Two-layer porous asphalt for urban roads

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1 Two-lyer porous sphlt for urn rods Hns Bendtsen, Bent Andersen, Jørn Råerg nd Lrs Ellejerg Lrsen Dnish Rod Institute/Rod Directorte Guldlderen 12, P.O. Box 235, DK-2640 Hedehusene, Denmrk, Jørgen Krgh DELTA Dnish Electronics. Light & Acoustics, Venlighedsvej 4, 290 Hørsholm, Denmrk, An experiment with two lyer porous sphlt pvements ws strted on n urn rod in Copenhgen, Denmrk in The noise reduction ws optimised y the use of smll ggregte size in the top-lyer nd rther gret thickness of the porous lyers. Three different two-lyer porous pvements s well s dense sphlt concrete s reference pvement were lid on rod. The gol of the project ws to follow the pvements in their structurl lifetime. Noise nd permeility hs een mesured every yer. When the pvements were new the noise reduction ws 4 to 6 db compred to the reference pvement of dense sphlt concrete with 8 mm mx. ggregte. Both the noise reduction nd the permeility hve decresed over the yers, proly due to clogging of the pores of the open pvement. The results over 6 yers period re presented in this pper. In 2004 new reserch project ws strted s co-opertion etween the Dnish Rod Institute / Rod Directorte (DRI) nd Rod nd Hydrulic Engineering Institute in the Netherlnds (DWW) clled the DRI-DWW noise tement progrmme. The project is focussing on investigtion in the clogging process, nd the gol is to develop concepts nd methods tht cn reduce the clogging of porous pvements. 1 Introduction Porous pvements re used in different Europen countries s tool for noise tement. Such pvements generlly prove to hve good noise reducing effect when they re new ut this my chnge s the pvements get older. There re not mny lifetime studies of the noise emission from rod pvements t ll, nd especilly not from trffic on porous pvements. In the 1990s Dnish experiment showed tht single-lyer porous pvement with rther smll mximum ggregte size of 8 mm mintined noise reduction of 3-4 db during the whole lifetime of the pvement. The reduction ws mesured y the SPB method reltive to dense sphlt concrete with mximum ggregte size of 12 mm. This experiment ws crried out on highwy where the speed limit ws 80 km/h. The sme type of porous pvement ws tested on n urn rod with speed limit of 50 km/h. Here n initil noise reduction of 3 db disppered fter only 2 yers due to clogging of the pores of the pvement. There seems to e tendency tht porous pvements on highwys keep the porous structures open during their lifetime. This is explined y self clening mechnism where the tires in riny periods press wter down in the pores of the pvement under high pressure. Wheres on low speed rods the wter pressure is not high enough to ensure continuous clening effect of the pvements, nd therefore they tend to clog nd y tht loose their noise reduction. 2 DRI-DWW progrmme There is ig need to understnd the clogging process s well s the process of self clening of porous pvements. In 2004 co-opertion etween the Dutch (DWW) nd the Dnish (DRI) rod institutes ws strted. The coopertion is clled The DRI-DWW noise tement progrm, [1]. A totl of projects re crried out in the frmework of the progrm which is prt of the Dutch Innovtion Progrm on Noise from rod trffic lso clled the IPG reserch progrm, [2]. Three of these projects re focussing on the cousticl s well s the structurl lifetime of porous pvements nd one of these is especilly dedicted to the clogging phenomenon of two-lyer porous pvements. In order to understnd nd e le to descrie the clogging process n intensive mesurement progrm hs een estlished with the gol to mke it possile over the lifetime of the pvements to descrie: 1. The cousticl properties of the pvements. 2. The structurl properties of the pvements. 3. The clogging of the pvements. Two-lyer porous pvements pplied on two different types of rods re included: 1. Urn rods with low verge speed of round 50 km/h. 2. Highwys with high verge speed round 110 km/h. 11

2 Forum Acusticum 2005 Budpest Bendtsen, Andersen, Rerg nd Krgh 3 Hypotheses of DRI-DWW progrmme The following hypotheses drwn up t the eginning of the clogging coopertion project re used s ckground to design the mesurement progrms s well s the nlyticl work in the clogging project: 1. The pvements get more clogged s they get older! 2. The tendency of clogging is reduced when lrger ggregtes re used! 3. The tendency of clogging is reduced when the initil ir voids re incresed! 4. The tendency of clogging is reduced when the verge speed of the trffic is incresed! 5. The clogging strts t the interfce etween the top nd the ottom lyer of two-lyered porous sphlt! 6. As long s the upper 20 mm of the porous pvement is open good noise reduction will e chieved!. There is less clogging in the wheel trcks thn etween the wheel trcks! 8. Clogging is initited t the ottom of the lower porous lyer! 9. The first lne tht clogs is the emergency lne! permeility results re presented in order to quntify the clogging phenomenon. No. Designtion I DA8-0 Porous sphlt II DA5-55 Porous sphlt III DA5-90 Porous sphlt IV AB8t (ref.) Tle 1: Test sections. Type Top-lyer Bottom-lyer Dense sphlt Thickness Aggreg te size Thickness Aggregte size 25 5/ / / / / / / Urn test field The urn test field is Øster Søgde in Copenhgen, [3]. It is two-lne urn rod with trffic volume of round 000 vehicles pr. dy nd speed limit of 50 km/h. The test fields for high speed rods re highwys nd motorwys in the Netherlnds. This pper descries the lyout of the urn clogging project in Copenhgen nd reports the first results. Noise nd permeility mesurements were mde t test sections of two-lne urn rod with vrious twin-ly porous sphlt pvements [3] with high uilt-in ir void of 22 to 26 %. As reference dense sphlt concrete with mximum ggregte size of 8 mm ws constructed t the test site t the sme time s the porous pvements. See Tle 1. A comprehensive mesurement progrm ws estlished. Mesurements were mde in 1999 just fter the test sections hd een uilt, nd hve een repeted ech yer to investigte the effect of geing, wer, nd clogging of ir voids in the porous sphlt. Three positions were chosen t ech section to ensure sptil verging, lthough in some yers mesurements hve not een crried out in every position. Twice yer the porous sphlt hs een clened y high-pressure wter / ir suction. In this pper the results from the SPB noise mesurements s well s the 118

3 Forum Acusticum 2005 Budpest Bendtsen, Andersen, Rerg nd Krgh 5 Permeility Figure 1: Out-flow time (s/10 cm) in the wheel-trck s function of pvement ge in months. : efore, : fter clening. Top figure represents the lne towrds south nd the ottom figure the lne towrds north. s/10cm s/10cm 0,0 60,0 50,0 40,0 30,0 20,0 10,0 0,0 0,0 60,0 50,0 40,0 30,0 20,0 10,0 0, Section I Section II Section III 4 4 Section I Section II Section III From Figure 1 it cn e seen, tht there is strong tendency for clogging in the lne towrds south where the two porous pvements with 5 mm ggregte were clogged fter to 20 months yers wheres the pvement with 8 mm ggregte stys in much etter condition. The out-flow time hs incresed rpidly in the lne towrds south t Section II nd III. The reson for this clogging is elieved to e dirt nd fine mteril from the djcent dense sphlt concrete pvement hving een drgged onto the porous pvements y vehicle tires, since clogging first ppered t position nerest to the reference section. In the lne towrds north much lower tendency for clogging cn e seen for ll the pvements. Also here the lowest level of clogging is found t the porous pvement with 8 mm ggregte. It is generlly not possile to see significnt reductions in the level of clogging from efore () to fter () the clening of the pvements Noise mesurements Tle 2. Trffic dt for the prediction of the modified Sttisticl Pss-By Index, SPBI [4]. Ctegory Light Hevy Pssenger Vn Two-xle Multi-xle Speed [km/h] W x, This pper, [-] Microphones were plced t horizontl distnces d of 9 m nd 11 m from the centre-line of the ner nd fr lne (towrds North nd South), respectively, 1.2 m ove the rod surfce. Results hve een corrected to d =.5 m y +20 log (d/.5). Pss-y noise from vehicles in the norml trffic ws nlysed. The specifictions of the Sttisticl Pss-By Method, [5], were followed s fr s possile. Mximum A- weighted noise levels with time constnt F, L AFmx, in 1/3-octve nds were mesured s well s the speed of ech vehicle, seprtely in four ctegories, x: pssenger crs, delivery vns, trucks hving two xles, nd trucks hving more thn two xles. For ech ctegory the Vehicle Noise Level, L veh, ws determined y liner regression nlysis of the noise level on the logrithm of the speed. L veh -vlues were determined for the speeds given in Tle 2, which differ from the reference speeds given in [5] in order to increse ccurcy nd relevnce in comprison etween test sections. Bsed on the L veh -vlues modified Sttisticl Pss- By Index, SPBI, ws clculted y mens of (1). L veh, x 10 SPBI ' = 10 log W x 10 (1) L veh,x is the vehicle noise level for ctegory x, nd W x is the weight for tht ctegory shown in Tle 2, [5] specifies 90% pssenger crs,.5% dul-xle trucks, nd 2.5% multi-xle trucks. Insted of 90% pssenger crs distriution of 80% pssenger crs nd 10% vns hve een ssumed. The results in Figure 2 nd Tle 2 supplements the dt presented in [6] with dt from 2003 nd 2004 []. 119

4 Forum Acusticum 2005 Budpest Bendtsen, Andersen, Rerg nd Krgh Figure 2: Results of the noise mesurements (top figure) nd the reduction of the Sttisticl Pss-By Index, SPBI, for mixed trffic (reltive to the DAC 8 pvement) mesured yer 0 to yer 5 (ottom figure). SPBI' [db] SPBI' I II III IV Tle 3. Noise reduction for mixed trffic (SPBI ) nd for pssenger crs (L veh, p ) reltively to the reference pvement (DAC8) of the sme ge. Noise reducti -on [db] Yer 5 (2004) Yer 4 (2003) Yer 3 (2002) Yer 2 (2001) Yer 1 (2000) Yer 0 (1999) I (DA8-0) II (DA5-55) III (DA5-90) SPBI L veh,p SPBI L veh,p SPBI L veh,p Noise reduction [db] SPBI' 4,5 4, ,9 3,6 2, 2,8 2, 2, 2,4 2,2 1, 1,3 1,4 0,9 1,0 1,1 I II III Figure 2 shows SPBI t ech section I-IV mesured ech yer nd the noise reduction clculted y sutrcting the noise level t the porous sphlt from the sme yer s noise level t the reference surfce IV (dense sphlt concrete with 8 mm mx. ggregte size). The noise reduction t section III with 5 mm ggregte in the top lyer ws etween 6 nd db when it ws new in At the two other test sections the noise reduction ws 5 db. The reduction hs decresed over the yers. After 5 yers the noise reduction ws etween 1 db nd 2 db. The noise reduction hs decresed more t the surfces with 5 mm ggregte in the top lyer thn t the surfce hving 8 mm stones in the top lyer. Tle 3 shows the noise reduction for mixed trffic s well s for the pssenger crs lone. The reson for highlighting pssenger cr results is tht the numer of hevy vehicles often ws smller thn the 80 vehicles required in [5]. For pssenger crs especilly section I with 8 mm ggregte in the top lyer hs etter noise reduction thn the two sections with 5 mm ggregte in the top lyer. 6,0 3,8 Thin nd plne section nlyses The Dnish Rod Institute hs developed technique where thin nd plne sections re cut out of drill cores nd nlysed in microscope, [9]. When the test sections were new nd every second yer since then cores hve een drilled nd nlysed using this technique. Figure 3 shows n exmple of n imge of plne section of new (upper picture) nd four yer old porous pvement (lover picture). The lue nd the drk green res of these cores re the stones of the pvements. The white rrers re the open spce (ir void) which is the porosity of the pvements. In the new porous pvement (upper picture) the very open structure of the pvement cn e seen s lrge white res. In the 4 yers old pvement some dirt cn e seen s light grey-green sustnce etween the stones of the pvement. It cn e seen tht it is especilly in the fine grded top lyer tht the dirt is clogging the porous. The ottom lyer with lrger stones nd lrger ir voids is not clogged s very little dirt is seen in the porous fter 4 yers. When the upper lyer of two lyer porous pvement gets clogged the effect of reducing the ir pumping noise is reduced. The noise sorption effect of the pvement is lso reduced. 1180

5 Forum Acusticum 2005 Budpest Bendtsen, Andersen, Rerg nd Krgh Figure 3.Imges of plne section of new nd four yer old porous pvement cut out of drill cores. Dirt cn e seen in the pores of the four yer old smple. When new, the thickest porous pvement with the smllest ggregte in the top-lyer (5 mm) hd the est noise reduction. As time hs pssed the porous pvement with the lrger ggregte (8 mm) in the toplyer seems to etter mintin the noise reduction. This is highlighted y the mesurements of permeility where the pvement with 8 mm ggregte in the toplyer gets significntly less clogged thn the pvements with smller ggregte. On the ckground of these preliminry results it is not possile to give finl evlution of the vlidity of the hypotheses of the DRI- DWW project (see section 3). Further mesurements nd nlyses re needed nd will e crried out. Anlyses of thin nd plne sections s well s the use of CT-scnning of drill cores will e used to evlute the clogging process of the porous pvements. 9 Acknowledgements The clogging project, which is prt of The DRI-DWW noise tement progrmme, hs only een mde possile y the finncil nd technicl support nd coopertion of Rod nd Hydrulic Engineering Institute in the Netherlnds (DWW) s prt of the frmework of the Dutch IPG progrm. The Øster Søgde experiment ws finnced y the Dnish Ministry of Trnsport, the Ministry of Environment, nd orgnistions nd compnies represented in the project group. The memers of the Dnish project group on the Øster Søgde experiment hve mde excellent nd importnt contriutions to the whole project. These people re (esides the uthors of this pper) Lene Michelsen from the Dnish Rod Directorte, Steen Kønigsfeldt nd Michel Rsmussen from the Municiplity of Copenhgen, Jørn Bnk Andersen from the Ntionl Union of Pvement Contrctors nd NCC nd Bjrne Schmidt from the Dnish Rod Institute/Rod Directorte. 8 Conclusion nd perspective 1181

6 Forum Acusticum 2005 Budpest Bendtsen, Andersen, Rerg nd Krgh References [1] The DRI-DWW Noise Atement Progrm - Project description. Note 24, Dnish Rod Institute, Rod Directorte ( [2] Noise Innovtion Progrm. Rod Trffic. (The IPG progrmme). DWW report [3] Bendtsen, Hns; Lrsen, Lrs Ellejerg; Greie, Poul. Development of noise reducing pvements for urn rods (Udvikling f støjreducerende vejelægninger til ygder (in Dnish with extended English summry)). Dnish Trnsport Reserch Institute. Report 4, [4] J. Krgh, H. Bendtsen: Performnce of New Twin-ly Dringe Asphlt lid in Denmrk, Proceedings Internoise 2000, Nice, 2000 [5] ISO (Acoustics) Mesurement of the influence of rod surfces on trffic noise Prt 1: The Sttisticl Pss-By Method [6] J. Krgh, H. Bendtsen. 3 Yers Performnce of Twin-Ly Dringe Asphlt in City Street, Proceedings Euronoise 2003, Neples 2003 [] B. B. Jessen, J. Krgh: Trffic noise t four test sections of Øster Søgde (in Dnish), DELTA Technicl reports AV 141/03, Lyngy 2003 nd AV 1493/04, Hørsholm 2004 [8] Clogging of ituminous porous pvements n investigtion in Copenhgen. Dnish Rod Institute. Report 120, 2002 ( 1182