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THE EFFECT OF WARM MIX ASPHALT ADDITIVE (SASOBIT®) ON DETERMINATION OF OPTIMUM BITUMEN CONTENT

Frag Ahmed Ma Kridan*, Ahmad Kamil Arshad & Mohd Yusof Abdul RahmanFaculty of Civil Engineering, Universiti Teknologi MARA, Shah Alam, Malaysia

*E-mail: fkridan@yahoo.com

ABSTRACTResearch in the laboratory was carried out to determine if addition of warm mix asphalt additive (sasobit) has potential to reduce the amount of optimum bitumen content comparison with control mix. To fulfil this purpose two types of mixes have been produced by Marshall method procedure.The first was control mix AC14 gradation mixed with unmodified bitumen 80/100 penetration. The other was identical in gradation proportion to minimize the varieties, it was mixed with modifed same bitumen penetration with sasobit additive in concentration 2 % identified as saso mix. Both mixes produced at mixing temperature 155°C and 135°C respectively. The volumetric properties Bulk density (Gmb), Air voids in compacted mix (AV), voids filled with bitumen (VFA) as well as Marshall stability and flow were within investigation to determine the effect of sasobit additive on the amount of optimum bitumen content. The specimens results which prepared by Marshall compacter showed significant reduction in air voids in compacted mix accompanied with adding the sasobit additive on the mix in most cases. The results also showed somewhat decrease in stability whereas slight increase regarding flow parameter values in saso cases in all bitumen content as well as slight increase in VFA while no clear trend in term of Gmm. With plotting volumetric values to both mixes (control and saso) versus bitumen content confirming with requirements set by PWD (Malaysian Public Work Department, Section 4 Standard Specification For Road works). The result drawn from these graphes have appeared the optimum bitumen content were 4.82 % and 4.78% to control and saso mixes respectively, which means that the addition of sasobit additive on the mix by using Marshall Method revealed very slight reduction in optimum bitumen content. Otherwise the addition of sasobit additive on virgin bitumen barely revealed different amount of optimum bitumen content between both investigated mixes.

Keywords: optimum bitumen content, sasobit additive, volumetric properties, mixing temperature.

1. INTRODUCTIONPavement industry as major beneficiary receives the benefits of warm mix technology which has attracted interest such as energy saving, gases and emission reduction in overall construction process. Such advantages reflect substantial economical and environmental benefits. This research describes scrutiny serious testing programme was conducted in the laboratory. Major factor must be taken into the consideration to produce the warm mix at mixing temperature lower than where the conventional mix produced to make sure that aggregate used has coated well and the mix possess good workability during the mixing and lay down stages with low viscosity of the bitumen as well as overall mix properties are not compromised. As a major part of mix design process, the optimum bitumen content should be determined to be suitable and capable of working successfully during the period of time which have designed for the pavement to be in service life in good condition. It hence the amount of bitumen should be enough without any increase or decrease in this amount which leads to the compromising performance of mixture.(Francken, 1998).The starting point for further investigation in this paper is to find out evidence on the hypothesis which saying that the optimum bitumen content should be determined without adding the warm mix asphalt additives. To avoid any unsuitable reduction in the bitumen which may lead to negative affects on mix durability and water susceptibility. Actually, there is no research available comfirms this supposition. Otherwise, this hypothesis needs to be investigated. It is reported that addition of sasobit which was used in this research on the virgin bitumens improves compactibility efforts, that obviously clear through reduces the amount of air voids contents by utilizig both the geratory compacter and vibirator compacter (Hurley and Prowell, 2005 ; Stacey, D. D el at. 2007; Joe W et al. 2007; Stacey, D. P and Amy, H., 2008; Raijib Mallick et al. 2008; Tejash Gandhi, 2008).The reduction rate in air voids in total compacted mix is depends on several factors such as the percentage of added additive , the type of the additive used with the mix and mixing and compaction temperature as well. This reduction creates the concern of addition such additive on bitumens which may has potential to readuce the optimum bitumen content to the mix.Literature review has showed that there is no extensive research investigating the effects of adding the warm mix asphalt additive Sasobit on selecting optimum bitumen content, particularly using Marshall Method procedure.

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2. RESEARCH SCOPE This research was pursued to investigate and compare the optimum bitumen content obtained from two designed mixes (with and without sasobit additive) in fabricating warm mix asphalt specimens in laboratory. Prior to mixing materials the sasobit additive was mixed with virgin bitumen 80/100 penetration grade which commonly used in Malaysia in concentration 2 % of weight of bitumen by using laboratory stirrer at blending temperature 125°Cwithin period of time extended to one hour to make sure that sasobit additive has fully dissolved and dispersed well within bitumen as advised from the manufacturer ( Sasol wax), this percentage was selected as average from advised percentages on bitumen from manufacturer ( 1-3 %). The chief purpose and the objective of such limited research is to determine the effects of warm mix asphalt additive (sasobit) on design and determination of bitumen content by using Marshall Method procedure. Other specific objective is to validate that finding obtained by gyratory and vibratory compacter in previous researches with respect to air voids reduction. Furthermore, the volumetric properties VTM, VFA, Gmb as well as stability and flow parameters within investigation. For the sake of fulfilling the research objectives the criteria followed set by PWD (Malaysian Public Work Department, standard specification for road works section 4).

3. RESEARCH MATERIALS3.1 The ModifierThe modifier used in this research is sasobit additive, which known also as paraffin wax. It is produced by Sasol Wax Company South Africa. Sometimes called as asphalt flow improver it's derived from coal gasification process. The chemical composition described as fine crystalline materials in long-chain hydrocarbons, produced by means of Fischer-tropsch (F-T) synthesis. It is long chain composed from 40 to 115 carbon atoms. As mentioned from producer the melting point of sasobit additive is circa 100 °C and it's completely dissolves in bitumen at temperature above 115°C.From the past experience with this modifier. It is reported that the addition of this additive significantly reduce the viscosity of binder. However, this reduction in viscosity allows mixing and compaction temperature to be below of that where conventional mix is produced. (Hurley and Prowell. 2005; Joe W et al. 2007; Nazimuddin et al. 2007; Raijib Mallick et al. 2008; Gandhi et al. 2009).

3.2 Aggregate and BitumenThe combined materials have been comprised aggregates and bitumen. This research has been used locally available granite aggregate produced by Kajang Rock Quarry in Selangor. Malaysia. Granite aggregate is used to produce both hot and warm asphaltic concrete mixes having a specific gravity of 2.607 gm /cm�. The combined aggregate included a coarse, fine and the Ordinary Portland Cement as mineral filler according to specification set by JKR. All the produced samples mixed by combination of the aggregate proportion and bitumen 80/100 penetration having a specific gravity of 1.02 gm/cm�. The basic properties and behaviours of the aggregate and bitumen within JKR requirements as presented in table 1 and 2.

Table 1. The basic properties of aggregate.

Property Test Result PWD Requirements

Designation

Aggregate Abrasion Value AIV % 23 < 25 % ASTM : C 131-96Aggregate Impact Value, AIV % 19.4 < 25 % BS 812: PART 112:1990Water Absorption % 0.5 < 2 % ( BS 812 : PART107:1995)Specific Gravity gm / cm� 2.607 ( BS 812 : PART 107:1995)Flakiness Index % 10.25 < 25 % ( BS 812 : PART 105: 1990)

Table 2. The basic properties of bitumenType of test Test result Designation

Penetration at 25°C, 100g (0.1mm) 91 ASTM D 5Softening point (°C) 47.5 ASTM D 36

Ductility at 25°C (cm) 111 ASTM D 113

4. EXPERIMENTAL SCHEMEAs mentioned earlier the virgin bitumen has blended with sasobit additive prior to mixing the materials in concentration 2 % by weight of the bitumen, this step has been believed to be better than the direct addition of

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sasobit on aggregate to obtain homogeneous mix and better scattering of sasobit within bitumens as evenly as possible. Albeit one research conducted to compare the effects of both addition of sasobit methods (direct and indirect) by utilizing Marshall method procedure has appeared similar stability values obtained from both methods (Brits, CH 2004).In order to accomplish the research objectives two types of dense grade mix AC14 gradation designed by using Marshall design conforming to PWD specification. The first mix has been designed with typical dense graded gradation mixed with unmodified binder 80/100 penetration identified as Control mix. The other mix has identical proportion of aggregate to minimize the varieties as much as possible and was mixed with modified binder identified as Saso mix. The selected aggregate proportion and it's specification limits and criteria followed in this research to determine optimum bitumen content are presented in table 3 and 4 respectively. Plot of the mix gradation is shown in Figure 1(a) and (b) which represent that the sieve sizes are raised to 0.45 powers.

Table 3. Gradation Limits for Asphaltic Concrete AC14 and job formula

Mix Designation Power ^ 0.45Wearing Course

AC 14 Specification Limits PWDB.S Test Sieve % Job Formula

20.0 mm 3.85 100 100

14.0 mm 3.28 95 90 – 100

10.0 mm 2.82 81 76 – 86

5.0 mm 2.06 56 50 – 62

3.35 mm 1.72 47 40 – 54

1.18 mm 1.08 26 18 - 34

425 μm 0.68 18 12 – 24

150 μm 0.43 10 6 - 14

75 μm 0.31 6 4 – 8

Filler OPC % 2 2

Bitumen Content % 4 - 6 %

(PWD Specification 2008)

Table 4. Criteria and Parameters limits for Asphaltic Concrete AC14

Parameter Wearing Course AC14

Stability, S > 8000 N

Flow, F 2 - 4 mm

Stiffness, S / F > 2000

Air voids in mix, VTM 3 % - 5 %

Voids in aggregate filled with bitumen, VFB 70 % - 80 %

(PWD Specification 2008)

The aggregate was used to produce two types of mixes. The first was control and other mix was Saso. Both mixes were produced at mixing temperature 155°C and 135°C and have compacted at temperature 135 and 120respectively. Each mix with five different bitumen content from 4 to 6 % by weight of bitumen at an interval of 0.5 % in accordance with PWD specification. Six samples have produced to each bitumen content. 60 samples were investigated in this research. The physic-mechanical properties of the produced both mixes (hot and warm asphaltic concrete) via conducting Marshall Standard test procedure according to ASTM (D1559). The properties required in determination of bitumen content based on PWD specification were bulk density, percentage of air voids in compacted mix, voids filled with bitumen, Marshall Stability and Marshall Flow.

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(a)

(b) Figure 1. (a) Gradation Chart of Control and Saso Mixes AC14,(b) Gradation raised to 0.45 powers.

From the plot of mix gradation as shown in figure 1(b), the most aggregate line falls over the maximum density line (MDL) which means that the job mix formula for the selected aggregate proportion classified as fine aggregate.

5. EXPERIMENTAL RESULTS5.1 Effect on Voids at Production and Compaction TemperaturesThe data presented in table (5) represents the volumetric properties as well as Stability and Flow test results for both mixes (Control and Saso) produced by Marshall test procedure. In this table,the values represent the average of six samples to each bitumen contant for both mixes. It can be deduced from air voids in total compacted mixes as shown in figure 2( c ) , 3 and table 5. The addition of sasobit additive significantly assists in lowering the amount of air voids within mixes in most cases . The reduction rates depends on additive percentage which was added on virgin bitumen. The differs in air voids between both mixes were 0.21, 0.19, 0.15 , 0.04. to 4 %, 4.5 %, 5 %, 5.5 % bitumen content respectively and value of 6 % seems to be same value in control and saso mixes. Also it can be deduced that the reduction rates in air voids decreased with increment of percentage of sasobit additive on bitumen.

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Table 5. Volumetric properties and Marshall test results of the Control and Saso mixes

Mix Type Bitumencontent

%

Mixing Temp °C

Bulk Gravity

Gmb

Maximum Gravity Gmm

A V %

VMA VFA Stability (N) Flow (mm)

Control 4 155 2.319 2.470 6.13 15.13 59.52 18930 3.12Control 4.5 155 2.344 2.452 4.42 14.66 69.87 21155 3.56Control 5 155 2.348 2.435 3.55 14.95 76.25 17131 4.05Control 5.5 155 2.253 2.417 2.67 15.24 82.47 14397 5.36Control 6 155 2.341 2.400 2.57 16.09 83.55 13392 5.75

Sasobit Mixing temperature = 135°CSasobit 4 135 2.324 2.470 5.92 14.94 60.45 17913 3.38Sasobit 4.5 135 2.349 2.452 4.23 14.49 70.83 18551 3.71Sasobit 5 135 2.352 2.435 3.40 14.82 77.06 15435 4.28Sasobit 5.5 135 2.354 2.417 2.63 15.2 82.71 13978 5.21Sasobit 6 135 2.340 2.400 2.58 16.15 83.50 13248 5.63

0

5000

10000

15000

20000

25000

3 3.5 4 4.5 5 5.5 6 6.5

STA

BIL

ITY

( N

)

BINDER CONTENT ( % )

STAILITY VS BINDER CONTENT

saso control

( a ) ( b )

( c ) ( d )

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(d)Figure 2. Effects of sasobit on Marshall Test Results of Hot and Warm Asphalt Concrete Mixes.Individual plot Bitumen Content versus (a) Stability, (b) Bulk Density, (c) Air Void, (d) Voids Filled with Bitumen and (e) Flow.

Figure 3. Air voids in Compacted Mix, Control and Saso Mixes AC14

With respect to voids filled with bitumen VFA as shown in table 5 and figure 2 ( d ) there is slighty increased in Saso mix comparing to control mix. This trend is normal with decreasing air voids in compacted mix, the general trend can be obsearved regarding bulk densities, no clear trend to increase or decrease the values of bulk densities in both mixes.

5.2 Effect on Marshall Stability and Flow ParametersIn term of flow parameter, it is obviously clear that both mixes values are considerably similar to the general trend of bulk densities while stabilities in Saso mixes were somewhat lower than control mixes in all bitumen content percentages. This indicates that the addition of sasobit has clear effects on stability values and can be attributed to sasobit structure within bitumen. The addition of sasobit on bitumen is obviously clear has potential to improve mix compactibility efforts accompained with decreace in their air voids in total compacted mix in most cases, also has been decreased stability values. Otherwise the Marshall Method is very sensetive to the added additive in all percentages on mixes which mean to clear effects on mix performance.

5.3 Effect on Determination of Obtimum Bitumen Content The results drwan from volumetric properties AV, VFA, Gmb, Marshall pararmeters Stability and Flow, were plotted in five graphs versus the bitumen content . According PWD requirements the optimum bitumen content shall

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be determined by averaging five optimum bitumen content from the plotted smooth curves and shall comply with design parameter given in table 2. The following should comferming JKR requirement. Avereging values of AV, VFA , Flow as mentioned in table 2.As well as the peak (largest) of curve taken from the stability and bulk specific gravity graphs.All values obtained of optimum bitumen content must comply with requirements given in table 2 and the results drwan from these graphs have appeared the optimum bitumn content were 4.82 % and 4.74 % to control and sasobit mixes respectively.

6. CONCLUSIONIt is vividly clear that the addition of sasobit on mix reduces the air voids in total compacted mixes. However this reduction has appeard very slight reduction in obtimum bitumen content and the difference obtained was 0.04 %,this finding agree in part with other research finding. (Hurley and Prowell 2005; Joe W et al. 2007; Cindy Estakhri, P.E et al. 2010) in reduction of air voids in total mix but disagree in regard to the used percentages of reduction in optimum bitumen content where this reduction rate was about one-half apercentage point below that of an equivalent conventional HMA as mentioned in some researches (Joe W et al 2007; Cindy Estakhri, P.E et al 2010). This difference can be attributed to mix design methods and compaction pattern used in previous researches, the gyratory and vibratory compacter were used instead of marshall compacter. Otherwise the concept of reduction of obtimum bitumen content accompanied with addition of sasobit additive needs to be further investigated with other various gradation. Until that time we should avoid addition of sasobit additive on virgin bitumen to determine obtimum bitumen content.

7. ACKNOWLEDGMENTSSpecial appreciation is given to the faculty of Civil Engineering (UiTM Shah Alam) and Highway Laboratory technicians for providing technical guidance and assistance. Acknowledgement is also given to the MITRANS Laboratory committee and technicians for their assistance to achieve this work in good condition.

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[7]. PWD. (2008). 20403 . 00030 Standard Specification For Road Works. Section 4 Flexible Pavement. Jabatan Kerja Raya. Malaysia. Kuala Lumpur.

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