Functional Performance of Stone Mastic Asphalt Pavements in Spain: Acoustic Assessment

coatings

Article Functional Performance of Stone Mastic Asphalt Pavements in Spain: Acoustic Assessment

Víctor F. Vázquez 1,* , Fernando Terán 1 , Jeanne Luong 2 and Santiago E. Paje 1

1 Laboratory of Acoustics Applied to Civil Engineering (LA2IC), University of Castilla-La Mancha, Avda. Camilo José Cela s/n, 13071 Ciudad Real, Spain; [email protected] (F.T.); [email protected] (S.E.P.) 2 Vibrations Engineering & Acoustics Consulting (VENAC), Rue des Vétérinaires 45–49 b0203, B-1070 Bruxelles, Belgium; [email protected] * Correspondence: [email protected]; Tel.: +34-926-295-300 (ext. 96778)

Received: 18 January 2019; Accepted: 13 February 2019; Published: 16 February 2019

Abstract: Environmental noise is one of the problems modern societies face today. Traffic noise, especially the noise produced from tire/pavement interaction, plays a main role in environmental noise. Pavement rehabilitation with new bituminous mixtures is a good option for combatting noise pollution in urban areas. This paper studies the functional performance of two bituminous mixtures of stone mastic asphalt (SMA), fabricated with the same polymer modified binder, but with different maximum aggregate size (MAS) (SMA11 and SMA16). The acoustic absorption, the dynamic stiffness, the surface texture and the tire/pavement noise were assessed. The bituminous mixture type SMA16 has higher texture levels at nearly every depicted wavelength of the texture spectra. This characteristic may lead to its higher average tire/pavement sound level compared to the mixture SMA11. The influence of each texture wavelength on the different frequency bands of the tire/pavement noise spectrum was studied, however, this relation is not a simple matter. This paper 2 also presents low-noise pavement labeling methodology (LNP labelingLA IC). The mixtures SMA11 and SMA16 are labeled at 50 and 80 km/h. An acoustic label is a valuable tool for construction companies and urban planners to use in order to define the best option against noise when pavement rehabilitation must be carried out.

Keywords: tire/pavement noise; close proximity; texture spectrum; functional performance; surface characteristics; stone mastic asphalt; noise label

1. Introduction Environmental noise is one of the main problems in modern societies. In urban areas, noise pollution is mostly due to traffic, whose main noise source is the tire/pavement noise that occurs when speed is higher than 40 km/h [1]. The European Noise Directive (END) 2002/49/EC [2] of the European Parliament and Council, relating to the assessment and management of environmental noise (and the Spanish Noise Law 37/2003 [3]), indicates that local authorities have to expand the noise maps and the action plans in order to mitigate this type of pollution. Some of the actions taken against noise are traffic management, the construction of noise barriers, or the vehicle speed reduction [4,5]. However, the only solution that reduces noise without affecting service level and without visual impact is pavement rehabilitation by means of new pavement with improved acoustic characteristics. The use of these surfaces is one of the most often applied actions against traffic noise all over the world [6]. Based on research reports and engineering studies, it has been shown that the use of stone mastic asphalt (SMA) bituminous mixtures (UNE-EN 13108-5 [7]) can improve the rutting resistance and durability of pavements (structural performance) [8]. On the other hand, the use of gap-graded

Coatings 2019, 9, 123; doi:10.3390/coatings9020123 www.mdpi.com/journal/coatings Coatings 2019, 9, 123 2 of 15 bituminous mixtures, such as SMA mixes, could reduce the noise generated by the tire/pavement interaction (functional performance) [9]. SMAs are hot bituminous mixes consisting of a coarse aggregate skeleton, and a high binder and filler content (5%–7% and 8%–12% by weight of mixture, respectively). These mixtures are designed to have a low air void content (3%–8%). The high binder content provides durability through an increased film thickness around the aggregate particles. In addition, these mixtures typically contain a cellulose or mineral fiber to prevent drainage of the binder. Despite their good performance, SMA mixtures are not commonly used in Spain, where the pavement industry has preferred the use of other gap-graded bituminous mixtures, such as bétons bitumineux très minces (BBTM mixes); asphalt concrete for very thin layers [10]. Nevertheless, the interest for this type of mixtures has recently grown in Spain. Research Projects such as the SMA Project (2010–2013) [11] have been developed in recent years. The main goal of the SMA Project was to increase knowledge about SMA mixtures’ behavior and to adapt them to the existing exigencies in Spain. Meanwhile, SMA mixtures are commonly used in other countries. Many international studies on SMA mixes and tire/pavement interaction (such as noise emission by the Close ProXimity method, or CPX) have been performed. Bennert and Maher [12] studied the tire/pavement noise emissions of two SMA pavements with different maximum aggregate sizes (MAS) in New Jersey, USA. This study established that the nominal aggregate size of hot mix asphalt influences the generated noise. Ahammed et al. [13] studied the relationship between texture and tire/pavement noise of SMA mixtures in Ontario, Canada. According to this work, certain textures limit the generation and/or propagation of tire/pavement noise. Miljkovićand Radenberg [14] studied the acoustic performance of an experimental “noise-reducing asphalt” (with a thin noise-reducing surface layer), developed from an SMA aggregate skeleton, in Germany. According to the conclusions of this paper, the research on noise-reducing surfaces and the experience from European countries should lead to the adoption of European specifications for noise-reducing asphalt pavements. In Belgium, Vuye et al. [15] studied tire/pavement noise evolution (up to 34 months after pavement construction) of an SMA mixture, regarding other experimental pavements such as the double-layer porous asphalt concrete. The evolution of the SMA mixture was better than those of the other experimental mixtures (with lower initial CPX levels). Sweczko-Zurek et al. [16] assessed the rolling resistance and the tire/road noise of the bituminous mixture type SMA11. Acoustic measurements were carried out by means of the TireSonic Mk.4, which was designed and developed by Technical University of Gdansk (TUG). According to this paper, the measured CPX levels of SMA11 pavements were between 89 and 91 dB(A) at 50 km/h, and between 96 and 99 dB(A) at 80 km/h. Gardziejczyk et al. [17,18] studied the noisiness and acoustic durability of low noise pavements in Poland. A SMA11 bituminous mixture was assessed in this study by means of the statistical pass by method (SPB). The SPB levels obtained were also related to a CPX noise classification, establishing that the SMA11 pavement was within the “normal noise class” (96.5–99.4 dB(A)). Vaitkus et al. [19] studied SMA bituminous mixtures from an acoustic absorption point of view. According to this research, their sound absorption coefficient was lower than 0.2. Finally, Sangiorgi et al. [20] have recently studied SMA11 bituminous mixtures (with and without crumb rubber (CR) added by a “dry-hybrid technology”) by means of the CPX method. The SMA11 mix without CR showed a CPX value of around 88.4 dB(A) at 50 km/h after 15 months in service. As deduced from the number of recent publications, there is great interest in knowing the acoustic behavior of this type of mixtures (SMAs), in order to establish specifications for noise-reducing asphalt pavements in the near future. This work assesses some surface characteristics of two experimental bituminous SMA type mixtures built in Spain (after two months in service conditions). These two mixtures were built with the same polymer modified binder, but a different maximum aggregate size (MAS) (11 and 16 mm respectively). The surface characteristics studied in this work are: the acoustic absorption, the dynamic stiffness, the surface texture, and the tire/pavement noise. The tire/pavement noise is assessed by means of the CPX method (near field conditions). According to the literature review, the acoustic behavior Coatings 2019, 9, 123 3 of 15

Coatingsof SMA 2019 mixtures, 9, x FOR has PEER indeed REVIEW been studied in different countries. However, there are research3 gaps of 15 that still needs to be addressed. This work aims to study some of them. First, the acoustic behavior research gaps that still needs to be addressed. This work aims to study some of them. First, the of SMA bituminous mixtures has not been studied according to the CPX methodology in Spain acoustic behavior of SMA bituminous mixtures has not been studied according to the CPX yet. The obtained results are compared and discussed with respect to those achieved in other methodology in Spain yet. The obtained results are compared and discussed with respect to those countries. The assessed mixtures have different MAS. The MAS influence on dynamic stiffness, achieved in other countries. The assessed mixtures have different MAS. The MAS influence on acoustic absorption, and tire/pavement noise is studied in this work. Finally, this paper presents dynamic stiffness, acoustic absorption, and tire/pavement noise is studied in this work. Finally, this a new labeling methodology to classify pavements in Spain according to their tire/pavement noise paper presents a new labeling methodology to classify pavements in Spain according to their emissions. The assessed pavements are classified by the Laboratory of Acoustics Applied to Civil tire/pavement noise emissions. The assessed pavements are classified by the Laboratory2 of Acoustics Engineering (LA2IC), according to the low-noise pavement labeling (LNP labelingLA IC) methodology. Applied to Civil Engineering (LA2IC), according to the low-noise pavement labeling (LNP Pavement labeling provides information about the acoustic performance of a given surface. This labelingLA²IC) methodology. Pavement labeling provides information about the acoustic performance information might be employed by local authorities in order to expand their implementation of action of a given surface. This information might be employed by local authorities in order to expand their plans for the European Noise Directive (END). Bituminous mixtures with a good noise reduction implementation of action plans for the European Noise Direc2 tive (END). Bituminous mixtures with capacity (previously labeled according to LNP labelingLA IC) might be employed in urban areas with a good noise reduction capacity (previously labeled according to LNP labelingLA²IC) might be problems related to traffic noise (environmental noise) [21,22]. employed in urban areas with problems related to traffic noise (environmental noise) [21,22]. 2. Project Design 2. Project Design Two pavement test sections, consisting of two types of SMA bituminous mixtures, were built and studiedTwo pavement in this researchtest sections work., consisting The mixtures of two were types built of SMA with differentbituminous MAS. mixtures The construction, were built andcharacteristics studied in ofthis these research mixtures work. are The shown mixtures in Table were1. The built volumetric with different and mechanical MAS. The propertiesconstruction of characteristicsthe mixes were of characterized these mixtures according are shown to differentin Table 1. laboratory The volumetric tests (Spanish and mechani Standardcal properties Association, of AENOR).the mixes were Theparameters characterized included according inTable to different1[ 23] are:laboratory maximum tests density(Spanish (UNE-EN Standard 12697-5Association [24]),, AENOR).apparent densityThe parameters (UNE-EN included 12697-6 in [25 Table]), mixture 1 [23] binder are: maximum content (UNE-EN density (UNE 12697-39-EN [1269726]), air-5 [ void24]), apparentcontent (UNE-EN density ( 12697-8UNE-EN [27 12697]), and-6 stiffness[25]), mixtur moduluse binder (UNE-EN content 12697-26 (UNE-EN [28 12697]). -39 [26]), air void content (UNE-EN 12697-8 [27]), and stiffness modulus (UNE-EN 12697-26 [28]). Table 1. Construction characteristics of studied mixtures stone mastic asphalt (SMA). Table 1. Construction characteristics of studied mixtures stone mastic asphalt (SMA). Layer Maximum Apparent Stiffness Layer Maximum Apparent BinderBinder Air Void Stiffness Mix Thickness Density Density Air Void Modulus Mix Thickness Density3 Density3 ((Mix)Mix) (%) Content (%)Modulus (cm) (kg/m ) (kg/m ) Content (%) (MPa) (cm) (kg/m3) (kg/m3) (%) (MPa) SMA11 4.0 2510 2345 5.58 6.55 2515 SMA11 4.0 2510 2345 5.58 6.55 2515 SMA16 4.5 2511 2391 5.66 4.75 3400 SMA16 4.5 2511 2391 5.66 4.75 3400

Both experimental experimental sections sections were were fabricated fabricated with with polymer polymer modiﬁed modified asphalt 45/80-65asphalt 45/80 and cellulose-65 and celluloseﬁbers (0.3% fibers byweight (0.3% of by the weight aggregate). of the The aggregate). experimental The test experimental sections were test located sections between were located the city betweenof Alzira the and city the of highway Alzira and CV-50 the highway (Figure1 CV). The-50 SMA11(Figure 1) section. The SMA11 has a length section of has 500 a m,length whereas of 500 the m, whereasSMA16 sectionthe SMA16 has asection length has of 250a length m. A of bridge 250 m. separated A bridge bothseparate experimentald both experimental sections, as sections shown, as in shownFigure1 in. Figure.1.

Figure 1. Experimental test tracks near near Alzira Alzira (Valencia), (Valencia), showing the GPS coordinates of the studied test sections of stone mastic asphalt mixtures SMA11 and SMA16.

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Coatings 2019, 9, x FOR PEER REVIEW 4 of 15 3. Measurement Methods and Equipment 3. Measurement Methods and Equipment 3.1. Close Proximity 3.1. Close Proximity Geo-referenced monitoring (CPX) of the experimental sections was carried out in order to assess the acousticalGeo-referenced performance monitoring of the (CPX) studied of the SMA experimental pavements. sections Trailer was TireSonic carried out Mk4-LA in order2IC to (TUG,assess 2 Gdansk,the acoustical Poland) performance (Figure2) was of the employed studied for SMA CPX pavements. measurements. Trailer The Tire equipmentSonic Mk4 is- composedLA IC (TUG of, aGdansk semi-anechoic, Poland)chamber, (Figure 2) within was employed which two for microphones CPX measurements. are mounted The equipment very close tois thecomposed wheel, of at a distancesemi-anechoic of 20 cmchamber, above thewithin pavement which andtwo 10microphones cm from the are wheel mounted (orientation very close angles to ofthe 45 wheel,◦ and 135at a◦ withdistance respect of 20 to cm the above plane the of thepavement wheel), and in order10 cm to from measure the wheel exclusively (orientation the sound angles produced of 45° and by 1 the35° tire/pavementwith respect to interaction.the plane of A the reference wheel), tirein order Pirelli to P6000 measure was exclusively employed for the acoustic sound produced characterization. by the Thetire/pavement inﬂation pressure interaction. of the A reference tire was 240tire kPa.Pirell Duringi P6000 was measurements, employed for the acoustic vehicle characterization speed was kept. closeThe inflation to the reference pressure speedsof the tire (50 was or 80240 km/h). kPa. During The tire/pavementmeasurements, soundthe vehicle levels speed were was corrected kept close for speedto the variations reference around speeds the (50 selectedor 80 km/h). reference The speedtire/pavement [29]. For thissound purpose, levels were the relationship corrected for between speed variations around the selected reference speed [29]. For this purpose, the relationship between sound sound levels (LCPtr), and the instant speed (v) was studied. The logarithmic regression between these magnitudeslevels (LCPtr), was and established the instant in eachspeed bituminous (v) was studied. mixture The (Equation logarithmic (1)): regression between these magnitudes was established in each bituminous mixture (Equation (1)): L = A + B·log(v) (1) CPtrLCPtr = A + B·log(v) (1)

FromFrom the logarithmic regression (Equation(Equation (1)), the coefﬁcientcoefficient B of each bituminous mixture was determined. Subsequently the measured soundsound levelslevels ((LLmeasuredmeasured) )were were corrected corrected (L (LCCorrectedorrected) according) according to toEq Equationuation (2), (2), where where v(tv)( tis) isthe the instant instant speed, speed, measured measured by by a a digital digital tachometer, tachometer, vref isis the the reference speed,speed, and the constantconstant B was determined from EquationEquation (1).(1).

LCorrected(t) = Lmeasured(t) + B·log(v(t)/vref), (2) LCorrected(t) = Lmeasured(t) + B·log(v(t)/vref), (2) Measurements were corrected by temperature, from the pavement temperature of 25 °C. The ◦ relationMeasurements between pavement were corrected temperature by temperature, and soundfrom levels the was pavement considered temperature to be −0.05 of 25 dB(A)/C. The°C , ◦ relationtaking into between account pavement previous temperature works and and literature sound levels [5,15,3 was0] considered. Although to the be − temperature0.05 dB(A)/ variationsC, taking intobetween account measurements previous works were and insignificant, literature [5 levels,15,30 were]. Although corrected the for temperature comparative variations purposes between (LNP LA2IC measurementslabelingLA²IC). were insigniﬁcant, levels were corrected for comparative purposes (LNP labeling ).

Figure 2. ReferenceReference tire i insidenside the semi semi-anechoic-anechoic chamber chamber,, and rear microphone.

3.2. Surface P Proﬁlerofile In situ situ texture texture measurements measurements were were carried carried out out on on the the experimental experimental sections sections by bymeans means of the of theso- 2 so-calledcalled LaserStaticPG LaserStaticPG-LA-LA2IC IC(Greenwood (Greenwood Engineering Engineering,, Brøndby Brøndby,, Denmark Denmark).). This This equipment equipment is composed ofof aa 6363 cm-longcm-long laser laser frame frame with with a scanner.a scanner. The The scanner scanner is movedis moved along along the the laser laser frame frame rail, andrail, aand magnetic a magnetic band band in the in railthe rail assures assures the the number number of of registered registered data data on on a a given given distance distance (data(data points every 0.1 mm). Due to the characteristics of the measurement device, data were not speed dependent, although the laser displacement was done manually.

Coatings 2019, 9, 123 5 of 15 every 0.1 mm). Due to the characteristics of the measurement device, data were not speed dependent, Coatingsalthough 2019 the, 9, x laser FOR displacementPEER REVIEW was done manually. 5 of 15 From the measured profile, the mean profile depth (MPD) was calculated for each studied pavement.From Thethe measuredMPD was calculated profile, the according mean p torofile the internationaldepth (MPD) standard was calculated UNE-EN for ISO each 13473-1 studied [31], pavement.and characterized The MPD the was macrotexture calculated amplitude according of to the the wearing international course s oftandard a pavement. UNE-EN ISO 13473-1 [31], andFrom characterize measuredd data, the macrotexture the texture spectra amplitude were of also the calculated. wearing course These of spectra a pavement. show the texture levelFrom in decibels, measured as a functiondata, the of texture the wavelength spectra were (or spatial also calculated. frequency). These The profilespectra texture show levelthe textureLt,m of levelthe fractional in decibel octaves, as aband functionm is of described the wavelength by the following (or spatial equation: frequency). The profile texture level Lt,m of the fractional octave band m is described by the following Equation: 2 Lt,m = 10·log(Zpm/Z ref), (3) Lt,m = 10·log(Zpm/Z2ref), (3) where ZZpmpm isis the the power power spectral spectral density density within within the the fractional fractional band band m, obtainedm, obtained from from the theresult result of the of Fourierthe Fourier transform transform of the of the filtered filtered profile profile amplitude amplitude,, and and ZrefZ refis is the the reference reference value value of of the the surface amplitude (10 −6 6m).m). The characterization of the texture spectrum of a given given pavement pavement contains contains valuable valuable information information regarding tire/road noise noise generation, generation, since since each each texture texture wavelength wavelength influences influences this this type type of of noise differentlydifferently.. As As shown shown in in Fig Figureure 33,, texturetexture wavelengths wavelengths between between 1 1 andand 10 10 mm mm may may lead lead to to noise noise reductionreduction,, due due to to a ahigher higher dispersion dispersion of ofthe the sound sound (lower (lower “horn “horn effect” effect” and lower and lower stick- stick-slipslip and stick and- snapstick-snap noise generation noise generation mechanism mechanisms)s) [9,32]. On [9 the,32 ].other On hand, the other texture hand, wavelengths texture wavelengthsaround 100 mm around lead to100 higher mm lead tire/pavement to higher tire/pavement noise levels, due noise to levels,impact due and to vibration impact and generation vibration mechanisms, generation mechanisms, since these wavelengthssince these wavelengths are of the same are oforder the sameof magnit orderude of magnitudeof the tire tread. of the tire tread.

Figure 3. Texture wavelengthwavelength range range for for each each of theof the categories categories and and their their inﬂuence influence (safety, (safety, comfort, comfort, noise, noise,wear, etc.)wear, [32 etc.),33]. [32,33]. 3.3. Sound Absorption 3.3. Sound Absorption Acoustic absorption relates the energy of the incident acoustic wave and the energy absorbed Acoustic absorption relates the energy of the incident acoustic wave and the energy absorbed by the pavement surface (without return). According to the literature, acoustic absorption may play by the pavement surface (without return). According to the literature, acoustic absorption may play an important role in tire/pavement noise attenuation when pavements with high air void content an important role in tire/pavement noise attenuation when pavements with high air void content (higher than 15%–20%) are employed [34]. Absorption measurements have been conducted using an (higher than 15%–20%) are employed [34]. Absorption measurements have been conducted using an impedance tube of 100 mm inner diameter, with a loudspeaker mounted at one end that produces impedance tube of 100 mm inner diameter, with a loudspeaker mounted at one end that produces plane, stationary, and random sound waves. The impedance tube allowed us to study the acoustic plane, stationary, and random sound waves. The impedance tube allowed us to study the acoustic absorption between 50 Hz and 1.6 kHz. Bituminous mixture was taken from the road during paving absorption between 50 Hz and 1.6 kHz. Bituminous mixture was taken from the road during paving operations and compacted in sample cores using a Marshall compactor (UNE-EN 12697-30 [35]). operations and compacted in sample cores using a Marshall compactor (UNE-EN 12697-30 [35]). Subsequently, the samples were covered laterally with Teﬂon in order to avoid the air gap between the Subsequently, the samples were covered laterally with Teflon in order to avoid the air gap between specimens and the tube. More details of the measurement technique are given elsewhere [36]. the specimens and the tube. More details of the measurement technique are given elsewhere [36].

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Coatings 2019, 9, x FOR PEER REVIEW 6 of 15 3.4. Dynamic Stiffness 3.4. Dynamic Stiffness Dynamic stiffness is a pavement property related to surface vibration and therefore, to traffic noise Dynamic stiffness is a pavement property related to surface vibration and therefore, to traffic (tire/pavement interaction). It is defined as the complex relationship between the vertical force applied noise (tire/pavement interaction). It is defined as the complex relationship between the vertical force to a given surface and its vertical displacement. Dynamic stiffness measurements were carried out in applied to a given surface and its vertical displacement. Dynamic stiffness measurements were the laboratory. Three Marshall samples for each mixture (from bituminous mixture taken during road carried out in the laboratory. Three Marshall samples for each mixture (from bituminous mixture construction) were assessed by means of a non-destructive procedure [37]. The measurement technique taken during road construction) were assessed by means of a non-destructive procedure [37]. The is composed of a shaker (Brüel and Kjaer 4809, Nærum, Denmark) and an impedance head (Brüel and measurement technique is composed of a shaker (Brüel and Kjaer 4809, Næ rum, Denmark) and an Kjaer 8001) that measures force and motion of the surface to be tested. Sweep signals between 10 Hz impedance head (Brüel and Kjaer 8001) that measures force and motion of the surface to be tested. and 7 kHz were used for sample excitation. From force and motion signals, the frequency response Sweep signals between 10 Hz and 7 kHz were used for sample excitation. From force and motion functions (coherence and dynamic stiffness) were determined with a 1 Hz resolution. In order to avoid signals, the frequency response functions (coherence and dynamic stiffness) were determined with a undesired vibrations, the samples were conditioned before testing, their bases were regularized by a 1 Hz resolution. In order to avoid undesired vibrations, the samples were conditioned before testing, thin plaster layer. their bases were regularized by a thin plaster layer. 3.5. Low-Noise Pavement Labeling Methodology in Spain 3.5. Low-Noise Pavement Labeling Methodology in Spain 2 Low-noise pavement labeling (LNP labelingLA IC) is an acoustic assessment methodology LA²IC developedLow-noise by the pavement Laboratory labeling of Acoustics (LNP labeling Applied to) Civil is an Engineering acoustic assessment in order to methodology classify the bituminousdeveloped bymixtures the Laboratory employed inof road Acoustics paving Applied and give to them Civil an Engineeringadded value related in order to theirto classify low-noise the bituminous mixtures employed in road2 paving and give them an added value related to their low- generation capacity. The LNP labelingLA IC methodology is based on the LA2IC experience in acoustic LA²IC 2 assessment,noise generation mainly capacity. by means The LNP of the labeling close proximity methodology (CPX) method. is based Subsequently,on the LA IC experience the assessed in acoustic assessment, mainly by means of the close proximity (CPX) method. Subsequently, the test track sections are classified into three categories of mezcla bituminosa sono-reductora (MBSR), or low-noiseassessed test bituminous track sections mixture, are by classified comparing into their three noise categories reduction of m capacityezcla bituminosa with that s ofono an-re asphaltductora (MBSR), or low-noise bituminous mixture, by comparing their noise reduction capacity with that of concrete pavement (bituminous mixture type AC 16 surf S) after eight years in service conditions. The an asphalt concrete2 pavement (bituminous mixture type AC 16 surf S) after eight years in service LNP labelingLA IC methodology establishes three MBSR classes [38]: conditions. The LNP labelingLA²IC methodology establishes three MBSR classes [38]: • MBSR Class A: Excellent tire/pavement noise reduction.  MBSR Class A: Excellent tire/pavement noise reduction. • MBSR Class B: Good tire/pavement noise reduction.  MBSR Class B: Good tire/pavement noise reduction. •  MBSRMBSR Class Class C: C: Acceptable Acceptable tire/pavement tire/pavement noise noise reduction. reduction. The acoustic assessment of the bituminous mixtures to be labeledlabeled was carried out according to the CPX methodology. TheThe testtest track sections must have at least 100 m length length,, and the measurem measurementsents are accomplished atat 50,50, 80,80, and/orand/or 110 km/h,km/h, depending depending on on the the section section characteristics characteristics and the scope of thethe study.study. Four Four consecutive consecutive measurements, measurements, with with three three reference reference tires tires (tourism (tourism tires), tires), should should be done be indone order in toorder achieve to achieve the homogeneity the homogeneity and the and mean the value mean of thevalue measured of the measured sound levels. sound The levels. sections The to besections assessed to be should assessed be locatedshould withinbe located urban within or peri-urban urban or peri areas,-urban where areas, tire/pavement where tire/pavement noise is mainly noise generatedis mainly generated by cars, not by bycars, heavy not by goods heavy vehicles. goods vehicles. The experimental The experimental sections sections must be must assessed be assessed after a minimumafter a minimum service of service two months, of two andmonths, measurements and measurements must be corrected must be bycorrected temperature by temperature (reference ◦ temperature(reference temperature 20 C) and speed 20 °C ) (50, and 80, speed and/or (50, 110 80 km/h),, and/or in 110 order km/h), to homogenize in order to the homogenize tire/pavement the noisetire/pavement levels of differentnoise levels measurements. of different Figuremeasurements.4 shows the Figure reference 4 shows values the for reference the pavement values labeling for the LA2IC accordingpavement tolabeling the LNP according labeling to the methodology.LNP labelingLA²IC methodology.

2 Figure 4.4. NoiseNoise reductionreduction referencereference valuesvalues (LNP(LNP labelinglabelingLALA²IC)) for for Spanish pavements classiﬁedclassified as MBSR Class A,A, Class B,B, and Class CC (50(50 andand 8080 km/h).km/h).

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4. Results and DiscussionDiscussion Reference sections were studied by different measurementmeasurement techniques in order to characterizecharacterize theirtheir functionalfunctional performance.performance. The The tests tests evaluate evaluatedd some of their surface characteristics such as the acoustic absorption, the dynamic stiffness,stiffness, thethe surfacesurface proﬁle,profile, andand thethe tire/pavementtire/pavement noise.

4.1. Acoustic Absorption and Dynamic Stiffness Measurements The acoustic acoustic absorption absorption of of the the studied studied bituminous bituminous mixtures mixtures was was assessed assessed in the in laboratory, the laboratory, using sampleusing sample cores fabricated cores fabricated with the with bituminous the bituminous mixture, and mixture employed, and employed during the during paving theoperations. paving Theoperati resultsons. obtainedThe results are obtained shownin are Figure shown5a. in Three Figure sample 5a. Three cores sample were testedcores were in each tested case. in Moreover, each case. theMoreover, base line the of base the emptyline of impedancethe empty impedance tube is also tube depicted is also in depicted Figure5a. in Figure 5a.

Figure 5.5. Acoustic absorption spectra ( a) and dynamicdynamic stiffness spectraspectra ((b)) ofof studiedstudied bituminousbituminous mixtures. Three sample cores werewere testedtested inin eacheach case.case.

As shown in this this ﬁgure, figure, the the acoustic acoustic absorption absorption coefﬁcients coefficients measured measured in both both experimental experimental sections diddid notnot reducereduce thethe noisenoise producedproduced inin thethe tire/pavementtire/pavement interaction as depicted values are lowerlower thanthan 0.20.2 forfor anyany frequencyfrequency band.band. Similar results were achievedachieved for bothboth mixturesmixtures SMA11 and SMA16. Acoustic absorption may lead toto noisenoise reductionsreductions atat highhigh frequenciesfrequencies ofof thethe tire/pavementtire/pavement noise spectra. This This reduction is is related to the air void content (interconnected voids) of of the mixes mixes.. Thus,Thus, high acousticacoustic absorption values are expected in mixtures with high air voidvoid contentscontents [[9]9].. TheThe studied bituminous mixes have air void contents lower than 10 10%% (Table 1 1),), therefore,therefore, anan outstandingoutstanding acoustic absorption capacity waswas notnot expectedexpected inin thesethese mixtures.mixtures. Dynamic stiffness was assessed in thethe laboratorylaboratory byby meansmeans ofof aa non-destructivenon-destructive testtest [[37]37].. TheThe dynamic stiffness measurements werewere carriedcarried outout onon the same sample cores used during the acousticacoustic absorption assessment. assessment. The The results results are are shown shown in Figure in Figure5b. According 5b. According to the achieved to the achieved results, dynamic results, stiffnessdynamic isstiffness not affected is not affected by the maximum by the maximum aggregate aggregate size of s theize of studied the studied bituminous bituminous mixtures. mixtures The. dynamicThe dynamic stiffness stiffness values values at 400 at Hz400 areHz 25.0are 25.0 MN/m MN/m (σ = (σ 1.3 = 1.3 MN/m) MN/m) and and 24.7 24.7 MN/m MN/m ( σ(σ= = 2.22.2 MN/m)MN/m) forfor bituminousbituminous mixture typestypes SMA11 and SMA16,SMA16, respectively. TheThe dynamicdynamic stiffness ofof bituminous mixtures does not depend on the MAS of the mixes mixes.. H However,owever, o otherther construction characteristics such as the binderbinder type or thethe additivesadditives of thethe mixturemixture mightmight leadlead toto higherhigher dynamicdynamic stiffnessstiffness variationsvariations (and(and thereforetherefore differentdifferent acousticacoustic behavior).behavior). TheThe deformation of a bituminous mixture is more related to the binder characteristics, since the binder holds the aggregates together and the stiffness of the binder is much lower than that of the aggregates.

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toCoatings the binder2019, 9, x characteristics, FOR PEER REVIEW since the binder holds the aggregates together and the stiffness of8 of the 15 binder is much lower than that of the aggregates. 4.2. Surface Profile Measurements 4.2. Surface Profile Measurements The surface profile measurements were conducted on the experimental sections after two monthsThe in surface service profile conditions. measurements These measurements were conducted were on thecarried experimental out on each sections experimental after two section. months inFrom service the texture conditions. profiles These, the measurements MPD was calculated were carried according out on to each the experimentalUNE-EN ISO section.13473-1 From[31]. The the textureaverage profiles, MPD values the MPD achieved was calculated were 1.9 accordingmm (σ = 0.6 to themm) UNE-EN and 2.2 ISO mm 13473-1 (σ = 0.7 [31 mm)]. The for average bituminous MPD valuesmixture achieved types SMA11 were and 1.9 mmSMA16 (σ =, respectively. 0.6 mm) and The 2.2 mmMPD ( σof= the 0.7 bituminous mm) for bituminous mixture SMA16 mixture is a types little SMA11bit higher and than SMA16, that of respectively.the SMA11. This The may MPD be of due the to bituminous their higher mixtureMAS. However, SMA16 istak aing little into bit account higher thanthe homogeneities that of the SMA11. (standard This maydeviation be due σ) to of their the higher measurements, MAS. However, the differences taking into between account their the homogeneitiesmacrotexture amplitudes (standard deviation (MPD) areσ) not of the big measurements, enough to justify the a differences different acoustic between behavior their macrotexture. amplitudesBesides (MPD) the characterization are not big enough of the to justify macrotexture a different amplitude acoustic behavior.of the experimental bituminous mixtures,Besides this the paper characterization studies their texture of the spectra. macrotexture The spectra amplitude were calculated of the experimental following the bituminous UNE-EN mixtures,ISO 13473 this-1. The paper calculated studies theirtexture texture spectra spectra. are shown The spectra in Figure were 6. calculated An inset followingin this figure the UNE-ENshows a ISOdetail 13473-1. of the surface The calculated of the studied texture bituminous spectra are mixtures. shown inThe Figure bituminous6. An inset mixture in this with figure a high shows texture a detaillevel at of higher the surface wavelengths of the studied is SMA16. bituminous This result mixtures. may be Thelinked bituminous to its higher mixture MAS. withOn the ahigh other texture hand, levelthe texture at higher levels wavelengths at low wavelengths is SMA16. are This rather result similar, may although be linked SMA16 to its higheris the mixture MAS. On with the higher other hand,texture the, again. texture Acc levelsording at to low these wavelengths results, the are bituminous rather similar, mixture although SMA16 SMA16 may produce is the mixture higher noise with higherlevels (higher texture, texture again. Accordinglevel at 100 to mm these wave results,length) the at bituminous low frequencies mixture (400 SMA16–500 mayHz), producedue to impacts higher noiseand vibrations. levels (higher However, texture this level bituminous at 100 mm mixture wavelength) also mayat low reduce frequencies noise (400–500(higher texture Hz), due level to impactsbetween and1 and vibrations. 10 mm wavele However,ngth) this at bituminoushigh frequencies mixture (2500 also–8000 may Hz) reduce due noise to a higher (higher dispersion texture level of betweenthe sound 1 and[34] 10. These mm wavelength)considerations at high will frequenciesbe evaluated (2500–8000 later (together Hz) due with to athe higher tire/pavement dispersion ofnoise the soundspectra [ 34 of]. the These studied considerations bituminous will mixtures), be evaluated since later the (together influence with of the the tire/pavement texture spectrum noise spectra on the oftire/pavement the studied bituminous noise also mixtures), depends since on the the dominant influence of noise the texture generation spectrum mechanisms on the tire/pavement of a given noisebituminous also depends mixture. on the dominant noise generation mechanisms of a given bituminous mixture.

Figure 6. Texture spectra LTT calculated from surface profile proﬁle measurements and a detail of the studied bituminous mixture typestypes SMA11 and SMA16.SMA16. 4.3. Close Proximity Measurements 4.3. Close Proximity Measurements The acoustic assessment of the experimental test sections has been accomplished by means of The acoustic assessment of the experimental test sections has been accomplished by means of the close proximity method (TireSonic Mk4-LA2IC). These sections were studied at 50 and 80 km/h, the close proximity method (TireSonic Mk4-LA2IC). These sections were studied at 50 and 80 km/h, since they were located within a peri-urban road. During auscultation, the pavement temperature kept since they were located within a peri-urban road. During auscultation, the pavement temperature constant at 25 ◦C, and the tire pressure (before measurements) was 240 kPa. Four consecutive CPX kept constant at 25 °C , and the tire pressure (before measurements) was 240 kPa. Four consecutive measurements along the experimental test track sections (SMA11 and SMA16) were carried out for CPX measurements along the experimental test track sections (SMA11 and SMA16) were carried out repeatability purpose at each reference speed (see Figure7). for repeatability purpose at each reference speed (see Figure 7). As shown in Figure7, the studied sections show a good repeatability. The longitudinal As shown in Figure 7, the studied sections show a good repeatability. The longitudinal tire/pavement noise levels agree among the different measurements. The data collected at the tire/pavement noise levels agree among the different measurements. The data collected at the bituminous mixture laid on the bridge (see Figure1) were not analyzed in depth, since this is out of bituminous mixture laid on the bridge (see Figure 1) were not analyzed in depth, since this is out of the aim of this research work. However, it is an interesting topic, since the tire pavement noise levels measured on the bridge seemed to be lower than those of the adjacent road sections. The characteristics of this infrastructure may somehow affect tire/pavement noise.

Coatings 2019, 9, 123 9 of 15 the aim of this research work. However, it is an interesting topic, since the tire pavement noise levels measured on the bridge seemed to be lower than those of the adjacent road sections. The characteristics Coatings 2019, 9, x FOR PEER REVIEW 9 of 15 Coatingsof this infrastructure2019, 9, x FOR PEER may REVIEW somehow affect tire/pavement noise. 9 of 15

Figure 7. Repeatability of the tire pavement sound levels (LCPtr, 50km/h) measured in the bituminous Figure 7. RepeatabilityRepeatability ofof thethe tiretire pavement pavement sound sound levels levels (L (CPtr,LCPtr, 50km/h 50km/h) )measured measured in in the the bituminous mixturesmixtures SMA11SMA11 andand SMA16.SMA16.

AlthoughAlthough vehicle vehicle speed speed speed was was was kept kept kept around around around the the the reference reference reference speed speed speed during during during measurements, measurements, measurements, tire/pavement sound levels should be corrected for small variations. Figure 8 shows the LCPtr sound tire/pavement sound sound levels levels should should be be corrected corrected for small variations. Figure8 8 shows shows the the LLCPtrCPtr sound levelslevelslevels as as as a a a function function function of the of of thevehicle the vehicle vehicle speed. speed. speed. The tire/pavement The The tire/pavement tire/pavement sound levels sound sound increase levels levels linearly increase increase in linearly linearly proportion inin proportionproportionto log(v). The toto log(log( valuevv).). ofTheThe the valuevalue coefficients ofof thethe coefficientscoefficientsB was obtained BB waswas from obtainedobtained the linear fromfrom fittingthethe linearlinear (see fittingfitting Figure ((s8seeee), whereFigFigureure the 8),8), wherewherecoefficient the the B coefficient coefficientis the so-called BB isis the “speedthe so so--calledcalled constant” “speed “speed [30]. constant” constant” This coefficient [30][30].. Thischaracterizes This coefficient coefficient the characterizes characterizesacoustic behavior the the acoustic behavior of the studied bituminous mixtures and allows us to correct the LCPtr levels for speed acousticof the studied behavior bituminous of the studied mixtures bituminous and allows mixtures us to correct and allow the LsCPtr us tolevels correct for speedthe LCPtr variations levels for around speed variationsvariationsthe reference aroundaround speed. thethe The referencereference coefficient speed.speed.B ofTheThe the coefficientcoefficient SMA11 ( BBB =ofof 36 thethe dB(A)) SMA11SMA11 makes ((BB == 3636 it more dB(A))dB(A)) suitable makesmakes for itit moremore high suitablesuitablespeed roads forfor highhigh than speedspeed the mix roadsroads with thanthan higher thethe mix MASmix withwith (B = higherhigher 39 dB(A)), MASMAS whereas ((BB == 3939 dB(A)), bothdB(A)), mixtures whereaswhereas could bothboth be mixturesmixtures used in couldcouldpaving be be operations used used in in of paving paving urban operationslanes. operations Figure of of8 also urban urban shows lanes. lanes. a measure Figure Figure of8 8 thealso also tire/pavement shows shows a a measure measure sound of of levels the the tire/pavementtire/pavementat 35 km/h (usual soundsound speed levelslevels in atat urban 3535 km/hkm/h areas) (usual(usual and spsp ateedeed 70 km/hinin urbanurban (interurban areas)areas) andand areas). atat 7070 km/hkm/h Due (interurban(interurban to their different areas).areas).B DueDuecoefficients, toto theirtheir different thedifferent sound BB levelscoefficients,coefficients, pointed thethe out soundsound by the levelslevels linear pointedpointed regression ououtt byby (Figure thethe linearlinear8) are regressionregression similar at (Figure(Figure 35 km/h 8)8) arearebut similarsimilar differ atbyat 3535 approximately km/hkm/h butbut differdiffer 2 byby dB(A) approximatelyapproximately at 70 km/h. 22 dB(A)dB(A) This atspeed-dependentat 7070 km/h.km/h. ThisThis speedspeed behavior--dependentdependent should behavbehav be alsoiorior shouldshouldappreciated bebe alsoalso in appreciatedappreciated the acoustic inin assessment thethe acousticacoustic at 50 assessmentassessment and 80 km/h atat 5050 that andand is 8080 presented km/hkm/h thatthat below. isis presentedpresented below.below.

((aa)) ((bb))

FigureFigure 8. 8. LinearLinearLinear regression regression regression of of of tire/pavement tire/pavement sound sound sound levels levels levels as as as a a a function function function of of of vehicle vehicle vehicle speed speed speed for for the the referencereference tiretire rolling rolling on on the the bituminous bituminous mixtures SMA11 SMA11 ( (aa)) and and SMA16 SMA16 ( (bb).).

The tire/pavement sound levels LCPtr at reference speeds (not corrected by temperature), are The tire/pavement sound levels LCPtr at reference speeds (not corrected by temperature), are presentedpresented inin TableTable 2.2. MeasuredMeasured valuesvalues havehave a a highhigh overalloverall homogeneityhomogeneity (low(low standardstandard deviationdeviation fromfrom the the four four whole whole measurements measurements),), sincesince the the auscultation auscultation methodology methodology (CPX) (CPX) is is a a very very reliable reliable measurementmeasurement technique. technique. Average Average values values shown shown in in this this table table must must be be corrected corrected by by temperature. temperature. TemperatureTemperature isis notnot aa keykey factorfactor whenwhen thethe measurementsmeasurements ofof differentdifferent bituminousbituminous mixturesmixtures areare carriedcarried outout aatt thethe samesame temperaturetemperature (SMA11(SMA11 andand SMA16SMA16 inin thisthis work).work). However,However, temperaturetemperature correctionscorrections

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The tire/pavement sound levels LCPtr at reference speeds (not corrected by temperature), are presented in Table2. Measured values have a high overall homogeneity (low standard deviation from the four whole measurements), since the auscultation methodology (CPX) is a very reliable measurement technique. Average values shown in this table must be corrected by temperature. Temperature is not a key factor when the measurements of different bituminous mixtures are carried out at the same temperature (SMA11 and SMA16 in this work). However, temperature corrections are needed in order to compare the tire/pavement noise levels measured under different conditions. In this work, the results have been corrected by temperature (from 25 to 20 ◦C) to label the surfaces 2 according to the LNP labelingLA IC methodology. After temperature corrections (−0.05 dB(A)/◦C), the average tire/pavement sound levels at 50 km/h were 88.3 and 89.2 dB(A), respectively, for bituminous mixtures SMA11 and SMA16, whereas the average values at 80 km/h were 95.3 and 96.6 (SMA11 and SMA 16, respectively). According to these results, the ∆LCPtr, 50km/h and ∆LCPtr, 80km/h values were 0.9 and 1.3 dB(A), respectively. This agrees with the conclusions extracted from the linear regression between LCPtr and speed (Figure8). The SMA11 mixture is more suitable for high speed roads than the SMA16.

Table 2. Mean tire/pavement sound levels of each continuous measurement, average, and homogeneity from the four measurements. Values are not corrected by temperature.

Reference Tire/Pavement Sound Levels LCPtr (dB(A)) Mix Speed M.1 M.2 M.3 M.4 Average Homogeneity (σ) SMA11 88.17 ± 0.4 88.06 ± 0.5 88.11 ± 0.5 88.05 ± 0.4 88.10 0.05 50 km/h SMA16 88.9 9± 0.7 88.82 ± 0.6 88.93 ± 0.6 88.88 ± 0.6 88.90 0.07 SMA11 95.12 ± 0.5 95.17 ± 0.5 95.12 ± 0.5 94.97 ± 0.5 95.10 0.08 80 km/h SMA16 96.42 ± 0.4 96.34 ± 0.5 96.28 ± 0.4 96.20 ± 0.4 96.31 0.08

From the continuous measurements of tire/pavement sound levels, the LCPtr spectrum of the two bituminous mixtures was calculated between 200 Hz and 5 kHz. Figure9 shows the comparison between both spectra (∆LCPtr = LCPtr-SMA16 − LCPtr-SMA11) at every one-third octave band of the sound spectra calculated at 50 and 80 km/h. From Figure9 some conclusions can be drawn:

• The shape of the ∆LCPtr curves (Figure9) is not speed-dependent. • The relation between both spectra is speed-dependent. Differences between SMA11 and SMA16 are higher at higher speeds, and therefore, this result agrees with Figure8.

• In spite of the different LCPtr average values and homogeneities (50 km/h) of each test track section (Table2), there are some points of the test track sections with similar tire/pavement noise levels, as indicated by the error range of each single measurement in Table2. This does not occur at 80 km/h, where the differences between the average noise levels are higher. • At low frequencies (up to 700 Hz), SMA11 is noisier than SMA16 in spite of its lower texture level at high texture wavelengths (Figure6), which are related to impacts and vibrations. • At high frequencies (from 2000 Hz), SMA16 is noisier than SMA11, in spite of its higher texture level at low texture wavelengths (Figure6) (sound dispersion) and their similar acoustic absorption spectra. • Medium frequencies (800–1000 Hz) are the dominant frequencies within the tire/pavement sound levels. The sound generation at these frequencies is governed by a combination of tire/pavement noise generation mechanisms [32]. Medium frequencies are responsible for the highest global sound levels measured in the mixture SMA16. Coatings 2019, 9, x FOR PEER REVIEW 10 of 15 are needed in order to compare the tire/pavement noise levels measured under different conditions. In this work, the results have been corrected by temperature (from 25 to 20 °C ) to label the surfaces according to the LNP labelingLA²IC methodology. After temperature corrections (−0.05 dB(A)/°C ), the average tire/pavement sound levels at 50 km/h were 88.3 and 89.2 dB(A), respectively, for bituminous mixtures SMA11 and SMA16, whereas the average values at 80 km/h were 95.3 and 96.6 (SMA11 and SMA 16, respectively). According to these results, the ΔLCPtr, 50km/h and ΔLCPtr, 80km/h values were 0.9 and 1.3 dB(A), respectively. This agrees with the conclusions extracted from the linear regression between LCPtr and speed (Figure 8). The SMA11 mixture is more suitable for high speed roads than the SMA16.

Table 2. Mean tire/pavement sound levels of each continuous measurement, average, and homogeneity from the four measurements. Values are not corrected by temperature.

From the continuous measurements of tire/pavement sound levels, the LCPtr spectrum of the two bituminous mixtures was calculated between 200 Hz and 5 kHz. Figure 9 shows the comparison between both spectra (ΔLCPtr = LCPtr-SMA16 − LCPtr-SMA11) at every one-third octave band of the sound spectra calculated at 50 and 80 km/h. From Figure 9 some conclusions can be drawn:

 The shape of the ΔLCPtr curves (Figure 9) is not speed-dependent.  The relation between both spectra is speed-dependent. Differences between SMA11 and SMA16 are higher at higher speeds, and therefore, this result agrees with Figure 8.  In spite of the different LCPtr average values and homogeneities (50 km/h) of each test track section (Table 2), there are some points of the test track sections with similar tire/pavement noise levels, as indicated by the error range of each single measurement in Table 2. This does not occur at 80 km/h, where the differences between the average noise levels are higher.  At low frequencies (up to 700 Hz), SMA11 is noisier than SMA16 in spite of its lower texture level at high texture wavelengths (Figure 6), which are related to impacts and vibrations.  At high frequencies (from 2000 Hz), SMA16 is noisier than SMA11, in spite of its higher texture level at low texture wavelengths (Figure 6) (sound dispersion) and their similar acoustic absorption spectra.  Medium frequencies (800–1000 Hz) are the dominant frequencies within the tire/pavement sound levels. The sound generation at these frequencies is governed by a combination of tire/pavement Coatingsnoise2019 generation, 9, 123 mechanisms [32]. Medium frequencies are responsible for the highest global11 of 15 sound levels measured in the mixture SMA16.

Figure 9. ∆L values at every one-third octave band frequency of the sound spectra (50 and 80 km/h). Figure 9. ΔLCPtrCPtr values at every one-third octave band frequency of the sound spectra (50 and 80 km/h). According to these results, the relationship between the different frequencies of the tire/pavement sound spectrum and the different wavelengths of the texture spectra should be further investigated. The mixture SMA16 had higher texture levels at almost every plotted wavelength (Figure6). The SMA16 texture is responsible for its higher average tire/pavement sound levels. However, the texture wavelengths that dominate the sound level at each frequency band may depend on the pavement surface that is the object of study. Higher texture levels of mixture SMA16 (Figure6) led to higher sound levels at medium/high frequencies (from 800 Hz) in its tire/pavement sound spectrum. In this sense, the differences between mixes at low texture wavelengths (Figure6) were not big enough to result in lower LCPtr values of mixture SMA16 at these frequencies (Figure9). On the other hand, the acoustic behavior of both mixtures at low frequencies seems to have been inﬂuenced by their texture levels at wavelengths between 30 and 50 mm. According to the overall noise results, the SMA16 bituminous mixture is noisier than the SMA11. The maximum aggregate size is directly related to higher overall tire/pavement noise levels, although this behavior is not reﬂected at every frequency of the tire/pavement noise spectra (Figure9). This result agrees with other research works where the CPX-noise/MAS dependence was also established [12]. On the other hand, the measured LCPtr values at 80 km/h were lower than those reported by other research works on the bituminous mixture type SMA10 (98 dB(A)) [15]. The measured LCPtr values at 50 km/h were also lower than other values reported in aSMA5 mixture type (90.6 dB(A)) [14], although all the data were normalized at 20 ◦C. However, the higher noise values of SMA5 and SMA10 bituminous mixtures (80 and 50 km/h respectively) should be related to different construction characteristics or differences between the measurement techniques (for instance, the trailer employed for the CPX measurements). Besides, the average tire/pavement sound level measured at 50 km/h of mixture SMA11 (88.10 dB(A)) agrees with that presented in literature [16,20]. The average values measured at 80 km/h (95.10) also agree with the literature [16]. Some of these measurements were carried out with equipment (TireSonic Mk.4 by TUG, Gadnsk, Poland) similar to that employed in this research paper.

4.4. Labeling The experimental test sections included in this research work are labeled after four consecutive measurements with the same reference tire (Pirelli P6000) at 50 and 80 km/h. Acoustic measurements were carried out according to the CPX methodology and subsequently corrected by temperature (20 ◦C) and speed. Measurements have been conducted with a single reference tire due to technical limitations. However, according to previous research works, the results obtained with the employed reference tire are representative of the acoustical performance of the studied sections [39]. According to the average values presented in Table2, the experimental tracks were labeled 2 according to the LNP labelingLA IC methodology. Figure 10 shows the labels of bituminous mixtures SMA11 and SMA16 at 50 and 80 km/h. Each label includes the denomination and location of Coatings 2019, 9, 123 12 of 15 the mixture assessed, the company responsible for the paving operations, the MBSR class of the experimental track, and the reference speed of the acoustic assessment. Both bituminous mixtures are labeled as Class B (good tire/pavement noise reduction) at 2 80 km/h. The LNP labelingLA IC methodology highlights the sound-reduction capacity of a given pavement. Additionally, the classification system presented by Gardziejczyk [18] is referred to the noise produced by the tire/pavement interaction (low, reduced, normal, increased, high). According to this classification system, the SMA11 mixture assessed in this research work would be classified as “reduced noise class” at 80 km/h. The labels presented in Figure 10 point out the most appropriate bituminous mixtures for paving operations, depending on the usual speed of each test section (reference speed). Besides the acoustic label, the LA2IC provides a report when the characteristics of the acoustic assessment and the tire/pavement noise values of each assessed section are included. LA2IC CoatingsThe 2019 acoustics, 9, x FOR labelPEER REVIEW of bituminous mixtures according to the LNP labeling methodology12 of is15 a valuable design tool for construction companies and urban planners to use in order to decide the bestpaving paving option option when when rehabilitation rehabilitation operations operations must must be becarried carried out out in in urban urban areas areas with with problems relatedrelated toto traffictraffic noisenoise (acoustic(acoustic pollution).pollution).

LA2IC Figure 10.10. Acoustic labels according to to the the LNP LNP labeling labelingLA²IC methodologymethodology:: (a)( SMA11a) SMA11 at 50 at 50km/h km/h;; (b) (SMA11b) SMA11 at 80 at km/h 80 km/h;; (c) SMA16 (c) SMA16 at 50 at km/h 50 km/h;; and and(d) SMA16 (d) SMA16 at 80 at km/h. 80 km/h. 5. Conclusions 5. Conclusions This research paper presents the functional performance (surface assessment) of two experimental This research paper presents the functional performance (surface assessment) of two sections built with SMA11 and SMA16 types of bituminous mixtures. Both mixtures have similar experimental sections built with SMA11 and SMA16 types of bituminous mixtures. Both mixtures construction characteristics with regards to their binder type and additives, but they differ in their MAS. have similar construction characteristics with regards to their binder type and additives,2 but they Moreover, this paper presents their acoustic labeling according to the LNP labelingLA IC methodology. differ in their MAS. Moreover, this paper presents their acoustic labeling according to the LNP The main conclusions at this stage are as follows: labelingLA²IC methodology. The main conclusions at this stage are as follows: • Acoustic absorption does not play an important role in the noise reduction capacity of the assessed  Acoustic absorption does not play an important role in the noise reduction capacity of the bituminous mixtures with an air void content lower than 10%. The dynamic stiffness value assessed bituminous mixtures with an air void content lower than 10%. The dynamic stiffness measured is similar in both mixtures. Although the SMA16 mixture has higher average dynamic value measured is similar in both mixtures. Although the SMA16 mixture has higher average stiffness at 400 Hz, the differences between mixtures do not justify the higher tire/pavement dynamic stiffness at 400 Hz, the differences between mixtures do not justify the higher sound levels of this mixture at medium frequencies. tire/pavement sound levels of this mixture at medium frequencies.  The different maximum aggregate sizes of the mixtures do not affect neither their acoustic absorption nor their dynamic stiffness.  The bituminous mixture SMA11 is better for noise reduction than the SMA16 at 80 km/h. At 50 km/h, the differences between both mixtures are lower. This result may be connected to their MAS. According to the sound spectra, the SMA 16 is noisier at frequencies from 700 Hz, regardless of the reference speed.  The acoustic behavior of SMA11 and SMA16 depends on the speed. This dependence makes the mixture SMA11 more suitable for paving operations in roads (higher usual speed).  The SMA16 bituminous mixture has higher MPD values. Its higher macrotexture amplitude might produce the higher LCPtr levels, however, the differences between the MPD values are not big enough to confirm this observation. Texture spectra measurements were conducted in order to identify the texture wavelengths related to the different frequencies of the tire/pavement sound levels.  The SMA16 has higher texture levels than the SMA11 at nearly every wavelength, except for 12.5 and 31.5 mm, where this mixture has slightly lower values. In spite of their texture spectrum, the

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• The different maximum aggregate sizes of the mixtures do not affect neither their acoustic absorption nor their dynamic stiffness. • The bituminous mixture SMA11 is better for noise reduction than the SMA16 at 80 km/h. At 50 km/h, the differences between both mixtures are lower. This result may be connected to their MAS. According to the sound spectra, the SMA 16 is noisier at frequencies from 700 Hz, regardless of the reference speed. • The acoustic behavior of SMA11 and SMA16 depends on the speed. This dependence makes the mixture SMA11 more suitable for paving operations in roads (higher usual speed). • The SMA16 bituminous mixture has higher MPD values. Its higher macrotexture amplitude might produce the higher LCPtr levels, however, the differences between the MPD values are not big enough to conﬁrm this observation. Texture spectra measurements were conducted in order to identify the texture wavelengths related to the different frequencies of the tire/pavement sound levels. • The SMA16 has higher texture levels than the SMA11 at nearly every wavelength, except for 12.5 and 31.5 mm, where this mixture has slightly lower values. In spite of their texture spectrum, the SMA 16 produces lower tire/pavement sound levels at low frequencies and higher levels at medium/high frequencies. The texture spectra may inﬂuence noise, but the main texture wavelengths affecting overall noise should be determined, as well as the wavelengths that rule the tire/pavement noise at each one-third octave band of a given bituminous mixture.

Author Contributions: Conceptualization, V.F.V.; Data Curation, V.F.V. and S.E.P.; Formal Analysis, V.F.V. and J.L.; Investigation, V.F.V., F.T., J.L. and S.E.P.; Methodology, V.F.V., F.T., J.L. and S.E.P.; Project Administration, S.E.P.; Supervision, S.E.P.; Visualization, V.F.V.; Writing—Original Draft, V.F.V.; Writing—Review and Editing, V.F.V., F.T., J.L. and S.E.P. Funding: This research was funded by the Spanish Ministry of Economy and Competitiveness with European Regional Development Funds (FEDER), No. [Project TRA2016-77418-R (AEI/FEDER,UE)]. Acknowledgments: The authors wish to acknowledge Project SMA (CDTI) and ELSAN (OHL Group) for its technical support. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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