate guidelines forthe country which suits to our condition and can be easily implemented forexecution of cold in place recycling with foamed bitumen.

1.6 The guidelines are formulated based on the experience gained from cold in place recycling with foamed bitumen project executed on the National Highway No. 5, Chennai - Tada road section. Wirtgen cold recycling technology manualand TG2, Technical Guidelines: Bitumen Stabilised materials, Guidelines forthe design and construction of bitumen emulsion and foamed bitumen stabilisedmaterials, issued by the Asphalt Academy, South Africa were followed fordesign of foamed bitumen mix in this project. The information and datacollected from the experimental investigation carried out on FB mixes at IITMadras adopting South African and Caltrans mix design procedure were alsoconsidered for formulating the guidelines.



2. SCOPE

2.1 These guidelines will apply to flexible pavements for Expressways,

National Highways, State Highways, Major District Roads and othercategories of roads predominantly carrying motorized vehicles.

2.2 The guidelines will apply to the rehabilitation of damaged bituminous layers byrecycling the existing bituminous layers and treating with foamed bitumen. Thescope of this guideline for mix design is applicable to both in place and in plantcold recycling with foamed bitumen. However, for construction and qualitycontrol the guidelines is applicable to only cold in place recycling with foamed

bitumen.

2.3 Pavement condition survey and structural adequacy of the pavement should beassessed to identify the type of distress occurred. Accordingly the decision forrehabilitation of pavement with cold in place recycling with foamed bitumen betaken. It is mentioned that distress such as rutting and all types of cracking in the

bituminous layers can be eliminated by cold in place recycling. The minimumand maximum depth of recycling is limited to 50 mm and 300 mm respectively.The recycling of the pavement also include base and sub base layers along with

bituminous layers.

2.4 For design of strengthening measures or overlays for existing pavements, thedesign procedure described in IRC:81-1997(6) "Tentative Guidelines forStrengthening of Flexible Road Pavements Using Benkelman Beam DeflectionTechnique" can be used . Falling Weight Deflectometer can also be used on the basisof the results of research scheme R-81(17,18) for design of overlays using theanalytical concept enshrined in the guidelines and available in the web site of Indianroads Congress.

2.5 At this stage the data collected in respect of cold recycling with foamed bitumen inIndia is very less. The guidelines may require revision from time to time in thelight of future experience and developments in the field. Towards this end, it issuggested that all the organisations intending to use the guidelines, should keep adetailed record of year of recycling carried out with foamed bitumen,

pavement composition and wearing course laid on top of FBS layer, traffic, pavement performance, overlay history after recycling, climatic conditions,etc.

3. MIX DESIGN

3.1 Few published guidelines and reports with procedures for project selection, mix design,

structural design, and construction are available for cold in-place recycling with foamed



bitumen. Currently av ailable reports and guidelines are “ Foamed Asphalt mixes, Mix

design procedure” report by Muthen (1999), “ Pavement Recycling guidelines for In-place

Recycling with Emulsion and Foamed Bitumen” published by World Road Association

(PIARC), (2003). “Development of Mix Design Procedure for Cold In -Place Recycling

with Foamed Asphalt” report by Kim and Lee. (2006), “Full Depth Pavement

Reclamation with Foamed Asphalt in California: Guidelines for Project Selection, Design

and Construction” published by Caltrans (2009), “ Technical Guidelines: Bitumen

Stabilized materials, Guidelines for the design and construction of bitumen emulsion and

foamed bitumen stabilized materials”, published by Asphalt Academy (2009), Pretoria,

South Africa, “Review of Foamed Bitumen Stabilization Mix Design Methods”,

Technical Report published by Austroads (2011), Sydney , Australia and “ Wirtgen Cold

Recycling Manual”, Second edition published by Wirtgen (2012), Windhagen, Germany.

However the overall framework of the mix design procedure is more or less the same in

each guideline. The outline of the mix design procedure followed by reports and

guidelines is given in Figure 1.

Determine Gradation of RAP and check grading envelope.

If grading requirement is not met, improve grading by adding virgin

aggregates. Find PI of the material.

Determine Binder type and select foaming temperature and foamed

water content.

Determine OMC and MDD of the untreated material.





3.2.1 South African mix design procedure (Asphalt Academy 2009)

The mix design procedure for Bituminous Stabilised Material (BSM) involves threelevels of testing on the mix. In South Africa foamed bituminous mix called as BSM.Table 1 shows the details of the parameters involved. While BSM1 material hashigh shear strength and can be used as a base layer for design traffic greater than 6million equivalent standard axles, BSM2 material has moderately high shearstrength and can be used for a base layer for design traffic less than 6 MESA. TheBSM3 material can be used as a base layer for design traffic less than 1 MESA.Based on the results of the mechanical tests, different levels are classified and thesedetails can be found in Asphalt Academy (2009).

Table 1: Details on levels of testing for BSM (Asphalt Academy 2009)

Level MechanicalTest

Specimensize

Compaction Curing Purpose

Level1

ITS dry ,ITS wet andTSR

100 mmdia and 63mm height

Vibratoryhammer orMarshall

72 hrs at 40°Cfor ITS dry , andthen specimensoaked in water

for 24 hrs forITS wet

Foamed bitumen contentoptimization:Active filler

type and contentdetermination

Level2

ITS equilibrium andITS soaked

150 mmdia and127 mmheight

Vibratoryhammer

20 hrs at 30°Cunsealed and 48hrs at 40°Csealed forITS equilibrium and

then specimensoaked in waterfor 24 hrs forITS soaked

Foamed bitumen contentoptimisation

Level3

Triaxial 150 mmdia and300 mmheight

Vibratoryhammer

72 hrs at 40°Cdry curing

Shear properties:Moistureresistance





3.2.3.2 Determination of optimum and mixing moisture content

In the Asphalt Academy procedure, the determination of optimum moisture content

(OMC) is carried out on the untreated material without any addition of active fillerusing Modified AASHTO compaction (AASHTO:T180-10 (2010)). Here, 75% ofOMC (called as mixing moisture content – MMC) is added before treating thematerial with foamed bitumen and the remaining 25% of OMC is added aftertreatment with foamed bitumen for making samples. The Marshall compactionmethod is followed in the absence of vibratory hammer compactor. In the Caltrans

procedure, the OMC of the untreated material with addition of active filler isdetermined using Modified AASHTO compaction (AASHTO:T180-10 (2010)). TheOMC determined is used as starting moisture content for determination of MMC. Itshould be noted that MMC is same as compaction moisture content and determinedafter addition of active filler in the Caltrans procure whereas in Asphalt Academy

procedure OMC is same as compaction moisture content. The compaction moisturecontent is the water content referred for mixing the material in field.

3.2.3.3 Determination of active filler

As per the Asphalt Academy procedure, the effectiveness, type and need of activefiller in the mix are a trial and error process. Using the ITS wet test results of curedand soaked 100 mm diameter specimen and the retained cohesion from the triaxialtest, the type and active filler are determined. Asphalt Academy (2009) also

prescribes the maximum quantity of cement and lime as 1% and 1.5% respectively.In the Caltrans procedure, the optimum active filler type and content is determined

by conducting ITS sealed (24 hrs curing in sealed plastic bag at 25°C) test on 100 mmdiameter specimen. The quantity of cement is varied up to a maximum of 2% andthe hydrated lime is varied up to a maximum of 3%. The percentage of the activefiller at which the maximum improvement of the ITS sealed value over the untreatedsample is obtained is chosen. In the Asphalt Academy (2009) procedure thedetermination of active filler is carried out before the determination of optimumfoamed bitumen content whereas in the Caltrans procedure the active filler

determination is carried out after the determination of optimum foamed bitumencontent values.

3.2.3.4 Determination of optimum foamed bitumen content

In the Asphalt Academy procedure, for determination of optimum foamed bitumencontent, the sample is prepared by mixing RAP, virgin aggregates (if any), OMC,active filler content and varying foamed bitumen content from 1.7 to 2.5%. The sizeof the specimen, compaction and curing is governed by the level of testing given inTable 1. For level 1 the optimum binder content is determined by ensuring that

ITS dry and ITS wet is sufficiently high. Once the optimum foamed binder content isdetermined in Level 1, Level 2 and Level 3 tests are carried out as per design traffic.



In the Caltrans procedure, the optimum foamed bitumen content is determined byconducting ITS wet test on 100 mm diameter specimen with varying quantity offoamed bitumen content with a maximum limit up to 4% by dry mass of mix andone sample is also casted without the addition of foamed bitumen as untreated

control sample. The mix manufactured is composed of RAP, virgin aggregates (ifany), MMC, and varying percentages of foamed bitumen content. It is to be notedhere that active filler is not added in the mix. The percentage of the foamed bitumenat which the maximum improvement of the ITS wet value of 100 kPa over theuntreated sample is obtained first is chosen.

3.3 Sampling

The first step in the mix design procedure is to collect samples from the field. To achieve

representative sample, on-site milling is most suitable method. If this is not possible, cores

should be taken and crushed in laboratory. The samples should be taken up to the depth

where recycling is proposed. Where the layer thickness varies along the length of the project,

the subsequent stretches should be identified and separate samples to be taken, as each stretch

with a different composition will have different design mix. None of the guidelines give

details about the quantity and the number of samples to be taken for the project.

Some of the guidelines suggest taking a minimum of four samples for a project. It is

recommended that one sample per two km to be taken on each side for project

length of any size. The project length should be divided into 10 km stretch, and foreach 10 km stretch a mix design should be carried out irrespective of the fact that

the pavement crust composition is same throughout the length of the project. This

means that 10 samples of RAP are to be taken from 10 km stretch for carrying out a

mix design. For small size projects, a minimum of at least four samples are to be

taken. From one location 50 kgs of material is to be taken for conducting gradation

tests.

3.4 Gradation

Grading of the RAP material is determined to know whether the material is suitable for

treating it with foamed bitumen or not. Once the samples are collected, the wet sieve analysis

of the RAP material should be carried out as per method prescribed in California Test 202

“Method of test or sieve analysis of fine and coarse aggregate”. Washing of aggregates is

important as the percentage of material passing 0.075 mm is the deciding criteria for addition

of virgin aggregate to the RAP material. The grading of all the samples collected from the

field are plotted on the graph and compared for variation. For establishing homogenous



section, the maximum variation should be ± 10 percent from the mean for the aggregate size

passing 4.75 mm sieve and above and ± 5 percent for the aggregate size passing 4.75 mm

sieve and below. For calculating the variation in the percentage passing of aggregates for all

the samples extracted, the average of percentage passing of aggregate on the sieve size should

be determined and subtracted from the maximum and minimum values of the percentage

passing on that sieve size. Example calculation is shown at Table 1.

Table 1: Gradation of milled RAP material to show variation

Sieve Size

(mm)

Percentage passing (%)

Variation from the mean

(%)

KM

32.500

KM

36.300

KM

45.300

KM

53.000

50 100 100 100 100 0

37.5 100 100 100 100 0

26.5 100 100 100 100 0

19 98.4 98.1 98.5 99.5 +0.6 to -0.8

13.2 87.5 88.5 87.7 94.9 +2.1 to -5.3

9.6 77.4 78.9 75.7 88.4 +4.4 to -8.3

6.765.0 62.4 61.3 73.2

+4.2 to -7.7

4.75 56.2 50.7 48.5 59.8 +5.3 to -6.0

2.36 35.9 31.2 32.4 37.6 +3.1 to -3.3

1.18 25.1 18.3 19.9 22.8 +3.2 to -3.6

0.600 16.2 10.9 10.6 11.0 +1.6 to -4.1

0.425 6.7 4.7 8.4 7.9 +2.2 to -1.5

0.300 5.9 3.7 6.1 5.4 +1.6 to -6.8

0.1504.2 1.9 4.1 3.0

+1.4 to -2.8

0.075 3.4 1.6 2.5 1.1 +1.1 to -1.3

If the variation is within the limits, it is confirmed that the entire stretch is homogenous and

RAP from any location can be taken for mix design. If the variation is more than ±10 percent,

then the road section can be subdivided into smaller stretches were variation is within ±10

percent. The grading requirements of FBM are given in Table 2. The same grading is adopted

for the Indian conditions as given in the South African procedure. Less suitable range is given



to accommodate variation in the RAP material. Approximately 200 kgs of material which is

to be recycled, is required for conducting tests from a location for mix design.

Table 2: Grading requirements for Foamed Bituminous Mixtures

Sieve Size (mm) Percentage passing %

Ideal Less suitable

50 100 -

37.5 87-100 -

26.5 77-100 100

19 66-99 99-100

13.2 57-87 87-100

9.5 49-74 74-100

6.7 40-62 62-100

4.75 35-56 56-95

2.36 25-42 42-78

1.18 18-33 33-65

0.6 14-28 28-54

0.425 12-26 26-50

0.3 10-24 24-43

0.15 7-17 17-30

0.075 4-10 10-20

If the grading of the material is not found suitable, fresh aggregates should be added with

missing fraction to improve the grading, so that the blended gradation meets the grading

requirements of FBM as shown in Table 2. For Indian conditions with heavily trafficked roadand hot climatic conditions especially in plain areas, 15-20% fine aggregate should be added

to RAP to provide a angular sand skeleton to improve the shear resistance of the mix, even if

the gradation of the RAP meets the requirement as per Table 2. On the blended material

representative proportioning is carried out. This is done to address the problem of variability

in the RAP. The process is reproduced below with the help of an example given below in

Table 3.



Table 3: Representative proportioning of blended material

Sieve analysis Quantity of material to be included for every 10 Kg of sampleSievesize(mm)

Percentagepassing(from sieveanalysison blendedsample)

Passing 4.75 mm Passing 13.2 mmand retained on 4.75mm

Passing 19 mmand retained on 13.2mm

19.0 98.43 58.12/100 x

10000=5812 gm

((90.69-58.12)/100 x

10000)=3257 gm

((100-90.69)/100

x10000)=931 gm13.2 90.69

4.75 58.12

The material obtained from the representative proportioning by the given method above

should be used for preparation of making samples for carrying out all the tests. There may be

a case, where there is no need of addition of fresh aggregate. In such cases also,

representative proportioning should be carried out to address the problem of variability.

3.5 Atterbergs limit

The Plasticity Index (PI) of the RAP material / Blended material (if fines are added to RAP

material to improve its grading) is determined to know whether it is necessary to pre-treat the

material or blend the material with filler to address any deficiencies. The PI of the blended

material should be determined as per method prescribed in IS:2720 (Part-V). The shear

strength of the material is drastically reduced with increase in PI. Hence it should be ensured

that the PI of the material to be treated with foamed bitumen should be equal to or less than

10. If the PI of the material is found to exceed this limit it should be treated with hydrated

lime to reduce its plasticity, and again retested for PI value for confirmation. Addition of

hydrated lime maximum up to 1.5% by mass of the material is recommended. The percentage

of addition of filler to improve its plasticity should always be less than percentage of bitumen

content.

3.6 Hygroscopic or initial moisture content

Hygroscopic or initial moisture content test is carried out to know the existing moisture

content present in the material and subtract it from OMC at the time of adding water to the

mix. The hygroscopic or initial moisture content is defined as the moisture which adheres to



the soil particles and does not evaporates at atmospheric temperatures. The initial moisture

content of the material should be determined as per method prescribed in IS:2720 (Part-II)

3.7 Determination of foaming characteristics of bitumen

Foamed bitumen is characterised by two parameters and they are Expansion Ratio (ER) and

Half-life time (HLT). Expansion ratio of foamed bitumen is the ratio between the maximum

volume achieved in the foamed state and the final volume of the binder after the foam has

decayed. Half life time is the time measured in seconds for the foamed bitumen to subside

from the maximum volume to the half of the maximum volume. The measurement of ER and

HLT are highly dependent upon the individual estimation and judgement because of rapid

foaming and settling of bitumen and the manual timings recorded by stop watch. Hence, the

measurements made for determining ER and HLT are empirical. Wirtgen WLB 10 S foaming

equipment should be used for foaming and determining ER and HLT as shown in figure 1.

Figure 1: Wirtgen WLB 10 S foaming equipment

The minimum limits for expansion ratio and half life time of bitumen is recommended as 8

and 6 sec respectively. The foaming characteristics of the grades of bitumen available for

foaming is carried out at temperature starting from 160 oC with varying foaming water content

from 2% to 6% with increment of 1%. 500 grams mass of bitumen is taken for each

observation. Three observations are taken for each set. If the criteria of minimum limits of

expansion ratio and half life time are satisfied at 160°C at particular foaming water content,

the same is adopted. If the requirement of expansion ratio and half life is not met, the

experiment is repeated at 170°C and then at 180°C with varying foaming water content from

2% to 6% till the expansion ratio and half life time is met. Bitumen with lower viscosity



foams more than bitumen with higher viscosity. Not much experiments and data have been

collected for foaming capability of VG 30. Hence VG 10 grade binder to be used for foaming

till further research is carried out on other grades of bitumen.

3.8 Optimum moisture content and Maximum dry density of untreated material

Analysis is done on the untreated material (without adding foamed bitumen) using Modified

Proctors compaction test as per IS:2720 (Part-VIII). It is to be noted that some of the

guidelines recommend addition of active filler before determination of OMC and MDD and

other do not prefer to add it. It is stated that while executing the work on ground the layer of

cement is spread on the top of the pavement and then further recycling process is carried.

Hence the same process should be adopted in the laboratory to create similar conditions that

prevail in site. It is clarified that active filler is to be added and further OMC and MDD on the

untreated material to be carried out. Six samples at different water content starting from 2%

to 12% with increment of 2% water content are prepared. Dry density at each water content is

determined and a graph is plotted between dry density and water content to find out OMC

and MDD.

3.9 Determination of Active filler

A lot of research is underway to study the effect of active filler on the mechanical properties

of FBM. Till date the effectiveness, type and need of active filler in the mix, is impossible to

predict, unless experimentation during mix design is done. This involves additional tests and

is time consuming. Addition of active filler imparts early strength to the mix and early traffic

can be allowed. Studies have shown that that the use of 1% cement as active filler have

yielded satisfactory results on the performance of FBM. The South African procedure also

recommends the use of 1% cement as active filler. Studies and research have shown that that

increase in percentage of cement beyond 1% imparts stiffness to the mix and reducesflexibility making it prone to cracks. Addition of cement less than 1% does not contribute

much to the strength of the material, hence as a general practice 1% cement OPC 53 grade

should be used as active filler.

3.10 OMC and MDD of the treated material

For determining the OMC and MDD of the foamed bituminous mix, analysis is done on the

treated material (after addition of foamed bitumen) using Modified proctor compaction test as per IS: 2720 (Part-VIII). The OMC of the foamed bitumen treated material is determined by



first adding 60% of the OMC of the untreated material which has already been determined

initially as per clause 3.8 stated above, and then injecting a constant percentage of 2 percent

foamed bitumen with the foaming equipment and increasing the amount of water in nominal

1% increments. The 60% of the OMC of the untreated material is also known as optimum

mixing moisture content (OMMC) of the FBM. At least five samples at different water

content starting from 60% of OMC to 1% increment are prepared. Dry density at each water

content is determined and a graph is plotted between dry density and water content to find out

OMC and MDD of the FBM. This OMC and MDD determined on the treated material is used

in field. It is to be noted that the initial moisture content of the RAP /blended material at site

is to be determined and the same is to be subtracted from the OMC determined on the treated

material for addition of water in field. The MDD determined on the treated material is taken

as the reference dry density.

3.11 Preparation of sample

After the preparation of representative samples, determination of hygroscopic or initial

moisture content, selection of the binder for foaming, foaming temperature, foaming water

content, selection of type and percentage content of active filler and determination of

optimum moisture content on treated sample and all the ingredients should be put into a

WLM 30 pug mill mixer (Figure 2) in appropriate quantities as determined previously. 10Kgs of material should be taken to prepare one sample for particular bitumen content. From

each sample six numbers of 101.60 mm diameter specimens were manufactured for testing

ITS dry and ITS wet values. The sample should be prepared by injecting foamed bitumen by

WLB 10 S foaming equipment in WLM 30 pug mill mixer at foaming binder content of 1.5,

2 and 2.5 percent, as shown in figure 2. OMC determined on treated material should be added

before adding foamed bitumen. The material should be mixed for 20 to 30 seconds. The mix

should be immediately immediately transferred into plastic bag and sealed to prevent any loss

of moisture before compaction.



Figure 2: Mixing of materials in WLM 30 pug mill mixer for sample preparation

3.12 Manufacture of 100 mm dia specimen

Six numbers of 101.6 mm diameter specimens and 63.5 mm in height, were manufactured

from each sample prepared at foamed bitumen content of 1.5, 2.0 and 2.5% by applying

standard Marshall compaction effort as shown in Figure 3. Approximately 1075 to 1120 gms

of mix material should be taken to achieve a compacted height of 63.5 mm ± 1.5 mm. The

mixture is compacted by applying 75 blows with the Marshall compaction hammer on either

side.

Figure 3: Compaction of 101.6 mm diameter specimen



3.13 Curing of specimen

Dry and wet curing of specimens should be carried out on prepared samples as shown in

Figure 4 and 5 respectively. For dry curing all the six specimens should be kept at 40 oC for

72 hours in a draft oven. After 72 hrs the specimens should be taken out and checked for

constant mass. Three specimens should be tested for ITS dry after cooling them at 25 oC. The

remaining three specimens should be immersed in water for 24 hours at 25 oC and after

surface drying, tested for ITS wet.

Figure 4: Dry curing of specimen at 40 oC Figure 5 Wet curing of specimen in water

3.14 Optimization of foamed bitumen content

The ITS test was carried out on dry and wet specimen after dry and wet curing as per ASTM

D 6931 (2012), for optimisation of foamed bitumen content. Figure 6 shows ITS test

conducted on 101.6 mm diameter sample. The average ITS test results values in wet and dry

condition with varying foamed bitumen content should be tabulated as shown in Table 4

along with their Coefficient of Variation (CV) expressed in percentage and Tensile Strength

Ratio (TSR).

Figure 6: ITS test on 101.6 mm diameter specimen



The foamed bitumen content at which the highest ITS wet value is achieved is chosen as the optimum

foamed bitumen content. However it should be ensured that the ITS dry values at optimum foamed

bitumen content should be greater than 225 kPa, ITS wet values at optimum foamed bitumen content

should be greater than 100 kPa and TSR should be greater than 50 %. The CV should be less than

10%. In case CV is more than 10%, the ITS tests should be repeated or odd test results not to be

considered.

Table 4: Average ITS test results in dry and wet condition

Foamed bitumen

content (%)

Av.ITS dry (kPa)

CV (%) Av. ITS wet (kPa)

CV (%) TSR (%) Dry density(gm/cc)

1.5 255.79 6.88 204.06 7.48 80 2.054

2.0 265.45 3.49 212.32 6.57 80 2.0832.5 200.90 2.71 170.22 3.04 85 2.048

4. STRUCTURAL DESIGN OF FLEXIBLE PAVEMENT WITH FOAMED

BITUMINOUS STABILISED LAYER

4.1 For structural design of flexible pavements the method and guidelines as mentioned as per

clause 10.4 of IRC: 37- 2012 “ Guidelines for design of flexible pavements” to be referred.

Documents

Draft Guidelines for Fbm