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1 Kuna, Airey, and Thom A Laboratory Mix Design Procedure for Foamed Bitumen Mixtures (FBM) 1 TRB Paper # 14-0416 2 3 Kranthi Kuna 4 PhD Student 5 Nottingham Transportation Engineering Centre 6 University of Nottingham 7 Nottingham, NG7 2RD, UK 8 Telephone: +44 115 9568424, Fax: +44 115 9513909 9 E-mail: [email protected] 10 11 12 Gordon Airey 13 Professor 14 Nottingham Transportation Engineering Centre 15 University of Nottingham 16 Nottingham, NG7 2RD, UK 17 Telephone: +44 115 9513913, Fax: +44 115 9513909 18 E-mail: [email protected] 19 20 21 Nick Thom 22 Lecturer 23 Department of Civil Engineering 24 Nottingham Transportation Engineering Centre 25 University of Nottingham 26 Nottingham, NG7 2RD, UK 27 Telephone: +44 115 9513901, Fax: +44 115 9513909 28 E-mail: [email protected] 29 30 Corresponding Author: Kranthi Kuna 31 32 Word Count: 4693 + 2 Tables + 9 Figures = 7443 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 TRB 2014 Annual Meeting Paper revised from original submittal.

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  • 1Kuna, Airey, and Thom

    A Laboratory Mix Design Procedure for Foamed Bitumen Mixtures (FBM) 1TRB Paper # 14-0416 2

    3Kranthi Kuna 4PhD Student 5

    Nottingham Transportation Engineering Centre 6University of Nottingham 7

    Nottingham, NG7 2RD, UK 8Telephone: +44 115 9568424, Fax: +44 115 9513909 9

    E-mail: [email protected] 10 11

    12Gordon Airey 13

    Professor 14Nottingham Transportation Engineering Centre 15

    University of Nottingham 16Nottingham, NG7 2RD, UK 17

    Telephone: +44 115 9513913, Fax: +44 115 9513909 18E-mail: [email protected] 19

    20 21

    Nick Thom 22Lecturer 23

    Department of Civil Engineering 24Nottingham Transportation Engineering Centre 25

    University of Nottingham 26Nottingham, NG7 2RD, UK 27

    Telephone: +44 115 9513901, Fax: +44 115 9513909 28E-mail: [email protected] 29

    30Corresponding Author: Kranthi Kuna 31

    32Word Count: 4693 + 2 Tables + 9 Figures = 7443 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

    TRB 2014 Annual Meeting Paper revised from original submittal.

  • 2Kuna, Airey, and Thom

    ABSTRACT 1The primary objective of this paper is to propose a practical and consistent mix design 2procedure for Foamed Bitumen Mixtures (FBM) with the main focus being the use of the 3gyratory compaction method in the proposed methodology. To attain this objective, the mix 4design parameters such as Mixing Water Content (MWC) and compaction effort have been 5optimised. This mix design parametric study was initially carried out on FBMs with virgin 6limestone aggregate (VA) without Reclaimed Asphalt Pavement (RAP) material and a mix 7design procedure was proposed. The proposed methodology was later validated on FBMs 8with 50% RAP and 75% RAP. Efforts were also made to optimise the Foamed Bitumen (FB) 9content in FBMs with and without RAP. 10

    Optimum MWC was achieved by optimising mechanical properties such as Indirect 11Tensile Stiffness Modulus (ITSM) and Indirect Tensile Strength (ITS-dry and ITS-wet). A 12rational range of 75-85% of Optimum Water Content (OWC) obtained by the modified 13Proctor test was found to be the optimum range of MWC that gives optimum mechanical 14properties for FBMs. As this study focussed on the use of the gyratory compactor for FBM 15compaction, efforts were made to suggest a design number of gyrations (Ndesign) for optimum 16compaction of FBMs. It was found that a unique Ndesign (mixture specific) which is 17independent of the FB content can be established. Ndesign for the virgin mixture was found to 18be 140, while Ndesign for the mixtures with 50% of RAP and 75% of RAP was 110 and 100 19respectively. It was also found that the presence of RAP influenced the design FB content, 20which means treating RAP as black rock in FBM mix design is not appropriate. 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

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    INTRODUCTION 1Unlike hot mix asphalt (HMA), there is no universally accepted mix design method for 2FBMs. Most of the agencies [1, 2] which use FBMs have their own mix design procedures 3which are the result of numerous efforts over decades [3-12]. In spite of all these efforts, 4Foamed Bitumen application in cold recycling in the United Kingdom suffers from the lack 5of a standardised mix design procedure specifically using the gyratory compactor. As a result, 6the mix design parameters such as Foam characteristics, mixing, compaction, curing and 7testing that are being adopted are far from being standardised. To overcome this, research 8was undertaken at the University of Nottingham by Sunarjono (2008) [13] to develop a mix 9design procedure by identifying critical mix design parameters. 10

    The research by Sunarjono (2008) was focussed on the influence of the bitumen type, 11the foaming conditions, foam characteristics and mixer type on the mechanical properties of 12FBM. The major outcomes of the work were recommendations for producing an optimised 13FBM in terms of mixer type and usage, selection of binder type, bitumen temperature, and 14foam characteristics. Therefore this present study focussed on other mix design parameters 15such as Foamed Bitumen (FB) content, MWC, and compaction effort. Thus, the primary 16objective of the present study is to propose a practical and consistent mix design procedure 17with emphasis on the use of the gyratory compactor. 18

    The amount of water during mixing and compaction is considered as one of the most 19important parameters in FBM mix design [14, 15]. The MWC of FBM is defined as the water 20content in the aggregate when the FB is injected [16]. The MWC helps in dispersion of the 21mastic in the mix [3, 17]. However, too much water causes granular agglomerations which do 22not yield optimum dispersion of the mastic in the mix [18, 19]. In view of this fact many 23studies have been focussed on the optimisation of MWC. Lee (1981) [20] and Bissada (1987) 24[21] optimised MWC with reference to Marshall stability and found that the optimum MWC 25was very much dependent on other mix design variables such as the amount of fines and 26bitumen content. Sakr and Manke (1985) [22], related the MWC to other mix design 27variables and recommended a relationship among them to obtain optimum MWC. However, 28this work was performed on a FB stabilised sand mixture which did not have any coarser 29fractions of aggregate. Moreover, the work was based on optimising the density, without 30considering any mechanical properties. The concept of optimum fluid content was later 31borrowed from emulsion mix design in which the sum of the water and bitumen content 32should be close to OWC [6, 23] obtained by the modified Proctor test. This concept considers 33the lubricating action of the binder in addition to that of water. Thus the actual water content 34of the mix for optimum compaction is reduced in equal amount to the amount of binder 35incorporated. However, the work of Kim and Lee 2006 [10] and Xu et al. (2012) [15], who 36optimised MWC based on both density criteria and fundamental tests (indirect tensile 37strength (ITS) and tri-axial tests) on FBM Marshall specimens, calls into question the 38lubricating action of bitumen in the mix. Although the above discussed works are very 39informative, they have their limitations and little attention has been paid to optimising MWC 40using gyratory compaction. Therefore, the present work was aimed at obtaining a rational 41range of MWC for mix design with the help of fundamental tests such as ITS (BS EN 12697-4223:2003) and indirect tensile stiffness modulus (ITSM) (DD 213: 1993) on FBM specimens. 43

    Because of the presence of the water phase, the compaction mechanism of FBMs is 44very different from that of HMA. Various laboratory compaction methods such as Marshall 45compaction [6, 10, 15, 17], vibratory compaction [3, 8, 24], gyratory compaction [17, 25-27] 46have been used in the past. There are very well established guidelines for Marshall 47compaction [2] and vibratory compaction [1, 28]. However, there are no established 48

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  • 4Kuna, Airey, and Thom

    guidelines for a gyratory compaction method for FBMs in terms of compaction effort 1(number of gyrations, gyratory angle and gyratory pressure). Past studies have evaluated the 2feasibility of using laboratory gyratory compaction on FBM (Table 1). In these studies efforts 3were made to obtain the design compaction effort in terms of compaction pressure, 4compaction angle and number of gyrations. The compaction pressures recommended by 5Australian guidelines (0.24MPa and 1.38MPa from Table 1) were taken forward in the 6Strategic Highway Research Program (SHRP) work on HMA, resulting in recommendations 7of 0.6MPa and 1.25 angle of gyration. Jenkins et al. (2004) [26]s tabulated conditions were 8based on single water content and a single FB content. From preliminary trials it was found 9that the 30 gyrations recommended by Kim and Lee (2006) were too few to achieve modified 10Proctor densities. The ideal compaction effort has to produce mix densities that are achieved 11in the field. Therefore, modified Proctor density which is used worldwide to represent field 12compaction is used as a reference in the present study. It was understood from the past 13studies [13] that the permanent deformation behaviour of FBMs is sensitive to the number of 14gyrations, which might be attributed to the arrangement of the aggregate skeleton. Hence 15efforts were made to propose design number of gyrations (Ndesign) and it was decided to use a 16compaction pressure of 600kPa and internal angle of gyration of 1.25. 17 18TABLE 1 Gyratory compaction effort on FBMs by different researchers 19

    Summary of gyratory compaction effort on FBM by different researchers

    Number of gyrations


    Compaction pressure (MPa)

    Compaction angle

    (degrees) Reference density Brennan (1983) 20 1.38 N/A 2.25kg/m3

    Maccarrone et al.1994 85 0.24 2 field density Jenkins et al. (2004) 150 0.6 1.25 Modified proctor density Kim and Lee (2006) 30 0.6 1.25 Marshall density (75 blows)

    Saleh (2006b) 80 0.24 2 Australian guidelines for HMA

    MATERIALS 20In HMA mix design, the expected traffic and the regional climate influence the selection of 21the bitumen type. However in FBM mix design, foamability (foaming potential) of the 22bitumen and the mixture compactability also has to be considered during selection of the 23bitumen. Harder bitumen has been avoided in the past as it produces poorer quality foam 24leading to poorer dispersion of fines. However, it was found that FBM with harder bitumen 25had a positive effect on mixture stiffness due to the high stiffness of the bitumen [13]. 26Nonetheless, in the present study a 70/100 penetration grade bitumen (90dmm penetration at 2725C and softening point of 45C) supplied by Shell was used. The virgin mineral aggregate 28used in this study was limestone from Dene Quarry, Derbyshire, UK. The RAP material used 29was supplied by Lafarge Aggregates Limited obtained from Elstow Asphalt Plant in 30Bedfordshire, UK. The RAP aggregate material from the quarry was initially air dried at 31room temperature in the laboratory at 202C for 24 hours and then placed in a 32thermostatically controlled oven at a temperature of 40C for 24 hours and thereafter stored 33in sealed containers for further use. A composition analysis of the RAP aggregate material 34was also conducted in order to determine the properties of the RAP and its extracted 35components and the gradation of RAP before and after recovery of bitumen is as seen in 36Figure 1. The amount of bitumen recovered from the aggregate was found to be 5.5%. Figure 371 also shows the design gradation adopted in the study which is within the recommended 38range of the Asphalt Academy, (2009) [1] guidelines. This design gradation is the target 39gradation for all the mixtures studied in the present work including mixtures with RAP. The 40

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  • 5Kuna, Airey, and Thom

    aggregates (both virgin aggregate (VA) and RAP) were stored separately in stockpiles of size 1fractions of 20mm, 14mm, 10mm, 6mm, dust (0.063mm < dust > 6mm) and filler 2(

  • 6Kuna, Airey, and Thom

    TABLE2Experimentaldesignformixdesignparametricstudy1Mix design parameter factorial levels Remarks

    Bitumen type 90pen (70/100 grade) constant throughout the experiment

    Target Foam Characteristics

    Expansion ratio = 10 Asphalt Academy (2009) and Sunarjono (2009) Half-life (seconds) = 6

    Foaming conditions Temperature (C):150,160,170

    variable to be optimised FWC(%): 1,2,3,4,5

    Mixer type Pug mill type mixer constant throughout the experiment Aggregate type lime stone constant throughout the experiment

    Aggregate gradation 20mm (maximum size) Asphalt Academy (2009), constant throughout the experiment

    MWC % of OWC: 65,75,85,95 variable to be optimised FB content % of total mix: 2,3,4,5 variable to be optimised

    Mechanical tests ITS-dry, ITS-wet, ITSM to obtain optimum MWC and design binder content 2

    Foamed bitumen was produced using a laboratory mobile foaming plant type Wirtgen WLB 310 in which the bitumen was foamed at a water pressure of 6 bars and an air pressure of 5 4bars. The characteristics of foamed bitumen (Expansion ratio and Half-life) were obtained by 5applying different foaming water contents ( (1% to 5% of the amount of bitumen by weight) 6and temperatures (150C, 160C and 170C). Figure 2 shows the effect of foaming water 7content on expansion ratio and half-life respectively. A minimum half-life of 6 seconds and 8expansion ratio of 10 were adopted as selection criteria. The optimum foam characteristics 9were obtained by plotting Expansion ratio and Half-life versus foaming water content. To 10ensure adequate levels of both Expansion ratio and Half-life a foaming temperature of 170C 11was adopted and the procedure for obtaining optimum foaming water content recommended 12by Asphalt Academy (2009) was used giving 3%. These foaming conditions were used 13throughout the remainder of the study. 14


    FIGURE 2 Effect of FWC and temperature on Expansion ratio (ER) and Half-life (HL). 16

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  • 7Kuna, Airey, and Thom

    Mixing 1Foamed Bitumen begins to collapse rapidly once it comes into contact with relatively cold 2aggregates. Therefore, the mixing process should be a dynamic one. Consequently FB is 3most often applied directly from the laboratory foaming plant to the aggregate as it is being 4agitated in the mixer. As different mixers can produce up to a 25% difference in strength [1] 5selection of an appropriate mixer is very important in production of FBM. It is always 6recommended to utilise a mixer that simulates site mixing. From the literature it was found 7that most of the research was carried out using a Hobart type mixer (blender type) [20, 22]. 8However, pug mill drum mixers and milling-drum mixers are the most commonly used 9mixers on site for the production of FBM. These mixers provide sufficient volumes in the 10mixing chamber and energy of agitation to ensure better mixing [3]. A pug mill type mixer is 11therefore recommended for production of FBM representative of the field [29]. Hence, a twin 12shaft pug mill mixer was adopted in this work (operated at 202C). Mixing time should be 13in accordance with the time required by the bitumen foam to collapse. In the laboratory a 14mixing time of 60 seconds is recommended [21] which is longer than in situ mixing but 15simulates the difference in the energy of the laboratory mixer and field plant and the same (60 16seconds mixing time) was adopted in this study. 17

    Mixing Water Content (MWC) 18The optimisation of MWC was carried out on specimens compacted using the gyratory 19compactor to densities that were obtained by modified Proctor compaction. Targeting 20modified Proctor densities meant that all specimens were compacted to the same compaction 21effort. This approach was considered suitable as it is not appropriate to compact mixtures 22with different water contents to the same density as they would need very different 23compaction efforts. For example, mixtures with 100% of OWC (6.5% by weight of 24aggregate) needed 200 gyrations to compact to maximum dry density (MDD) while a mixture 25with 65% of OWC (4.25% of weight of aggregate) required around 340 gyrations. Hence, 26modified Proctor compaction was carried out on aggregate and water mixtures in accordance 27with BS EN 13286-2: 2004. The results of the modified Proctor compaction can be seen in 28Figure 3, including results of modified Proctor compaction on mixtures with RAP. As can be 29seen from Figure 3, the OWC for 100% VA mixtures was found to be 6.5% and for mixtures 30with RAP the OWC was around 6%. 31

    Once OWC from modified Proctor compaction had been obtained, mixing was carried 32out with varying water content (95%, 85%, 75% and 65% of OWC) and varying FB content 33(2%, 3%, 4%, and 5% by weight of aggregate). These mixtures were compacted using 34modified Proctor compaction; densities were obtained and the results presented in Figure 4. 35The results shown are in terms of wet densities as these were targeted in the gyratory 36compactor during compaction. After obtaining the densities, these possible combinations of 37mixtures were mixed and compacted using gyratory compactor (angle of gyration -1.25 and 38compaction pressure 600kPa) to the achieve modified Proctor densities that were obtained. 39Gyratory compacted moulds after compaction were kept at room temperature for 24 hours 40and then the specimens were extracted. The extracted specimens were cured at 40C and the 41water content of the specimen was monitored over time. Mechanical tests were carried out on 42the cured specimens after 3 to 5 days depending on the amount water in the specimen. The 43tests were carried out on all specimens at approximately the same water content (between 440.6% and 0.65%) to eliminate the effect of water content in on the measured mechanical 45properties. The effect of mixing water content on the mechanical properties can be seen in the 46plots in Figure 5. 47

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    FIGURE 3 Modified Proctor test results on aggregate and water (only) mixtures. 2


    FIGURE 4 Modified Proctor compaction results on 100%VA-FBM with varying FB and water content. 4

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    FIGURE 5 Mechanical properties of 100%VA- FBM with varying FB and water content. 2

    Compaction effort 3As discussed in the earlier sections, one of the objectives of this study is to propose a design 4number of gyrations (Ndesign) for FBM mix design. For this aggregate mixtures with 80% of 5OWC (which is the optimum MWC discussed in later sections) and different FB contents 6were prepared. Then the mixtures were compacted to 200 gyrations and densities were 7plotted against number of gyrations as shown in Figure 6. From the data, the number of 8gyrations required to reach modified Proctor density (Figure 4) was identified as can be seen 9in Figure 6. 10

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    FIGURE 6 Obtaining Ndesign for 100%VA-FBM (Note: 0%FBM (100%VA) is FBM without any RAP and 50%FB content (no bitumen)). 6








    0 40 80 120 160 200



    3 )


    0%FBM (100%VA)

    Target density = 2330kg/m3)MWC = 80% ( OWC) = 5.2%

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  • 11Kuna, Airey, and Thom

    DISCUSSION OF RESULTS 1The results of the foaming experiment that was conducted on 70/100 grade bitumen are 2shown in Figure 2. The experiment was conducted varying FWC and temperature and 3keeping all other factors constant. It can be observed from the plots that as foaming 4temperature increased from 150C to 170C, the expansion ratio increased while the half-life 5decreased. These observations are fully in accordance with other published experience. 6

    The mechanical properties (ITSM, ITS-dry and ITS-wet) gyratory-compacted and 7cured specimens were plotted against MWC in terms of % of OWC in Figure 5. Each ITSM 8value in the plot is an average of tests on 8 specimens and ITS-dry and ITS-wet are averages 9of 4 specimens. The properties were all measured at the same water content (0.6-0.65%). As 10can be seen from the figures, the approximately peak ITSM values were 85% of OWC, 11except for 2%FBM (FBM with 2% FB content). When ITS-dry results were considered, the 12optimum MWC was seen at 85% of OWC for 2%FBM and 3%FBM; and for 4% FBM and 135% FBM the peak was at 75%. For ITS-wet values the optimum was found at 85% except for 145% FBM. Overall, the optimum MWC for all mixtures was consistently found to lie between 1575% and 85% of OWC. In this study MWC of 80% OWC has been adopted. 16

    To study the optimum compaction effort and to obtain the design number of gyrations 17(Ndesign), the changing height was recorded from the gyratory compactor during compaction. 18From the height data density was calculated and plotted against number of gyrations (Figure 196). The marks on the curves are the target densities that were obtained from modified Proctor 20data. It can be seen from the plots that, though the target densities were different, the number 21of gyrations required compacting to those target densities are in a similar range. That means, 22a design number of gyrations required to compact to modified Proctor densities can be 23established, independent of FB content in the mixture. Ndesign for all FBMs considered was in 24the range of 120-160 gyrations. An average of 140 gyrations was adopted as Ndesign. 25

    As discussed earlier the present paper focusses on the optimisation of mix design 26parameters such as FB content, Mixing Water Content (MWC) and compaction effort and 27their effect on mechanical properties. The effect of other mix design parameters (Bitumen 28type, Foam characteristics, foaming temperature, FWC and mixer type) on mechanical 29properties have been discussed and recommendations were made by Sunarjono [13]. In the 30present study the recommendations made by Sunarjono (2008) [13] were considered during 31experimental design and methodology. From the above discussed results, the outcome of the 32present study is that optimum MWC is in the range 75 - 85% (80% is used) of OWC obtained 33from modified Proctor test, and that Ndesign is 140 gyrations. It was found that Ndesign is 34practically independent of the amount of bitumen in the mixture. 35

    VALIDATION 36The mix design parametric study discussed in the previous sections was done on the mixtures 37with 100%VA (100%VA-FBM). In this section, a study has been conducted on mixtures with 3850%RAP (50%RAP-FBM) and 75%RAP (75%RAP-FBM) to validate the proposed 39recommendations. To validate the MWC range proposed (75% - 85% of OWC), aggregates 40with 50%RAP and 75%RAP and 4% FB were mixed and compacted with varying MWC 41(95%, 85%, 75% and 65% of OWC) to modified Proctor densities of similar mixtures. 4% FB 42was selected as it was the design FB content obtained for 100%VA mixes and it was assumed 43that the presence of RAP didnt affect the design FB content (an assumption that was later 44shown to be incorrect). The specimens were cured as discussed for 100%VA-FBMs. The 45results mechanical tests carried out on cured specimens are presented in Figure 7. ITSM 46

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  • 12Kuna, Airey, and Thom

    values shown in Figure 7 are the average of 10 tests while ITS-dry and ITS-wet are the 1average of 5 tests each. As can be seen from Figure 7, the optima for ITSM and ITS-dry were 2found at 75% of OWC and 85% of OWC respectively. For 75%RAP-FBM, optimum ITS-dry 3and ITS-wet were found at 75% of OWC. Although ITS-wet for 50%RAP-FBM and ITSM 4for 75%RAP-FBM didnt showed any optimum, other properties of both the mixtures have 5their optimum in the proposed range (75% - 85% of OWC). 6

    To validate the Ndesign, the aggregates with 50%RAP and 75%RAP were mixed and 7compacted at 0%, 3%, 4% of FB and the density data is plotted in Figure 8. For clarity Figure 88 shows only data for 75%RAP-FBM with 0%FB and 3%FB; the 4% FB lies in same region 9on plot. It can be seen that the Ndesign range is same between 80 and 120 gyrations. The mid-10point of this range which is 100 was considered as Ndesign. A similar study was also 11conducted on 50%RAP-FBM and Ndesign was found to be 110 gyrations. 12

    FOAMED BITUMEN (FB) CONTENT OPTIMISATION 13The results of mechanical tests on the mixtures that were compacted at optimum MWC (80% 14of OWC) and to Ndesign , and varying FB content, are plotted in Figure 9. As can be seen in 15the plots there is a clear optimum ITSM value for all mixtures. For 100%VA mixtures, the 16optimum was found at 4% FB content. Similarly, the optimum ITSM values for 50%RAP and 1775%RAP mixtures were found at 3.5% and 3% FB content respectively. If ITS-dry values are 18considered, there was no optimum for 100%VA mixtures. ITS-dry values for these mixtures 19increase with increased FB content without any optimum value. However, an optimum could 20be located for both the mixtures with RAP (50% RAP and 75% RAP). The optimum values 21were found at 3% FB for both mixtures. When ITS-wet results are considered, the optimum 22ITS-wet was found only for 75% RAP mixtures, which is at 3% FB content. There was no 23optimum for any mixtures if ITSR was considered. However, it can be noted that, though 24ITS-dry values were higher for 100%VA mixtures than for mixtures with RAP, the ITS-wet 25and ITSR values were found to be superior for mixtures with RAP. This indicates that the 26mixtures with RAP have better resistance against water than mixtures without any RAP. This 27could be attributed to the presence of fully bitumen coated RAP aggregates in the mixture. 28Overall, from the results at 4% and 3% FB contents, optimum mechanical properties were 29found for 100%VA and 75%RAP mixtures respectively. However, optimum FB content was 30less clear for 50%RAP mixtures. 31


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  • 13Kuna, Airey, and Thom


    FIGURE 7 Mechanical properties on 50%RAP-FBM and 75%RAP-FBM with 4% FB content 2(Validation). 3


    FIGURE 8 Validaion of Ndesign for 75%RAP-FBM. 5

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  • 14Kuna, Airey, and Thom


    FIGURE 9 Mechanical properties of FBMs that were mixed at optimum MWC (80% of OWC) and 2compacted to Ndesign. 3

    According to Wirtgen cold recycling manual[2], the RAP material has to be 4considered as active in cold recycling only if the penetration test at 25C on recovered 5bitumen results in more than 25 dmm penetration. Hence, during the mix design of mixes 6with RAP, the RAP was assumed as black rock (bitumen in RAP is inactive) as the tests on 7recovered bitumen gave an average penetration of 16 dmm. However, as can be seen from the 8results (Figure 9), the optimum FB content is not the same for FBMs with RAP and without 9RAP. For mixtures with RAP, the optimum was shifted towards the left indicating that the 10RAP material in the mixtures has influence on mechanical properties. This could be attributed 11to the presence of bitumen in the RAP material. Therefore, treating RAP as black rock during 12mix design of these FBMs is not a valid concept. 13

    CONCLUSIONS 14The conclusions that were drawn in relation to the mix design parameters that were 15considered in the study are: 16

    1. A rational range of optimum MWC was suggested; which is 75-85% of OWC 17obtained by modified Proctor test. It is considered appropriate that MWC is expressed 18relative to OWC obtained since this is a parameter that depends on the amount of 19fines, which is an important mix design parameter. 20

    2. It was found that a unique design number of gyrations (Ndesign ); the compaction effort 21equal to modified Proctor compaction, This was established for FBM with a specific 22aggregate gradation but is independent of amount of FB present in the mixture. 23Therefore, to identify the optimum compaction effort, one just needs to obtain 24modified Proctor density of the mixture with 80% (i.e. a value between 75% and 2585%) of OWC and determine the number of gyrations required to compact to that 26

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  • 15Kuna, Airey, and Thom

    density. The number of gyrations obtained is Ndesign which can be adopted for 1mixtures with any FB content. 2

    3. It was observed that the presence of RAP influenced the design FB content; which 3means treating RAP as black rock in FBM mix design is not appropriate. 4 5REFERENCES 6

    1. Academy,A.,AGuidelinefortheDesignandConstructionofBitumenEmulsionandFoamed7BitumenStabilisedMaterials,2009.8

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    SouthAfrica,Durban,1979.198. Bowering,R.H.andC.L.Martin.FoamedBitumenProductionandApplicationofMixtures20


    9. Castedo,F.L.,L.E.Wood,andA.G.Altschaeffl,Laboratorymixdesignprocedureforfoamed23asphaltmixturesIndianaDepartmentofHighways,Indianapolis,1982.24

    10. Kim,Y.andH.Lee,Developmentofmixdesignprocedureforcoldinplacerecyclingwith25foamedasphalt.JournalofMaterialsinCivilEngineering,Vol.18,No.1,pp.116124.26

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    14. Bowering,R.H.,SoilStabilisationwithFoamedBitumen.HighwayEngineeringinAustralia,331971.34

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    TRB 2014 Annual Meeting Paper revised from original submittal.

  • 16Kuna, Airey, and Thom

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    TRB 2014 Annual Meeting Paper revised from original submittal.