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International Journal On Engineering Technology and Sciences – IJETS™ISSN(P): 2349-3968, ISSN (O): 2349-3976

Volume I, Issue III, July - 2014

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LABORATORY STUDY OF WARM MIX ASPHALTSASOBIT ADDITIVES AND CECASBASE

ADDITIVESRenugadevi Arunachalam,

PhD Scholar, Techno Global University, MeghalayaMail Id: [email protected]

Abstract- Rabid global warming and the fuel energy crisis have made rethink the use of conventional technologieslike Hot Mix Asphalts (HMA) technologies. The asphalt industry is constantly attempting to reduce its emissions asconcerns are growing on global warming. This can done by Warm mix asphalt (WMA) technology which producemore environmental friendly asphalt mixtures. A laboratory study was conducted by adding additives such asSesobit (organic) and cecabase (chemical). The mixture characteristics for these product were evaluated at fourdifferent temperature after using two different compaction methods. Finally the testing results indicate that theperformance of Sesobit was found to be better.

Key words- Asphalt, Organic and Inorganic Additives, Sasobit, Cecabase, viscosity, compaction, curing, StiffnessModulus, Gyratory compaction.

I. INTRODUCTION

The environmental issue has become the mostimportant challenges for society due to the over-exploitation, increased populations and consequentlydegradation of natural sources. Transportation is oneof the major global consumers of energy, currentlyrepresenting between 20% to 25% of aggregateenergy consumption and CO2 emissions and a stronggrowth has been projected in all sectors with thesame proportion from Transportation. Energyefficient technologies are developed to response tothe problems and also considered in constructionphases of asphalt mixes for road construction. Theconcept driving warm mix technologies is thereduction in asphalt binder viscosity, which allowsthe asphalt to attain suitable viscosity for coating ofthe aggregate and compaction of the mix at lowertemperatures. The implementation of warm mixtechnology (WMA) as a viable option for pavingoperations is a promising concept. HMA is producedat temperatures between 140°C–180°C andcompacted at temperatures between 120°C – 160°C.These temperatures ensure that aggregate is dry, theasphalt binder coats the aggregate and HMA isworkable. WMA is a modified hot mix asphaltmixture that is produced, placed and compacted ata10°C –40°C lower temperature than theconventional hot mix asphalt mixture. WMA could

be described as the asphalt mixture produced at 20°C– 40°C lower temperatures than the hot mix asphaltbut at a higher temperature than the water boilingtemperature. When asphalt is produced at lowertemperatures, there are many potential benefits suchas reduced energy consumption (fuel) in asphalt plantand reduced noxious gases emissions, increasedworkers safety due to reduce of smoke emissions,possibility to place asphalt mix in cooler ambienttemperatures and to haul farther distances withoutcompromising workability.

Recently various technologies available to increasethe workability at lower temperatures for theproduction of WMA. Most technologies involve theaddition of chemical or plain water additives toemulsify or foam the oil, allowing a reduction inviscosity and an evenly coating of the aggregate mix.

• Organic additives (including waxes)• Chemical additives

1.1 Sasobit (or) Organic additives (includingwaxes)

In this technology, organic additives or waxes areused which lower the asphalt binder viscosity abovetheir melting points. Wax additives such as FischerTropsch, Montan waxes, fatty acid amides. Theseorganic waxes have longer chemical chain lengths so

mailto:[email protected]



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their melting point is at about 100°C. The longerchains help keep the wax in solution and it reducesbinder viscosity at typical asphalt production andcompaction temperatures. The use of organicadditives enables asphalt mix production and layingtemperatures to be reduced by 20°C – 30°C. Sasobit,Ashphaltan B, Licomont BS 100.

1.2 Cecabase (or) Chemical additives

Chemical additives do not change the bitumenviscosity. As surfactants they work at themicroscopic interface of the aggregates and thebitumen. They regulate and reduce the frictionalforces at that interface at a range of temperatures,typically between 140 and 85°C. It is thereforepossible to mix the bitumen and aggregates and tocompact the mixture at a lower temperature.Chemical additives may reduce the mix andcompaction temperatures by about 20 - 40°C.Evotherm, Rediset, Iterlow T, Cecabase, REVIX.II. OBJECTIVE

The proposed research was carried out to accomplishthe following objectives:i. Determination of the optimum mixing andcompaction temperature for Sasobit additives andCecabase additives of the WMA;ii. Examination of the differences in test resultsbetween samples that are preparedwith Marshall hammer and gyratory compactor;iii. Study of the performance of WMA andcomparison to HMA in terms of densificationcharacteristics, stiffness, and permanentdeformations;

III. MATERIALS

3.1 Sasobit (Additive)

Organic additives, that have melting points below anormal asphalt production temperature, can be addedto asphalt to reduce its viscosity. With organicadditives, the viscosity of asphalt is reduced at thetemperature above the melting point in order toproduce asphalt mixtures at lower temperatures.Below the melting point, organic additives tend toincrease the stiffness of asphalt. Sasobit® has been

used in three different sizes for WMA pavements.They are pellets, flakes and powder. Sasobit is aFischer-Tropsch (FT) wax produced from the coalgasification process and is typically added at the rateof 1.5% by weight of asphalt. Recently it has startedproduction from natural gas using the FT process. InFischer- Tropsch process, the carbon-monoxideatoms get converted into a mixture of hydrocarbonshaving molecular chain lengths from 1 to 100 carbonatoms or greater. In this process, white hot coal istreated with a blast of steam. Iron or cobalt act as acatalyst in the reaction. The reaction can berepresented as follows: -

(2n+1)H2 + nCO → CnH(2n+2) + nH2O

The makers of Sasobit® claim that there exists adifference between the generic paraffin wax and theFT wax. They say that Sasobit® has a much longerchain length - 40 to 115 carbon atoms and thus has amelting point around 99°C compared to 20 to 45carbon atoms and a melting point of 50°C to 80°C forgeneric paraffin wax. The makers also claim thatSasobit forms a lattice structure in the asphalt binderwhich is the basis for the stability of asphalt thatcontains Sasobit. Sasobit can be added to the asphalt(wet process) or the asphalt mixture (dry process).Sasobit helps in increasing the compactibility of themixture and thus creates lower air voids in thespecimen Sasobit is completely soluble in bitumen attemperatures in excess of 115°C. It forms ahomogeneous solution with base bitumen on stirringand produces a marked reduction in the bitumen’sviscosity. This enables mixing and handlingtemperatures of the asphalt to be reduced by 10°C−30°C. Temperature reductions of up to 50°C can bereached by process optimization between the mixingplant and paving. This in turn results in a significantreduction of bitumen fumes emissions and CO2 (=energy savings) during such operations. Duringcooling the Sasobit crystallizes out and forms alattice structure in the bitumen which increases theasphalt stability. The melting point range ofSASOBIT is between 85°C - 115°C.

3.2 Cecabase RT



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Cecabase is an organic Additive which is liquid at25°C used as an additive in the production of theWMA. The Cecabase RT® additive acts at theinterface between mineral aggregate and asphalt, in asimilar way that a surfactant acts at an interfacebetween water and asphalt that does not significantlychange the rheological properties of asphalt.CECABASRT 945 enables to reduce the asphalt mixproduction and lay down temperature by 20 to 40°Cand keeps the same mechanical properties as astandard HMA. The effectiveness of the CecabaseRT® was demonstrated in a field test, where aproduction temperature was reduced by up to 27°Cyielding a WMA mixture comparable to a typicalHMA mixture. It is a product of Arkema Group,France and confirms that the total of 80,000 tons ofwarm paving materials were produced with theseadditives in 2007 and over 300,000 tons of WMAincorporating CECABASE RT laid on Europeanroads in late 2007 [13]. CECABASE RT 945 can beadded either in the bitumen storage tank, or directlyin line before the drum. CECABASE RT 945 isstable under the temperature of the bitumen.

IV. Plan for Testing

4.1Testing plan

In order to accomplish these tasks, a test plan wasdesigned and the evaluation was performed in thefollowing stages

1. Mixture composition is defined. Three type ofmixtures are produced in the laboratory:

• Reference mixture,• Mixture with Sasobit,• Mixture with CECABASE,

2. The primary compaction temperature is defined foreach mixture. The compaction temperature of 155oCis defined for the reference mixture for VG 30bitumen and additionally the temperature of 135 oCis applied. Compaction temperatures of 115 oC, 125oC, and 135 oC is defined for the modified mixture.Three different mixtures are prepared of mixtures ofreference HMA and WMA: a. one with no curing, b.one with 2 hour curing at compaction temperature, c.one with 4 hour curing at compaction temperature,

3. Compaction is performed for test samplesa. one sample with the Gyratory compactor,b. two samples with the Marshall hammer.

4. Testing is performed for:a. bulk density,b. stiffness modulus,After determining the stiffness modulus for samples

from the gyratory compactor, the necessary curingtime is defined and compaction for the other WMAmixtures at 115oC and 125oC is performed after atcuring the O defined time.

5. Evaluation of obtained test results,a. Comparison of the results with reference HMAmixture,b. Comparison of the results between impactcompaction and gyratory compaction,c. Evaluation of the impact of curing.

IV. METHODALOGY

t

Mixture Composition

General Sasobit Cecabase

Compaction Temperature Compaction Temperature

135͘͘͘º C 155º C125º C 115º C135͘͘͘º C

Curing Curing Curing

0h 2h 4h 0h 2h4h2h

Marshall Hammer Gyratory Compactor

TestingTesting

Density Stiffness

Evaluation of the Result

StiffnessDensity

Compaction

4.1 Experimental plan for mixture testingA. Curing

Curing, when performed, was carried out in a forceddraft oven (with air circulation) at compactiontemperature according to AASHTO PP2 (61). Themixture was placed on a shallow pan ofapproximately 3 cm thickness and stirred every 1hour. The stirring process took approximately 2minutes.



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B. CompactionCompaction was performed according to the

desired method: Marshall (impact) compaction.Compaction at desired temperature with 50 blowsfrom each side; Gyratory compaction. Compaction atdesired temperature with 200 gyrations at 600kN for1.25ºangle. Moulds of 100mm diameter were used.

Fig 4.1 Principle of gyratory compaction

Different compaction energies were applied in orderto examine mechanical properties at differentcompaction levels and to determine the compactioncharacteristics with gyratory compactor. Compactiontemperature of 155oC for reference HMA was chosenaccording to EN 12697-35 (85) for bitumen VG 30.An additional specimen with Marshall hammer wasprepared at 135oC. Both WMA products werecompacted at three different temperatures: 135 oC,125 oC, 115 oC.

C. Curing of HMA

At first the effect of curing of HMA wascompared between the specimens compacted with theMarshall hammer and gyratory compactor. This wasdone in order to determine whether curing has adifferent effect on these compaction methods. Thecompaction results show that the number of air voidshas a slight tendency to decrease with longer curing,but the effect was minor and is considered not toinfluence further testing. The results of stiffnessmodulus for these specimens are presented in Figure48. It can be seen here that the stiffness modulus

results for gyratory compactor was significantlylower than for Marshall hammer in all cases. This isprobably due to the higher density of gyratory cores.However, good linear correlation of both compactionmethods could be established meaning that curing hasthe same effect of hardening on both methods ofcompaction. The linear increase of the stiffnessresults also proves why there is no necessity toperform curing when evaluating conventional HMAas the results would remain with the same ratio onewith other even after curing.

Fig 4.2 Correlation of stiffness modulus for Marshallhammer and gyratory compactor

V. Indirect Tensile Strength Test

5.1.Bulk Density

The maximum density for the mixture wasdetermined as an average of two results for controlmixture and it is 2532 kg/m3. The results of bulkdensity for specimens compacted at differenttemperatures with Marshall hammer and gyratorycompactor are shown in Figure 5.1.a. and Figure5.1.b



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5.1.a Bulk density at differentcompaction temperatures for Marshall specimens

5.1.b Bulk density for different compactiontemperatures for gyratory specimens

Production and compaction temperature, thecomparison between bulk density of HMA atreference temperature and WMA technology atdifferent temperatures can be a way to determine theoptimum compaction temperature for the specifictechnology. The results between the compactionmethods do not correlate which is probably due todifferent compaction energies used. The density ofthe reference HMA at 155oC for gyratory specimenswas lower than for WMA whilst for Marshallspecimens it was higher in all cases. This can beexplained with the lower viscosity of binder, whichallows further densification when continuing to applycompaction force. The temperature sensitivity of eachcompaction method could be another explanation.

Whilst the Marshall hammer historically is proven tobe very sensitive, the gyratory compactor isspeculated to be insensitive to temperaturechanges(44). However, it must be noted thatnumerically the difference between all of the WMAspecimens and HMA, except Marshall at 115oC, isminor and the cores can be attributed to have almostthe same density. The small variety in results alsoexplains the decrease in Sasobit density after raisingthe temperature from125oC to 135oC, as it can beattributed to statistical error in test method. It must benoted that the compaction method itself can beimportant regarding this research, as it is consideredto be especially important for SMA asphalts tosimulate the actual field compaction. The finaldensity and mechanical characteristics for this type ofasphalt depends on the aggregate orientation and theinterlocking of the mineral skeleton and gyratorymovements allow particles to re orientate themselvesthus reproducing the actual in-situ compaction moreadequately than by impact compaction of Marshallmethod. It must also be noted that in actual fieldcompaction, a temperature of 155oC is considered tobe very high and usually compaction takes place atlower temperatures. Therefore, it can be concludedthat the compaction temperature can be reduced to atleast 125oC if not to 115oC without losing thecompactibility and similar density can be achievedwith the same compaction effort. Densificationcharacteristics The gyratory compactor allows anillustration of how the density of the asphalt mixtureincreases with increasing number of gyrations. Thecompaction in percent of maximum density f or bothWMA products and the control mix at differenttemperatures is illustrated. All specimens in this casewere compacted after 2 hour of curing. It requires toverify three different compaction levels – N.Ensuring that the density at these compaction forcesdoes not exceed the Super pave requirements makesit possible to design mixtures that do not exhibitclassic tender mix behavior and do not compact todangerously low air void contents under traffic action(77). The necessary compaction parameters at theselevels depend on the transport intensity of the road. Itwas assumed that the highest intensity (>30 ESALs)would be applied tothe section with the tested mixture, so compactionparameters at 9, 125 and 205(reduced to 200 at this



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study) gyrations are required. The results that arelisted in Table 22 show that the density at designedcompactive effort is higher than the required for 1.1%for the Reference mix and for1.4% by average forWMA. The initial and maximum compaction levelsare within the necessary range. This means that noexcessive hardening will occur at traffic much greaterthan the designed.

Fig 5.1.c Compaction characteristics fromgyratory compactor of Sasobit (left) andCecabase (right) at different temperatures

It is visible that the compactibility for temperaturesof 125oC and 135oC is almost the same for Cecabaseand similar to Sasobit. It is also very similar to thereference mix at temperature of 155oC, the onlydifference being that the density continues to increasein the last quarter of the compaction for WMA whileit had almost already reached its final density forHMA. This may mean that a higher density can beachieved for WMA than for HMA by continuing toapply compaction force at these temperatures. It canbe explained through reduction of binder viscosity.However, as stated above, numerically the differenceis small and could be very well a statistical error.However, WMA at 115 oC has noticeably differentcompaction characteristics for both products. Thedensity at the first part of compaction is significantlyhigher than for other samples and reaches its finalbulk density at about 100gyrations for Sasobit and 70 gyrations for Cecabase.After this point the density remains almost the samedespite a continued compaction effort. It isconsidered that compaction energy of about

70gyrations simulates the actual field compaction,meaning that with this compaction effort, higher in-situ density than for HMA would be achieved. It isalso important to note that this final density is thesame as for HMA at 200 gyrations, meaning that thatsimilar final level of density can be achieved withless effort. This behavior could be attributed to thereduced hardening of binder, because of a lowercuring temperature. But after reaching the limit ofworkability due to binder viscosity at thistemperature, the densification does not continuedespite applied force. To verify this statement,additional testing with uncured specimen preparationin a gyratory compactor would be required. Thisfinding collaborates to some extent what Germanfield trial reported in 6.2 Compaction, and ifconfirmed in other field trials, this can be importantin determining the necessary compaction effort forWMA. If the desired density can be reached withfewer roller passes than for HMA, there is no need tocontinue the densification, thus reducing the pavingcosts.

5.2 Stiffness

The stiffness modulus is determined by theindirect tensile test method in accordance with theEN 12697 26,annex C (69) standard method. It wascarried out at 20oC, with target horizontaldeformation of 5 μm and rise time of 124 ms.Poisson’s ratio of 0.35 was used. The scheme ofdetermining the resilient modulus is shown on Figure5.2. All specimens were prepared after 2 hours ofcuring except of the Marshall core at 135Cwhich wascompacted uncured.

Figure 5.2: Type of the cylindrical specimen load



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The results of testing are presented in Figure 56 forgyratory specimens and in Figure 5.3 for Marshallcores. The results of gyratory specimens show a clearincrease in stiffness modulus for Sasobit, compactedat temperatures of 135oC and 125oC and a similarresult at 115oC as the reference mix. The results ofRediset WMX are lower than for control in alltemperatures. The stiffness for both WMA show atendency to decrease when lowering the compactiontemperature.

Figure 5.3: Stiffness modulus test results forgyratory specimensFor Marshall samples, stiffness modulus for bothWMA showed a tendency to raise stiffness between135oCand 125oC which is more likely to be test errorthan actual performance of these mixtures. Theresults of both WMA are lower than for referencemix at 155oC, but higher than mix compacted at135oC, with an exception of Cecabase at 115oC.However, as the control mix of 135oC was not curedit is not correct to compare the results directly, butfrom the previous analysis of curing times it can beroughly assumed that this mix would have gainedapproximately 1000 MPa of stiffness after 2 hours ofcuring. This would mean that the stiffness of Sasobitwould still be higher, but for Cecabase it would belower than for reference at 135oC.

Figure 5.20: Stiffness modulus test results forMarshall specimens

A comparison between stiffness modulus of Marshalland gyratory cores did not show good correlation asthe control mix at 155oC had a different relativevalue in comparison with WMA mixtures. Therefore,the judgement of stiffness modulus against referencemix depends not only on the type of additive usedand the compaction temperature, but also on thecompaction method and the applied compactionforce. The choice of an adequate laboratorycompaction method proves to be significant inevaluation of the WMA technologies. Nonetheless,the results showed that the stiffness of Sasobit washigher than for Cecabase at all compactiontemperatures for both methods. It is also clear that thedifference between stiffness of both WMA at 135oCand 125oC is not significant and therefore it can beassumed that lowering the temperature to at least125oC is possible with maintaining the highestpossible stiffness modulus for both WMA products.A further temperature reduction is considered tolower the stiffness of mixture.

II. TEST RESULTS

Densification data showed contrasting evidence fromtwo different compaction methods. While the WMAsamples that were compacted with gyratorycompactor had better density than the control HMA,for compaction with the Marshall hammer it was the



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other way around. However, the difference betweendensity of the WMA and HMA was small in all caseswith exception of Marshall samples at 115oC, whichhad significantly higher number of air voids. Thissuggests that use of both tested WMA productsallows a reduction of the compaction temperature atleast to 125oC, but still giving a similar density asHMA. Even more – analysis of gyratory compactiondata suggests that less compaction force may berequired to reach the same density and withapplication of further compaction higher density maybe attained than for HMA. Sasobit showed betterstiffness modulus results than Cecabase and both ofthese products gave best relative performance forsamples compacted at 125oC. Analysis of stiffnessmodulus for WMA compared to HMA depends onthe compaction method used.

VIII. EMERGING FUTURE

1.Evaluation of asphalt concrete (AC) and other typesof asphalt mixtures with WMA technology.

2.. Since results in literature research showsignificant differences in test results depending on theaggregate type used, it is necessary to perform testingwith other types of aggregate materials that are usedin local conditions.

REFERENCES

1. Goh, S. W., You, Z. P., and Dam, T. J. V. (2007).―Laboratory Evaluation andPavementDesign for Warm-mix Asphalt.‖ Proceedings ofthe 2007 Mid-ContinentTransportation.

2.Hurley, G. C. and Prowell, B. D. (2006c). ―Evaluationof Potential Processes forUse in Warm Mix Asphalt‖, Journal of the Association ofAsphalt PavingTechnologists, 75,41-90.3. Institute, Asphalt. Asphalt handbook MS-4 7th edition.USA : Asphalt Institute,2007, pp. 765-767.4. Kandhal, P. S. NCAT Evaluates Warm Mix Asphalt.National Center for AsphaltTechnology, Asphalt.5. Lee, Robert., A Summary of Texas' Experience withWarm Mix Asphalt.Shreveport,LA : Presentation at Louisiana Warm-Mix Demonstration,2008.6. Sampath, A. (2010). Comprehensive Evaluation of FourWarm Mix Asphalt Mixture

Regarding Viscosity, TensileStrength, Moisture Sensitivity,Dynamic Modulus andFlow Number. University of Iowa: Master Thesis.7. Sargand, Shad, et al.Performance Assessment of WarmMix Asphalt (WMA)Pavements. Ohio : Ohio Department of Transportation,September 2009. TechnicalReport.8. van de Ven, M.F.C., Jenkins, K.J. and Bahia, H.U.Concepts used for developmentof bitumen specifications. Sun City :s.n., 2004. Conferenceon Asphalt Pavements forDouth Africa.Vol. 8.only development of Europespecifications (Section 2.1.) used inthe thesis.9. Van der Poel, V., A general system describing thevisco-elastic properties of bitumenand its relation to routine test data. s.l. : Shell Bitumen,1954, J. Appl. Chem., Vol.No.4, pp. 221-236.10. Walker D. (2009). ―Gaining Experience with WarmMix Asphalt.ǁ The OnlineMagazine,Asphalt.11. Zaumanis, M. (2010). Warm Mix AsphaltInvestigation. Riga TechnicalUniversity: Master Thesis

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