Crumb Rubber Modified Asphalt Concrete For Low Noise

2y ago
33 Views
2 Downloads
1,003.73 KB
17 Pages
Last View : Today
Last Download : 2m ago
Upload by : Baylee Stein
Transcription

Crumb Rubber Modified Asphalt Concretefor Low Noise SurfacesMassimo Losa, Pietro Leandri, Patrizia RocchioUniversity of Pisa, Department of Civil Engineering (DIC)Largo Lucio Lazzarino, 1 – 56122 Pisa (Italy)losa@ing.unipi.it, pietro.leandri@ing.unipi.it, patrizia.rocchio@ing.unipi.itABSTRACT.The principal advantage of introducing some percentages of crumb rubber inproduction of asphalt mixtures is related to pavement environmental sustainability, since thisprocess allows to recycle a significant amount of an industrial waste and, in some specificcases, to reduce tire/road noise emissions; there are some other not unanimously recognizedadvantages related to this process that are the improvement of asphalt mixture mechanicalproperties and durability as well as friction on pavement surface. This paper reports on aresearch project carried out to evaluate the advantages of using crumb rubber inconstruction of low noise gap graded asphalt concrete surfaces, specifically designed toreduce rolling noise by optimizing surface texture. The study also aimed to define themechanical and functional performances of the mix obtained by using the wet process inorder to assess its potential for use as viable alternative to other low noise asphalt surfacesaimed to improve pavement sustainability by reducing environmental, social and economicimpacts. Results of laboratory and on site tests, carried out on one specifically built fieldtrial, clearly show this mix can have optimal mechanical and functional performance as wellas it can reduce tire/road noise and warrant greater durability of wearing layers; thisconsidering, crumb rubber modified asphalt concrete can be classified as a constructionmaterial that can enhance the three dimensions of sustainability.KEYWORDS:environmental sustainability, low noise asphalt surface, wet process, crumbrubber, pavement sustainabilityInformation about research of the paperInformation about research of the paper

2Crumb Rubber Modified Asphalt Concrete for Low Noise Surfaces1. IntroductionScrap tires form a major part of the world’s solid waste management problem;in addition, market groups forecast that in the next years post consumer tires willincrease. At the same time, the increasing demand for road transportation hascaused serious problems of noise pollution due to vehicular traffic.These are only two of the problems resulting from the continuous increase intransportation demand, which has prompted the international scientific communityto search for innovative solutions that allow to use crumb rubber tire in asphaltpavements.The advantage of using crumb rubber in the production of asphalt mixtures isnot limited to the improvement of road sustainability, but it can be related to animprovement of mechanical properties or a reduction of noise emissions, inaddition an increase of friction ([1], [2] and [3]). At the present time, theinternational scientific community is not unanimous in judging the positive effectsof crumb rubber in terms of reduction of noise emission. According to Sandbergand Ejsmont [4] there is no evidence that the insertion of small quantities of crumbrubber within asphalt mixtures can allow to significantly reduce tire/road noise.The use of crumb rubber in asphalt pavements dates back to many years ago ([5]and [6]). In the Wet process, crumb rubber and bitumen are mixed and left to reactat high temperatures: the final result is known as “Asphalt Rubber (AR)” ([5], [6]and [7]). The AR is used as a modified bitumen in the production of porous asphaltconcretes (open graded) and gap graded asphalt concretes characterized by binderpercentages ranging between 7 and 9%, to which corresponds a crumb rubberpercentage of 1 – 1.5% on the mixture weight. Moreover, for the need of allowingthe reaction between bitumen and crumb rubber ([8], [9] and [10]), in the Wetprocess it is necessary to use specific mixers for production of the modified asphaltat high temperatures.This paper reports on research conducted to evaluate the feasibility of using ARin the construction of low noise gap graded asphalt surfaces. The study also aimedto define the mechanical and functional performances of the resulting mix in orderto assess its potential for use as a viable alternative, in terms of environmentalcompatibility and costs, to low noise open-graded asphalt surface. This mix allowsoptimal mechanical and functional performance, it reduces tire road noise andguarantees greater durability of wearing layer performance; in addition, it isenvironmentally friend, by offering a better life-cycle assessment for scrap tire.

Crumb Rubber Modified Asphalt Concrete for Low Noise Surfaces32. Use of crumb rubber modifier in asphalt mixesThe material widely used in vehicle tires is Styrene-Butadiene-Rubber (SBR)that is a synthetic rubber copolymer consisting of styrene and butadiene. It hasgood abrasion resistance and good aging stability when protected by additives;crumb rubber used in this study comes from mechanical grinding of scrap tires atroom temperature; they are represented by 50% by weight of truck tires and 50%by weight of car tires. Figure 1 represents size gradation of crumb rubber used toproduce gap graded mix, according to the wet processes, overlaid to the typicalCRM gradations for production of the Asphalt Rubber. The size gradation of crumbrubber fulfils the requirements of CRM for the production of Asphalt Rubber [11].10090Percent passing [%]80Crumb rubbermodified7060504030Typical Gradation CRM for AR201000.010.101.0010.00Sieve size [mm]Figure 1. The size gradation of crumb rubber3. Description of experimentThe experiment involved a first step of mix design to define the aggregate grainsize distributions and the optimum asphalt contents to be used in the mix; in thesecond step, laboratory tests were carried out to evaluate mixture performance.The gap graded asphalt mixture produced by the wet process, was utilized for asurface layer, 3 cm thick, laid on a roughly 150 m long test section within the“Leopoldo” research project [12]. This project has the specific aim of improvingroad safety and environmental compatibility.Cores were taken from pavement to check the compliance with the designmixture in terms of aggregate gradation, asphalt content and air void percentage.The in-situ characteristics of the mixture was substantially the same of thelaboratory mixture with regard to the aggregate gradation and the bitumen content;

4Crumb Rubber Modified Asphalt Concrete for Low Noise Surfacesas far as the air void contents of in situ mixture, they were approximately 2% morethan the air void contents of the laboratory mixture.This asphalt wearing course was then evaluated in terms of surfacecharacteristics (friction and texture) and acoustic performance.4. Mix designMix design was carried out by the volumetric method. The optimum asphaltcontent was identified by optimizing the air void contents.4.1. Aggregate gradationPhysical properties of aggregates, determined according to the UNI-EN 10976/7 procedures, are shown in Table 1.Physical proprietiesBasalt 4/6SandMineral FillerBulk Specific Gravity(kg/m3)275326292650Apparent Specific Gravity(kg/m3)286326902650Water Absorption(%)1.390.860.00Table 1. Asphalt binders characteristics10090AggregategradationPercent passing [%]807060Max densityline50403020GradationSpecificationsSieve size [mm - raised to 0.45 power]Figure 2. Aggregate size gradation86.3420.50.250.0630.1250110

Crumb Rubber Modified Asphalt Concrete for Low Noise Surfaces5The grain size distribution of the studied mixture respects the aggregategradation required by the project specifications for gap graded asphalt mixtureswith the maximum aggregate size equals to 8.0 mm (Figure 2).The resulting internal structure of the mixture determined by the discontinuousaggregate grading curve can be appreciated in Figure 3.Figure 3. Internal structure of the mixes4.2. Optimum asphalt content and volumetric properties of the mixtureThe aggregates were mixed with Asphalt Rubber (AR) (Table 2), consisting of20% CRM by weight of binder and the remaining 80% of 50-70 penetration gradebitumen. The optimum asphalt content of the mix was determined by gyratorycompaction, assessing the volumetric characteristics of four mixtures with asphaltcontents ranging from 7.5% to 9.0% (Table 3).In determining the volumetric properties of the mixes, the aggregate absorptionpercentage was assumed to be equal to 1/3 of water absorption, as required by UNIEN 12697-5.From the mix design it is possible to determine the optimum percentage ofbitumen capable of minimizing the void percentage and guaranteeing at thecompaction level Nmax a void volume higher than 2% and at the compaction levelNdesign a void volume ranging between 3 – 5%. From the results obtained it wasselected the optimum bitumen content equal to 8.5%.

6Crumb Rubber Modified Asphalt Concrete for Low Noise SurfacesUnitValueReferencePenetration at 25 CDmm25 – 55UNI EN 1426Softening point, Ring & Ball C 58UNI EN 1427Fraass breaking point C -7UNI EN 12593Flash Point C 250EN ISO 2592Elastic recovery at 25 C% 70UNI EN 13398Resistance to hardening RTFOT (163 C – UNI EN 12607-1)Loss in mass% 0.5UNI EN 12607-1Retained penetration at 25 C% 45UNI EN 1426Increase in softening point C 12UNI EN 1427Table 2. Physical properties of aggregatesAC 7.5 %AC 8.0 %AC 8.5 %AC 9.0 %Number (%)VB(%)Ninitial 1014.0025.9846.132191254774.0211.98Ndesign 506.8119.7965.602374254780.2112.99Nmax 1303.9517.3377.212446254782.6713.38Ninitial 1013.0126.3050.512191251973.7013.28Ndesign 505.8520.2271.092372251979.7814.38Nmax 1303.0217.8383.062443251982.1714.81Ninitial 1012.1926.4453.902197250273.5614.25Ndesign 505.0120.4375.472377250279.5715.42Nmax 1302.1718.0587.962448250281.9515.88Ninitial 1011.7026.8656.432195248673.1415.16Ndesign 504.5420.9278.312373248679.0816.39Nmax 1301.7118.5890.802443248681.4216.87NOTE: AC, asphalt content as percentage of mass of aggregates; VA, air voids; VMA, voids in mineralaggregate; VFA, voids filled with asphalt; Gmb, bulk density of the compacted mixture; Gmm,maximum density of the mix; VG, volume of aggregate, the bulk volume including the aggregatepores; VB, volume of effective asphalt binder.Table 3. Volumetric properties of the mixes

Crumb Rubber Modified Asphalt Concrete for Low Noise Surfaces7In Figure 4 the gyratory densification curve of the studied mixture is comparedto the curves obtained for a dense asphalt concrete 0/8 mm (DAC 0/8) with 5.5%bitumen (50-70 penetration grade pure bitumen) and for a stone mastic asphalt 0/8mm (SMA 0/8) with 7.2% bitumen (50-70 penetration grade polymer modifiedasphalt). The results show that the curve referring to the studied mixture has aslight steeper slope and a higher density than the curves referring to the DAC 0/8and SMA 0/8. This highlights that, at the same compaction temperatures, thestudied mixture shows better compaction properties as compared to DAC 0/8 and toSMA 0/8.1009896Crumb rubber modifiedasphalt concrete94%Gmm9290DAC 0-88886SMA 0-8848280781101001000Number of GyrationsFigure 4. The gyratory densification curves of the studied mixture5. Mechanical characteristics of the mixtureIn order to characterize the mix from a mechanical point of view, IndirectTensile Strength Tests, Resilient Modulus Tests and Fatigue Resistance Tests werecarried out on specimens compacted by the Gyratory Compactor at Ndesign. Theseparameters allow to check both the compliance of the mixture with nationalspecifications for wearing courses and to compare performance of AR withpolymer modified asphalt. Considering the reduced thickness of the layer (30 mm),the rutting performance was neglected.

8Crumb Rubber Modified Asphalt Concrete for Low Noise Surfaces5.1. Indirect tensile strengthIndirect Tensile Strength (ITS) measurements were carried out at thetemperature of 25 C, according to UNI EN 12697-23. ITS values (Table 4) arehigher than the minimum values required by the national standards for gap gradedasphalt mixes to be used as wearing courses. To evaluate moisture susceptibility,the Indirect Tensile Strength Ratio (ITSR) according to UNI EN 12697-12 wasdetermined. This is represented by the ratio between ITS of samples afterconditioning in water (ITSw) and ITS of unconditioned samples (ITSd). The resultsobtained (Table 4) clearly show that no problems pertaining to moisturesusceptibility arise for the studied mix.Mechanical propertiesSampleITSd at 25 C(N/mm2)ITSw at 25 C(N/mm2)10.700.6220.700.7330.780.69Mean value0.730.68St. Dev.0.050.06COV (%)6.48.2SpecificationsITSR(%)ITSd at 25 C(N/mm2)ITSR(%)93.6 0.60 75Table 4. Indirect tensile strength test results5.2. Resilient modulusIn order to evaluate mix stiffness, the laboratory resilient modulus (MR) wasdetermined by the indirect tensile test on cylindrical specimens (IT-CY) accordingto UNI EN 12697-26 Annex C procedure. MR values of the studied mix are shownin Table 5 together with values determined on specimens of a stone mastic asphalt0/8 mm (SMA 0/8), containing 7.2% bitumen (50-70 penetration grade polymermodified asphalt) and compacted according to the same procedure at Ndesign.Results obtained by the studied mix showed an increase of 50% in MR mean valuescompared to the SMA 0/8. This increase can be explained by the greater stiffness ofAsphalt Rubber binder as compared to polymer modified asphalt binder.5.3. Fatigue resistanceThe fatigue resistance was determined by the Indirect tensile test on cylindricalspecimens (IT-CY) according to UNI EN 12697-24 Annex E. Tests have beencarried out at the temperature of 20 C and at a load repetition time equal to 500 ms.

Crumb Rubber Modified Asphalt Concrete for Low Noise Surfaces9Figure 5 shows the plot of fatigue resistance curve for the studied mixturetogether with fatigue resistance curve determined on specimens of a stone masticasphalt 0/8 mm (SMA 0/8), containing 7.2% bitumen (50-70 penetration gradepolymer modified asphalt). The studied mixture shows fatigue resistance curvealmost overlapping with SMA 0/8. This means that Asphalt Rubber binder showsfatigue attitude similar to that of modified asphalt binder. In particular the studiedmixture shows a greater fatigue resistance at high strains and a lower fatigueresistance at low strains compared to the SMA 0/8.MR (MPa)Cycle duration(s)Rise time(ms)Test temperature( C)Studied mixSMA 0/813 0.1124 4203247287223 0.1124 4203521202033 0.1124 4203515285143 0.1124 420Sample38181723Mean value35252367St. Dev.233585COV (%)6,624,7Table 5. Resilient modulus test results1000Initial tensile to Strain - ε0 [με]y 1,258.91x -0.15R² 0.90Crumb rubber modifiedasphalt concrete100y 2,444.82x -0.24R² 0.95SMA 0/810100100010000Cycles to Failure - NfFigure 5. Fatigue resistance curves1000001000000

10Crumb Rubber Modified Asphalt Concrete for Low Noise Surfaces6. Field performancePerformances of the experimental wearing course (Figure 6) were evaluated interms of surface characteristics, texture, friction and acoustic performance only ona short time interval since the pavement was laid in 2010. In order to evaluate fieldperformance over time, factors like real traffic loading and climatic situation shouldbe taken into account, but this short time isn’t enough to draw valid considerationsthat, at this stage, can be only qualitative. The evaluation of acoustical properties ofexperimental road sections was conducted by the Environmental Protection Agencyof Tuscany.Figure 6. Crumb rubber modified asphalt concrete6.1. TextureSurface texture was determined by recording the pavement profiles with amobile laser profilometer.The mobile profilometer was used for continuous recording of the pavementprofile at sampling intervals of 1 mm. MPD values were evaluated from the profile,allowing ETD estimation ([13]) of the entire experimental section. Figure 7 showsthe variation of the texture at different age; the texture is expressed in terms of themean of ETD values over 10 m long sub-sections, together with the MTD thresholdvalue. Over time, the studied mixture shows texture values which are higher thanthe threshold value.Using the profile recorded by the mobile profilometer, we calculated the onethird octave band mean texture spectrum (Ltx) on the wavelength range between 2mm and 250 mm, according to the ISO/CD 13473-4 and 5 procedures.

Crumb Rubber Modified Asphalt Concrete for Low Noise Surfaces111.00.9after 1 month0.8ETD [mm]0.7after 6 months0.60.50.4after 11 8090100 110 120 130 140Distance [m]Figure 7. Texture profilesFigure 8 shows the texture spectra of the experimental wearing courses togetherwith the typical spectrum of a dense asphalt concrete (DAC) with maximumchipping size equal to 12 mm. In order to obtain a low noise asphalt surface capableof reducing tyre/road noise emissions as compared to the noise level of a traditionalasphalt surface, the texture spectrum (Figure 8) should have the followingcharacteristics ([13] and [14]):- the highest Ltx value should be found in the wavelength fields 10 mm;- Ltx values should tend to minimum values in the wavelength fields 10 mm.Texture Level [dB rel. 10 -6 m RMS]45after 1 month42after 6 months39after 11 months36DAC 0-1233Texture wavelength [mm]Figure 8. Texture 0.025.031,540.050.063.010080.012516020025030

12Crumb Rubber Modified Asphalt Concrete for Low Noise SurfacesFigure 8 clearly shows that over time the studied mix fulfils these requirements;in particular the studied mixture shows an increasing macrotexture amplitude atlow wavelengths and a decreasing macrotexture amplitude at high wavelengths. Asdescribed in the following sections, these results were confirmed by themeasurement of rolling noise.6.2. FrictionFriction measurements were carried out by using Skiddometer BV11 equipment.The test was conducted at a speed of 20 km/h, by adequately wetting the pavementin order to simulate the presence of a 1 mm thick water film.By using the PIARC model, and after suitably calibrating the model parametersfor the specific equipment used, the Friction Number (F60) of the InternationalFriction Index (IFI) was determined on the basis of friction values measured by theSkiddometer BV11 and texture values (MPD) measured by the mobile profilometer.Figure 9 shows the values measured for F60, averaged over 10 m, together withthe friction threshold likewise expressed in terms of F60, determined from thenational standards for a newly built traditional asphalt surface, which ischaracterized by a Speed Constant (Sp) equal to 33.85 km/h. The results show theoptimum friction levels which can be obtained over time by using the studied mix.0.500.45after 1 month0.400.35after 6 monthsF600.300.250.20after 11 0708090100 110 120 130 140Distance [m]Figure 9. Friction

Crumb Rubber Modified Asphalt Concrete for Low Noise Surfaces13The friction levels measured are roughly two times the levels required by thetechnical specifications, which can be obtained by using crumb rubber modified inthe production of asphalt concrete. This is due to the high adhesion of the asphaltrubber binder to the aggregate in order to guarantee optimal friction levels whichalso increase road safety by reducing significantly stopping distance.6.3. Acoustic performanceThe basic assessment of acoustical properties of the research mix was carriedout by an in situ set of measurements, according to the ISO 13472-1 (“Adrienne”Method), and to the ISO/CD 11819-2 (“Close-Proximity Index” Technique), asmodified in [15]. Measurements were carried out at air and pavement temperatureswithin the ranges defined by the standards. Moreover, the software provides toautomatically correct the output according to the same standards.The Adrienne Method allows to com

Flash Point C 250 EN ISO 2592 Elastic recovery at 25 C % 70 UNI EN 13398 Resistance to hardening RTFOT (1 63 C – UNI EN 12607-1) Loss in mass % 0.5 UNI EN 12607-1 Retained penetration at 25 C % 45 UNI EN 1426 Increase in softening point C 12 UNI EN 1427

Related Documents:

Pavement Performance, yrs. Ohio High/Low Asphalt 16 Low Composite 11 High Composite 7 North Carolina ---- Concrete 6 –10 Ontario High Asphalt 8 Illinois Low Asphalt 7 –10 New York ---- Asphalt 5 –8 Indiana Low Asphalt 9 –11 Austria High/Low Asphalt 10 High Concrete 8 Georgia Low Asphalt 10

rubber levels increased, shear values increased significantly (Table 2). However, differences between particle sizes were not significant. To help explain this scenario, crumb rubber was topdressed in 1993 but not 1994. In 1993, the crumb rubber had not settled down to the crown tissue area, when the shear vane apparatus was

COMPACTION OF HOT MIX ASPHALT CONCRETE BY F. N. Finn and J. A. Epps RESEARCH REPORT 214-21 . Aggregate Characteristics 13 Asphalt Properties 13 Asphalt Concrete Properties 16 . manual on mix design methods for asphalt concrete, Chapter V ( ). Also,

asphalt concrete stiffness should be in a form that can be programmed. It is an established fact that asphalt concrete is neither elastic nor viscous but vis coelastic; i.e., its stiffness is a function of temperature and loading time. Moreover, the aging of asphalt adds an important dimension to the stiffness of the asphalt concrete.

that the asphalt plant be calibrated as specified in AASHTO M-156. Airport Specification 401-4.2 requires the asphalt plant to conform to ASTM D 995. The Asphalt Institute's Manuals MS-3 Asphalt Plant Manual and MS-22 Principles of Construction of Hot-Mix Asphalt Pavements contain much more information on asphalt plants. Batch Plants

rubber is the largest single market for ground rubber, consuming an estimated 220 million pounds, or approximately 12 million tires. California and Arizona use the most asphalt rubber in highway construction (over 80% of asphalt rubber utilized). Florida is the next largest user.

Rubber Lined Pipe, Rubber Bellows, Rubber Gasket, and much more. About Us Established in the year 2000, Arul Rubber Products is one of the prominent and topmost . Rubber Expansion Bellows Rubber Lining Valve Rubber Lined Diaphragm Valves All Type M S Roller Manufacturers P r o d u c t s & S e r v i c e s. OTHER PRODUCTS: Idler Impact Rings .

Asphalt Terminology Recycled Asphalt Pavement (RAP): Old asphalt pavement that is incorporated into new asphalt mix. Replacement Binder–recycled asphalt binder from RAS or RAP that is replacing some of the virgin binder in HMA. Performance Grade Asphalt Binderis specified based on performance within a temperature range.