deliverable - qcity · 2020. 10. 18. · reference asphalt type standard abt11, tested 2004. temp...

TIP4-CT-2005-516420 Page 1 of 64

QCITY issued: 2006-02-15

DELIVERABLE D3.18 CONTRACT N° TIP4-CT-2005-516420

PROJECT N° FP6-516420 ACRONYM QCITY

TITLE Quiet City Transport Subproject 3 Vehicle/Infrastructure interface related noise Work Pack-age

3.5 Refine and optimize the road surface

D3.18 Studies of poroelastic road surfaces in a lab-scale.

Written by Nils Ulmgren Henrik Malker, Peter Malm, Nils-Åke Nilsson

NCC ACL

Date of issue of this report 2006-02-15

PROJECT CO-ORDINATOR Acoustic Control ACL SE PARTNERS Accon ACC DE

Akron AKR BE Amec Spie Rail AMEC FR Alfa Products & Technologies APT BE Banverket BAN SE Composite Damping Material CDM BE Havenbedrijf Oostende HOOS BE Frateur de Pourcq FDP BE Goodyear GOOD LU Head Acoustics HAC DE Heijmans Infra HEIJ BE Royal Institute of Technology KTH SE Vlaamse Vervoersmaatschappij DE LIJN LIJN BE Lucchini Sidermeccanica LUC IT NCC Roads NCC SE Stockholm Environmental & Health Administration SEA SE Société des Transports Intercommunaux de Bruxelles STIB BE Netherlands Organisation for Applied Scientific Research TNO NL Trafikkontoret Göteborg TRAF SE Tram SA TRAM GR TT&E Consultants TTE GR University of Cambridge UCAM UK University of Thessaly UTH GR Voestalpine Schienen VAS AU Zbloc Norden ZBN SE Union of European Railway Industries UNIFE BE

PROJECT START DATE 2005-02-01 DURATION 48 months

Project funded by the European Community under the SIXTH FRAMEWORK PROGRAMME PRIORITY 6 Sustainable development, global change & ecosystems

D3.18 Poroelastic Road Surfaces

Nils-ÅkeNy stämpel

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T A B L E O F C O N T E N T S 1 INGRESS ..............................................................................................................................................................8

2 PROTOTYPE ROAD SURFACES - MEASUREMENTS ON LAB PLATES. ........................................................9

2.1 LAB PLATES ........................................................................................................................................................9 2.1.1 Basic design ............................................................................................................................................9 2.1.2 Manufactured slabs 2005 ..................................................................................................................10

2.2 ROAD SURFACE IMPEDANCE ............................................................................................................................10 2.2.1 Measurement methology .................................................................................................................11 2.2.2 Measurement equipment .................................................................................................................13 2.2.3 Poroelastic asphalt lab plates..........................................................................................................13 2.2.4 Results .....................................................................................................................................................13

2.3 ROAD SURFACE ABSORPTION...........................................................................................................................16 2.3.1 Impedance tube measurement method.....................................................................................17 2.3.2 Measurement equipment .................................................................................................................17 2.3.3 Measurement set-up ..........................................................................................................................17 2.3.4 Results .....................................................................................................................................................18

2.4 RESISTANCE AGAINST WEAR .............................................................................................................................21

3 SELECTION OF RUBBER GRAIN .....................................................................................................................22

3.1 DETERMINATION OF RUBBER GRAIN SIZE............................................................................................................22 3.1.1Measured specific surface for standard aggregate material 4/8 mm vs. specific surface for the cubical aggregate particle model (6 mm)..............................................................................23 3.1.2 Results from calculations of max rubber grain size based on the cube model.................23

3.2 GENERAL CONCLUSIONS REGARDING MAXIMUM RUBBER GRAIN SIZE ...............................................................27 3.3 QUESTIONS STILL TO BE ANSWERED ...................................................................................................................28

4 STRESS AND STRAIN IN POROELASTIC ROAD SURFACES - FEM-CALCULATIONS. ............................29

4.1 CONCEPTS AND SIMPLIFICATIONS IN THE FEM-MODEL ....................................................................................29 4.1.1 Composition..........................................................................................................................................29 4.1.2 Applied forces ......................................................................................................................................32 4.1.3 The FEM-model of the poroelastic road surface. .......................................................................33

4.2 CALCULATION RESULTS FROM A 2D FEM-MODEL ............................................................................................35 4.3 CONCLUSIONS ................................................................................................................................................43 4.4 CONTINUED WORK ..........................................................................................................................................44

5 PRE-TREATMENT WITH BITUMEN OF THE RUBBER GRAIN .........................................................................45

5.1 USING BITUMEN EMULSION FOR PRETREATMENT .................................................................................................45 5.2 USING BITUMEN FOAM FOR PRE-TREATMENT......................................................................................................46 5.3 DEVELOPMENT OF METHODS FOR DISINTEGRATION OF PRETREATED RUBBER GRAINS..........................................47


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6 DEVELOPMENT OF ROAD SURFACE CONSISTING OF AN UPPER OPEN GRADED ASPHALT SURFACE SUPPORTED BY AN ELASTIC SUB LAYER (PERFORMING PARTNERS: CDM & HEIJMANNS). ..48

7 INPUT DATA FOR AN IMPEDANCE MODEL TO CALCULATE THE ROLLING POWER DISTRIBUTION BETWEEN THE TYRE AND THE ROAD SURFACE. ..................................................................................................49

8 REFERENCES .....................................................................................................................................................50


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E X E C U T I V E S U M M A R Y

OBJECTIVE OF THE DELIVERABLE To present the results from

• theoretical studies made to obtain a better understanding of the poroelastic road surface concept and the relative influence of different parameters such as rubber content and grading and the stresses built up in the binder.

• the first stage of studies of materials for poroelastic road surfaces in laboratory. These studies involves the influence on sound emission and wear of parameters such as grading of rubber grains, pre-treatment of rubber grains with bitumen, content of bitumen in the rubber-bitumen mix, composition of a poroelastic mix (content of rubber grain, content of bitumen, type of bitumen, aggregate maximum size and grading, void content etc.).

The laboratory studies are planned for two years with the addition of paving of smaller test sites during the second year, why this deliverable only is a part report presenting the results obtained so far from these studies in laboratory.

STRATEGY USED AND/OR A DESCRIPTION OF THE METHODS (TECHNIQUES) USED WITH THE JUSTIFICATION THEREOF Parallel with more theoretical studies the influence of amount and characteristics of components on acoustical and mechanical behaviour of the poroelastic road surface concept are basically studied in a lab scale on plates because of the many variants involved. The interesting compositions will then be tested on small test sites. A full scale test road will be made in 2007.

PARTNERS INVOLVED AND THEIR CONTRIBUTION Acoustic Control (ACL)

Measurement of acoustical and mechanical impedances as well as FEM-analysis of binder strain and selection of rubber grain size.

Composite Damping Material (CDM)

Development (together with Heijmans) of an asphalt surface with an elastic sub-layer. Providing rubber mats for this surface. Providing granulated rubber for the poroelastic road surfaces.

Goodyear (GOOD)

Studies of the influence from elastic road surfaces on vehicle dynamics; studies of con-tact pressure distribution for elastic road surfaces for typical tyre/road combinations.

Heijmans (HEIJ)

Development (together with CDM) of an asphalt surface with an elastic sub-layer.


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NCC Roads AB (NCC)

WP-leader for WP 3.5. Development of poroelastic road surface together with TRAF and ACL. Responsible for lab tests of road surfaces. Responsible for paving of test surfaces in connection to field tests.

Trafikkontoret Göteborgs Stad (TRAF)

Development of poroelastic road surfaces together with NCC and ACL. Responsible for selection of test sites for field testing of poroelastic road surfaces.

ACHIEVEMENTS AND CONCLUSIONS The project is ongoing and the below presented achievements is what has been achieved so far.

A method in which the rubber grains can be pre-treated with bitumen in order to get better adhesion and wear life has been developed.

Recipes which meet the requirement of a 15 dB lower dynamic stiffness of the poroelas-tic road surface compared to a dense standard surface have been developed and tested in lab environment. The figure below presents measurement results for dynamic stiffness of some of these lab tested poroelastic road surfaces.

B

Diagram 6. Summary of the measured dynamic stiffness, asphalt surfaces tested during 2005.

100

110

120

130

140

150

160

100

Freq

Dyn

amic

stif

fnes

s dB

re 1

N/m

Reference asphalt type standard ABT11, tested 2004. Temp 21-22 degrees.

Poroelastic asphalt Sample 1 2005




Measurements of absorption factors for dthickness have resulted in a way to optimise to steer the peak sound absorption to frequin a maximum noise reduction in dB(A).


15 d

1000 10000

uency [Hz]



All samples tested in 2005 had surface temperature of 19 Degree.

ifferent poroelastic asphalt surfaces and the thickness of the asphalt surface in order ency regions around 1000 Hz, which results

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Equations for selection of optimal sizes of rubber grains for different recipes have been developed, see figure below.

5%

6%

7%

8%

9%

10%

0.60

0.80

1.00

1.20

1.40

1.60

1.80

Rubber cont ent [ %(weight ) ]

Bit umen cont ent [ %(weight ) ]

A FEM-based tool has been developed in which the fatigue strength of a poroelastic asphalt mix can be calculated (see figure below for a combined vertical and horizontal load onto the poroelastic model.

The FEM calculated strain has been compared to the fatigue limits for typical bitumen binders used for asphalt mixes. As seen in Figure below, the calculated strain of 0,008 for passenger car loads can be handled for one megacyles by PmB binders of good qual-ity.


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It can be concluded that important and valuable tools have been developed for the creation of a stable wear-resistant low-noise poroelastic road surface.


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1 I N G R E S S The object of this study is to develop the poroelastic concept for road surfaces. Earlier studies have given a basic idea about the composition but at the same time pointed at some special aspects that influence the behaviour of the poroelastic road surface. Be-sides the composition of the mix special attention are given to rubber size and pre-treatment of rubber with bitumen and their influence on sound absorption and resis-tance to wear.

The work is set up in two parts and starts with tests in lab scale together with theoretical studies of the behaviour of an elastic material (rubber) included in a composite mix (asphalt). The lab tests is made of manufacturing a larger number of test surfaces (plates) for measurements of parameters relevant to tyre excitation and radiation such as mechanical impedance, surface roughness and sound absorption together with dif-ferent tests for determining the wear resistance.

While the lab tests will be continued over a period of two years, the second year will be devoted to smaller test sites. These will be paved with the new surface for which sound emission wear/durability, friction, handling will be measured. Testing will be made for noise but also for wear/durability and safety.

The objective is to refine and optimise the poroelastic road surface with respect to composition, thickness, void content and production methods.

Some alternative ideas will also be looked at such as dense surface with highly compli-ant sub layer.


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2 P R O T O T Y P E R O A D S U R F A C E S - M E A S U R E M E N T S O N L A B P L A T E S .

2.1 LAB PLATES Lab plates are used for testing at one hand for dynamic stiffness and sound absorption and at other hand for wear resistance.

The plates are produced by compacting laboratory mixed mixtures in a mould with a small roller (see Figure 1). The plates are normally 40 mm thick and have a dimension of 500 x 500 mm.

Variables for lab plates that are being studied are at first hand rubber grading, amount of rubber, pre-treatment of rubber, binder type, binder content, aggregate grading and aggregate size.

2.1.1 Basic design Earlier trials with testing poroelastic road surfaces have given a rough idea of a suitable composition of the mix. It’s a sensitive balance between the effect on noise reduction and resistance against wear and the wear mechanism for vehicles rolling on a poroe-lastic road surface is not fully understood (see Selection of rubber grains). To have a ba-sic design to work with and be able to study different mix parameters influence on noise reduction compositions given in Table 1 were tested for impedance (see chapter 2.2.3). The rubber grains were pre-treated with emulsion and PmB20, which is a SBS-modified bitumen from Nynas Bitumen.

Table 1. Test plates for chosing Basic design.

Aggregate, % Pre-treated rubber, %, with added bitumen in brackets Plate no 0/4 mm 4/8 mm 0/0,5 mm 0,5/2 mm

Binder PmB20, %

1 15 77 8,0 (25 %) 7,5 2 17 77 2,4 (35 %) 3,6 (25 %) 7,8 3 15,7 77 3,3 (35 %) 4,0 (25 %) 7,8 4 14,5 77 4,3 (35 %) 4,3 (25 %) 7,8

Of this four mixes no 4 gave the best result and 15-17 dB lower dynamic stiffness com-pared to the reference ABT11 asphalt was achieved. This is judged to be sufficient for fully utilizing the elastic characteristics in order to obtain the desired noise reduction of the road surface.

This mix has been used as basic design in the following work done so far. With basic de-sign should in this case be understood that the composition is unchanged for aggre-gate grading and size and bitumen and total rubber content. This design is probably not the optimal solution and will be changed whenever input is given from other stud-ies, e.g. see chapter 3 and 4.


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2.1.2 Manufactured slabs 2005 Plates have been manufactured to study the influence of the pre-treatment of rubber on the lab mix process in regard to practical questions and homogeneity of the mixture and at the same time some other variations have been studied, e.g. type of binder and proportions of rubber gradings. The plates are listed in Table 2. The mix numbers for pre-treated rubber grains refer to chapter 5.1. As a practical alternative to PmB a rubber modified binder (RmB) has been utilized (see Table 2). The basic design has been used for these mixes/plates (with one exception), which means constant aggregate grading, 14,5 % of 0/4 mm and 77 % of 4/8 mm, and constant binder content, 7,8 %. The void content has been estimated by measurement to be 15-20 %.

The exception is plate 6:1 for which the mix was made in Drammen with rubber pre-treated with foamed bitumen. Composition: 84 % aggregate size 8/11 mm, 8 % rubber grains 0/1,6 mm (25 % dry bitumen of the total rubber weight) and 8 % bitumen 70/100.

Table 2. Composition of lab plates.

Plate no Binder type 1) Rubber grain

0/0,5 mm 0,5/2 mm

Mix 9 % Stored days

Mix 10 %

Stored days

1 RmB 1 4,25 13 4,25 11 2-4 2) RmB 2 3,8 15-27 4,7 13-25 5 160/220 3,8 30 4,7 28 6:1 3) 6:2 RmB 2 3,8 4) 4,7 4)7 RmB 2 8,5 63 61 8 PmB20 3,8 64 4,7 62

1) RmB 1 = 10 % of 0/0,5 mm rubber in bitumen Laguna 70/100, RmB 2 = 10 % of 0/0,5 mm rubber in Laguna 160/220. 2) Modified mixing process: The components are added at different stages of the mixing process, e.g. the fine rubber is added at a later stage or all the rubber is added at a later stage. But no real significanse is found. 3) Plate from mixture mixed in Drammen (see above). 4) Untreated rubber.

These plates have been tested for wear and for its noise reducing properties (see re-spective chapter 2.2.3 and 2.3).

More lab plates are being manufactured especially to study the effect of bitumen pre-treatment of the rubber in regard to amount of bitumen and its effect on resistance to wear over time (see chapter 5).

Initially the lab tests are only performed on single layers. Depending on the results, lab tests for twin layer versions of this surface, could take place at a later stage.

2.2 ROAD SURFACE IMPEDANCE The dynamic stiffness of a structure is the ratio of the force divided by the responding vibration displacement (displacement is achieved by double integration of measured vibration acceleration), when the test object is excited with a force from e.g. a ham-mer impact. In this study the dynamic stiffness has been analysed as a function of fre-


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quency (in the continuation called Frequency Response Function, FRF). Normally it is dis-tinguished between point and transfer FRF. Point FRF is obtained when the force and response is measured in the same position. Transfer FRF is obtained when the response is measured at a greater distance from the force excitation. The mechanisms involved with the sound generation at the tire/road are mostly local and occur close to the lead-ing and trailing edge of the contact area. Therefore, in this study, it has been focused only on the point FRFs in order to as closely as possible measure parameter relevant for the excitation process.

Measurements have been performed in the laboratory at Acoustic Control as well as at NCC’s road laboratory in Upplands Väsby. During the autumn of 2004 four different poroelastic asphalt samples (referred to as Sample 1 – Sample 4, 2004) and one refer-ence asphalt of the type ABT11 was tested. During the fall of 2005, six additional poroe-lastic asphalt samples (referred to as Sample 1 – Sample 6, 2005) were tested at NCC’s road laboratory in Upplands Väsby.

To avoid edge effects the samples in this study have had a size of appr. 0,5x0,5 m. The surface temperature of the samples during the tests did fall in the interval of 18-22 ˚C.

2.2.1 Measurement methology The measurements have been performed with aid of an impedance measurement head. The impedance head for measurement of the Dynamic Stiffness of road surfaces was developed by ACL and was first presented at the ICSV conference in 2003 (see ref [1]). Here is presented a short summary of the impedance head technology and its ad-vantages compared to the traditional method where the force and response trans-ducers are mounted side-by-side.

2.2.1.1 The traditional way of measuring mechanical impedance - the side-by-side-method.

The commonly used method when measuring the mechanical impedance of a road surface has been to employ the side-by-side technique (ref [2]). This means that the force excitation and the resulting vibration response are not measured along the same axes. Instead the response is measured some centimetres from the excitation position.

2.2.2.1 The IMPEDANCE HEAD concept.

When using the side-by-side technique and hammer excitation, it is for practical rea-sons not possible to keep a constant distance between the excitation and response position. Consequently transfer impedance rather than the desired point impedance will be obtained. This means that the influence e.g. from local deflection will vary in a more or less uncontrollable way. The excitation force is also working on a small surface determined by the dimensions and elastic characteristics of the hammer-tip. All this to-gether result in that the side-by-side method is uncertain with respect to the actual im-pedance seen by a tire tread block at in-service conditions.

If the (in-line) impedance head technique is used, influence from both the non-propagating local deflection as well as from propagating waves such as Rayleigh waves, shear waves, bending waves and compression waves will be obtained. The ad-


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vantage of applying the impedance head technique thus increases at increased compliance of the road surface. The method is therefore of particular interest for poroe-lastic road surfaces.

2.2.3.1 Impedance head for use on poroelastic road surfaces - design

In order to comply with the below mentioned characteristics, a special impedance head adapted for measurements on road surfaces have been designed. Among the features that have been the design targets are:

• All resonance frequencies of the impedance head and particularly the contact plate below the force transducer should be well above the upper limiting fre-quency for the frequency range of the measurement.

• The mass of the contact plate below the force transducer should be low enough in order not to create a mounting resonance below the upper limiting frequency for the measurement. The lower dynamic stiffness of the surface, the lower mass of the impedance head is required.

The above criteria have been met by using aluminum as material of the impedance head housing as shown in Figure 1. The thickness of the contact plate has also been se-lected to create a first plate resonance around 2 kHz.

Figure 1. Impedance head for measurement of the dynamic stiffness of poroelastic road surfaces. The contact plate diameter is tuned to give relevant data for the dynamic process of a tire tread block in the contact patch.

Impedance hammer here only used for creating the right force impulse.

Housing for accelerometer mounted in-line with the force transducer.

Force transducer

Contact plate with the size of a tread block.


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2.2.2 Measurement equipment The used measurement equipment is presented in Table 3 below.

Table 3. Used measurement equipment. Equipment Type Serial no.

Front-end Brüel&Kjaer PULSE 7 channels 2414019

Accelerometers PCB 353B11 25541 Impedance head Force transducer PCB 208C04 19099

2.2.3 Poroelastic asphalt lab plates. The impedance tests have been performed on four poroelastic asphalt samples and one reference ABT11 during the autumn of 2004 and six additional poroelastic asphalt samples in November 2005. The poroelastic asphalt surfaces had recipes according to Table 1 (chapter 2.1.1) and Table 2 (chapter 2.1.2, sample 6 corresponds to sample 6:1).

2.2.4 Results The measurement results are presented in appendix 1 (Diagram 1-5) for measurements performed in 2004 and Appendix 2 (Diagram 1-7) for measurements performed in 2005. The results are presented as dynamic stiffness in the frequency range 100 – 3200 Hz. The Diagram 1 presents a summary of all tested road surfaces (in each year) followed by separate diagrams for each sample surface compared to the reference ABT11 asphalts surface. Below in Figure 2 and Figure 3 the summary diagrams from measurements 2004 and 2005 are presented.


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Diagram 1. Summary of the measured dynamic stiffness, asphalt surfaces tested during 2004

100

110

120

130

140

150

160

100 1000 10000

Frequency [Hz]

Dyn

amic

stif

fnes

s dB

re 1

N/m

Reference asphalt type standard ABT11.Temp 21-22 degrees.

Poroelastic asphalt Sample 1 Temp 21-22 degrees.

Poroelastic asphalt Sample 2 Temp 18 degree.



Figure 2. Summary of the measured dynamic stifness for earlier tested asphalt surfaces in 2004. Also presented in as Diagram 1 in Appendix 1.

Figure 3. Summary of the measured dynamic stifness for tested asphalt surfaces in 2004. Also presented in as Diagram 1 in Appendix 1.

Diagram 6. Summary of the measured dynamic stiffness, asphalt surfaces tested during 2005.

100

110

120

130

140

150

160

100 1000 10000

Frequency [Hz]

Dyn

amic

stif

fnes

s dB

re 1

N/m








All samples tested in 2005 had surface temperature of 19 Degree.


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2.2.1.4 Revealed characteristics by the 2004 measurements of dynamic stiffness

• Sample 1 had high elasticity, but not enough strength. This was due to production problems in that the total amount of asphalt mix was not enough to fill up the frame in order to ensure complete full scale compaction of the sample.

• Sample 2 had good strength, but low elasticity. This was due to too low content of rubber grains (6 %).

• Sample 3 also had good strength qualities, but only a little higher elasticity com-pared to sample 2. The slightly increased elasticity is probably due to the increased amount of rubber grains (7,3 %).

• Sample 4 had both good strength and high elasticity. The reason for the sudden decrease of Dynamic Stiffness due to a rather small increase of rubber grains (same increase as between sample 2 and sample 3) could be due to the total amount of rubber grains reaching a level (8,6 %) ensuring a high percentage of stone-rubber-stone contact resulting in low dynamic stiffness. The lower dynamic stiffness could also be explained by a lower degree of compaction due to the more elastic hot mix.

Sample 4 has 15-17 dB lower dynamic stiffness compared to the reference ABT11 as-phalt. This is judged to be sufficient for fully utilizing the elastic characteristics in order to obtain the desired noise reduction of the road surface.

2.2.2.4 Measurements (2005) of dynamic stiffness for lab. test plates of poroelastic road surfaces

The purpose of the test on road surface lab samples during the fall 2005 was to investi-gate the influence from

• Treatment of the rubber by foam bitumen • Different binder types e.g. rubberized bitumen (rubber powder treated in heated

bitumen for 30 – 60 minutes) • The order of mixing of different components in order to achieve a more homoge-

neous mixture.

Samples 1-4 displayed excess amount of rubber in the surface layer for the sample which is believed to be one of the reasons for the low dynamic stiffness for these sam-ples. The excess rubber resulted in low surface porosity, see Figure 4. The excess rubber in the surfaces of sample 1-4 is likely to be worn off rather quickly in normal traffic. There-fore we believe that the low dynamic stiffness of these samples would not be main-tained over a longer period of time.

Sample 5 and 6 of 2005 display a Dynamic Stiffness close to that of sample 4/2004, which had been judged to be the target for an efficient poroelastic road surface (an optimal value with respect to the compromise between strength and noise reduction). Sample 5 and 6 displayed no excess rubber in the surface layer, see Figure 5. The void content has been estimated to be in the range of 15 – 20 %.


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Figure 4 Poroelastic asphalt sample 2/2005. This sampe displayed a large amount of excess rubber in the surface layer.

Figure 5 Poroelastic asphalt sample 5/2005. Less rubber in the surface layer and more porosity.

2.3 ROAD SURFACE ABSORPTION Measurements of absorption according to the two microphone method in an imped-ance tube have been performed on drill samples of poroelastic asphalt surfaces during 2004. One of the samples was cut in two to investigate the influence of different thick-ness on the absorption curve.


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2.3.1 Impedance tube measurement method The absorption factor is defined as the reflected sound intensity divided with the normal incident sound intensity. The absorption factor is a number between 0 and 1, where 0 is achieved for a totally reflecting surface and 1 for a totally absorbing surface. Absorp-tion factors for tested poroelastic surfaces have been measured with the two micro-phone method in an impedance tube. Figure 6 below presents a sketch of the imped-ance tube for measurements of absorption factor with the two microphone method. The loudspeaker sends out a sound signal (broadband white noise) that is partially ab-sorbed and partially reflected by the test sample. By measuring the complex transfer function between two fix microphone positions the absorption factor for the test sample can be calculated.

Figure 6. Sketch of the impedance tube for measurements of absorption factor with the two microphone method.

2.3.2 Measurement equipment • Noise generator: Larson Davis SRC 20

• Power amplifier: OSC Professional Power Amplifier Type USA 370

• Impedance tube: Brüel & Kjaer typ 4206

• Analyser: Brüel & Kjaer Portable Pulse

2.3.3 Measurement set-up Figure 7 shows the measurement set-up for measuring absorption factor with the im-pedance tube.


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Figure 7. Measurement set-up – Impedance tube, noise generator, power amplifier and computer connected to the multy channel Brüel & Kjaer Pulse portable system.

2.3.4 Results The three poroelastic asphalt surfaces that were measured for absorption factors were the Sample 1, 2 and 4 from 2004, see chapter 2.1.1. Figure 8 presents measured absorp-tion factor in the frequency range 100 Hz – 1600 Hz for the three test samples. Samples 1 and 4 has approximately the same level of absorption, but the maximum of the absorp-tion factor curve occur at different frequencies 730 Hz for sample 1 and 630 Hz for sam-ple 4. Sample 1 has a thickness of 40 mm compared to sample 4 that is 50 mm thick. Sample 2 had an overall lower absorption. The absorption factor for all three samples level out for higher frequencies where sample 4 has a little better absorption than sam-ple 1 and 2.


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0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600

Frequency [Hz]

Abs

orpt

ion

fact

or α

Sample 1

Sample 2

Sample 4

Figure 8. Measured absorption factor for the test samples 1, 2 and 4 from 2004. Test sample 1 have been appr. 40 mm thick and 100 mm in diameter. Test sample 2 and 4 have been appr. 50 mm thick and 100 mm in diameter.

Sample 4 was cut by focused high pressure water in two slices 15 mm and 35 mm thick, see Figure 9. The aim was to investigate the influence of sample thickness on the meas-ured absorption factor. Figure 10 presents the measured absorption factor for sample 4 with two different thickness, 50 mm and 35 mm. The frequency for the maximum ab-sorption is shifted from 630 Hz to 1150 Hz when reducing the thickness from 50 mm to 35 mm.

Sample 4 Sample 1

Sample 2


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Figure 9. The sample 4 is cut by focusand 35 mm. To the left the othe reduced sample 4, 35 mm

0.00

0.10

0.20

0.30

0.40

0.50

0.60or

0.70

0.80

0.90

1.00

100 200 300 400 500 600 700

Frequen

Abs

orpt

ion

fact

α

Sample 4

Sample 4

Figure 10. Measured absorption factor

m

Sam50 m

ple 4 m thick


50 m

d high pressure water in two slices of 15 iginal sample 4, 50 mm thick and to the r

ick.

er

th

800 900 1000 1100 1200 1300 1400 1500

cy [Hz]

cut in two and put together, thickness appr. 50 mm

cut, thickness 35 mm

for the sample 4 with two different thickne

m

Sample 4 35 mm thick

35 m

mm ight

1600

ss.

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2.4 RESISTANCE AGAINST WEAR Tests for mechanical behaviour (wear, water sensitivity and deformation) are being per-formed on samples taken from plates (se chapter 2.2.1). This is performed at NCC Road Laboratory at Upplands Väsby. These tests are going on at the moment and will be re-ported in the next delivery. The tests, which are being performed on cored or sawed samples depending on method, are

• W nce in accordance with EN 12697-16 Abrasion by studded tyres - Part A, t.

o A cylindrical specimen having a diameter of 1 a length of 30 mm is brought to a temperature of 5 °C. The specimen is worn by abrasive action during 15 min by 40 steel spheres. The loss of volume in millilitre is recorded and is reported as the abrasion value.

• Wear resistance in accordance with EN 12697-17 Particle loss of porous asphalt specimen, the Cantabro test.

o Particle loss is assessed by the loss of mass of porous asphalt samples after turns in the Los Angeles machine.

Even if it is not normally part of the test it will also be performed after condi-tioning in water in accordance with EN 12697-12 Water sensitivity.

ment Analyzer).

o The susceptibility of bituminous materials to deform is assessed by the rut formed by repeated passes of a loaded wheel at constant temperature.

ear resista the Prall tes

00 mm and

• Wheel tracking test (rutting test) with and without water in APA (Asphalt Pave-

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3 S E L E C

3.1 ETERMINATION OF RUBBER GRAIN SIZE Previous studies of poroelastic test surfaces show that it is possible to get an excellent noise reduction performance. The studies also show that a poroelastic road surface could be 12 dB(A) less noisy compared to a standard dense asphalt surface of type ABT11 (=AC 11, Dense Asphalt Concrete with 11 mm maximum aggregate size). How-ever, the wear resistance has up to now been poor in the poroelastic road surface. Fur-thermore the wear mechanism for vehicles rolling on a poroelastic road surface is not fully understood. Among the factors that could be the cause for the poor wear charac-teristics are:

• Too big rubber grains

If the rubber grain size is bigger than the average binder film thickness, it is then believed that the binder film would not completely cover the aggregate, result-ing in poor adhesion.

• Rubber grains absorb part of the bitumen binder material

It has been found that rubber can absorb large quantities of bitumen. This proc-ess is very slow in normal outdoor temperatures, but will be clearly visible after some months. The amount of binder left “free” in the mix is then not enough to provide the necessary strength.

• Increased strain and stress on the bitumen binder due to the rubber content

(see FEM calculations). Since the rubber grains normally are softer than the bitu-men binder material, the bitumen binder has to take the entire load from the traffic. This means that load on the binder material can exceed the fatigue stress limit. The recipe of the mix must then be carefully designed to be below the stress limits for the applied stress (i.e. adopted to the type of traffic for the particular road section (passenger, cars light trucks or heavy trucks)

The aim of the analysis below is to determine what parameters that should determine the maximum rubber grain size in order to achieve maximum strength of the finished poroelastic asphalt mix.

We then base the analysis on the assumption that:

No rubber grain shall be bigger than the average film thickness of the bitumen-binder/rubber mix.

T I O N O F R U B B E R G R A I N

D


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3.1.1 Measured specific surface for standard aggregate material 4/8 mm vs. specific article model (6 mm)

cific surface area for a aggregate mix within a certain interval and with a onventional size distribution, resembled by a mix of spherical bodies of same size dis-

tribu io gate mix, has the same specific surface area as a cubical

surface for the cubical aggregate pIn order to simplify the calculation we view the rubber grains as part of the binder mate-rial and assume a cubical aggregate particle model with the rubber grains as a “ma-trix” on the particle walls (see figure in section 4). When comparing the specific surface for a aggregate mix 4/8 mm it has been found that it coincide with the specific surface of cubical aggregate particle of the average size of the aggregate mix (in the exam-ple the size of the cubical aggregate particle will be 6 mm).

In other words:

The total spec

t n as the actual aggrebody w f the aggregate mixith the average size o .

Therefo minimum and maximum rubber grain size shown below hav b

The sabitume

Table 4. fic surface for a mix of spherical bodies and

re all calculations ofe een made using the cubical aggregate particle model.

me model has also been used for the FEM-calculations of strain and stress in the n/rubber mix.

Comparison between specispecific surface for a cubical body of average aggregate size

Aggregate mix

Lower limit [mm]

Upper limit [mm]

Specific surface for mix of spherical bod-

ies of different size [mm2/mm3]

Specific surface for cubical body of

average aggregate size [mm2/mm3]

Average particle

size [mm]

0,5 1 8 8 0,75 1 2 4 4 1,5 2 4 2 2 3 4 8 1 1 6 8 11 0,63 0,63 9,5

11 16 0,44 0,44 13,5 8 16 0,5 0,5 12

16 25 0,29 0,29 20,5

3.1.2 ber grain size is to use the surface area of the

aggregate mix. We then apply the selected amount of bitumen and rubber and calcu-late the film thickness of the bitumen/rubber slurry mixture that will cover each aggre-gate.

Results from calculations of max rubber grain size based on the cube model One way of calculating the maximum rub


TIP4-CT-2005-516420 Page 24 of 64


In practice this can be made using three parameters;

• the density (ρ) for the components,

• the size (l) of the aggregate grains and

• the mass fraction (mf) of the components.

Using these parameters the rubber/bitumen film thickness can be calculated. As previously stated the rubber grain size shall not exceed the binder film thickness.

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fillermfρbitume

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Where the mass fraction is defined as; total

component mmf = .

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gregate powder).

componentm = total weight of a component in the mix [kg].

componentmf = mass fraction of a component (ex fillermf =mass fraction of the fine ag


TIP4-CT-2005-516420 Page 25 of 64


componentV = volume of a component in the mix [m3].

he aggregate mix [m2].

gA1 2

totA = total surface area of t

particleggre ate = area of one aggregate [m ].a

particlen = number of aggregates in the mix.

componentρ = compact density of a component [kg/m3]

particleaggregatel = length of side in cubical aggregate in model [m].

It can be seen that if larger aggregate particles are used but the same percentage (weight) of aggregate in the mix is kept, it allows us to use larger rubber grains.

Calculations have been performed for an aggregate mix of 4/8 mm assuming that the oversize particles are 11 mm. The very fine aggregate powder (filler) included in the road surface recipe has also been viewed as belonging to the bitumen/rubber mix, hence the film between aggregates consists of a mix of bitumen/rubber/filler.

The calculations show that, for a 4/8 mm aggregate mix, the maximum rubber grain size is about 1 mm for a mix of 10% rubber, 8% bitumen and 4.5% filler. The result is achieved using the dimensions for the oversize particles as aggregate particle size.


TIP4-CT-2005-516420 Page 26 of 64


Figure 11.

grain size f approximately 0.4 mm with the same mix of components as above.

Figure 12. Rubber grain size as a function of rubber fraction and different bitumen contents for an aggregate particle size of 4 mm. Here shown as an example of the determination of minimum rubber grain size for a 4/8 mm aggregate mix.

Rubber grain size as a function of rubber fraction and bitumen contents for an aggregate size of 11 mm (11 mm is here selected as the oversize particle for a aggregate mix of 4/8 mm).

The smallest aggregate particles in the mix are 4 mm. This generates a rubbero

5%

6%

7%

8%

9%

10%

1,00

1,20

1,40

1,60

0M

axi

mum

rub

ber

gra

in s

ize

[mm

]Bitumen content

0,60

5% 6% 7% 8% 9% 10%

11%

12%

13%

14%

15%

Rubber content [%(weight)]

0,80

1,8

[%(weight)]

Ag regasize 11 mm

g te

5%

6%

7%

8%

9%

10%

0,20

0,30

0,40

0,50

0,60

0,70

5% 6% 7% 8% 9% 10%

11%

12%

13%

14%

15%


Ma

xim

um ru

bb

er g

rain

siz

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m]

Bitumen content [%(weight)]

Aggregate size 4 mm


TIP4-CT-2005-516420 Page 27 of 64


It is also of interest to se how the rubber grain size interval varies with the amount of

Figure 13. tion of the maximum rubber

A

For very of rubber grain in the total mix (typically, a rubber grain content around 3%), the grain size should not exceed 0,7 mm. A grain size interval for this frac-tion of rubber could be 0,3/0,7 mm.

For higher fraction of rubber grain in the mix (typically rubber grain content around 10%) the grain size should not exceed 1,1 mm. A grain size interval for this fraction of rubber could be 0,4/1,1 mm.

For very high fraction of rubber grains in the mix (typically around 15%) the grain size should not exceed 1,5 mm. A grain size interval for 15 %w rubber could be 0,5/1,5 mm.

3.2 GENERAL CONCLUSIONS REGARDING MAXIMUM RUBBER GRAIN SIZE Some conclusions can be drawn from the calculations reported above:

• For a aggregate mix with particle sizes between 4/8 mm and a bitumen content , the rubber grain size should be in the interval 0,4/1 mm.

• Less ru tent of only 3

rubber in the asphalt mix. As seen in the graph (Figure 13.) the interval becomes largerwith increasing rubber content.

aggregate size 4 mm

aggregate size 6 mm

aggregate size 11 mm

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

3% 5% 8% 10% 13% 15% 18%

Ma

xim

um ru

bb

er g

rain

siz

e [m

m]

8 %(weight) bitumen


Percentage rubber (%(weight)) as a funcgrain size for three different aggregate aggregate sizes.

s can be seen in the diagram, an increase in rubber content also allows for biggerrubber grains. Below is mentioned some examples for an aggregate mix 4/8 mm andfor 8 %(w) bitumen binder.

low fraction

of 8 %

bber content means smaller rubber grains. E.g. for a rubber con % and 8 % bitumen the rubber grain size should not exceed 0,7 mm.


TIP4-CT-2005-516420 Page 28 of 64


• Increase in aggregate particle size allows larger rubber grains to be used. E.g. for an aggregate mix of 8/16 mm the rubber grain size should be in the interval of 0,8/2 mm.

3.3

QUESTIONS STILL TO BE ANSWERED Influence of type of rubber grain

Desired grain curve

Characteristics of bitumen/rubber mix.


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4 S T R E S S A N D S T R A I N I N P O R O E L A S T I C R O A D S U R F A C E S - F E M - C A L C U L A T I O N S .

oroelastic road surface with a high content of rubber gh noise reduction (more than 12 dB(A) units), though

f the reasons why the poroelastic road surface have sistance compared to normal asphalt road surfaces, could be the

nder when highly elastic rubber grains are pre-

order to get some idea on the excess stress and strain imposed on the bitumen binder due to the presence of rubber grains, calculations with aid of the Finite Element Method (FEM) have been performed.

4.1 CONCEPTS AND SIMPLIFICATIONS IN THE FEM-MODEL The structure and composition of a road surface is by definition of stochastic nature.

Modelling of aggregate with random distribution in size with rubber grains also ran-domly varying in size and then mixing them would of course be a correct manner of modelling. The procedure of building a FEM-model of a road surface with randomly dis-tributed aggregate particles and rubber grains would be both very time consuming and require extreme computational resources. It would probably not produce usable results in a realistic time frame.

It is clear that the model must include some rather drastic simplifications to be feasible with respect to modelling and computing time. In this study we therefore decided to build a deterministic and symmetric FEM-model, where the aggregate particles- and rubber grains are modelled as a matrix “glued” together with bitumen binder.

Even if this model could be viewed as oversimplified, it has been able to produce seemingly realistic results and have added new knowledge regarding how to over-come the, up to now, poor wear resistance of the poroelastic road surfaces.

4.1.1 Composition When the composition and the aggregate size are set, the maximum rubber grain size is obtained from calculations described in section 3 using the mean aggregate particle size. Now there are three major parameters to be considered; the rubber grain size, the thickness of the bitumen layer between aggregate and rubber and the number of rub-ber grains on each side of the cubical aggregate particle model.

As mentioned in chapter 3 the pgrain, has been found to give hiwith poor wear resistance. One omuch poorer wear reextra strain imposed on the bitumen bisent.

In


TIP4-CT-2005-516420 Page 30 of 64


Figure 14. One aggregate particle is covered with rubber grains on three sides. The

egate particle is covered with rubber grains on 3 sides.

e bitumen thickness between the aggregate and the rubber to 0 mm (zero) and changing the

er grains in the control volume matrix will change the composition of the

entire space between the particle and the rubber grains is filled with bitumen. Here is shown a 5x5 matrix with a total number of 91 grains including edge and corner grains.

As seen in Figure 14, one aggrPlace more of these “modules” around the first one and they are covered with one layer of rubber grains on all sides. Figure 14 shows a control volume containing 1 parti-cle and 91 rubber grains. The space inside the control volume and between the grains is filled with bitumen.

As an example a composition of 82% aggregate, 10% rubber and 8% bitumen film (mass fraction * 100, %(weight)), and a aggregate particle size of 7 mm1 generates a maximum rubber grain size of approximately 0.8 mm. The matrix model has the limita-tion that it cannot give the desired composition of the asphalt mix. Setting th

number of rubbmix in the asphalt model. As shown in the graph, Figure 15, the mix has a minimum error compared to the desired mix, mentioned above, when the number of rubber grains in the control volume reaches 127 (6x6 rubber grain matrix) . The fractions of different in-gredients are now 85.6% aggregate, 8.4% rubber and 6.0% bitumen.

1 7 mm was selected as average aggregate size for the 4/8 mm aggregate mix in order to compen-

sate for oversize particles.

Control volume

Rubber grain

Aggregate particle


TIP4-CT-2005-516420 Page 31 of 64


Figure 15. f the e model simplification. On the x-axis is

shown error for a 4x4 (61 rubber grains), 5x5, 6x6, 7x7 and 8x8 matrix. Note

in the FEM-software to perform the calculations. The complexity

-4,2% -3,9% -3,6% -3,2%-2,7%

5,9%3,9%

1,6%

-1,2%-4,3%-1,7%

0,0%

2,0% 4,3%7,0%

14,0%

8,7%

7,1%7,8%

11,8%

-10,0%

-5,0%

0,0%

5,0%

15,0%

10,0%

20,0%

Erro

r fra

ctio

n

Aggregate Rubber Bitumen Total error

61 91 127 169 217

Number of rubber grains inside the control volume

The number of rubber grains inside the control volume as a function omass-fractional error due to the cub

that the number grains also include the edge and corner grains in addtion to the matrix grains. The total error curve is the sum of the absolute value of the error for each component in the mix.

A 2D model was usedof a 3D model generated too many degrees of freedom to be computed on a PC. Representing the selected composition of the mix in a 2D FEM-model with fixed aggre-gate particle sizes also require compromises. If the composition is calculated from the area representing each of the components in the 2D model, the composition will not be fully consistent with the original 3D model. The “minimum error” due to the differ-ences between the 3D model and the 2D model, is presented in Figure 16.


TIP4-CT-2005-516420 Page 32 of 64


Figure 16. The control volume with two slices showing the difference between the 2D

and 3D models. The selected 2D representation used for FEM calculations represents a cross section through the 3D model.

4.1.2 Contact pres

The vertical r pressure insid kPa (2,4 kg/cm ) is used.

orizontal shear load pressure

Figure 17. Conceptual sketch on how the loads are applies to the model.

Applied forces sure generated by the vertical load.

pressure in the contact patch for a tire is approximately equal to the aie the tire. In the calculations a pressure of 240 2

H

For the horizontal load a deceleration of 5 m/s2 is used based on a retardation from 10 m/s to 0 in 2 seconds and assuming a typical total weight of a passenger car of 1500 kg. This generates a horizontal shear stress in the contact patch of 160 kPa (1,6 kg/cm2).


TIP4-CT-2005-516420 Page 33 of 64


4.1.3

ff e

d

The FEM-model of the poroelastic road surface. Although, the selected FEM model has some rather drastic simplifications the com-pleted model is quite large. It consists of 171 040 degrees of freedom. The mesh hasbeen made coarser inside the aggregate particles to reduce computation time and toallow for a finer meshing of the rubber grains and its adjacent binder material. A stiload distributing body has been located on the top of the road surface to resemble thload from one tread block in the tyre/road contact area.

As can be seen the model is not porous. One simplification in the modelling work was to make sure that a dense model without porosity could be designed to resist the applieloads without being subject to fatigue cracks.

Table 5. Data for materials used in the FEM model.

Material Young’s Modulus [MPa] Poisson’s ratio

Aggregate 6E4 0.25

Rubber 1.7 0.35

Bitumen 4.5 at 50Hz 0.33


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Figure 18 The automatically generated mesh from the FEM-software. The loads were applied via a stiff plate on top of the surface model to distribute the load evenly over the area resembling one tread block in the contact area.


TIP4-CT-2005-516420 Page 35 of 64


4.2

Figure 19. Surface graph of stress levels with a pure vertical load. The scale factor of the deformation is set to 10 in order to give a more intuitive sense of the motion of the asphalt surface under load.

CALCULATION RESULTS FROM A 2D FEM-MODEL


TIP4-CT-2005-516420 Page 36 of 64


Figure 20. Detail of surface graph of stress levels with a pure vertical load. The scale factor of the deformation is set to 10 to give a more intuitive sense of the motion of the asphalt under load.

As seen in Figure 20, when a pure vertical load is applied, the soft rubber will be stretched. Since the Young’s modulus of the bitumen binder is higher than that of the

sequently, th e FEM-software g between rubber and aggre-

ate. Thus no sliding between the rubber grains and the aggregates is possible in the FEM-model. This is probably not the case for an actual asphalt mix which may cause an overestimation of the stress levels in the rubber aggregate interface.

The aggregate particles, to the right of the applied load (a pure vertical load is ap-plied), have a tendency to rotate counter clock wise. As an effect of the rotation, the aggregate particles may “cut” into the bitumen and rubber grains, causing internal wear in the mix.

When the pure horizontal load is applied in the positive x-direction a similar behaviour compared to the previous case occur. The aggregates to the right of the applied load now rotate clock wise.

rubber, the binder will take up the load and thus receive the highest stress levels. Con-e stress level in the rubber itself is very low. The model made with aid of th (FEM-LAB) does only allow a fixed couplin

g


TIP4-CT-2005-516420 Page 37 of 64


Figure 21. Surface graph of stress levels with a pure horizontal load. The scale factor of the deformation is set to 10 to give a more intuitive sense of the motion of the asphalt under load.


TIP4-CT-2005-516420 Page 38 of 64


Figure 22. tress levels with a pure horizontal load. The scale factor of the deformation is set to 10 to give a more intuitive sense of the motion of the asphalt under load.

Detail of surface graph of s


TIP4-CT-2005-516420 Page 39 of 64


Figure 23. Surface graph of stress levels with combined vertical and horizontal load. The scale factor of the deformation is set to 10 to give a more intuitive sense of the motion of the asphalt under load.


TIP4-CT-2005-516420 Page 40 of 64


l

For the case where both horizontal and vertical load is applied, some interesting re-marks can be made. The rotation of the aggregate particles near to the applied load more or less becomes a translation. This may be one of the wear mechanisms for the poroelastic road surface.

Figure 24. Detail of surface graph of stress levels for combined vertical and horizontaload. The scale factor of the deformation is set to 10 to give a more intuitive sense of the motion of the asphalt under load.


TIP4-CT-2005-516420 Page 41 of 64


strainFigure 25. Detail of surface graph of levels with both vertical and horizontal load. The scale factor of the deformation is set to 10 to give a more intuitive sense of the motion of the asphalt under load. The yellow rectangle shows the close-up in Figure 26.

Due to the relative large deformation of the soft rubber much of the load has to be taken up by the bitumen causing high stress and possible fatigue.

Laboratory measurements reported in ref [2] for various bituminous materials suggest a ε6 value from 440E-05 to 900E-05. The ε6 value is the calculated strain level needed to have fatigue failure – measured as a 50% decrease in stiffness after one million load cy-cles. A higher value for ε6 indicates better fatigue resistance.


TIP4-CT-2005-516420 Page 42 of 64


Figure 26. Close-up detail of surface graph of strain levels in the bitumen for combined vertical and horizontal load. The scale factor of the deformation is set to 10 to give a more intuitive sense of the motion of the asphalt under load.


TIP4-CT-2005-516420 Page 43 of 64


As seen in Figure 26 the strain in the bitumen reaches as high as 0.012. The peaks in bi-tumen strain may be an effect of the model, thus neither the rubber nor the bitumen can slide relative to the aggregate surface. A mean value may be 0.008. Note that the stains in Figure 26 show the part of the model where the maximum strains in the bitumen occurs.

Figure 27. Fatigue lines for some bituminous binders showing the strain vs. the number of cycles needed to have a 50% decrease in stiffness. Diagram from ref [2].

Figure 27 shows fatigue data for a number of laboratory manufactured bituminous binders. The calculated strain of 0.008 by the FEM model for combined vertical and horizontal load would comply to normal fatigue life criteria for the bitumen binder ma-terial (the fatigue life criteria for bituminous binders are normally that the material should resist 1 000 000 load cycles for less than 50 % decrease of Young’s Modulus).

4.3 CONCLUSIONS s is an

of n rubber and bitumceiving m

• The fatigue life of a bitumen binder has been found to be proportional to the total strain imposed onto the material (see ref [2]). Calculations show that the load from

• The stress on the bitumen increase with the amount of rubber in the mix. Thieffect the difference in Young’s-modulus (at a given frequency) betwee

en. The binder will then take up the greater part of the load, hence re-ost of the stress.


TIP4-CT-2005-516420 Page 44 of 64


a typical passenger car generates a strain value of 0.008 in the bitumen film. To withstand such a high strain at 1 000 000 load cycles the binder has to be a highly polymer modified bitumen (PmB).

• Combined horizontal and vertical load leads to rotations and translations of the aggregates in the asphalt mix. The sharp edges of the aggregate particles could then “cut” into the bitumen film and thereby cause damage, reducing wear resis-tance.

4.4 CONTINUED WORK It is important that a tool is now available by which we can check and tune new reci-pes by computation before even initiating laboratory tests. A mix have been found that can withstand passenger car traffic without fatigue cracks in the binder material, 10%(w) rubber grain and 8%(w) bitumen binder and 82%(w) aggregate.

To construct a recipe that can withstand load from light and heavy trucks there are three major ways of modifying the recipe:

1. Reduce the amount of rubber in the mix to allow more bitumen binder to share the load and thereby reduce the strain level in the bitumen binder.

2. Select a harder binder for reduced binder strain.

3. Use harder rubber and softer bitumen binder in order to direct the load to the rubber material which then will receive the maximum stress level.

Measure 1 and 2 will increase the dynamic stiffness of the mix. In order to maintain the high noise reduction capability it is then important to tune the recipe to achieve the necessary low dynamic stiffness in the 500 - 1500 Hz region.


TIP4-CT-2005-516420 Page 45 of 64


5 P RG R A I N Witif than tween rubber and bitumen that is not fully understood. It might be a transport of bitumen into cracks and pores in the rubber grains, a chemical reaction or

ombination of both. To avoid this drying up of the mix a pre-treatment of the rubber solution. This process involves several steps such as mixing, stor-

5.1

espect to a realistic storage time and efforts to d

One e he tests. The em o contains about 50 % bitumen 160livere Mixing of rub-ber grains and emulsion has been done in a laboratory asphalt mixer, constructed as a

t even that turned out to be uch why 10 kg of rubber has been utilized in all mixes after that.

The first mixing tests were made with rubber grains 0,5-2 mm, with bitumen content of 16,7 % and with and without addition of extra water, and the following mixing variations were used.

• Mix 2. 10 kg of rubber grains 0,5-2 mm with 4 kg of emulsion. The mixture shows tendency to agglomeration after 1 minute and is stopped

• Mix 3-4. The same as mix 2 but with water added before the emulsion (mix 3 = 2 li-tres and mix 4 = 1 litre). This gives the expected effect that the mixer works easier and a good mixing effect can be ascertained. Agglomerations but the mixer is not stopped until after 2,5 minutes. The water gave a good effect for the mixing process, but after the mix has dried the effect is gone, i.e. that the mix is a clumpy as the one mixed without added water. There is no real difference be-tween the two mixes with different amount of water.

The conclusion from these small tests are that perhaps 16,7 % of bitumen is too much and that the addition of water might ease the mixing process but it does not change the hardening of the mix, so it is skipped in the further tests.

After that two grades of rubber grains and different amount of added emulsion were studied (Table 6).

E - T R E A T M E N T W I T H B I T U M E N O F T H E R U B B E R

h a high amount of rubber in an asphalt mix this will with time become very dry even e added amount of bitumen is enlarged from normal content. The reason for this is interaction be

a cwith bitumen might be aing and disintegration of eventually built up clumps.

USING BITUMEN EMULSION FOR PRETREATMENT Earlier small tests have shown that mixing rubber grains with emulsions works well. To mix with hot bitumen does not work. Tests have now been performed with the aim to find out the optimum content of bitumen with r

isintegrate the treated rubber back to powder grains again.

mulsion and two rubber grain gradings have so far been used for tulsi n is normally used for tack-coats, BE50R, which /220. The rubber grain gradings are 0-0,5 mm and 0,5-2 mm of the same quality de-

d by CDM. It has been produced by traditional shredding process.

miniature asphalt plant mixer. The capacity is normally 25-30 kg but as the density of rubber is much lower than for normal aggregate the mixing capacity will be much lower. The first mix (Mix 1) was made with 15 kg of rubber bum


TIP4-CT-2005-516420 Page 46 of 64


Table 6. Tests with pre-treatment of rubber in laboratory mixer.

Mix no Rubber size mm Bitumen content % Notes

5 0,5-2 13,0 The mixer works hard after 50 s and is stopped 6 0,5-2 9,1 The mixer works hard after 35 s and is stopped

7 0-0,5 16,7 The mixer is stopped after 1 minute when the mixture shows tendency to agglomeration

8 0-0,5 13,0 The mixer is stopped after 1 minute when the mixture shows tendency to agglomeration

9 0-0,5 9,1 The mixer is stopped after 50 s when the mixture shows tendency to agglomeration

10 0,5-2 5,2 The mixer is stopped 1 minute when the mixture shows tendency to agglomeration

re that the emulsion breaks rather quickly and even if the mixture looks homogenous and well blended it is really difficult to assess

All the above mixtures are stored without covering indoors in ambient temperatures

ests with and without water to see possible stripping effects. All these tests are made in order to see if there is

5.2 USINAn etec iwhich in the grains.

Some in Dram

ns and 20 and 30 % respec-

holm in two buckets, the buckets were emptied and the mixes stored at ambient temperatures. The mixes differs from the ones mixed with emulsion in that

The conclusions from the performed tests a

this. A prolonged mixing time might be achieved by adding water, but that is only nec-essary if the bitumen content is very high. But it is still a question if this is feasible in the production (see chapter 5.3).

(only partly heated locality). The mixtures 9 and 10 have been used to manufacture plates (see chapter 2.1.2).

Further testing will be made to optimize the amount of bitumen in the pre-treatment process. The required storage time and the time and effort for making powder of the pre-treated rubber grain shall be short and as simple as possible. Tests with different amount of bitumen in the pre-treatment e.g. with 5, 10, 15, and 20 % (of weight) bitu-men. Bored cores will be taken from the plates with certain time interval for tests with Prall or modified Los Angeles tests and/or wheel tracking (rutting) t

any adverse long term effect for rubber grain with sparse bitumen content in the pre-treatment.

G BITUMEN FOAM FOR PRE-TREATMENT alt rnative to pre-treatment with emulsion may be to use the foam technique. In this hn que some water (3-5 %) is added to the hot bitumen (normally a pen bitumen)

leads to a rapid expansion of the water in form of vapour. The volume increase is magnitude of 15-20 % which gives a good coverage of the aggregate / rubber

preliminary tests have been executed with this technique at the NCC laboratory men i Norway.

For the tests a bitumen 70/100 have been utilized with different amounts on two grad-ings of rubber grains, 0-0,5 mm and 0,5-1,6 mm.

To study the effect of storage time two mixes with fine graitively of foamed bitumen 330/430 were made. These mixes were transported from Drammen to Stock


TIP4-CT-2005-516420 Page 47 of 64


the disinte tion seems to take much longer time and even after fstill to be regarded as more or less solid. See also chapter 2.2.3.

gra ive months they are

Som will be performed wit itumen, e.g. bitu 3000.

5.3 DEVELOPMENT OF METHODS FOR DISINT ATION Pre-treatment of rubber rains gives ix th amount of bitumen, ks together is on hen stored is changes. itumen and rubb and more easily disintegrated. To study he effmen, mi ng technique and storage time tests h n.

sintegration of the rubber/bitumen mixture during or after storage is very important as

ult with low bitumen content. But as mentioned above

tion of months. This study is still ongoing, as it also involves a

e tests h much softer b men V

EGR OF PRETREATED RUBBER GRAINS g

stic a m

andat when new, with even a rather lowly with difficulties disintegrated. W

th The b the er interact and the mix gets to be dryer t ect of rubber grading, amount of bitu-

ave been made and are still going oxi

Diit is necessary to be able to measure the correct amount when e.g. screw feeding the mixture into the plant mixer.

When freshly mixed the mixture of rubber and bitumen (added as emulsion) will stick together in clump that is very difficult to disintegrate. Even if it is worse with a high con-tent of bitumen it is also difficwith time the rubber will ‘consume’ the bitumen and get dry and more easy to disinte-grate. With low bitumen content it seems to be a question of weeks, but with high con-tent of bitumen it is a quesquestion of how much force might be needed for disintegration and how to apply it.

Alternative disintegration methods for remaining pellets of integrated pre-treated rub-ber grains are being studied.


TIP4-CT-2005-516420 Page 48 of 64


6 U P -

P O R T E D B Y A N E L A S T I C S U B L A Y E R .

D E V E L O P M E N T O F R O A D S U R F A C E C O N S I S T I N G O FA N U P P E R O P E N G R A D E D A S P H A L T S U R F A C E S

( P E R F O R M I N G P A R T N E R S : C D M & H E I J M A N N S )Preliminary test plates of the road surface consisting of an upper open graded asphalt surface supported by an elastic sub layer will be performed. Test plates and initial de-sign will be performed by Heijmanns and CDM.


TIP4-CT-2005-516420 Page 49 of 64


7 I N P U T D A T A F O R A N I M P E D A N C E M O D E L T O C A L C U L A T E T H E R O L L I N G P O W E R D I S T R I B U T I O N B E T W E E N T H E T Y R E A N D T H E R O A D S U

R F A C E .

y formulation of an impedance model for the tyre/road system, which uses the infor-mation of driving point mobility for tyres and road surfaces, it will be possible to calcu-late the power flow from the excitation point at the interference between tyre and road. The amount of power transmitted to the tyre is proportional to the emitted sound. An impedance model will be performed and the measured impedances for different tyres and road surfaces will be tested further downstream in the project.

Figure 28. Examples of measured driving point mobility for tyres performed by Goodyear.

Earlier in chapter 2.2 measured impedances for poroelastic road surfaces were pre-sented. Figure 28 presents measured driving point mobility for tyres performed by Goodyear.

B


TIP4-CT-2005-516420 Page 50 of 64


8 R E F E R E N C E S /1/ N.Å. Nilsson and O Sylwan: “NEW VIBRO-ACOUSTICAL MEASUREMENT TOOLS

CHARACTERIZATION OF POROELASTIC ROAD SURFACES WITH RESP FOR

ECT TO TIRE/ROAD NOISE.”, Tenth International Congress on Sound and Vibration, Stock-holm (2003)

/2/ O Bennerhult: “Acoustical and Mechanical Impedances of Road Surfaces and the Influence on Tire Noise”, International Tire Noise Conference Stockholm (1979)

/3/ Hilde Soenen, Chantal de La Roche, Per Redelius: ”Fatigue behaviour of bitumi-nous materials: From binders to mixes. “, International Journal of Road Materials and Pavement Design, Vol. 4, No. 1, 2003, pp. 7 - 27.


TIP4-CT-2005-516420 Page 51 of 64


sured Dynamic Stiffness for tested poroelastic as-

Diagram 1. Summary of measured dynamic stiffness, tested asphalt surfaces during

Diagra ic asphalt Sample 1, dynamic stiffness

Diagra

Diagra

Appendix 1. Meaphalt surfaces, 2004

2004

m 2. Poroelast

Diagram 3. Poroelastic asphalt Sample 2, dynamic stiffness

m 4. Poroelastic asphalt Sample 3, dynamic stiffness

m 5. Poroelastic asphalt Sample 4, dynamic stiffness


TIP4-CT-2005-516420 Page 52 of 64

TY issued: 10-02-06

3.18 Poroelastic Road Surfaces

Diagram 1. Summary of the measured dynamic stiffnessasphalt surfaces tested during 2004

100

110

120

130

140

150

160

100 1000 00Frequency [Hz]

Dyn

amic

stif

fnes

s dB

re 1

N/m

,

100

Reference asphalt type standard ABT1Temp 21-22 degrees.

1.

Poroelastic asphalt Sample 1 Aggregate size 4-8 mm 77 %, aggregate size 0-4 mm 15 % and rubber granules 0-0.5 mm 8%. Added binding medium PMB 20 7.5 %.Temp 21-22 degrees.

PorAggaggrubrubAddTem

oelasregaregaer ger ged bp 18

tic ate site siranuranuindin deg

sphze 4e 0-les 0les 0g mree.

alt e 2 -8 m 7 %,

z 4 m 7 %, b -0. m 2.4 % and b .5- m 3.6 %.

ediu MB 20 7.8 %

Samplm 7m 1

5 m2 mm P .

Poroelastic asphalt Sample 3 Aggregate size 4-8 mm 77 %, aggregate size 0-4 mm 15.7 %, rubber granules 0-0.5 mm 3.3 % and rubber granules 0.5-2 mm 4.0 %. Added binding medium PMB 20 7.8 %.Temp 19 degree.

PorAggaggrubrubAddTem

oelasregaregaer ger ged bp 18

tic ate site siranuranuindin deg

sphze 4e 0-les 0les 0g mree.

alt e 4 -8 m 7 %,

z 4 m 4.5 %, b .0- mm 4.3 % anb .5- m 4.3 %.

ediu MB 20 7.8 %

Samplm 7m 1

0.5 2 mm P

d

.

QCI

D

TIP4-CT-2005-516420 Page 53 of 64


Diagram 2. Poroelastic asphalt Sample 1, 2004 Dynamic stiffness

100

110

120

130

140

150

160

100 1000 10000Frequency [Hz]

Dyn

amic

stif

fnes

s dB

re 1

N/m


Poroelastic asphalt Sample 1 Aggregate size 4-8 mm 77 %, aggregate size 0-4 mm 15 % and rubber granules 0-0.5 mm 8%. Added binding medium PMB 20 7.5 %.Temp 21-22 degrees.

Appr. 20 dB


TIP4-CT-2005-516420 Page 54 of 64



100

110

120

130

140

150

160

100 1000 10000Frequency [Hz]

Dyn

amic

stif

fnes

s dB

re 1

N/m


Poroelastic asphalt Sample 2 Aggregate size 4-8 mm 77 %, aggregate size 0-4 mm 17 %, rubber granules 0-0.5 mm 2.4 % and rubber granules 0.5-2 mm 3.6 %. Added binding medium PMB 20 7.8 %.Temp 18 degree.

Appr. 6


TIP4-CT-2005-516420 Page 55 of 64



100

110

120

130

140

150

160

100 1000 10000Frequency [Hz]

Dyn

amic

stif

fnes

s dB

re 1

N/m


Poroelastic asphalt Sample 3 Aggregate size 4-8 mm 77 %, aggregate size 0-4 mm 15.7 %, rubber granules 0-0.5 mm 3.3 % and rubber granules 0.5-2 mm 4.0 %. Added binding medium PMB 20 7.8 %.Temp 19 degree.

Appr. 8 dB


TIP4-CT-2005-516420 Page 56 of 64



100

110

120

130

140

150

160

100 1000 10000Frequency [Hz]

Dyn

amic

stif

fnes

s dB

re 1

N/m


Poroelastic asphalt Sample 4 Aggregate size 4-8 mm 77 %, aggregate size 0-4 mm 14.5 %, rubber granules 0.0-0.5 mm 4.3 % and rubber granules 0.5-2 mm 4.3 %. Added binding medium PMB 20 7.8 %.Temp 18 degree.

Appr. 15-17 dB


TIP4-CT-2005-516420 Page 57 of 64



Appendix 2. Measured Dynamic Stiffness for tested poroelastic as-phalt surfaces, 2005

Diagram 1. Summary of measured dynamic stiffness, tested asphalt surfaces during 2005







3.18 Poroelastic Road Surfaces

Diagram 1. Summary of the measured dynamic stiffasphalt surfaces tested during

100

110

120

130

140

150

160

100 1000 000Frequency [Hz]

Dyn

amic

stif

fnes

s dB

re 1

N/m

ness, 2005.

10

Refe ard Atested 2004. Temp 21-22 degrees.

rence asphalt type stand BT11,



Poroelastic a alt Sample 2 2005sph

Poroelastic a alt Sample 4 2005sph

Poroel hal mple 5 2astic asp t Sa 005

Poroela h ple 6 20stic asp alt Sam 05

All samples temperature of 19 Deg

tested in 2005 had surface ree.

D


100

110

120

130

140

150

160

100 1000 10000

Frequency [Hz]

Dyn

amic

stif

fnes

s dB

re 1

N/m


Poroelastic asphalt Sample 1 2005 size 4-8 mm 77 %, stone size 0-4 mm 14.5 %; and rubber granulate 0.0-0.5 mm 4.25% and rubber granulate 0.5-2 mm 4.25%. Pre-treatment of the granulate with bitumen emulsion with 9 % (0.0-0.5 mm) and 5% (0.5-2 mm) dry bitumen of the total rubber weight. 7.8 % added binding medium, Pen bitumen 70/100 modified with 10 % rubber.

Appr. 30 dB



100

110

120

130

140

150

160

100 1000 10000

Frequency [Hz]

Dyn

amic

stif

fnes

s dB

re 1

N/m


Poroelastic asphalt Sample 2 2005Aggregate size 4-8 mm 77 %, aggregate size 0-4 mm 14.5 %; and rubber granules 0.0-0.5 mm 3.82% and rubber granules 0.5-2 mm 4.68%. Pre-treatment of the granulated rubber with bitumen emulsion with 9 % (0.0-0.5 mm) and 5% (0.5-2 mm) dry bitumen of the total rubber weight. 7.8 % added binding medium, Pen bitumen 160/220 modified with 10 % rubber.

Appr. 23 dB



100

110

120

130

140

150

160

100 1000 10000

Frequency [Hz]

Dyn

amic

stif

fnes

s dB

re 1

N/m



Appr. 25 dB



100

110

120

130

140

150

160

100 1000 10000

Frequency [Hz]

Dyn

amic

stif

fnes

s dB

re 1

N/m



Appr. 26 dB



100

110

120

130

140

150

160

100 1000 10000Frequency [Hz]

Dyn

amic

stif

fnes

s dB

re 1

N/m


Poroelastic asphalt Sample 5 2005Aggregate size 4-8 mm 77 %, aggregate size 0-4 mm 14.5 %; and rubber granules 0.0-0.5 mm 3.82% and rubber granules 0.5-2 mm 4.68%. Pre-treatment of the granulated rubber with bitumen emulsion with 9 % (0.0-0.5 mm) and 5% (0.5-2 mm) dry bitumen of the total rubber weight. 7.8 % added binding medium, Pen bitumen 160/220.

Appr. 15 dB



100

110

120

130

140

150

160

100 1000 10000

Frequency [Hz]

Dyn

amic

stif

fnes

s dB

re 1

N/m


Poroelastic asphalt Sample 6 2005Aggregate size 8-11 mm 92 % and rubber granules 0.0-1.6 mm 8 %. Pre-treatment of the granulated rubber with bitumen foam with 25 % dry bitumen of the total rubber weight. 8 % added binding medium, Pen bitumen 70/100.

Appr. 14 dB


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