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ISAP 2012 Fakhri et al: Evaluation of different Warm Asphalt additives 1/10

Evaluation the effect of different Warm Asphalt additives onBitumen and Asphalt Mix Properties

M. Fakhri, School of Civil Engineering, K. N. Toosi University of Technology, IranS. M. Sadati lamardi, School of Civil Engineering, K. N. Toosi University of Technology, Iran

Hassan Firouzifar, Pasargad Petrolum Co, Iran A.R. Ghanizadeh, Department of Civil Engineering, Sirjan University of Technology, Iran

ABSTRACT: WMA is gaining attention in all over the world because it offers severaladvantages over conventional asphalt concrete mixtures. The benefits of using WMA are toreduce the production temperature by using additives, to increase the workability of binder atlower temperatures, a longer paving season, reduced emissions and the ability to travelover longer distance to paving site. In this paper five different WMA additives and theirinfluence on bitumen and asphalt mixtures behavior have been investigated. These additives

contain Polyphosphoric acid, Sasobit, Cecabase, Iterlow and Polyethylene wax. Some ofthese additives, like Sasobit, Cecabase and Iterlow, are exclusively used in WMA industryand others are used sometimes as binder modifiers. The study shows that Cecabase hasbetter behavior than other additives, because it decreases the viscosity at mix andcompaction temperature without significant change of binder viscosity at temperatures lowerthan breaking point. Decreasing viscosity by 0.5% of Cecabase makes it possible to mix andcompact Asphalt mixes at a temperature 12°C lower in comparison of origin bitumen.G*/Sin() for both origin and modified RTFO aged binder at 58°C and 64°C pass theSuperpave specification and this approves that using CecaBase has no adverse effect onrutting potential of origin binder at high temperatures. Furthermore, Adding Cecabase, PPAand Iterlow to bitumen material do not improve asphalt concrete properties significantly,although they do not lower the quality of asphalt concrete.

Key words: Warm Mix Asphalt, WMA additives, CecaBase, Iterlow, Polyphosphate Acid

1. IntroductionConventional HMA is produced between 138°C and 160°C and placed and compactedbetween 121°C and 135°C [1]. A number of new technologies have been developed to lowerthe production and placement temperatures of hot-mix asphalt (HMA). Generically, thesetechnologies are referred to as warm-mix asphalt (WMA). The range of productiontemperatures for warm mix asphalt is wide, from mixes that are 20 to 30 oC below HMA totemperatures slightly above 100°C. WMA has been used in all types of asphalt concrete,including dense-graded, stone matrix, porous, and mastic asphalt. It has also been used in arange of layer thicknesses, and sections have been constructed on roadways with a widevariety of traffic levels [2].

The concept of WMA was introduced in the year 2000 in Europe and Australia [3,4], and bythe year 2004 it attracted considerable attention of the highway engineering community [5,6].WMA is gaining attention in all over the world because it offers several advantages overconventional asphalt concrete mixtures. Using WMA should result in reduced volatile organiccompounds (VOCs), carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx),and particulates. Since most plant emissions result from burning fuel and WMA uses lessfuel, there should be lower emissions. The amount of emissions reduction will depend on thetemperature reduction, the type of fuel used, plant settings, moisture content of the aggregateand RAP use. Workers should find that WMA provides a more comfortable workingenvironment. The cooler material should be more pleasant to work around, and there shouldbe fewer burns. Worker exposure to asphalt fumes will be reduced. WMA can be easier tocompact than HMA. Some WMA methodologies have been added to mixes containing highlymodified binders (PG 82s, etc.) to facilitate aggregate orientation, which results in better field

densities. Lab specimens of WMA routinely have less air voids and VMA than corresponding




HMA specimens. The reduced viscosity of WMA mixes’ binders and the slower cooling rate ofWMA mixes allow paving to be completed under cooler conditions than normally associatedwith HMA. This condition allows for extended paving seasons or longer haul distances andtimes. Some additional benefits have been found from the early WMA projects. Oneadvantage is the ability to avoid the common problem of bumps forming when paving overcrack sealants. The reduced mat temperature does not trigger the formation of the bumps. Another benefit observed in Texas has been reduced cracking, both in the lab from theirOverlay Tester and on the road [7].Warm asphalt technology seems to be quite promising. It consumes 30% less energy [8]. Italso reduces CO2 and SO2 emission by 30–40%, volatile organic compounds by 50%, Co by10– 30%, nitrous oxides by 60–70% and dust emission by 20-25% compared to hot mixasphalt [9]. This technology does not involve any major modification to the mixing plant andthe construction procedure.There are many ways to classify WMA technologies; one of them is by the degree oftemperature reduction. Generally, the warm mix asphalt production and lay downtemperatures are 20 to 30

oC below HMA to temperatures slightly above 100

oC [2]. If the

temperature of the mix at the plant is less than 100

o

C, the mix is considered as half warmmix, which is in between cold mix and warm mix [2]. The other way to classify the WMAtechnologies is by those that use water and those that use some other form of organicadditive or wax to effect the temperature reduction. These methods are based on processengineering, aerogenous agents or special bitumens and additives [10]. Thus, several WMAtechniques are available and have been studied by several authors, namely; the double-coating or 2-phase mixing method; the application of the double-barrel green process, withreductions of 10–30°C; the half-warm mix asphalt technologies that use water or vapor,produced at 90–100 °C with foamed bitumens or at 70–115 °C with emulsions [11].

Figure 1: Classification of asphalt mixes by temperaturerange, temperatures, and fuel usage [2].

Several investigators have studied the performance of the WMA additives, binders [12,13,14]and mixtures [15], in order to investigate and improve their behavior. This study work isassigned to evaluate five different WMA additives and influence of them on bitumen andasphalt mixtures behavior. These additives contain Polyphosphoric acid, Sasobit, Cecabase,Iterlow and Polyethylene wax. Some of these additives, like Sasobit, Cecabase and Iterlow,are exclusively used in WMA industry and others are used some times as binder modifiers.

2.Introduction of different additives used in this studyPolyphosphoric acid , or PPA, is a liquid mineral polymer and just one of many additives used

to modify and enhance paving grade asphalts. According to Asphalt Institute, the correct use




of PPA, in the appropriate amount, can improve the physical properties of bituminous pavinggrade binders. On the other hand, incorrect application of PPA technology can result inconstruction or performance problems. When used in combination with a polymer, PPAprovides flexibility in reaching the requested test specifications (Dynamic Shear Rheometer,Elastic Recovery, etc.) while limiting the asphalt viscosity at 135°C (275°F) [16].Sasobit® is a product of Sasol Wax (formerly Schümann Sasol), South Africa. Sasobit isdescribed as a modifier or "asphalt flow improver". Sasobit

® is a mixture of long-chain

hydrocarbons produced by the Fischer-Tropsch synthesis. When road bitumen are admixedwith Sasobit

®, their properties are markedly improved. Adding 3% weight to a 50/70 bitumen

results in a large increase in R&B softening point to the level of that of 10/20 bitumen. Theplasticity range (the difference between the R&B softening point and the Fraass breakingpoint) is considerably extended [17].Cecabase® is an organic Additive which is liquid at 25°C used as an additive in theproduction of the WMA. The Cecabase RT

® additive acts at the interface between mineral

aggregate and binder, in a similar way that a surfactant acts at an interface between waterand asphalt that does not significantly change the rheological properties of binder. Cecabase

RT

®

945 enables to reduce the asphalt mix production and lay down temperature by 20 to40°C and keeps the same mechanical properties as a standard HMA. The effectiveness ofthe Cecabase RT

® was demonstrated in a field test, where a production temperature was

reduced by up to 27°C yielding a WMA mixture comparable to a typical HMA mixture [18].Iterlow is a technology based on a liquid product, that, added to bitumen in quantities of 0.3-1%, allows to produce the warm mix at temperatures between 90°C-120°C. Iterlow acts onthe bitumen's surface tension, therefore doesn't modify the chemical and physicalcharacteristics of the bitumen (R&B, penetration, viscosity, paraffin content). It was firstlyused in 2002 in testing areas all around Europe, on wearing course, binding coatings andbases, with RAP in addition as well. (RAP) [19].Polyethylene wax , also known as low molecular weight polyethylene, whose softening point isover 100

oC, approximate to macro-molecular weight polyethylene. While its melting viscosity

and hardness are close to paraffin. Polyethylene wax has good compatibility with

polyethylene (PE), polypropylene(PP), polyvinyl acetate (PVA), polyvinyl chloride (PVC),ethylene-propylene-Diene monomer(EPDM), butyl rubber. It can improve the fluidity of PE,PVC, PP, ABS (acrylonitrile-butadiene styrene) and the demoulding performance of PMMA(polymethyl methacrylate ) and PC( polycarbonate)[20].

3.Binders characterizationTo study the influence of each additive on conventional properties of origin bitumen, thesoftening point, penetration, ductility and viscosity of each binder were determined. Thesoftening point (Ring and Ball test) of origin and modified binders was measured according to ASTM D36. In this test, two disks of bitumen were cast into shouldered rings, and then thedisks were trimmed to remove excess asphalt. The disks were then heated at a constant rate(58°C/min) in a water bath using a special apparatus. The penetration test was carried out at25°C according to ASTM D5. The penetration of a standard needle under a standard load

(100 g) was measured during 5s and reported in forth of a millimeter. Ductility wasdetermined at 25°C with an extensional speed of 5 cm/min in accordance with ASTM D113.The viscosity properties of bitumen samples were determined by a kinematic viscometeraccording to ASTM D2170. Since the bitumen 60/70 covers a wide range of climate conditions in Iran, this type ofbitumen has been used in the present research in order to study the influence of differentadditives on physical and rheological properties of bitumen 60/70 and also on Asphaltmixtures contain different additives. As summarized in Table (1) and Figure (2), increasing Iterlo and CecaBase content has nosignificant effect on softening point of binder, while increasing the content of other additives(Sasobit, Polyethylene Wax, and Polyphosphoric acid) increases the softening point ofbinder. This means that with increasing the content of Sasobit, Polyethylene Wax, andPolyphosphoric acid, thermal sensitivity of binder decreases and the binder can be employed

in warmer climates. According to the allowable limits of softening point for pure bitumen




(35°C -60°C), it is obvious that Sasobit, Polyethylene Wax, and Polyphosphoric acid do notsatisfy specifications. Binders containing Iterlo and Cecabase have allowable softening pointand are comparable with the origin bitumen which can have softening point between 49 to56°C.

Table 1: Conventional Tests results for Origin and Modified Bitumen. Ductility

(cm)Penetration at 25°C

(0.1mm)Softening Point

(°C)Material

WMA Additives

>1007054Origin Binder 60/70-

>1006849.23B60/70+Iterlo(0.4%)

Iterlow >1007048.7B60/70+Iterlo(0.7%)

>1007250.2B60/70+Iterlo(1.0%)

1056063.1B60/70+PW(0.2%)

PolyethyleneWAX

96.45564.2B60/70+PW(0.4%)

34.747.3367.25B60/70+PW(0.6%)

1039547.7B60/70+PPA(0.4%)

Polyphosphate Acid

81.176.6650.3B60/70+PPA(0.7%)

36.45856.8B60/70+PPA(1.0%)

>13047.375.3B60/70+Sasobit(0.2%)

Sasobit 62.84285.3B60/70+Sasobit(0.4%)

58.345.389.2B60/70+Sasobit(0.6%)

123.865.655B60/70+CB(0.5%)

CecaBase 73.66454.2B60/70+CB(1.0%)

108.68153B60/70+CB(3.0%)

Figure 2: Penetration of binders containing different percentages of additives.

Origin

Bitume




Figure 3: Softening point of binders containing different percentages of additives.

As summarized in Table (1) and Figure (2), increasing Iterlo and CecaBase content has nosignificant effect on softening point of binder, while increasing the content of other additives(Sasobit, Polyethylene Wax, and Polyphosphoric acid) increases the softening point ofbinder. This means that with increasing the content of Sasobit, Polyethylene Wax, andPolyphosphoric acid, thermal sensitivity of binder decreases and the binder can be employedin warmer climates. According to the allowable limits of softening point for pure bitumen(35°C -60°C), it is obvious that Sasobit, Polyethylene Wax, and Polyphosphoric acid do notsatisfy specifications. Binders containing Iterlo and Cecabase have allowable softening pointand are comparable with the origin bitumen which can have softening point between 49 to56°C.Table (1) and Figure (3) show that increasing the content of Polyethylene Wax and

Polyphosphoric Acid decrease the penetration of binder. Using lower percentages of Iterloand CecaBase (0.5 to 1.0%) does not change the penetration of origin bitumen. In case ofSasobit, binder penetration decrease significantly which approves the binder containingSasobit is harder and more brittle than base bitumen. Mixtures containing hard binder shouldnot be used in cold weather because may experience cracking at low temperatures. Also with increasing the content of Polyethylene Wax, Polyphosphoric Acid and Sasobit inbinder, ductility and so cohesion of binder decreases significantly.Figure (4) shows the relation of viscosity to temperature for origin and modified binders.Temperature in Figure (4) covers both higher and lower temperature than breaking point.Binders containing Polyphosphoric Acid have viscosity more than 30000pc at temperaturesless than 80°C. The most adapted additive as Warm Asphalt additive is one which decreasesthe viscosity of binder at higher temperature without changing the viscosity of binder at lowertemperatures. This additive is able to decrease the mix and compaction temperature without

significant effect on the behavior of bitumen at service temperature. As it can be seen inFigure (4), the Cecabase shows better behavior than other additives, because it decreasethe viscosity at mix and compaction temperature without significant change of binder viscosityat temperatures lower than breaking point. Decreasing viscosity by 0.5% of CecaBase makesit possible to mix and compact Asphalt mixes at temperature 12°C lower in comparison oforigin bitumen. According to the mentioned physical properties of binders containing different additives, it canbe concluded that the CecaBase is the most proper alternative among other Warm Asphaltadditives.

Origin

Bitumen




Figure 4: Viscosity vs. temperature for binders containing different additives.

4.Rutting potential of unaged and RTFO aged binderRutting potential of binder containing CecaBase was determined using the comparison ofrheological properties of origin and modified binder. Measurement of the rheologicalproperties of the binders was carried out in a stress controlled rotational DSR with parallelplate sample geometries of 40 mm diameter and 1 mm gap. Dynamic shear modulus G*,phase angle () and G*/sin() were calculated. The complex shear modulus (G*) is definedas:

GiGiG ′′+′=

+

= δ

γ

σδ

γ

σsincos*

0

0

0

0

(1)

Where:G* = Complex shear modulus, Pa;G' = Storage modulus, Pa;G" = Loss modulus, Pa; = Phase angle, degree.

Three different temperatures 58, 64 and 70°C were applied at a fixed frequency of 10 rad/s todetermine the rheological properties of both origin and modified binder. Results have beenrepresented in Figure (5) and (6). Determination of rheological properties for original andmodified binder was carried out at two different conditions, first using unaged binder andsecond using RTFO aged binder. The Rolling Thin-Film Oven (RTFO) test provides simulatedshort term aged asphalt binder for physical property testing. Based on Superpavespecification, The complex modulus (G*) can range from about 0.07 to 0.87 psi (500 to 6000Pa), while the phase angle () can ranges from about 50 to 90°. A of 90° indicates thecomplete viscous behavior of binder. To control the rutting potential of binder, Superpavelimits the value of G*/Sin() ! 1.0 kPa and G*/Sin() ! 2.2 kPa for unaged and aged bitumenrespectively. Rutting parameters for both unaged and RTFO aged binder was represented in

Figure (5) and Figure (6). G*/Sin() for both origin and modified RTFO aged binder at 70°C




does not pass and at 58°C and 64°C pass the Superpave specification and this approves thatusing CecaBase has no adverse effect on rutting potential of origin binder at hightemperatures.

Figure 5: Comparison of rutting potential for unaged binder.

Figure 6: Comparison of rutting potential for RTFO aged binder.

5.Mixture designTo compare the Asphalt mixtures produced by origin and modified binders, the mix designof HMA was carried out according to the marshal method and then, for the WMA mixtures,the same binder content, aggregate type and gradation was used in order to evaluate theinfluence of the binder type on Asphalt mix. The standard dimensions of the cylindricalspecimens are 101.6 mm diameter by 63.5 mm height. The specimens were compacted byapplying 75 blows on each side of the specimen at 150 °C in accordance with ASTM D 1559. After having been cooled at room temperature for 1 day and before performing Marshalltests, the compactness is measured after which, standard specimens were left in water at60°C for 30 min and then loaded to failure at a constant rate of compression of 51 mm/min.




The Marshall stability value (in kg) corresponds to the maximum force recorded during testwhile the flow (in mm) is the deformation noted at the maximum force. The ratio of stability toflow, called Marshall Quotient “MQ (in kg/mm)” had calculated to give indication of the mixstiffness. For Marshall Test, each result is an average of three test specimens.

Table 2: Properties of Aggregates used in the studied mixtures

Aggregate Test MethodCoarse

AggregateFine

AggregateFiller

Sand Equivalent (%) AASHTO T176 - 79 -

Los Angeles Abrasion Test (%) AASHTO T96 14 - -

Percentage of particles with onefractured face (%)

ASTM D 5821 95 - -

Percentage of particles with twofractured faces (%)

ASTM D 5821 88 - -

Flat & elongated particle fraction (%) BS:812 18 - -

Coating and Stripping of Bitumen-

Aggregate (%)

AASHTO T182 >95 - -

Sodium Sulfate Soundness (%) AASHTO T104 0.6 2.6 -

Plastic Limit AASHTO T89 & T90 N.P. N.P.

Bulk Specific Gravity(gr/cm ) 2.502 2.408 2.690

The Original Bitumen which is used to prepare samples was the bitumen 60/70. Theproperties of Aggregates are summarized in Table (2). The grading curve of aggregates canbe observed in Figure (7). Upper and lower limit of grading curve is based on no. 4 gradationof asphalt mix which is selected from Road General Technical Specification [21]. Thisgradation may be used for both binder and surface courses.

Figure 7: Grading curve of the aggregates used in the studied mixtures.

After drawing needed curves of Marshal Mix Design (unit weight, air void, stability, VMA, flowand VFA) in different bitumen contents, the optimum bitumen content which results in 4% ofair void was selected as 5.2%. It should be noted that 5.2% of bitumen in mixture satisfied allthe other requirements.Properties of different mixtures prepared using original and modified binder was represented

in Table (3).




Table 3: Properties of different mixtures in optimum content of bitumen and with or withoutadditives

BinderOrigin

Bitumen(60/70)OB60/70 +

0.5CecaBaseOB60/70 +

0.5PPAOB60/70 +0.5Iterlow

Bulk Specific Gravity(gr/m ) 2.240 2.197 2.215 2.211

Air Void (%) 4.0 6.0 5.2 5.4

VMA (%) 14.4 16.1 15.4 15.6

VFA (%) 72.0 62.7 66.0 65.1

Marshal Stability (kg) 855 899 922 875

Flow (0.25mm) 10.7 10.7 11.3 11.5

Marshall Quotient (kg/mm) 319.62 336.07 326.37 304.34

6.Mixtures Comparison Although bitumen contains PPA and Iterlow were ignored in first stage of study because oftheir influence on viscosity at temperatures under breaking temperature, but the results ofmarshal test show that these two additives have no adverse effect on quality of asphaltconcrete. Moreover, it may be summarized that using of these additives has no significantinfluence on asphalt concrete properties like stability, unit weight. Therefore, adding theseadditives to bitumen material for production of asphalt concrete do not improve asphaltconcrete properties, although they do not lower the quality of asphalt concrete.

7.Conclusion

1. Bitumen contains 0.5 percent of Cecabase by weight; do not show significant change insoftening point, penetration and ductility at 25°C.

2. Temperature –Viscosity chart shows that Bitumen contains 0.5 percent of Cecabase hasa break point which is the most important properties of this additive as a WMA additive. As it was shown, using Cecabase as WMA additive does not change the bitumenbehavior at normal temperatures, and then it has no adverse effect on behavior ofasphalt concrete at service temperatures.

3. Cecabase shows better behavior than other additives, because it decreases theviscosity at mix and compaction temperature without significant change of binderviscosity at temperatures lower than breaking point. Decreasing viscosity by 0.5% ofCecabase makes it possible to mix and compact Asphalt mixes at temperature 12°Clower in comparison of origin bitumen.

4. Air void content in WMA mixtures is similar to that for HMA mixture. 5. Adding Cecabase, PPA and Iterlow to bitumen material do not improve asphalt concrete

properties significantly, although they do not lower the quality of asphalt concrete.

6. G*/Sin() for both origin and modified RTFO aged binder at 70°C does not pass and at58°C and 64°C pass the Superpave specification and this approves that usingCecaBase has no adverse effect on rutting potential of origin binder at hightemperatures.

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