VTlnotat
No: TF 52-12 Date: 1988-12-08
Title: VISIT TO THE LABORATOIRE CENTRAL DES PONTS ET CHAUSSEES
(LCPC) - THE CENTER AT NANTES, FRANCE
Author: Ulf Sandberg
Division: Road User and Vehicle Division
Project No: 53342-2
Project title: Measuring Systems and Instrumentation for Evaluating Pavement Maintenance Effectiveness
Sponsor:
PTI/SHRP
Distribution: /restricted/
. Pa: 5__81 01 Linköping. Tel. 013-2040 00. Telex 50125 VTISGIS. Telefax 013-14 14 36
InStltutgt Besok: Olaus Magnus väg 32 Linköping
CONTENTS
10. 11. 12.
BACKGROUND
THE TEXTURE MEASURING DEVICES
THE "NUMERISATEUR"
THE "PROFILON"
THE "PAVIAMETRE"
THE "MOIRE" TECHNIQUE
THE "SURTRONIC" DEVICE FOR MEASURING MICROTEXTURE
THE "DRAINOROUTE"
SPLASH AND SPRAY PROPERTIES OF ROAD SURFACE THE LCPC TEST TRACK
FRICTION MEASURING VEHICLES NOISE RESEARCH
APPENDIX
l. Background
From various personal contacts, as well as some recent documents, it was
obvious that a lot of experimental work had been done and was continuing
in France with the purpose to develop or refine instrumentation for the measurement of road surface Characteristics, especially macrotexture. Efforts are also made to develop a contactless measurement of road surface microtexture.
A reason for putting so much effort into this, it turned out during the
visit, is that there are advanced plans to introduce a new standard for tire/road friction on the French road network. The standard would require primarily the measurement of macrotexture, and if those measurements
indicate macrotexture to be lower than the "recommended" but higher
than the "minimum" values, call for additional friction measurements. Apart from this, it turned out, there are efforts made to replace pendulum friction tests for determining the PSV value of stones by direct microtexture measurement.
Most of the relevant work is done at the Division Structures et Caracté-ristiques des Chaussées, headed by Mr. Michel Boulet, at the Center at
Nantes of the LCPC. The person with 'the most technical knowledge and
most experience in this area is probably Mr. Jean Lucas, who was the author's host during the visit. He is probably the best expert on this subject in the whole of France.
The LCPC Center at Nantes is located in Bougenais (a suburb of Nantes)
and covers anarea of 150 hectares (roughly 350 acres) and has a staff of
150. Within the premises there is a test-track designed for studies on road
surface Characteristics. The facilities also include one of the most impressive circular test tracks for testing road durability and wear
(outdoors, 40 m diameter).
The aim of this visit was to study the techniques and instrumentation employed to investigate road surface Characteristics, especially contact-less measurement of macrotexture.
2. The texture measuring devices
The following devices have been studied:
a. The "Rugolaser", which can be used on the SCRIM, on the rear bumper
of any vehicle or on a special trailer
b. The TRRL "Mini Texture Meter" (MTM)
c. The "Defocalisation Sensor" (under development)
d. The "Optimess" which in turn is employed in three devices:
dl. The "Numérisateur" (lab model)
d2. The "Macroprofilographe" (version of the above for field use)
e. The "Paviamêtre"
f. The "Moiré" technique
g. The "Surtronic" device, which is the only one for microtexture
measurement and which is a contact-type profilome'ter
h. The "Drainoroute"
Devices "a-f" are contactless and all measure macrotexture. Device "h" makes contact with the road surface during the measurement and
measures the "drainage" which, however, is related very well with
macro-texture. Those which are of particular interest to the SHRP projects are listed systematically in the appendices and the others are discussed briefly below under separate headings since they are of general interest.
3. The "Numérisateur"
This device is intended purely for lab applications and consists basically of a laser probe ("Optimess", Swiss made) for macrotexture measurement, a
stand with a traversing device for longitudinal as well as lateral move-ment of the probe and a computer system for data processing and
evalua-tion. The movement is very slow and thus a mapping of a surface may take several hours; however, it can be run without human presence. It can be used to map surface texture in three dimensions with an arbitrary resolution, but no better than 0.1 mm vertically and O.5-l.0 mm
horizont-ally. Measuring range is 20 mm. The software includes texture amplitude distribution (vertical displacement) and spectral analysis.
ll. The "Profilon"
The probe of the "Numérisateur" and its computer system are applied for
field use by mounting the probe on a 4-wheel carriage which is stationary on the road during measurement while the probe is moved along the carriage by an electric motor (continuously). This is the
graphe" which is described in the Appendix. However, this
"Macroprofilo-graphe" will be replaced by a new device named "Profilon" which will be finished 1989. The "Profilon" will use the ingredients of its predecessor except that the carriage will be replaced by a 2 m long beam along which
the probe will be moved. This beam will thus enable twice as long profiles
to be recorded and will be much lighter and more practical. One person should be able to lift it in/out of the carrying van, while two persons are
necessaryto lift the "Macroprofilograph".
5. The "Paviametre"
This is a measuring system used exclusively to determine maintenance priority on stone set pavements (mainly paving stones of historical type)
which are still in wide use in cities and towns in France for cultural
reasons.
Had it not been for its very narrow application, it could have beenvery
There is only one "Paviamêtre" and it is stationed in the LCPC center in the Parisian suburb of Trappes.
The main parts are:
I. A displacement sensor of laser type from Selcom in Sweden (the old
"Optocator" type) and accompanying data processing unit. Measuring
range is 64 mm.
II. Two computers, one for processing on-line the texture profile signal J and the other for calculating maintenance priority.
III. A vehicle to carry the equipment.
The driving speed at measurement is 12 km/h, probably limited due to the sampling rate of the laser and for practical reasons in inner-city traffic. The "raw" signal thus is a profile. However, it is not recorded, instead this profile is used to identify the periodic joints between the stones (period
generally around 100 mm) and to calculate the average depth of those joints underneath the "peak stone level". This is a rather complicated
process in practice and gives one value each 10 m. Then, this average joint depth is used to classify the pavement in 5 or 6 (?) classes of maintenance priority; the higher priority the deeper the joints are. The priority class is the only output of the system.
6. The "Moiré" technique
By using a special monochromatic light source and a special photographic
technique it is possible to map the vertical displacement of a surface in
terms of vertical interference level lines; each line representing a level at
a multiple of (say) X mm above some reference plane. This technique, which gives a three-dimensional map of the surface, is called the "Moiré" technique after its inventor and is a relatively old technique in surface analysis in other applications. However, the French are the only ones 'to apply it to road surface mapping.
The technique is not fast and practical enough to warrant a field use at large scale and is mostly suited to document a surface textu're, perhaps as an alternative to producing moulded replicas. The resolution is connected
to the range, since only about 20 interference fringes are possible to obtain over the vertical range. It means that if a resolution of 0.1 mm is required a vertical range of only 2 mm can be used. For a range of 20 mm,
the resolution will be 1 mm. An area of about 250 x 250 mm2 is covered by each photo.
7. The "Surtronic" device for measuring microtexture
In many European countries, the polished stone value (PSV) is used to characterize the friction and wear properties of stone material. At LCPC, efforts are made to make such measurements more efficient. Firstly, the polishing of stones takes several hours (4?), a time which by a new, tentative LCPC method is stated to be cut down to the order of 5 minutes! Secondly, the measurement of friction, after the polishing, is traditionally made by the British Pendulum Meter (BPM). At LCPC, trials
have been made to replace this friction measurement by a microtexture
measurement. Ultimately, a non-contact method is desirable (laser e.g.),
but in the lack of such equipment at present, trials have been made with a contact-type profiling method, namely by use of the so-called "Surtronic" device. A main reason for replacing the pendulum method is that it is dependent on the rubber properties of the rubber Slider. A direct microtexture measurement would be "cleaner" and more fundamental.
The "Surtronic" device is designed for measuring roughness (Ra and Rq
values) of machined metal surfaces. The principle is similar to the "gramophone pick-up" technique. The most suitable version for road application, type P3, has a measuring range of only 0.25 mm, using a needle 0.5 mm tall. Even if the resolution is a fraction of a micrometer, this limits the practicability of the device seriously. Only very short traces on individual stones can be measured (1-4 mm).
Despite 'these difficulties, Mr. Georges Blot at the LCPC has performed
tests and found that the Surtronic device is able of distinguishing the
microtexture of polished and non-polished surfaces (limestone material
changes its microtexture due to polishing, but quartzite and porophyry do not change) and between various materials. The measured values had a correlation with the MDE method of measuring wear (scrambling in
bucket with water) but no correlations with the corresponding Los Angeles
method (dry bucket).
A secondary result of the trials is that pendulum friction measurements
seem to have a good correlation with microtexture, something which is
always å priori assumed, but which has not been sufficiently tested.
Even though the results are encouraging, the microtexture measurements by this method are too time consuming to motivate a replacement of the
pendulum method.
The results are documented in an internal LCPC note (in French): Faer l.02.4l.7.
The efforts to render the method more effective will continue as soon as
a contactless microtexture probe is available.
8. The "Drainoroute"
The "Drainoroute" equipment is wellknown and well documented, even in
English. However, it should be mentioned here that it has appeared that it
cannot measure the deep drainage through a porous surface; it is sensitive only to the surface drainage and then has limited, if any, advantages over laser texture measurements. As porous surfaces gain popularity, this is a very serious disadvantage.
At present, there are 5 "Drainoroute" vehicles built in France of which one is a towed trailer version.
9. Splash and spray properties of road surfaces
LCPC has studied the water spray merits of different pavements on their
surface dressing, and surfaces with smooth macrotexture the worst. This is not surprising; however a surprising result was that a smooth surface
with high microtexture was worse than one with low microtexture. Perhaps the water is retained more easily and thus prevented from transversal run-off by some microtextures.
These results were obtained by a subjective estimation by a "jury" (persons riding in cars behind a spray-producing car) and with simulated
rain. However, measurements of spray from water pick-up of a tire
enclosed in a "box" in front of which water was poured at constant rate
gave other results. For instance, it was noted that the water poured out
by a friction trailer watering system caused much spray by itself.
It is probable that it is important to simulate rain by a rainfall simulator rather than by pouring out water just in front of a test tire if surface properties should be properly measured.
The work will continue 1989 with construction of a laser-type instrument
for measuring visibility reduction by water spray at the side or rearward
of a spray-producing tire. The aim is to enable Characterization of spray properties of road surfaces.
10. The LCPC Test Track
The Test Track admits testing at up to 130 km/h on several 250 m long by
3 m wide surfaces. Allsurfaces may be watered by a watering Sprinkler system with the capacity of 40 m3/h allowing a water depth of up to
2 mm (not all surfaces at the same time). The crossfall is 1.5 96.
The surfaces are listed in the table together with subjective estimations
of texture by the author (see ARRB internal report No. 000-243)
Desig- Type Chipping Estimated texture
nation (typ.=Typica1 size Mega Macro Micro
road surface) (mm)
A
Surface dressing (typ.)
10-11
4
63
7
Surface dressing 4-6 5 66 9
+12-14
+520
C Resinous surface similar 1-3 1 52 8
but not equal to
"Shell-grip" Quartzite aggregate
E Bituminous concrete (typ.) 0-10 2 52 3
N / Resinous surface, very 0-6 1 44 1
fine material. Will be
sealed with epoxy 1989
G Porous asphalt (typ.) 0-10 2 61 8
19 96 voids. 40 mm thick
M "Semi-porous" asphalt 0-10 2 62 7
ll. Friction measuring vehicles
The SCRIM which was bought in 1974 and still is the only one in France
has been rebuilt on a French truck and equipped with a much bigger water
tank: 5 m3.
In the track where friction is not measured (left track), a "Rugolaser" has
been mounted in order to measure the macrotexture. The SCRIM is considered to be most sensitive to microtexture according to Mr. Lucas, since the tire is very narrow, and it needs a supplementing macrotexture-sensitive instrument. The "Rugolaser" is essentially the TRRL laser-typehigh-speed texture meter.
The "Rugolaser" output, called VRA, is used in an equation, empirically
derived, to get the calculated sandpatch texture depth (HSC) relevant for
France:
HSC = 2.8 - VRA - 12
This last month, actually, a new friction measuring vehicle has been manufactured (finished) in three copies. It is named
The LCPC Trailer
and is essentially a one-wheeled trailer of the locked-wheel principle with
a special towing car (more like a van). See the enclosed photo. It has a
600 dm3 water tank and supplies 1 mm water depth in front of the tire. No documentation is available so far.
Fig. 1
The brand new LCPC trailer for locked-wheel braking
12. Noise research
I also had the opportunity to speak to Dr. Yves Delanne, who is the LCPC tire/road noise expert. He verified that the ambitious work done at LCPC a few years ago to investigate the relation between road macrotexture and tire/road noise, using the same principles of correlating noise at
various frequencies with texture at various wavelengths, gave similar
results to those of Sandberg öc Descornet included in my thesis. The
extensive work was never published because it did not give anything new (I regret this).
Dr. Delanne will continue their noise research and supplied a list of projects which will be started 1989-1990. See the enclosed list (two lists actually - one for porous surfaces and one for research on generation
mechanisms).
Regarding the projects on porous pavements, there will be some coopera-tion with Mr. Hamet of INRETS. His labora'tory work reported earlier this year will be the basis for some activities. Some of the activities are similar to activities in other countries, e.g. Sweden, Holland, Germany and the U.K.
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ST AT E of RE SEAR CH 89 P R O G R A M M E Pl an ne d dur at io n C O M M E N T S Prof il e an d ac ous ti c spec tr a re la ti on sh ip _t yr e/ ro ad 'n oi se mi ti ga ti on me ga te xt ure ef fe ct s 1 En gi ne er (L .C .P .c .) . St atis ti ca l co rr el at io n 1/ 3oc t sp ec tr a, pa ss by pr oc ed ur e Near fi el d m e a s ur em e n t .2 year s -tr aile r -Re na ul t 5 Co mp leme nt ar y ap pr oa ch to th e pa ra me tr ic mo dell in g 1 'E ng in ee r 1' Te ch ni . Sup . (L .R .) Re na ul t 5 éq ui pm en t Exp er imen t wi th th eeq ui pp ed Re na ul t 5 1 ye ar En d of a 4 ye ars pr og ra mm e No is e/ Vi br at io n te xt ur e re la ti on sh ip No is e Vi brat io n pr od uc ti on fr om pr of il e 2 En gi ne er 3 Te ch ni ci an s 1 Re se ar ch As si st an t (L .C .P .C .) AR MA X mo de ll in g si ng le in put si ng le oup ut M I M O A R M A X mo de llin g »4 ye ar s Co ll ab or atio n wi th M E T R A V IB (us e of Ante nn a) 1 Te ch ni .Sup . (L .R .) Tr ai le r bui ld ing an d eq ui pm ent Exp er im en tan d tr ai le r ad ius tmen t 2 ye ar sAppendix 1(12)
APPENDIX
DESCRIPTION OF THE MAJOR FRENCH TEXTURE MEASURING DEVICES
The following equipment is numbered from No. 5 to 10, depending on its inclusion into a more complete description of European texture measuring
Appendix
2(12)
TEXTURE MEASUREMENT: EQUIPMENT NO. 5
Name of equipment
Rugolaser
Principle of operation
Measuring the relative displacement of 'the road texture w.r.t. vehicle body. (For the relevant frequencies the vehicle body is assumed to be a stable reference.) Measurement is non-contact. For field use only.
Main parts
Non-contact laser sensor on rear bumper. Processing unit(s). Mounted on
SCRIM truck. Based on TRRL High Speed Texture Meter. Output
Called VRA = some type of value prop. to average texture depth. This
value can be converted to sand patch texture depth(HS) by the formula HS
= 2.8 - VRA - 12 (mm). Recording media Unknown. Measuring speed 40 - 100 km/h. Operators 1 or 2. Resolution
0.3 mm vertically. Light spot size = 0.5 mm diameter. 2.5 mm
horisont-ally (= sampling rate)
Range
Texture wavelengths shorter than 5 mm and longer than 120 mm imposs-ible to measure due to sampling rate and data collection. Vertical dis-placement up to at least 70 mm.
Data collection
The "texture depth" is sensed over 120 mm distance each 250 mm. This is repeated 79 times over totally 20 m distance and the average presented.
Appendix 3(12)
Commitation used See "data collection". Implementation
One instrument is used in France; normally on SCRIM truck but can also be mounted on trailer or rear bumper of other vehicle.
Advantage
Fast, easy to implement. Suitable for surveys.
Disadvantage
Not operational in wet weather. Does not include macrotexture in 'the
"fine" wavelength range (under 5 mm). Provides rather limited
informa-tion. Drop-out rate can be high on certain surfaces. Comment
Similar (?) device mounted on Italian SCRIM.
The data, obtained from LCPC, on light spot size, resolution and range are somewhat in conflict with data for the TRRL HSTM (equipment No.
Appendix lM12)
TEXTURE MEASUREMENT: EQUIPMENT NO. 6
Name of equipment
Paviamêtre
Principle of operation
Measuring the relative displacement of the road texture w.r.t. vehicle
body. (For the relevant frequencies the vehicle body is assumed to be a stablereference.) Measurement is non-contact. For field use only.
Main parts
Non-contact laser sensor: Selcom Optocator of old type. Data processing unit. Two computers - one for processing on-line the texture profile signal and the other for calculating pavement maintenance priority. Mounted on vehicle.
Output
Classification of maintenance priority in 5 or 6 (?) classes, one value each
10 m. Recordirgmedia Unknown Measuring speed 12 km/h Operators 1 or 2. Resolution
The raw sensor output is a profile signal, probably with a resolution of
around 0.03 mm vertically. The bandwidth is probably 2 kHz and the light
spot 1 mm in diameter, giving a horizontal resolution ofapprox. 2 mm, Range
Vertical displacemen't up to 64 mm.
Data collection
The "raw" signal, which is a profile, is not recorded; instead it is used to identify the periodic joints between the stones (period generally around
100 mm) and to calculate the average depth of those joints underneath the
"peak stone level". This is a rather complicated process in practice and
Appendix
5(12)
Computation used
The average joint depth is used to classify the pavement in 5 or 6 (?) classes of maintenance priority; the higher priority the deeper the join'ts are. The priority class is the only output of the system.
Implementation
One instrument at LCPC in Paris. Advantage
Probably well suited for investigating surfaces of type paving stones. Disadvantagg
Rather low speed. Operational only on one type of pavement. However, in principle it should be possible to change software to suit other purposes.
Comments
The laser sensor is probably the same as that used in the VTI Stationary Laser Profilometer described earlier..
Appendix
6(12)
TEXTURE MEASUREMENT: EQUIPMENT NO. 7
Name of equipment Macroprofilographe Principle of operation
Measuring the displacement of the road texture w.r.t. l m long 3-wheeled
carriage. The sensor can be displaced also laterally so that traces can be recorded along several parallell lines. Probe moved by electric motor. For
field use. Main parts
Optimess laser sensor (Swiss made). 3-wheeled carriage. Data procesing unit.
Output
Profile curve, profile amplitude distribution or profile spectrum. Recordingmedia
Disc, e.g.
Measuring speed 1 m takes 3 minutes. Operators
Two needed to lift carriage in and out of van.
Resolution
Vertically 0.1 mm. Light spot size = 0.25 mm diameter. Arbitrary
sampl-ing rate horizontally. Range
Texture wavelength: Approx. from O.5-1.0 mm up to 1 m. However, with
the limited vertical resolution, a "true" low wavelength limit may rather
be approx. 3 mm for smooth surfaces. Vertical displacement is max 20 mm.
Data collection
Appendix
7(12)
Computation used See "output". Implementation
One instrument in use at LCPC, Nan'tes, France.
Advantage
Gives a comprehensive quantification of road macrotexture and mega-texture. Suitable for research as well as surveys.
Disadvantage
Very slow. Two operators necessary. Operational only in dry weather.
Comments
This is a field version of lab equipment called "Numérisateur" which can be operated automatically e.g. overnight and do three-dimensional surface
maps.
A new version will be manufactured in 1989, called Profilon. It will use the same principle and sensor, but be moved along a 2 m long beam
Appendix 8(12)
TEXTURE MEASUREMENT: EQUIPMENT NO. 8 Name of equipment
Profilon
Appendix 9(12)
TEXTURE MEASUREMENT: EQUIPMENT NO. 9 Name of equipment
Defocalisation sensor Principle of operation
A slightly conical laser light beam shines vertically on the road surface.
The light spot, the size of which is proportional to "out-of-focus", i.e. surface height, is projected onto a sensor capable of sensing the area of
the light spot. Thus, "defocalisation" is proportional 'to surface height. Measurement is non-contact and in direction normal 'to the surface. For
field or laboratory use.
Main parts
Laser, beam splitter, lenses, laser drive unit, data processing unit. Equip-ment still under developEquip-ment.
Output
Depending on data processing. Profile possible to measure, if desired. Recording media
Arbitrary. Measuring speed
Limited by bandwidth which is stated as potentially at least 20 kHz. Would enable 1 mm as a lower wavelength limit at 20 m/s (70 km/h). However, it is suspected that resolution and noise put a much longer
wavelength limit.
Operators
Depending on future development. However, would potentially be easily Operated by one person.
Resolution
Vertical resolution is stated to be no worse than 0.05 mm. Longitudinal
resolution is depending on light spot size which is 0.2 mm diameter at best and approx. 1 mm when the light spot is 30 mm out of focus.
Range
The vertical resolution and the max light spot size will probably limit the
lower wavelength limit to 2 mm in the best case and 5 mm in the worst
case. The vertical measuring range is probably possible to tailor, up to
Appendix
10(12)
Data collectionArbitrary.
Computation used
Arbitrary. Not yet implemented. Implementation
Prototype version at LCPC, Nantes, France. Still under development. May be possible to test by late 1989.
Advantages
Unique principle, enabling completely freedom of drop-out due to
shadow-ing since the light is viewed in direction normal 'to the surface. Small light
spot and high speed possible, in theory at least.
Disadvantages
Probably requires dry surfaces.
The principle is sensitive 'to light reflection properties within the light
spot area, giving a distorted and "noisy" signal.
Vertical resolution is not the very best. Not yet fully developed.
Comments
Appendix
11(12)
TEXTURE MEASUREMENT: EQUIPMENT NO. 10
Name of equipment
TRRL Mini Texture Meter (MTM)
Principle of operation
Measures the relative displacement of the road texture w.r.t. two-wheeled frame (for the relevant frequencies the frame is assumed to be a stable reference). Measurement is non-contact. For field use only.
Main parts
Non-contact laser sensor. Data processing unit. Two-wheeled frame with
disconnectable handle for transportation in e.g. car boot. Output
Sensor Measured Texture Depth (SMTD), averaged for each 10 m as well
as a 50 m average. Recording media Paper tape only. Meauring speed
Walking pace (3-9 km/h). May cover up to 5 km daily.
Operators
1.
Resolution
Vertical resolution is approx. 0.08 mm. Horizontal sampling rate is
approx. 3 mm at 5 km/h walking pace. Range
Vertical range is 20 mm. Horizontal range is from approx. 6 mm texture
wavelength due to sampling rate and up to approx. 60 mm (estimated) due to wheel enveloping.
Data collection
Paper tape printout giving average SMTD each 50 m and each 10 m. One
Appendix
12(12)
Computation used
Sensor Measured Texture Depth (SMTD), corrected in case of high
drop-out rate based on empirical relationship. The SMTD is meant to replace texture depth measured with the sand-patch method. Regression formula, with high significance, relating SMTD to sand-patch measured texture depth is given. Repeatability is tested 'to be around 0.07 mm in SMTD under adverse conditions.
Implementation
Used in many countries over the world, including the U.K., France and
New Zealand. In France there are in 1988 12 units, to be increased to
some 20 in 1989. Advantages
Gives an easily understandable texture depth value. Easy to operate and transport. Commercially available, at approx USD 13,000.
Disadvan'tages
Does not cover the shortest macrotexture wavelengths. The values pre-sented contain rather little information. They just replace the sand patch method. The device is not operational in wet weather. High drop-out rates
are a problem on certain rough surfaces. Comments
French users claim the device "works well"; however, it gives a too high
value for smooth surfaces. The device is particularly designed for
