Possibilities to reduce tyre/road noise emission on paving stones and other block surfaces

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EUROPEAN COMMISSION

DG RESEARCH

SIXTH FRAMEWORK PROGRAMME

PRIORITY 6

SUSTAINABLE DEVELOPMENT, GLOBAL CHANGE & ECOSYSTEMS

INTEGRATED PROJECT – CONTRACT N. 516288

Possibilities to reduce

tyre/road noise emission

on paving stones and

other block surfaces

Deliverable no. F.D1

Dissemination level Internal (SILENCE SP F)

Work Package WP F.1 New production Technologies for surfaces on urban streets Author(s) Ulf Sandberg, Swedish National Road and Transport Research Institute

(VTI) and Hans Bendtsen, Danish Road Institute (DRI)

Co-author(s) Sigurd N. Thomsen, Jørgen Kragh, DRI, Björn Kalman, VTI, and Darko Kokot, ZAG (Zavod za gradbenistvo Slovenije), Slovenia

Status (F: final, D: draft) F 2007-03-20

File Name FD1 Reducing noise on paving stones – Final 070320.doc Project Start Date and Duration 01 February 2005, 36 months

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Preface

The EU project SILENCE includes a task F1 “New production technologies for surfaces on urban streets”. In subtask F1.1 with the title “Noise reduction for paving stone surfaces for streets of high cultural or historic importance” investigations of noise from streets with paving stones are carried out. The objectives are stated as:

1. To produce a ranking in relation to noise of commonly used types of paving stones in Europe.

2. To develop and test quieter types of paving stones.

The subtask includes production of this report, Deliverable F.D1, which shall be a State-of-the-Art Report on paving stone surfaces and identification of possibilities for noise reduction. This report is produced by Ulf Sandberg from the Swedish National Road and Transport Research Institute (VTI) and Hans Bendtsen from the Danish Road Institute/Road Directorate (DRI), assisted by a number of contributing co-authors, as a part of the work carried out by the Forum of European Highway Research Laboratories (FEHRL) in Task F1 of the EU-project SILENCE. Apart from VTI and DRI, also Skanska AB in Sweden takes part in Task F1. There is also a certain cooperation with another EU project, named NR2C.

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Summary

Block surfaces, made of stones or cement concrete, have a widespread use in today's cities and towns. One major use is to preserve the ancient cultural style of an old city, with its historical cobblestones or stone setts on the streets. Another major use is, as an integrated part of traffic management schemes, to alert vehicle drivers that they drive on an intermodal street; i.e. a street shared by vehicles of various kinds (e.g. cars, busses, bicycles) and pedestrians, where one would like to keep them apart as much as possible. The message conveyed by the paving stones or blocks increases traffic safety and improves the urban environment by making drivers more alert, reducing speeds, and maybe also the traffic volume. A third use is to enhance the aesthetical impression of the street and its environment. In both the latter cases, the type of block pavement used is mostly modern interlocking blocks made of cement concrete.

There are many examples where the use of block surfaces has led to complaints from people living or working close to streets with such pavements; complaints that mostly focus on the extra noise generated by the traffic on such surfaces. The authorities then will have to balance the needs for a quieter environment against the needs of preserving the historic and cultural values that these pavements generally represent.

The EU-project SILENCE has recognized this sensitive balance and therefore included a subtask F1.1 with the title “Noise reduction for paving stone surfaces for streets of high cultural or historic importance”. In this subtask investigations of noise from streets with block pavements ("paving stones") are carried out. The objectives are stated as:

1. To produce a ranking in relation to noise of commonly used types of paving stones 2. To develop and test quieter types of paving stones

This report constitutes the result of this SILENCE subtask as it stands at the time of writing. Experiments have been or are being conducted in Denmark, Slovenia and Sweden to study the mentioned topics; results of which are reported here. There is also a section providing a review of results of similar studies presented in the open literature.

To achieve the first objective, experiments were carried out in Denmark. Five streets, each with different types of block pavements in the Copenhagen area, were selected for noise measurements according to ISO 11819-1 "Measurement of the influence of road surfaces on traffic noise - Part 1: Statistical Pass-By method" (popularly referred to as "the SPB method"). The study included one type of cement concrete blocks and four types of granite setts, with different levels of surface texture and roughness. To achieve the second goal a special type of granite blocks, developed by the municipality of Copenhagen (one of the setts mentioned above), was applied on a street in Copenhagen in the summer/autumn 2005 and tested within SILENCE.

From the Danish study, the following simple, practical guidelines for design of paving stone and other block surfaces having as favourable acoustic properties as possible are offered:

• The individual blocks should have as even (plane) a surface as possible • The joints between the blocks should be as narrow as possible

• The blocks should have a uniform size in order to ensure the same width of the joints and by this making it easier to minimize the width

• It is better to have an angle of 45° than 90° between the direction of the joints and the driving direction of the vehicles on the road

In general, the stone setts were noisier than the flat concrete or granite blocks. The best noise performance in this investigation was achieved by using flat concrete blocks or flat

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granite blocks. The difference between the noisiest and the quietest block surface was found to be 10 dB.

Compared to the NORD 2000 reference, as practised in Denmark and later to be used in the five Nordic countries, all pavements showed a reduction in high frequency (air pumping) noise with the exception of the large and old stone setts. When using traditional stone setts as compared to modern concrete or flat granite blocks, the low-frequency vibration-excited noise is substantially increased.

Considering the Danish results and measurements regarding the acoustical properties of block surfaces reported in the literature; i.e. the influence on traffic noise emission, it is clear that there are substantial differences between existing block surfaces. The range between existing ones would be at least 12-13 dB and if the futuristic interlocking block pavement with poroelastic cover is included it will be at least 15-17 dB. These are dramatic differences. In cases where one can accept to surrender some of the historic/cultural values, it would be possible to replace the older type of stone setts with visually rather equal blocks with a flatter surface; such as the flat granite setts tried in Copenhagen and reported here. Depending on the old type of surface, and the orientation of the blocks, one may gain some 4-8 dB in this way. This type of surface would not be noisier than an ordinary asphalt surface, and it may then be preferred to use this one rather than to pave the street with asphalt, and in this way save some of the cultural value of the street.

In general, the orientation of the blocks should be such that the tyres roll over them at an angle of 30-60o_{rather than hitting the blocks and the joints at right angles.}

The use of interlocking blocks would generally not generate more traffic noise than an ordinary asphalt surface. With an appropriate design and good workmanship in the laying, as well as a stable sand bedding or other base material, one may even obtain a certain noise reduction compared to a dense asphalt surface; say about 1-2 dB. The use of a porous layer on the top of the blocks would (tentatively) improve the acoustic qualities a little extra, with a potential noise reduction in comparison to dense asphalt surfaces (DAC 0/11 and SMA 0/11) of at least 2-3 dB; although this benefit is likely to diminish by time when clogging occurs. The ultimate choice would be an interlocking block surface with a cover of poroelastic material of the type described in this report. With such a surface one would obtain a traffic noise reduction corresponding to the best that can be offered by the most advanced (double-layer) porous asphalt surfaces. However, compared to the porous asphalt surfaces, the one with blocks and poroelastic cover would most probably be able to keep its low-noise properties for a longer time due to the elasticity of the surface which would prevent dirt from getting stuck in the voids. It is important, however, to provide for a very stable base material to lay the blocks into.

It should be observed that tear and wear, stability problems, as well as poor maintenance, might increase the noise emission from stone setts and other block pavements over the years. This report can therefore only provide some "snapshots" of the overall situation. Nevertheless, it is hoped that this report will advance the knowledge about this family of road surfaces.

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Possibilities for reducing tyre/road noise emission on paving

stones and other block surfaces

1 Introduction

Different types of block surfaces have been used historically and are still used on many urban roads in European cities. Modern types of block surfaces use interlocking blocks, which have become popular in urban streets where there is a desire to give the street a certain profile; focusing on environment, safety or priority for pedestrians. Block surfaces can be made of natural materials like wood, stones (e.g. granite) or clay, or they can be made of cement concrete.

Historically, block surfaces were the only way to obtain a durable surface to run vehicles on. Today, the objectives of using block surfaces may be:

• To preserve a historical environment

• To provide higher aesthetical qualities in urban areas

• As a part of a traffic management scheme to reduce the speed of the vehicles by increas-ing the noise inside the vehicles and by reducincreas-ing driver comfort if speed is too high [1] • To distinguish between different lanes of a street; such as parking lanes, driving lanes,

bicycle lanes, etc.

• As markings in the middle of the road in order to make the drivers stay in the driving lane and prevent vehicles from using the opposite driving lane for overtaking

• To give a vehicle driver the message that the block paved street is shared by other road users, such as pedestrians or bicyclists and extra attention is needed.

The terminology may be confusing for people who are not used to deal with such surfaces. Therefore, the following tries to clarify this issue.

A generic term is block surfaces. Block surfaces may consist of: • Stone paving

• Cobblestones • (Stone) setts

• Wood blocks (see chapter 3) • Bricks

• Interlocking (concrete) blocks; which are the modern type of block surfaces

These types of block surfaces are illustrated in Figures 1.1-1.6. The types which are most common today are setts, bricks and interlocking blocks. This report therefore is focused on these.

The type referred to as "setts" or "stone setts" has frequently in modern technical literature been named "paving stones"; sometimes "paving stones" has even been used as a generic term for cobblestones, setts, and bricks. This confusion about terminology is probably mostly caused by the old term "setts" gradually becoming forgotten and historical/cultural knowledge poorly transferred to the latest generations of road engineers or researchers.

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When the term "paving stones" occur in this report, it exclusively refers to stone setts. However, the term is today sometimes used in a more generic sense which includes also cobblestones and interlocking block surfaces; albeit cement concrete blocks are not really "stones".

Fig. 1.1 (left): Stone paving 2000 year old near Forum Romanum, Rome, Italy Fig. 1.2 (right): Cobblestones, probably from the 19th century, in Strängnäs, Sweden

Fig. 1.3 (left): Stone setts, Visby Sweden

Fig. 1.4 (right): Wood block pavement in Habana, Cuba (photo: L Sjögren, VTI)

Fig. 1.5 (left): Brick pavement, Delft, the Netherlands

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2 Purpose of this report

The objectives of this report are:

1. To produce a state-of-the-art report related to commonly used types of block pavements in Europe.

2. To report the latest results of experiments with quieter block pavements made within SILENCE.

3. Identify possibilities and methods to reduce tyre/road noise emission of old and modern types of block pavements

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3 The historic use of block pavements

Most of the information contained in this chapter has been extracted from reference [2], which, in turn, is based on [3].

The first and simplest roads had a surface of just beaten earth - compacted soil - sometimes reinforced with stones or gravel. The Romans systematically paved their main roads with large and fairly flat stones; see Fig. 1.1. Cobblestones (which are uncut and often waterworn stones) were used in cities; see Fig. 1.2. For example, in 1533 an act was passed in London requiring cobblestones to be brought to London from the seashore. They were usually placed on a bed of sand and then wedged shoulder-to-shoulder into place; the longest side usually placed vertically to improve its stability. In 1876 there were 150 km of cobblestone roads in both New York and Cincinnati.

Wheeled urban traffic would favour the use of flat-faced stone blocks, known as setts. In Paris, setts about 125x125x150 mm were introduced in 1415 and by 1720 had increased in size to 230x230x230 mm. In Italy, there are such surfaces of even larger area. Later sizes in Europe decreased to approximately 160x160x100, eventually dropping to 75x75 mm; see Fig. 1.3. Such pavements were laid in Swedish cities from 1908 and from 1920 also on extra-urban roads. As a maximum, 700 km of Swedish extra-extra-urban roads had this type of pavement. Even today, granite setts (nowadays often called "paving stones") are produced for historical city centres, see Fig. 4.1. For example, within the part of Visby which is surrounded by a medieval wall, it is required that that setts or cobblestones are not replaced by any modern paving material, in order to preserve the ancient style of the city1_.

Timber blocks were first used for paving in 14th century Russia. Even in the 10th century there are records of timber-plank paving being used in Novgorod. Of course, a problem was that these pavements rotted away in 5-10 years. Nevertheless, wood blocks, about one hundred years ago, improved with creosote against rotting, were widely used as paving material in urban areas. In fact it was one of the major pavement types before the bitumen surfaces became common; mostly due to its low-noise characteristics. There are lots of records of merchants and residents of cities in North America and Europe who demanded the city authorities to replace a dusty dirt pavement, cobblestones or setts with wood blocks because of its noise- and dust-reducing properties. Road engineering educational books in the beginning of the 20th_{century had large parts dealing with wood block pavements; see for} example [4]. Such pavements continued to be used to a small degree into the 1950's. For example, the last wood-block pavement in Paris was constructed in 1938. In Havana, Cuba, they were still in use in 2002 (see Fig. 1.6).

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4 Examples of the current use of block pavements

Presently, block pavements are used in many different ways in Europe, as it can be seen from the examples in this chapter. Most of them are setts ("paving stones") or interlocking block pavements.

Figure 4.1: Paving stones used as a road surface construction material on a fairly modern street in Copenhagen, Denmark.

Copenhagen, Denmark Græsted, Denmark

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Road hump with interlocking blocks Delft, the Netherlands

Road hump Esrum, Denmark

"Rumble area" Skjern, Denmark

Reminder of speed reduction Copenhagen, Denmark

Marking of pedestrian crossing Skjern, Denmark

Marking of intersection Skjern, Denmark

Figure 4.3: Examples where block pavements are used as part of a traffic management scheme to alert drivers or give them some message.

As part of some traffic management schemes block pavements (stone setts or interlocking blocks) are used over a long distance of a road or driving lane. This will have an effect on the general noise level along this road section. In other cases, blocks are only used on short road sections with a length of 1 to 10 m. This will influence the noise only at the moment when vehicles pass this short section, and will result in increased maximum noise levels. This short-time increase might have a character of impulsive noise, which might cause increased annoyance for people living along this specific short section with paving stones. In [1] it is discussed if a noise penalty of, for example, 5 dB should be added to the equivalent noise levels to compensate for the additional annoyance caused by the impulsive character of the noise.

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It is common that block pavements are used to mark areas where the vehicles are not supposed to drive (see Figure 4.4). This will normally not have an influence on the noise emission. Only in situations where vehicles drive on these pavements, despite they should not do so, will this result in increased noise levels; but then generally only for short time periods. Displacement of lane Roskilde, Denmark Displacement of lane Roskilde, Denmark Displacement of lane Saltrup, Denmark Displacement of lane Saltrup, Denmark Centre of roundabout Malmø, Sweden Roundabout Skjern, Denmark

Figure 4.4: Examples where paving stones are used to mark areas where vehicles are not normally supposed to drive. Such areas might, nevertheless, be used by some

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Nantes, France Prague, Czech Republic

Skjern, Denmark "Museums town"

Aarhus, Denmark

Copenhagen, Denmark Copenhagen, Denmark

Figure 4.5: Examples where cobblestones, setts or interlocking blocks are used to influence the aesthetical appearance of a road and its surroundings.

In historical urban areas, paving stones are often used on longer road sections. This will have an effect on the general noise level along this road section and is often a matter of complaints from the residents.

Not uncommon is to combine a speed reduction to 30 km/h with a block pavement, mostly of the interlocking type; see Fig. 1.6. The intention is to amplify the message "drive slower". As can be seen from the above collection of examples, block pavements can be and are used in many different ways. Also the pattern of the pavement blocks varies from rectangular patterns in the direction of travel, or in diagonal direction, to arcs in various fashions, or even combinations of these.

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5 Noise characteristics of block pavements

Different factors have an influence on the tyre/road noise generated when vehicles pass over areas with block pavements. These factors, illustrated in Figure 5.1, are:

A. The texture of the upper surface of the blocks

B. The shape (flatness and edge) of the upper surface of the blocks C. The depth of the joints between the blocks

D. The width of the joints between the blocks E. The variation of height of the different blocks

F. The angle between the joints and the driving direction of the vehicles

G. The stiffness of the blocks (if they are of softer materials, such as wood or rubber)

A

C

B

E

D

Figure 5.1: Noise-influencing factors for block pavements

Noise is generated and influenced in the following ways:

The shape (B) of the blocks as well as the joints (C and D) between them are enveloped by the tyre during the rolling process; except that the deepest part of the joints, and the sharpest slopes of them, may not be in full contact with the tyre tread rubber. As is described in [2] the

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most sensitive wavelengths to vibration excitation are in the range 40-100 mm, which is close to what the dimensions of the blocks and joints are. It means that vibration excitation from the shape of the blocks and their joints may be very prominent, unless the shape is flat and the depth and width of the joints are small. A curved shape such as indicated in Fig. 5.1 is unfavourable. The vibration excitation will be maximum if a block is hit by the tyre simulta-neously over the entire width of the tyre; i.e. if the block is orientated in right angle to the rolling direction, and if the blocks also have a different height (E); the latter of which will create extra low frequency "rumble". If the angle between the block orientation and the rolling direction is smaller than 90o_{, say 45}o_{, the impact between tyre and block seen over the entire} tyre/road contact area will be more gradual and thus less noisy.

In order to transfer horizontal forces, there must be some slip between the tyre tread and the block surfaces. In most cases, the blocks are polished and have a rather low microtexture. This will mean low friction and will create a need for a relatively high degree of slip to transmit a certain horizontal force for propulsion of the vehicle. At the same time, when the tyre tread needs to move not only in the horizontal plane but also to some degree vertically (if the blocks have a curved shape, and/or if they have a different height), one may expect a relatively high degree of stick-slip motions in order to follow the surface profile, which may create stick-slip vibrations.

The texture (A) on top of the block will create an additional "local" vibration excitation, if the dominating texture wavelengths are long; say 10 mm or longer. Shorter wavelengths will not be possible for the tread rubber to envelope, so they will not be unfavourable.

Air pumping or other aerodynamic effects will be active and very unfavourable for the part of the tyre tread which is in contact with the surface of the block. Polished block surfaces, which are the most common condition of these surfaces, will have a smooth texture which will mean good tightening against the tread rubber cavities; which will create air pumping and air resonant radiation; see [2]. This will be modulated by the hits between tyre and blocks. If the blocks have some texture with short wavelengths (about 10 mm and shorter), this may provide escape channels for the trapped air which may reduce the air pressure gradients and consequently the aerodynamic noise generation.

A rubber block pressed against a smooth, polished stone surface should give relatively high adhesion forces by physical adsorption or intermolecular bonds, which will break up when the tyre block rolls out of the contact area. This break-up creates stick-snap noise [2].

Would there be some effects with a favourable acoustic influence? Yes, the joints between the blocks may be filled with a rough sand fraction which creates some porosity which may reduce air pumping (but just over the joints) but more importantly create a sound absorption which may act over most of the block areas due to the most important frequencies having a wavelength around 200-400 mm and thus affecting the sound not only over the joints but within at least a decimetre or so from the joints (this is due to basic acoustic laws).

As appears above, not only the vertical vibration-excitation and air pumping mechanisms, but also the stick-slip tangential vibration and stick-snap mechanisms are active and may be relatively strong on block surfaces of common types. In fact, such surfaces tend to create a situation when virtually all known noise generation mechanisms may be prominent at the same time; which fortunately is uncommon.

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6 Principles of noise reduction for paving stones and other block

surfaces

6.1 Block shape optimization

In order to reduce the vertical vibrations of the tyre, the block should be made as flat as is possible. This is difficult on cut stones, but is easy on interlocking blocks. Furthermore, the joints between the blocks should be as narrow as is technically suitable. There must be some spacing between the blocks to allow for thermal expansion and to allow for the stabilizing material (most often sand) to give a suitably "elastic" or firm joint. However, any excess spacing shall be avoided. Some interlocking blocks may be possible to design with as narrow joints as one mm; not requiring any sand inside the joints.

The joint shall be filled with material up to the block surface in order to avoid tyre tread to penetrate deep into the joint. The blocks should have no chamfer; any chamfer may only assist the tyre in reaching lower parts of the joint and thus give higher vibration excitation. Finally, the height of each block should be as uniform as possible; i.e. the overall surface shall be as even as possible.

6.2 Texture

optimization

As indicated in the previous chapter, a texture on top of the block, made up of short texture wavelengths, will reduce the air pumping and other aerodynamic mechanisms. When the blocks are natural uncut stones, there is no such texture. For stone setts, when the upper horizontal surface is a cut surface, some texture might have been created due to the splitting of the stone. For most materials and for common cutting procedures, such a surface is not normally created; more likely it will be a surface dominated by wavelengths around 20-40 mm which are unfavourable.

For interlocking blocks made of cement concrete; however, it is easy to create such a surface by adding suitable aggregate sizes to the concrete mix. This is often also made; albeit not generally for low-noise purposes but for wet skid resistance purposes. The authors consider the following design as a potentially quiet surface:

• A flat cement concrete block made essentially of sand with maximum 1 mm grain size, to create as flat and smooth surface as possible.

• On top of this, a surface dressing of 2-4 mm (sharp) stone aggregate, bound with a strong binder; possible epoxy might be needed. One shall spread the aggregate in such a way as to minimize the spacing between the grains (they shall be packed as close together as possible). A near-cubic aggregate shape would be somewhat more favourable than a flaky type since it is likely to result in a lower roughness.

An alternative way to create a suitably fine-textured surface, both on original stones and on concrete blocks, may be by knocking on the surface with small but extremely hard pins or needles; a kind of "macro-blasting".

6.3 Creating

porosity

In the previous chapter it was mentioned that the joints between the blocks may be partly porous. This may be a very effective way of reducing noise. It requires the sand in which the blocks are set to be carefully graded in order to provide for or allow airflow through it. This was believed in [5] to be a major reason why some interlocking block pavements appeared to be quieter than a conventional asphalt surface. It may not be so easy to optimize the sand for high porosity while still providing sufficient mechanical stability properties.

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It may be surprising that sand may provide sound absorption, but it is known that dry sand has a very high voids content. The air voids may for a mix of crushed sand with a continuous grading from 0 to 2 mm grain size be as high as 50 % in non-compacted and 30 % in compacted cases2_{. This must result in significant sound absorption of unbound sand} materials. However, wetness decreases the air voids substantially.

Another way to create porosity is to add on top of the block an extra layer of a porous material. This may be done on interlocking blocks where one may make the top layer of a porous material; in fact such products are produced and used in the Netherlands. One brand name is "Stilstone" and another one is "SilenTONE" [11][12]. Both feature a top layer which is porous; the SilenTONE has a 13 mm porous top layer. The Stilstone seems to have a similar construction judging from visual impression on the website, but it is not specified. The noise reduction of SilenTONE is not given, but for Stilstone it is specified as follows at 50 km/h: 6 dB quieter than a "fired brick paving"3

1.4 dB quieter than a conventional Dutch dense asphalt concrete4 2.5 dB quieter than a conventional German dense asphalt concrete5

Even the entire interlocking block may be made porous. Hitherto it has not been tried as far as the authors are aware, but it may become a very efficient low-noise surface, provided the structural stability can be guaranteed, since factory production would promise to give homogeneous and good properties.

Finally, it should be mentioned that clogging of the air voids by dirt is a potential problem of this kind of surface, as is the case for porous asphalt surfaces. Clogging will after some time reduce the acoustic efficiency of the porous layer, but there is no experience reported about at what extent and how fast this occurs for a material of this kind.

6.4 Soft

cover

The most common types of blocks are hard stones or hard cement concrete. If such blocks are made half or double as hard will not affect noise, since they are already so much harder than any tyre rolling on them. However, if the blocks are made of softer and lighter materials such as wood; this might give the tyre rubber a softer impact on the blocks; in particular as the block impulse may be partly softened/absorbed by the stabilization layer (sand) it is laid in. This was definitely the case with iron wheels in past times.

The ultimate softening material may be rubber. Flat and dense rubber may be too slippery and dense to be useful, but a porous rubber layer with suitable additives would provide for better skid resistance while at the same time absorbing sound and eliminating the pressure gradients in the tyre/road interface which creates air pumping.

2_{According to VTI materials laboratory staff}

3_{The authors do not know what this is; a guess is that it is conventional Dutch bricks (like in Fig. 1.5).} 4_{Normally the Dutch reference is a DAC 0/16 (dense asphalt concrete with maximum 16 mm}

chippings) but the reference gives no guidance regarding this

5_{The authors guess that this surface is a "Gußasfalt" (mastic asphalt) but have no idea what the}

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7 Review of earlier studies

7.1

Review in the Tyre/Road Noise Reference Book

A review appears in the Tyre/Road Noise Reference Book [2]. This is partly copied into this subchapter. Note that data and views expressed are those of the references, if not otherwise noted. In many cases descriptions of the tested surfaces are very vague in these documents. First, a summary of a number of measurements with the CPX method on various surfaces in Europe are shown in Fig. 7.1. The measurements were made in Poland by the Technical University of Gdansk (TUG). The four last surfaces in the diagram are block surfaces. The two first ones are interlocking blocks made of cement concrete and the two last ones are stone setts. It appears that the interlocking blocks may not be noisier than a DAC or an SMA with large chippings (maximum 14-16 mm), but evidently an interlocking block pavement may also be substantially noisier. However, the setts are by far the noisiest surfaces measured. In [7] there is a review of the effect on noise emission of block surfaces. The noise increase is 1.5 - 8 dB(A) according to this. In some types of streets, interlocking blocks of modern types have been introduced, usually made of cement concrete. Although the traffic usually is not intense on such streets, there has sometimes been some concern over the increased noise they cause. This has been investigated by [8] who did not find any consistent noise increase due to the blocks. Later studies include an Austrian study [9] and two German studies [10], [5].

The first German study [10], tested three modern block pavements (proprietary names Eskoo Tavalo, Eskoo Tegula and Eskoo Tacato). It was found that the Tavalo resulted in pass-by car noise at 30-50 km/h that was similar to that on a conventional DAC 0/11, while the other two were 1-3 dB(A) noisier.

The second German study [5], also concluded that cement concrete block pavements can be constructed with a surface resulting in the same traffic noise level as that on dense asphalt surfaces. These authors reported that the (acoustically) best surfaces are smooth surfaces having a fine texture (grains 2 to 5 mm), or finely scrubbed or sand-blasted surfaces. These are better than plain smooth surfaces. Larger block sizes (more than 120x240 mm) are better than smaller ones. It was also reported that the joints between the blocks contributed to noise reduction (by sound absorption?). Such joints, especially when wide, should be directed in parallel to or diagonally to the driving direction, if possible. If joint widths are < 5 mm, the laying pattern and joint direction are not important, according to [5]. Blocks having a chamfer, especially if rectangular, should be laid diagonally. It is stressed that the preser-vation of evenness over the service life is crucial. Furthermore, some detailed explanations with regard to causes for increased noise on such surfaces are presented in [5].

The Austrian paper is not very detailed. However, the author claimed a very good noise reduction of three of the twelve tested block types [9]. He observed a reduction of 3.0-3.5 dB(A) in relation to a newly laid dense asphalt concrete and 6 dB(A) in relation to an old and somewhat noisy DAC. On the other hand, seven types were 1-6 dB(A) noisier than the new DAC. One of the low-noise types had an interlocking function that makes it suitable for heavy-duty roads, while one of the other low-noise block types is more adequate for decorative purposes. The latter is in fact one of the most frequent reasons to select a block pavement.

The Austrian low noise types seem to have almost incredibly low noise according to the authors of [2].

Many of the conclusions are contradictory to those reported above in [5]. Therefore, it seems that more research is required on the Austrian block pavements, hopefully verifying the excellent low-noise properties reported, again according to [2].

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90.0 92.1 95.3 96.8 94.3 96.3 96.8 100.6 99.8 97.8 97.7 98.1 98.3 97.7 99.5 100.1 101.0 96.2 100.2 100.6 104.1 106.1 107.0 85 90 95 100 105 110

PAC, two layers, 2-4m m (top) + 11-16m m PAC, two layers, 4-8m m

(top) + 11-16m m Porous asphalt concr. (PAC),

<12-16 m m Slurry seal < 5 m m ISO 10844 ref. surface Stone m astic asphalt (SM A),

<4-6 m m

Stone m astic asphalt (SM A), <8-10 m m

Stone m astic asphalt (SM A), <12-16 m m Asphalt concrete, dense,

<12-16 m m Germ an "Gussasfalt" surface

Surf. dressing, two layers, 6.3-10 + 2-5 m m Surf. dressing, one layer,

<6-9 m m (on CC) Surface dressing, one layer,

<6-9 m m

Surf. dressing, one layer, <8-12 m m , worn Surf. dressing, one layer,

<8-16 m m , worn Cem ent concr. (CC), exposed aggr., <8 m m Cem ent concr., exposed

aggr., <16 m m Cem ent concr., burlap drag Cem ent concr., transversely

brushed

Concrete block pavem ent, type 1

Concrete block pavem ent, type 2

Paving stones, type 1 Paving stones, type 2

C P X I [dB ]

0 1 2 3 4 5

MP D [m m ]

Figure 7.1: Comparison of A-weighted sound levels (CPXI) measured by TUG with the CPX method on different surfaces. Test tyres in accordance with ISO/CD11819-2.The

Mean Profile Depth (MPD) of the macrotexture of each surface is indicated by red diamonds connected with red lines. Each bar is filled with a photo of the surface 7.2

Work in the Netherlands

In the Netherlands, there are at least two types of interlocking blocks with a porous upper layer. Both are proprietary surfaces. Refer to Section 6.3 for a presentation of these surfaces.

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8 Experiments with a poroelastic cover on a block surface

8.1 Experiment with poroelastic cover on interlocking blocks in Japan in 2002

In 1994, research on poroelastic road surfaces (PERS) was started at the Public Works Research Institute (PWRI) in Japan. By 1997, attempts were made to start cooperation between PWRI and VTI on this subject, but it failed due to financing problems from the Swedish part. However, from 2000 also the Swedish part obtained some funding for this research and the two institutes have since then had cooperation on this subject.

The first field experiment with poroelastic surface in Japan was carried out in the Akita prefecture in northern Japan in October 2002. This experiment was carried out in the town of Tazawako on National Highway R46 which is one of the major north-south highways in northern Japan, carrying a very high proportion (20 %) of heavy vehicles; see Fig. 8.1. A total road length of 20 m paved with two types of PERS (10 m of each type) was constructed, with a base structure as shown in Fig. 8.2.

Fig. 8.1: Location and background data for Japanese field experiments with PERS. Picture from [13], improved by the authors.

Fig. 8.2: Base struc-ture of the test in Akita with 30 mm PERS on top of interlocking blocks (ILB). Picture from [13], improved by the authors.

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The test section is shown in Fig. 8.3 and a close-up of the cement concrete blocks with PERS on top is shown in Fig. 8.4.

Fig. 8.3: Test section (darker part) of 20 m length on R46 in Akita.

Fig. 8.4: Test two types of PERS tested on R46 in Akita. The left one has some recycled plastic particles included, potentially to increase friction.

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The subjective difference in noise when standing at the roadside was impressive. However, the test section had some unevenness which could be heard as a rumble inside the car; although the overall subjective noise difference inside the car was also positive. The Japanese measured a noise reduction compared to the conventional Japanese asphalt surface (DAC 0/13) of 6 dB at 50 km/h and 8 dB at 80 km/h, for cars.

Unfortunately, the high volume of heavy traffic on this road soon was noticed in terms of severe rutting on the pavement. It was not any kind of wear or compression of the rubber. Instead, it was a displacement of the intermediate layer of asphalt-coated sand on which the ILB were placed. The sand was pressed up between the ILB and spread along the road. More about experiments with PERS in Japan and Sweden, can be found in [14].

8.2 Experiments underway in NR2C and SILENCE - Introduction

One of the tasks in SILENCE WP F1 is to construct a block pavement with a soft and thus quiet cover. For this purpose, a poroelastic road surface has been selected as the soft cover. The projected use of such a surface would be in urban or suburban streets where noise emission is a major problem while at the same time one would prefer to have a surfacing which stands out as "unusual" in order to notify vehicle drivers of the need to drive softly. Since in such a location, homes and businesses are likely to be close to the street, also aesthetical properties would be important. Normally, in such a location one would choose to use interlocking blocks to meet the two latter purposes (unusual surface with pleasing visual appearance), but the noise problem would still be there. The design described in the following is intended to take care of also the first problem, i.e. the noise emission. One might say that this solution would be the modern variant of the wood block pavements described in Chapter 3.

During the course of this project, it was found that the EU project NR2C ("New Road Construction Concepts"; see http://nr2c.fehrl.org/) had partly similar aims as SILENCE WP F1 and it was decided to have a cooperation between the two projects aiming at producing and testing a couple of interlocking block pavements with PERS cover.

8.3 Experiments underway in NR2C and SILENCE - Description

6

As mentioned in [14] all field tests with poroelastic road surfaces has either been prematurely terminated due to lack of adhesion between the underlying surfaces or due to wet friction properties being below regulatory limits at some point of the tests. The one exception is the trial in Japan with a block pavement covered with poroelastic material. In that case the test was interrupted due to severe rutting and pavement blocks becoming displaced. Insufficient drainage of the stabilizing sand layer immediately below the paving blocks was a plausible cause for the rutting. However, even if this surface had not been forced to be removed due to the rutting, it would most probably not maintain a sufficient wet friction after some months of operation, as the problem with durability of the frictional properties had not been solved at that occasion.

The SILENCE and NR2C cooperation is focused on solving two major problems with this type of surface:

• The stability of the system of blocks and stabilizing layer must be sufficient for a reason-able operating time and for a mix of light and heavy vehicles typical of an urban street • The wet skid resistance must be maintained at an acceptable level for a reasonable

operating time for a typical urban street condition

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A laboratory test scheme has been set up to study means for having an interlocking block surface covered with a poroelastic material that (together with the blocks) is both resistant to rutting and has a durable wet friction. For improving the frictional properties, a test will be conducted to study the influence on the durability of friction of binder hardness, addition of silicon carbide to the mix and pre-treatment of the rubber crumb.

For simulation of the polishing effect of rolling tyres on a road surface, the VTI pavement testing machine will be used. The pavement testing machine is a circular track with a diameter of approximately 5 metres. Four or six wheels are rolling on this surface at a speed up to 70 km/h. See Fig. 8.5. The power to the traction of the wheels is delivered by electrical engines attached on each of the wheel axles. The load on each wheel is adjustable but is usually fixed at 450 kg. The wheels do not follow a circular track; rather there is a latter movement of the wheels to simulate a realistic distribution of wheel paths. The test can be made in dry or wet conditions. When wet conditions are used, fresh water is constantly sprinkled over the surface. The evolution of the friction will be tested with the British Pendulum method and by a manually pushed equipment developed at VTI which measures the friction on a partially slipping wheel pushed at a speed of approximately 5 km/h.

Fig. 8.5: The Pavement Testing Machine at VTI.

In the planned test, the test track in the pavement testing machine will be divided in seven different sections. In each section, a different type of mix will be produced. After curing and initial check of friction, stiffness and permeability, the traffic polishing will commence in wet conditions. At regular intervals the friction and rutting will be measured. The test will continue until several years of traffic polishing has been simulated. Afterwards the test will continue in dry conditions.

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In many of the previous experiments the lack of adhesion between the poroelastic layer and base-layers was the reason for failures. This is also the reason for choosing a pavement structure where poroelastic layer is laid on concrete (paving) blocks. In this way the critical gluing can be made in a more controlled and proper manner and environment.

Taking7_{into account problems and reasons for failure of previous test fields in Japan, the} project participants identified and selected a keypoint topic for further research work at the ZAG institute8_{; namely the foundation for the blocks (bedding layer) has to be improved,} intending to avoid the Japanese failure.

To solve problems with displacement of the intermediate layer of asphalt-coated sand on which the interlocking blocks in the Japanese tests were placed, ZAG will focus on the bedding layer onto which the cement concrete blocks are placed. The entire pavement structure will be as “strong” as possible to avoid bearing capacity failures, but it will also be as traditional as possible.

Except for the poroelastic layer, the proposed pavement structure for testing in Slovenia is a traditional pavement structure for stone/cement concrete blocks paved on roads in Slovenia, and for preparing it only local materials are used.

The testing structure was prepared in a wooden mould, where each pavement layer was placed and compacted. This procedure can be seen in Figures 8.6-8.9.

Figure 8.6: The unbound layer is placed in the mould

7_{The section about the experiments at ZAG in Slovenia has been written by Mr Darko Kokot at ZAG} 8_{ZAG Ljubljana (Zavod za gradbenistvo Slovenije) is Slovenia's national building and civil engineering}

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Figure 8.7: Compacting the asphalt layers

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Figure 8.9: The test construction is finished

Four different setups will be tested, as illustrated in Figure 8.10. First, ZAG will perform tests on a structure where cement concrete blocks with a glued poroelastic overlay are placed onto a sand bedding layer. The second test setup is similar but will include watering of the structure. The third and fourth setups are similar to the first two ones, except that the cement concrete blocks will be placed onto a cementitious screed bedding layer.

In total there will be four test cycles. One cycle will consist of a piston-induced dynamic loading of the test structure, as can be seen in Figure 8.11. There will be 100,000 vertical loadings applied through a heavy vehicle tyre, each time of 3 tons. The loading equals 100,000 passes of 12 ton axle load. The vertical displacement of the structure will be monitored and followed by three LVDTs, mounted on a framework and placed along the tyre. In case the laboratory experiments indicate that the friction and the structural performance are acceptable and above regulatory limits, field test will be performed. The structural performance will first be tested in an approach ramp to an asphalt mix plant, where there is only heavy trucks running. This test will give a clear indication if whether the bearing capacity of the chosen block pavement construction is sufficient.

Following this, a test site will be constructed in Nova Gorica, Slovenia, to evaluate the surface in actual trafficked conditions. A preliminary test site has been chosen but the detailed planning of this test site will have to wait until proper materials been developed, a producer for the material been contracted, and construction with sufficient bearing capacity has been chosen.

Depending on the outcome of the Slovenian experiments, a field test is planned to be conducted also in Sweden in the late summer of 2007, learning from the Slovenian experience. Critical topics will be the winter performance, durability/stability, clogging, skid resistance durability, and ability to endure the passing of snow removal vehicles.

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unbound layer 30 cm asphalt layers 6 + 3 cm sand, bedding course 5 cm cement concrete blocks poroelastic overlay

A) Construction with sand bedding course B) Sand bedding course, adding water

unbound layer 30 cm asphalt layers 6 + 3 cm cementitious screed,

bedding course 5 cm cement concrete blocks poroelastic overlay

unbound layer 30 cm asphalt layers 6 + 3 cm cementitious screed,

bedding course 5 cm cement concrete blocks poroelastic overlay

C) Construction with screed bedding course D) Screed bedding course, adding water Figure 8.10: The four different test setups

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8.4 Concluding

remarks

At the time of writing the status of the experiment is as described in 8.3. However, it shall be mentioned that there have been problems to find a PERS material which meets the specifications desired for this project despite extensive attempts; most notably a durable wet skid resistance. In the previous experiments in Sweden [14], material from a British supplier was used. However, this supplier is unwilling to modify its original material to meet the wet skid requirements of this project. To this end, an addition to the material is needed. VTI will, therefore, as soon as possible try to find another potential supplier of the material, who is willing to cooperate on this matter. There is one in Denmark which has been contacted earlier and which is the main target and main hope at the moment.

It must be noted that this is cutting-edge research, the outcome of which is not given in advance.

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9 Experiments with quieter stone setts carried out in Denmark

9.1 Objectives of the Danish experiments

The objectives of the Danish experiments are:

1. To produce a ranking in relation to noise of commonly used types of paving stones9 2. To develop and test quieter types of paving stones

To achieve the first objective, four different types of paving stone surfaces in the Copenhagen area have been selected for SPB noise measurements. This includes one type of cement concrete interlocking blocks, as well as three types of granite blocks with different levels of surface texture. These pavements are described in detail in Section 9.3.1.

To achieve the second objective, a special type of granite blocks has been developed by the municipality of Copenhagen and these have been applied on a section of "Nordre Frihavns-gade" in Copenhagen in the summer/autumn of 2005. This pavement is described in detail in Section 9.2.

9.2 Optimization of the Danish paving stone surfaces

"Nordre Frihavnsgade" is a main shopping street with through-traffic and five-floor residential buildings very close to the 900 m long street. The traffic volume is 7000 vehicles per day and there are approximately 10 % heavy vehicles, including busses. The speed limit is 50 km/h. There are conflicts between the traffic and people living and shopping along the street. The street is located in a more than 100 years old area of Copenhagen built in the last part of the 19th_century.

Figure 9.1: The street "Nordre Frihavnsgade" in a more than 100 years old area of Copenhagen, before changing the old surface to granite blocks.

In order to improve conditions for pedestrians, a traffic management scheme has been planned. The main goal is to reduce the driving speed of cars by changing the pavement and

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the layout of two sections, each 120 m long, with displacements of the driving lanes and by introducing a 40 km/h speed limit. Raised areas will be used at the beginning and end of these sections.

Figure 9.1: Close-up of the flat granite blocks used on "Nordre Frihavnsgade". The old worn asphalt concrete pavement with patchwork repair was replaced by specially designed granite blocks that were produced in India. The objective was to develop a type of granite blocks which causes less noise than the ordinary types.

The top surface of the blocks is produced by sawing the material in order to obtain a surface which is as flat (plane) and even as possible in order to reduce noise from vibrations in the tyres. The surface is produced to have some texture consisting of small cavities chopped in the granite in order to create a reasonable skid resistance. These cavities might have a small potential for reducing air pumping noise. The joints between the blocks have a width of about 15 mm and are filled with fine unbound gravel. In order to reduce noise when tyres hit the joints, as well as for aesthetical reasons, the blocks are placed at an angle of 45 degrees to the driving direction. The blocks have a size of 150 × 200 mm (see Figure 9.2).

A dark grey type of granite was selected for aesthetical reasons.

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9.3 Measurement

program

9.3.1 Paving stone surfaces included

A total of five road sections with different types of paving stones and concrete blocks have been selected for SPB noise measurements10_:

1. A section with “rough” old setts of granite on "Amagerstrandvej" (see Figure 9.4) with relatively large dimensions and rather polished by traffic.

2. A section with more ordinary, smaller setts on "Kildevældsgade" (see Figure 9.5). 3. A section with new flat and relatively large setts on "Ørestad Boulevard" (see Figure

9.6).

4. A section with flat cement concrete blocks on "Kollerødvej" placed at an angle of 45 degrees in relation to the driving direction (see Figure 9.7).

5. A section with new, (hopefully) noise-optimized, flat granite blocks on "Nordre Frihavnsgade" placed at an angle of 45 degrees in relation to the driving direction (see Figure 9.8).

All five types of pavement blocks are laid on unbound gravel. The joints between the blocks of all the five types are filled with fine unbound gravel. The widths of the joints differ (see Table 9.1).

Figure 9.4: Overview and close-up photographs of the old “rough” and relatively large setts of granite on "Amagerstrandvej". The length of the black and white squares on

the left hand photo is 10 mm.

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Figure 9.5: Overview and close-up photographs of the ordinary small stone setts on "Kildevældsgade".

Figure 9.6: Overview and close-up photographs of the new, flat stone setts on "Ørestad Boulevard".

Figure 9.7: Overview and close-up photographs of the flat concrete blocks on "Kollerødvej" placed at an angle of 45 degrees in relation to the driving direction.

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Figure 9.8: Overview and close-up photographs of the new, optimized flat granite blocks on "Nordre Frihavnsgade" placed at an angle of 45 degrees in relation to the

driving direction.

Table 9.1: Overview of the paving blocks included in the survey, including dimensions of the blocks.

Type Location Material Size of

blocks

Width of joints

Angle relative to driving direction Large old stone setts

(Fig. 9.4) Amagerstrand vej Granite 13 × 23 cm varying 10 - 40 mm 90° Ordinary small stone

setts (Fig. 9.5) Kildevælds-gade Granite 10 × 10 cm 5 - 25 mm Around 45° varying Flat new stone setts

(Fig. 9.6)

Ørestad Boulevard

Granite 10 × 19 cm 10 mm 90° Flat concrete blocks

(Fig. 9.7)

Kollerødvej Concret e

8 × > 20 cm 5 – 7 mm 45° Flat granite blocks

(Fig. 9.8)

Nordre Frihavnsgade

Granite 15 × 20 cm 10 - 15 mm 45°

9.3.2 Measurement method

A typical measurement setup can be seen in Figure 9.9. The microphone was placed 1.2 m above the pavement at a distance of 7.5 m from the centre line of the vehicles. The radar equipment for measuring the vehicle speed was placed at a distance of about 15 to 35 m from the microphone. Corrections due to the angle "a" between the radar and centre line of motion was carried out for measurements at Kollerødvej and Ørestad Boulevard where the angle "a" exceeded 8°, corresponding to a speed correction factor exceeding 1.010. The measurements are documented in a separate report from DRI [15].

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Figure 9.9: Typical setup for the SPB measurements.

9.3.3 Measurement conditions

The average air temperatures during measurements were 17 to 24 ºC; see Table 9.2. As the temperature variation is very small no temperature corrections were carried out. In Table 9.2, the cloud cover is indicated as a fraction from 0/8 to 8/8, where for example 4/8 means that the clouds covered a fraction of approximately 4/8 (50 %) of the sky.

Table 9.2: Date, time, and meteorological conditions during SPB measurements [15].

Measurement site Date Time [hh:mm] Air temperature [ºC] Cloud cover [-/8] Amagerstrandvej 10 May 2006 9:30 – 12:14 17 - Kollerødvej 9 May 2006 12:28 – 14:52 21 0/8 Kildevældsgade 8 May 2006 9 May 2006 11:28 – 12:35 8:50 – 10:55 22 18 0/8 0/8 Ndr. Frihavnsgade 8 May 2006 9:05 – 15:54 24 0/8

Ørestad Boulevard 10 May 2006 13:45 – 15:45 21 0/8

The number of vehicles that were included in the measurements is listed in Table 9.3. Table 9.3 also shows that it was not possible to fulfil the requirement of 100 light vehicles at "Kildevældsgade", "Ndr. Frihavnsgade" and "Ørestad Boulevard" within a reasonable time period. Even though the requirements are not always fulfilled the statistical uncertainty of the results are acceptable (smaller than 0.5 dB - see Section 9.4.3). The number of dual-axle trucks and busses included in the measurements was limited; at most the noise levels from 32 dual-axle heavy vehicles were measured at "Kildevældsgade" due to a bus service passing by. Therefore the results for dual-axle heavy vehicles are only indicative. There were so few multi-axle trucks and busses that these results have been omitted in the analyses.

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Table 9.3: Number of vehicles included in the measurements [15].

Measurement site Passenger cars Dual-axle trucks/busses Multi-axle trucks/busses Amagerstrandvej 102 4 14 Kollerødvej 102 10 7 Kildevældsgade 38 32 0 Ndr. Frihavnsgade 62 13 1 Ørestad Boulevard 45 9 0

9.4 Measurement results from the Danish experiments

9.4.1 Maximum noise levels

Logarithmic regression analyses of the relation between the measured maximum A-weighted noise levels with time weighting F and the vehicle speeds have been carried out. The resulting regression lines for passenger cars are shown in 9.10 and Lveh, cars noise levels at the reference speed are shown in Table 9.4. The regression lines are shown for a range of ± 1.5 standard deviations around the actual average speed. Because of the low number of heavy vehicles and the noise levels at the reference speed of these having a 95 % confidence interval of several dB, analyses are mainly based on passenger cars. However, results for dual-axle trucks and busses are included as indicative results and are shown in Figure 9.11 and Table 9.4.

The noise levels (see Table 9.4) for passenger cars (Lveh, cars) are reported at a non-standardized reference speed of 40 km/h because of the low average speed on the test sites, while the results for dual-axle heavy vehicles are reported at a reference speed of 30 km/h. For comparison, reference values have been calculated by the NORD 2000 prediction model at 40 and 30 km/h. The reference values are based upon the average noise levels on surfaces in good condition of dense asphalt concrete (DAC 11) and stone mastic asphalt (SMA 11) both with maximum aggregate size 11 mm, and an age of more than two years, but not being at the end of their life span.

The relatively large and old stone setts gave rise to much more noise than the flat concrete blocks (see Figure 9.10). At the reference speed a difference in noise levels of up to 10 dB was measured between roads with large stone setts and roads with flat concrete blocks. Noise levels measured at the sites with ordinary small stone setts and flat but somewhat larger stone setts were very much the same. By using flat concrete blocks compared to old traditional stone setts a noise reduction of up to 10 dB is achieved. For cars the reference value calculated by the NORD 2000 prediction model was 0.2 dB to 1.8 dB higher than noise levels on roads with flat stone setts and flat concrete blocks, respectively, and 4.4 dB to 8.2 dB lower than the noise levels on roads with small or large stone setts.

Table 9.4: Noise levels expressed as LpAFmax, 7.5 m for passenger cars at 40 km/h and

dual-axle heavy vehicles at 30 km/h. Parentheses around the noise levels indicate that the 95 % confidence limit exceeds ± 2 dB [15].

Large old stone setts (Fig. 9.4) Flat concrete blocks (Fig. 9.7) Ordinary small stone setts (Fig. 9.5) Flat granite blocks (Fig. 9.8) Flat new stone setts (Fig. 9.6) NORD 2000 reference level Lveh, cars [dB] 77.8 67.8 74.0 69.4 74.2 69.6 Lveh, dual-axle [dB] (78.6) (71.6) 77.3 65.5 74.1 75.9

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62 64 66 68 70 72 74 76 78 80 82 84 86 25 30 35 40 45 50 55 60 Speed [km/h] LpAFma x [d B]

Large old stone setts Flat new stone setts Ordinary small stone setts NORD 2000 reference (DK) Flat granite blocks Flat concrete blocks

Figure 9.10: Maximum A-weighted noise levels for cars, time weighting Fast, and at a distance of 7.5 m, as a function of vehicle speed. The reference speed is 40 km/h [15].

62 64 66 68 70 72 74 76 78 80 82 84 86 18 23 28 33 38 43 48 Speed [km/h] LpA Fm a x [d B]

Large old stone setts Ordinary small stone setts NORD 2000 refefrence (DK) Flat new stone setts Flat concrete blocks Flat granite blocks

Figure 9.11: Same as for the previous figure but for dual-axle heavy vehicles. Reference speed 30 km/h [15].

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As mentioned above, the results for dual-axle heavy vehicles are only indicative, and show that the noise levels on roads with cobblestones are greater than noise levels on roads with concrete and granite blocks, and on roads with big and ordinary small cobblestones the noise levels were 1.4 dB to 2.7 dB greater than the NORD 2000 reference value. The best noise performance was found at roads with granite or concrete blocks. The measurement results from the sites with big cobblestones and flat concrete blocks showed a statistical uncertainty of 2.0 dB and 4.2 dB, respectively.

9.4.2 Frequency spectra

The results of the 1/3-octave band frequency analyses are shown in Figure 9.12. The levels in the frequency region below 1.5 kHz for the stone setts are clearly higher compared to the reference levels predicted from the NORD 2000 model. This is most likely a result of the substantially rougher and more uneven surface of these setts compared to the asphalt on which Nord 2000 is based. However, below 400 Hz, the noise is reduced in comparison to Nord 2000 for the flat granite and concrete blocks. In general when comparing the spectra above 1.6 kHz to the reference spectrum, all types show a reduction in noise levels except the larger stone setts; which is probably due to reduced air pumping noise.

The 1/3-octave band frequency spectra for dual-axle heavy vehicles are broader, because of the increased levels in the low and high frequency regions.

9.4.3 Statistical uncertainty

The statistical uncertainty is expressed as half the width of a 95 % confidence interval and is listed in Table 9.5. An uncertainty of 0.5 dB is normally considered as "just acceptable" when considering passenger cars. Results for heavy vehicles measured on roads with the larger stone setts or the flat concrete blocks are very uncertain.

Table 9.5: Statistical uncertainty (half width of 95 % confidence interval) of the SPB results for cars and dual-axle heavy vehicles [15].

Large old stone setts (Fig. 9.4) Flat concrete blocks (Fig. 9.7) Ordinary small stone setts (Fig. 9.5) Flat granite blocks (Fig. 9.8)

Flat new stone setts (Fig. 9.6) Uncertainty, for cars [dB] 0.3 0.2 0.5 0.2 0.3 Uncertainty,

for dual-axle trucks [dB]

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33 38 43 48 53 58 63 68 73 63 100 160 250 400 630 1000 1600 2500 4000 6300 10000 Frequency [Hz] A -weig ht ed so und pr essur e level [d B ]

Large old stone setts Flat new stone setts Ordinary small stone setts Flat granite blocks Flat concrete blocks NORD 2000 reference (DK)

Figure 9.12: 1/3-octave band frequency spectra of the maximum A-weighted noise levels (time weighting Fast and at a distance of 7.5 m) for passenger cars, normalised

to 40 km/h [15]. 33 38 43 48 53 58 63 68 73 63 100 160 250 400 630 1000 1600 2500 4000 6300 10000 Frequency [Hz] A -w e ighte d sound pr e s s ur e l e v e l [ dB ]

Big cobblestones Flat new stone setts Ordinary small stone setts Flat granite blocks Flat concrete blocks NORD 2000 reference (DK)

Figure 9.13: Same as for the previous figure but for dual-axle heavy vehicles, normalised to 30 km/h [15].

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9.5 Maintenance issues

It is recognized that tear and wear, stability problems, as well as poor maintenance, might increase the noise emission from stone setts over the years. One problem is the gradual disappearance of part of the sand which usually fills the joints between blocks. As an example of such maintenance problems, and attempts to solve them, work carried out in Cardiff in Wales is interesting to study [16]. This is, however, but one of many solutions. Cardiff city centre features granite setts and slabs which require intensive maintenance to ensure that these are kept clean. However the street cleaning has caused erosion of the sand joints between the setts and slabs, creating unstable joints. A company named Instarmac has then suggested to use one of its products that sets quickly, which is a flowable grout that is designed for applications where a fluid consistency and early trafficking are required [16]. The material is mixed with clean water on-site, poured over the surface using a large vessel and worked into the joints. Shortly after application, a water spray has been used to remove excess material and leave an exposed aggregate finish.

This treatment is claimed to provide a surface which needs less maintenance and has a higher durability.

9.6 Discussion and conclusions concerning the Danish measurements

The following simple, practical guidelines for design of paving stone and other block surfaces having as favourable acoustic properties as possible are offered:

• The individual blocks should have as even (plane) a surface as possible. • The joints between the blocks should be as narrow as possible.

• The blocks should have a uniform size in order to ensure the same width of the joints and by this making it easier to minimize the width.

• It is better to have an angle of 45° than 90° between the direction of the joints and the driving direction of the vehicles on the road.

In general, roads with stone setts which are worn or otherwise have no special provisions for being flat are noisier than roads with flat concrete or flat granite blocks. The best noise acoustical performance in this investigation was achieved by using flat concrete blocks or flat granite blocks.

Compared to the NORD 2000 reference (as used in Denmark) all pavements showed a reduction in high frequency (air pumping) noise, with the exception of the old and large stone setts.

When using traditional stone setts as compared to modern concrete or flat granite blocks, the low-frequency vibration-excited noise is substantially increased.