Analysis of cleaner technologies based on waxes and surfactant additives in road constructionMiguel Pérez-Martínez a,Fernando Moreno-Navarro a,Jesús Martín-Marín a,Carolina Ríos-Losada b,M a Carmen Rubio-Gámez a,*a Laboratorio de Ingeniería de la Construcción,University of Granada(LabIC.UGR),E.T.S.Ingenieros de Caminos,Canales y Puertos,Ed.Politécnico,Avda. Severo Ochoa,s/n,C.P.18071Granada,Spainb ServiàCantó,Spaina r t i c l e i n f oArticle history:Received11April2013 Received in revised form4September2013Accepted10September2013 Available online7October2013Keywords:Warm mix asphaltCleaner productionTriaxial testFour point bending testControl emissionsFuel consumption a b s t r a c tThe manufacture of hot mix asphalt for road construction is associated with a high consumption of fossil fuels and a high level of emissions.The use of temperature reduction technologies in the manufacture of warm mix asphalts favors a cleaner production of such materials,and therefore its use has become a major objective in thefield of road engineering.Thus,during the last few years different types of techniques are appearing in order to achieve this objective.This article presents the comparison established in terms of mechanical performance of three processes of temperature reduction technol-ogies in order to select one of them for its manufacture in plant,where control of emissions and fuel consumption have been collected.The results showed that the use of warm mix asphalt technologies with waxes or surfactant additives may not incur in a detrimental effect on the mechanical properties of the pavement.The use of surfactant bitumen in plant is possible to produce warm mix asphalts,reducing the consumption of fuel in the process.Ó2013Elsevier Ltd.All rights reserved.1.IntroductionRoad construction is one of the principal works in thefield of civil engineering,and in turn is a major consumer of fossil fuels for the production of asphalt mixtures.The need to adapt this type of production to cleaner processes leads to a search for reducing manufacturing temperature,trying to make it more sustainable and healthy,reducing at the same time the greenhouse gases emissions rates(Rubio et al.,2012)that are so harmful to the environment.Traditionally the asphalt mixtures used in road construction are manufactured at170 C(HMA)(D’Angelo et al.,2008),and are characterized by developing the mechanical properties that guar-antee an appropriate behavior during its life of service(General Management of Roads,2008).On the contrary,during its produc-tion process,the emissions of gases generated,and the fuel con-sumption required are important(Kristjansdottir,2006).As an alternative to HMA’s,during the last few years new processes have been appearing in order to reduce the manufacture temperature.Within these temperature reduction technologies,three types of mixtures can be distinguished by the temperature range of manufacture,warm mix asphalt WMA(100 C e140 C),half warm mix asphalt HWMA(60 C e100 C)and cold mixtures(0 C e40 C) (EAPA,2010).Discarding cold mixtures due to their lack of use out of surface patches rehabilitation,the reduction is achieved by the application of different processes and technologies,mainly dis-tinguishing between three for the WMA,the foaming process and the use of organic or chemical additives(Zaumanis,2010),and two for the production of HWMA,the use of emulsions and eventually foamed bitumens(Rubio et al.,2013).In the case of HWMA’s,not only has been proved that the reduction of emissions and fuel consumption is a fact(Rubio et al., 2013),but also that the mechanical performance achieved by this type of mixtures is not as satisfactory as it was desired(Punith et al., 2013).On the other hand,WMA’s have shown a better mechanical performance than HWMA and comparable to HMA(Reyes-Ortiz et al.,2009),reducing at the same time the consumption of fuel and greenhouse emissions in the manufacturing process(Hamzah et al.,2010).*Corresponding author.E-mail addresses:fmoreno@ugr.es(F.Moreno-Navarro),crioslo@fcc.es(C.Ríos-Losada),mcrubio@ugr.es(M a C.Rubio-Gámez).Contents lists available at ScienceDirect Journal of Cleaner Productionjournal homep age:www.elsevi/locate/jclepro0959-6526/$e see front matterÓ2013Elsevier Ltd.All rights reserved./10.1016/j.jclepro.2013.09.012Journal of Cleaner Production65(2014)374e379Based on the number of advantages associated to WMA mix-tures(D’Angelo et al.,2008),which result in environmental(lower emissions),economical(cost savings and lower energy consump-tion)and constructional benefits(better workability and larger compaction window,greater hauling distances and less opening time to traffic)this research compare three WMA technologies for reducing the manufacture temperature of conventional hot mix asphalts.Thefirst is one of the most common additives used for this purpose,the organic waxes,which are aliphatic hydrocarbons of long-chain produced by the Fischer e Tropsch process(Wax,2005). Meanwhile as growing alternative,surfactant additives are an en-ergetic reducing agent allowing the manufacture of WMA to a reduced temperature while maintaining their mechanical proper-ties,the addition was considered in two different ways,mixing the bitumen and the surfactant in plant before adding to the mixture (dry process),and a surfactant modified bitumen(wet process) blended in refinery to compare their influence.This paper shows a laboratory level characterization of an asphalt concrete AC16S mixture for the surface course(EN13108-1,2008)under three temperature reduction technologies.Based on the results obtained,one of the mixtures was chosen to adapt a HMA plant for the production of WMA mixtures and measure the emissions and fuel consumption during the manufacturing boratory works on the mixtures was based on Marshall test,water sensitivity test,triaxial test and four point bending test established the parameters to select the most appropriate mixture for being produced at bigger scale.During the manufacturing process in plant measurement of the emis-sions and fuel consumption of a HMA and the WMA were taken. Finally,the main the conclusions obtained from the analysis of results are exposed.2.Materials and methods2.1.Materials2.1.1.AggregatesAn AC16S(EN13108-1)mixture,which is found in roads and highways all over the world,was used to carry out the study.The aggregates were porphyry for the coarse fraction(12/18and6/12),and a combination of porphyry(0/6)and limestone(0/4)for the fine fraction.Moreover,thefiller employed was calcium carbonate. Table1lists the aggregate properties.The aggregates combination by percentage is shown in Table2, where the gradation of the mixture(Fig.1)was kept constant for all the mixtures developed at lower temperature and with different additives.2.1.2.BitumensFour different binders have been used for the attainment of the objectives of the investigation.Thefirst binder used was conven-tional50/70,and besides being used alone,it was the base for the other three bitumens.50/70bitumen,modified with an organic surfactant additive was used as second binder in order to improve its workability at lower temperatures.The bitumen modification was made in labo-ratory and the percentage of additive used was chosen following the manufacturer recommendations(1%over bitumen weight).The third one was modified50/70bitumen with surfactant products to improve the wettability of the binder as an alterna-tive to the conventional for the reduction of temperature.The last binder used was50/70bitumen modified with microcrys-talline waxes produced by the Fischer e Tropsch process as addi-tive.In both cases,the bitumen was modified in refinery.Table3 describes all the mixtures designed and the additives used,as well as the temperature reduction applied on their manufacture process.2.2.MethodologyThe methodology followed is composed of two phases,labora-tory works and the manufacturing industrial process in plant,being thefirst one divided in three steps and focused on the analysis of the working formula for its adaptation to the manufacture process under different temperature reduction technologies.And the sec-ond one based on the adaptation of a hot mix asphalt plant for the production of a warm asphalt mixture.In laboratory,firstly the optimum bitumen content needs to be determined for the conventional mixture of reference without additives.Based on the values of air voids(%),deformation(mm) and stability(kN)of the Marshall test(NLT-159,2000)the optimumTable1Reference values of the aggregates and mineral dust.Test/aggregate type Coarse aggregate Fine aggregate FillerGrain size(EN933-1)/(EN933-10)Sieves(mm)12/18Porphyry6/12Porphyry0/6Porphyry0/4Limestone Carbonate(CaCO3)24.4100100100100e1684100100100e8162100100e4158792e21160681000.51129301000.251121201000.125e e e e970.0630.50.911.81187Sand equivalent(EN933-8)(>50)4554Bulk density(EN-1097-3)(0.5e0.8Mg/m3)0.7Percentage of fractured face(EN933-5)(100%)100100Flakiness index(EN933-3)(25)1625Resistance to fragmentation(EN1097-2)(20)1515Cleaning(organic impurity content)(UNE146130,Annex C)(0.5%)0.50.5Particle density andabsorption(EN1097-6)r a(Mg/m3) 2.73 2.73 2.77 2.71r SSD*(Mg/m3) 2.70 2.71 2.72 2.67r RD(Mg/m3)2.69 2.70 2.70 2.65Water absorption after immersion(%)0.600.400.910.77M.Pérez-Martínez et al./Journal of Cleaner Production65(2014)374e379375content of binder was set,using the same in all the WMA ’s mix-tures.Furthermore,several test were carried out to assess the mechanical behavior of the conventional mix:water sensitivity test (EN 12697-12,2009),cyclic triaxial compression test (EN 12697-25,2006,method B)in order to study the plastic deformations,and the four point bending fatigue cracking test (EN 12697-24,2013,annex D)to assess the long term response of the mixture.In the second stage the Marshall test,with the optimum bitumen content determined,is undertaken for the three mixtures with temperature reduction technology at 140 C to study their Marshall stability (kN),voids content (%)and deformation (mm).The mechanical performance was also evaluated in the WMA mixtures applying the same test procedures and conditions as in the first stage for the Reference Mix.Finally,a comparative analysis of the four mixtures is developed.With this purpose their stability (kN),retained strength against water (%),creep modulus (MPa)and fatigue life parameters are compared.Based on this analysis,the warm mix asphalt technology with the best overall performance will be selected for its adaptation to the plant production and to construct a road section test.In plant works are centered on the adaptation of a HMA plant for the manufacture of a WMA mixture.For this purpose a HMA and WMA mixtures are produced,measuring during the process the emission of pollutants,as well as the consumption of fuel required.In the case of the control of emissions,the methodology was similar to the one followed by Rubio et al.in (2013).In-point source emissions were measured (Fig.2);humidity,wind,and temperature data were also collected to assure the spreading in similar atmospheric conditions for HMA and WMA gases to compare the results.The parameters evaluated were the Combustion Gases (CO,NO x ,O 2,CO 2)measured by a multi-parameter analyzer (TESTO MXL),the Total Organic Carbon (TOC)through a flame ionization detector (FID,M&A PT)and the emission of Particles (collected in a 47mm filter and subsequently calculated in the laboratory by gravimetry).To complete the investigation,the consumption of fuel used is also measured.3.Analysis of results 3.1.Marshall testThe Marshall test results in regards to the optimum bitumen content is shown in Table 4.As can be seen,the values of me-chanical resistance developed by the mixtures in terms of stability and deformation are slightly lower in the case of warm mix as-phalts produced at lower temperature.Furthermore,in the case of surfactants additives (both dry and wet process)a decrease in terms of density is attained by the mixtures as well as an increased in the air voids content.This is due to this type of additives,which produce an improvement in the adhesiveness aggregate/binder and a better wetting of the aggregate,but no change in the viscosity of the bitumen,and therefore it may have certain dif ficulties associ-ated to perform the compaction of the mixture at lower tempera-ture.In the case of wax bitumen,this fact does not occur as waxes modi fied binder viscosity and consequently the values of density and air voids are not affected by reducing the temperature of manufacture and compaction.3.2.Water sensitivity testA new set of 6specimens per mixture using the optimum bitumen content were produced to perform the water sensitivityTable 3Studied mixtures and bitumens used.DenominationBitumenAdditive natureAddition processMixturemanufacture temperature ( C)Reference Mix 50/70Nonee 160Dry Surfactant Mix50/70þ1%additive Surfactant Dry 140Wet Surfactant MixSurfactantmodi fied 50/70Surfactant Wet 140Wet Wax MixWax modi fied 50/70Microcrystalline waxesWet140Fig.1.Aggregate gradation for asphalt mix type AC-16S.Table 2Aggregates combination by percentage.Aggregate fraction PercentagePorphyry 12/1815Porphyry 6/1244Porphyry 0/620Limestone 0/415Calcium carbonate filler6Fig.2.Simpli fied HMA plant distribution and in-point source.Table 4Marshall results and optimum bitumen content.ParameterReference Mix Drysurfactant Mix WetSurfactant Mix Wet Wax Mix Optimum bitumen content (%) 4.8 4.8 4.8 4.8Bulk density (kg/m 3)2423236423772437Marshall stability (kN)10.7079.4788.2049.053Marshall def.(mm) 2.3 2.9 3.5 3.7Vm (%) 4.0 5.1 4.6 3.1VMA (%)15.316.115.614.5M.Pérez-Martínez et al./Journal of Cleaner Production 65(2014)374e 379376test(EN12697-12,2009).Table5resumes the values of strength obtained in the test.Once again the resistance values,in this case indirect tensile strength,shown by warm mix asphalts are slightly lower than those of the Reference Mix,perhaps indicating that may be inter-esting to increase the energy of compaction when using this type of mixtures,but higher than the ones obtained by Oliveira et al.(2013) with and without rubber.However,the retained strength(ITSR) shown by warm mix asphalts is higher,and therefore can be considered that such materials will be less affected by the action of water.This is because,in the case of surfactant additived mixtures to the improvement of adhesiveness that they generate(not only improving the coating of the aggregate,but also acting as its stimulator).Meanwhile,in the Wet Wax Mix may be related to its compaction improvement and its lower void content.3.3.Cyclic triaxial compression testPlastic deformations were evaluated by the cyclic triaxial compression test(EN12697-25,2006,method B),taking at the same time the service stresses and strains into account by means of a confining load.The conditions selected involved the com-bined application at a constant temperature of40 C of a confining load of120kPa and another cyclic sinusoidal out-of-phase axial loading of300kPa at a frequency of3Hz during12,000load cycles.The creep modulus and permanent deformation parame-ters for each mix were calculated.Table6shows the triaxial test results.The values obtained for the creep modulus indicate that the most resistant mix against plastic deformations is the Wet Wax Mix.The Wet Surfactant Mix behaves similar to the Reference Mix, even manufactured at lower temperature and the permanent deformation experienced only varies in0.03%.In the case of the Dry Surfactant Mix,results showed an increase in plastic deformation, probably due to a lack of mix compaction(as it is showed in its void content).3.4.Four point bending testTo perform the test,specimens of408Â50Â50mm with sawn faces were manufactured,and a sinusoidal waveform load was applied.The tests were carried out at20 C,in strain control mode and at a frequency of10Hz.The mixtures were tested in six different strain amplitude levels,250m m/m;200m m/m;175m m/m; 150m m/m;125m m/m and100m m/m Fig.3shows the potential fatigue laws derived from the four-point bending test performed in the4types of mixtures tested.As can be observed,independently of the warm mix technology used,the fatigue behavior of the mixtures evaluated is very similar, which coincides with thefindings of other researchers(Jones et al., 2010).On the other hand,the correlation coefficients of the fatigue laws obtained are high,indicating a uniform mechanical behavior of the warm mix asphalts.This aspect agrees with the results ob-tained by Johnston et al.(2006),which showed that additive did not affect the homogeneity of its long-term mechanical behavior.Moreover,the fatigue behavior of the Dry and Wet Surfactant Mixes is very similar,regardless of the method used to add the additive.Meanwhile,it should be noted that the fatigue behavior of the Wet Wax Mix is slightly different.At higher strain amplitudes fatigue life is smaller,while for lower strain amplitudes it increases in relation to the other mixtures evaluated.This behavior is typical of more rigid materials,aspect which is supported by the results obtained in the triaxial test,where the Wet Wax Mix showed a low rate of permanent deformation(which means that is a more rigid material).Table6Triaxial test results.Parameter ReferenceMix DrySurfactantMixWetSurfactantMixWet WaxMixCreep modulus(MPa)178.57153.45175.95202.70Permanentdeformation(%)1.68 1.96 1.71 1.48Table5Water sensitivity test results.Parameter ReferenceMix Dry SurfactantMixWet SurfactantMixWet Wax MixITSR(kPa)dry group2030.01469.01749.71464.3ITSR(kPa)wet group1741.71281.01575.71357.3ITSR(%)85.587.290.192.7Fig.3.Fatigue behavior of the studied mixtures at strain controlled test(T¼20 C,f¼10Hz).M.Pérez-Martínez et al./Journal of Cleaner Production65(2014)374e3793773.5.Control of emissionsData collection for controlling emissions took place during the process of manufacturing the conventional HMA at 176 C and the mixture Wet Surfactant Mix selected as WMA at 140 C.Table 7resumes the results obtained.Fig.4shows the emissions results obtained from the manufacturing of WMA and HMA mixtures.They have been compared with the HMA and HWMA results from Rubio et al.(2013).In terms of CO 2and NO x WMA slightly reduces the emis-sions,while in TOC and CO the values obtained have been increased,which was not expected.It can be appreciated how HMWA reduce the emissions in comparison with the hot asphalt mix while no reduction is appreciated between the WMA and the hot asphalt mix.3.6.Fuel consumptionTable 8indicates the results from the measure of the fuel needed for the manufacture of HMA and WMA mixtures.According to the values obtained in plant,the consumption of fuel for the manufacture of WMA is 35%lower.Decreasing the flame modulator by 60%would save fuel.The increase of the time of mixing by 5s is to guarantee the good cover of the aggregates;it induces to a decrease in production but the savings on fuel consumption balances it.4.ConclusionsIn this paper,mechanical performance testing on three asphalts mixtures modi fied under different temperature reduction tech-nologies was conducted.The aim of the research was to select one of the processes to adapt a HMA plant into the manufacture of WMA mixes,and measure the emissions and consumption of fuel during the process.The results obtained during the investigation led to the following conclusions:e The use of both,surfactants and waxes,as additives can reduce the manufacture temperature of asphalt mixtures to 140 C,providing materials with similar mechanical behavior than the hot mix asphalt.e In the case of surfactant additived mixtures,its incorporation into the mixture directly through the bitumen modi fied intheFig.4.Gases emissions of HMA,WMA and HWMA (Rubio et al.,2013).Table 7Emissions data collected.ParameterHMA WMA Manufacture temperature 176 C 140 C CO (ppm)616.8635.5NO x (NO 2)(ppm)55.653.2TOC (mgC/Nm 3)33.553.2Oxygen (%)16.516.5CO 2(%)2.5 2.6Speed (m/s)15.414.6Humidity (%)5.85.7Table 8Fuel consumption.ParameterHMA WMA Manufacture temperature 176 C 140 C Flame modulator 95%33%Time of mixing (s)3540Production (tn/h)200180Fuel consume (l/tn)5.83.8M.Pérez-Martínez et al./Journal of Cleaner Production 65(2014)374e 379378refinery plant(wet process),seems to offer further guarantee of success than incorporating it directly on the mixture(dry pro-cess).Although not offering an improvement in the compaction process of the mixture,the improvement of adhesiveness in the mixing offered by this additive allows manufacturing such materials at lower temperatures while maintaining their me-chanical properties.Thus,retained resistance values are pre-served against the action of water,plastic deformation,and fatigue behavior,showing how the use of this type of additived bitumens may offer bituminous mixtures with similar charac-teristics to HMA,assuming an environmentally cleaner alter-native to road construction.e In turn,wax modified bitumens let ensure acceptable compac-tion of the mixes at lower temperatures,offering a good response to the action of water and plastic deformation,as well as good fatigue life.Based on the results obtained in this research,this technology presents itself as an interesting alter-native for the environmental improvement in the production of asphalt mixtures.e Among the temperature reduction technologies studied,thebest results provided,in terms of mechanical performance is the Wet Wax Mix.Nevertheless,the Wet Surfactant Mix has also shown good overall mechanical response.So,when deciding which technology could be used for the next phase of the investigation,surfactant modified bitumen in refinery could be considered if it results economically and more competitive than using waxes.e In relation to the pollutant emissions,data collected do notshow a decrease as expected.On the other hand,other studies where a higher decrease of temperature takes places(as HWMA manufacturing process)provide a more significant reduction of emissions.In this sense,to achieve a better knowledge and significant conclusion more research needs to be develop about emissions during the manufacturing process of asphalt mixes with reduction of temperature(evaluating other asphalt plants and WMA technologies).e Fuel consumption can be decreased by35%respect to the pro-duction of HMA due to the reduction of theflame to dry the aggregates.When reducing this temperature of drying the time of mixing may be increased,but the savings in fuel can be considerable.AcknowledgmentsAuthors would like to acknowledge the Ministerio de Economía y Competitividad for its assistance in the project:INMBERS:Investigación de nuevas mezclas de baja energía para rehabilitación superficial.IPT-420000-2010-12.ReferencesD’Angelo,J.,Harm, E.,Bartoszek,J.,Baumgardner,G.,Corrigan,M.,Cowsert,J., Harman,T.,Jamshidi,M.,Jones,W.,Newcomb, D.,Prowell, B.,Sines,R., Yeaton,B.,2008.Warm-mix Asphalt:European Practice.Report FHWA-PL-08e 007.Office of International Programs,U.S.Department of Transportation, Washington DC,USA.EAPA,European Asphalt Pavement Association,January2010.The Use of Warm Mix Asphalt.EAPA position paper (accessed09.10.12.).EN12697e12,2009.Bituminous Mixtures.Test Methods for Hot Mix Asphalt.Part 12:Determination of Water Sensitivity of Bituminous Specimens.European Committee for Standardization,Bruxelles,Belgium.EN12697e24,2013.Bituminous Mixtures.Test Methods for Hot Mix Asphalt.Part 24:Resistance to Fatigue;Annex 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