Asphalt surface
courses
skid resistance
Package of measures
for design and work-execution
Deutscher Asphaltverband e.V.
Asphalt surface courses skid resistance
Package of measures for design and work-execution
Measures
..................................................
Planning and tender for bid
Mix-design, -production and paving
Opening to traffic
Testing
Future activities
Team of authors:
Dipl.- Ing.
Lothar Drüschner,
Dr.- Ing.
Heinrich Els,
Obering.
Ulrich Habermann,
Dipl.- Ing.
Bernd Nolle,
Prof. Dr.- Ing.
Volker Rauschenbach,
Dipl.- Ing.
Siegfried Sadzulewsky,
Dipl.- Ing.
Matthias Schellenberger,
Dipl.- Ing.
Helmut Schgeiner,
Dipl.- Ing. Dipl.-Wirt.- Ing. Hans Schmidt,
Dr.- Ing.
Norbert Weiland,
Berlin
Bonn
Berlin
Leinfelden-Echterdingen
Dresden (Team Leader)
Cologne
Regensburg
Berlin
Linz
Hanau
Asphalt surface courses skid resistance
Package of measures for design and work-execution
Table of Contents
1
2
3
4
5
6
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Seite
Preliminary remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Skid resistance: Definition and requirements . . . . . . . . . . . 2
Basics of planning and tendering . . . . . . . . . . . . . . . . . . . . . 5
Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Mix design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Mix production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Paving and compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Opening to traffic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
Self-monitoring activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Compliance Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Test-methods and devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Evaluation of skid resistance measurements . . . . . . . . . . . . . . .21
Future activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Publishers:
Deutscher Asphaltverband e.V.
(German Asphalt Pavement Association)
Schieffelingsweg 6 · 53123 Bonn
+49 228 9 79 65-0
Fax
+49 228 9 79 65-11
E-Mail dav@asphalt.de
Internet www.asphalt.de
☎
Hauptverband der Deutschen Bauindustrie e. V.
(German Construction Industry Federation)
Kurfürstenstraße 129 · 10785 Berlin
+49 30 2 12 86-0
Fax
+49 30 2 12 86-297
E-Mail verkehrswegebau@bauindustrie.de
Internet www.bauindustrie.de
☎
Zentralverband des Deutschen Baugewerbes e. V.
(German Construction Confederation)
Kronenstraße 55–58 · 10117 Berlin
+49 30 2 03 14-0
Fax
+49 30 2 03 14-419
E-Mail bau@zdb.de
Internet www.zdb.de
☎
2nd revised edition
April 2006, english translation 2011
Elke Schlüter Werbeagentur +49 228 64 79 89
1. Preliminary remarks
Skid resistance is one of the most
important properties of the road surface for road users. The requirement
that surface courses have sufficient
roughness has always been part of
the ZTV Asphalt-StB (Supplementary
Specifications for Asphalt Surface
Courses). Upon the introduction of
the 2001 edition of the ZTV Asphalt-StB 01, skid resistance specifications to be met on the date of
acceptance and until the defects
liability period expires, were
stipulated in figures for the first time
and are now an integral part of
building contracts.
Skid resistance specifications are
applicable to all traffic categories,
so category SV as well as traffic
categories I to VI, with the exception
of residential collector roads, access
roads, pedestrian zones, local roads
that are open to traffic, and parking
areas of municipal roads, provided that the ZTV Asphalt-StB or the
ZTV BEA-StB (Supplementary Specifications for Structural Maintenance
of Traffic Areas – Asphalt Pavements)
have been agreed upon.
This package of measures sums up
current know-how regarding the
planning and execution of surface
courses and the demonstration of
skid resistance. It also provides an
outlook on still urgently required data
collation and evaluation, design of
testing equipment and future research
activities. This goal requires close
cooperation between all parties involved.
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1
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2
2. Skid Resistance:
Definition and requirements
Skid resistance designates the impact of
roughness on the frictional resistance
(grip) between the vehicle tyres and
the roadway, and is measured on the
wetted roadway. The surface texture
and the surface course properties affect
the roughness (microtexture, macrotexture and megatexture) which is influenced by traffic, weather and the environment. When the road is accepted after
completion the roughness is primarily
influenced by the surface texture achieved during paving operations. While
it is being used the properties of the
mix and its components come to the
fore due to the impact of traffic and
weather.
Skid resistance is determined with different measurement techniques to demonstrate that the specifications of the
construction contract have been met or
to ascertain the condition of the road
network. The device used for skid resistance measurements under construction
contracts is the Sideways Force Coefficient Routine Investigation Machine
(SCRIM) as described as measuring
method SKM in the 2001 edition of the
German Technical Test requirements for
skid resistance measurements in road
engineering (TP Griff-StB (SKM), Ausgabe 2001 „Technische Prüfvorschriften
für Griffigkeitsmessungen im Straßenbau, Teil: Messverfahren SKM“).
The PSV value of the aggregates
used is a significant but not the sole
influencing factor. The Polished Stone
Value is determined under standard
laboratory conditions and
indicates to which extent an aggregate
is resistant to polishing under the
action of traffic.
The table summarizes the threshold values as specified in ZTV Asphalt-StB 01
[including the amendments pursuant to
the Interim Advice Note [(Allgemeines
Rundschreiben – ARS) no. 24/03 of the
German Federal Ministry of Transport,
Building and Urban Development –
BMVBW, dated July 7, 2003] when
applying the SKM method at different
speeds. Five values are measured consecutively for a length of 20 meters and
then adjusted to account for varying
temperatures and speeds. These values
are then processed into an individual
value for a 100 meter section.
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3
µSKM
[–]
Measuring
Speed
Time of
Acceptance
Until the period
of liability for defects
expires
0,46
0,51
0,56
0,43
0,48
0,52
[ km/h ]
80
60
40
ZTV Asphalt-StB 01 sets forth the following provision if the values taken
are below the threshold values specified in the table at the time of acceptance:
„Individual values for 100 meters
which are more than 0.03 below the
applicable threshold value for skid
resistance constitute a defect. In such
case the contractor may request a
repeat compliance test based on the
SKM method. …If the values are
more than 0.06 below the threshold
values, or if the prescribed skid
resistance requirements are not met
in the repeat compliance test, the
contractor shall determine the reasons for such non-compliance and
take action to permanently improve
skid resistance.”
If the skid resistance value is below the
specified value, the client shall have
the burden of proof until the period of
liability for defects has expired, as set
forth in the BMVBW Interim Advice
Note, dated September 2, 2003.
The „Guidelines on how
to improve skid resistance
of asphalt roads“ (Merkblatt für griffigkeitsverbessernde Maßnahmen
an Verkehrsflächen aus
Asphalt) published by the
FGSV (German Road and
Transportation Research
Association) provide guidance on how to improve
skid resistance.
µSKM
threshold values
at varying speeds
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4
Skid Resistance: Definition and
requirements
This schematic compares the values of
the scheme for the road network condition surveillance with the skid resistance
target values specified in the construction contracts that have to be verified
and met using the SKM method on the
acceptance date, and until the liability
period for defects and defect evaluation expires.
Grade
µ-SKM 80 km/h3)
2,5
0,46
Construction
contract1)
Acceptance
(0,51/0,56)
0,03
3,0
0,43
(0,48/0,524))
0,40
0,06
No
defect
Remedial action
or repeat
compliance test
„Measurements with the SKM method
are not required during skid resistance compliance testing, if the following reference values are ob-served
Surveillance of when testing skid resistance with the
condition of
road network2) combined method: SRT/ Pendulum
Tester/outflow meter:
Until period
of liability for
defects expires
No
defect
䡲 SRT value
≥ 60 *)
䡲 Outflow time (sec) ≤ 30.”
0,03
(0,45/0,505))
3,5
Investigatory value
0,39
(0,44/0,49)
Remedial
action
4,5
0,32
Subsection “Mix and practical completion” under Section 1.6.4.1. of the
ZTV Asphalt-StB 01 contains the following provision pertaining to compliance testing:
Monitoring
Action value
(0,37/0,42)
Traffic
management
and/or skid
improvement
measures
1) ZTV Asphalt-StB 01
2) Guidelines for the evaluation of wet road skid resistance (M BGriff), 2003 edition
3) Bracketed values at a speed of 60 and 40 km/h as set out in the General Newsletter
(ARS) 24/2003, dated July 7, 2003
4) Under “acceptance”: 0.53
5) Under ”Until expiry of period of liability for defects“: 0.49
Target skid resistance values to be reached
with the SKM method (valid since July 2003)
When conducting measurements with
the combined measuring method, noncompliance with threshold values does
not automatically mean that these values
are at variance with the contract. Any
deviation from the contract may be
assessed exclusively on the basis of
the SKM measurement results. SRT/
OM measurements are only intended for
acceptance testing and not for the expiry of the period of liability for defects.
*) Amendments to the ZTV Asphalt-StB 01 in accordance with the resolution of the Joint Committee
of the Federation and the German States for Road
Engineering (Bund/Länder-Ausschuss „Straßenbautechnik“), dated February 21, 2005, pp 17/
38.56.00-01/8 Va 2005.
3. Basics of planning and tendering
Skid resistance of roadways constitutes
a complex property that is specified as
early as during the design phase, and
at the latest during the tendering.
䡲 Section 1.4.1 of the
䡲 When selecting the type and
„Depending on the intended use,
aggregates and crushed sands
that are used for surface courses
or as gritting material must have
a high resistance to polishing
(PSV value). The specified PSV
values are
grade of mix, not only traffic
classification and the traffic
load, but also route surveying
elements such as narrow curves,
uphill and downhill sections,
deceleration and acceleration
zones, and lane restrictions
have to be taken into account.
䡲 Mix types where the maximum
aggregate size is smaller tend
to exhibit better skid resistance.
The reduced drainage effect at
high travelling speeds, however,
should not be neglected.
ZTV Asphalt-StB 01 sets forth
the following specifications for
the PSV value of aggregates:
䡲 for roads with the classification class III to VI under normal
traffic load:
PSV ≥ 43,
The PSV
Polishing
Machine
䡲 for roads with the heavy traffic
classes as well as for streets
categorized as class III under
special loads: PSV ≥ 50.
䡲 It is urgently recommended to
use Polymer modified Bitumen
for stone mastic surface courses
designed for heavy traffic classes
and in cases where the surface
course is exposed to special
loads.
䡲 When using mix types with a
high percentage of maximum
size aggregates the individual
aggregates are subject to more
polishing.
Detail of
the PSV
Polishing
Machine
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5
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6
Basics of planning and tendering
When surface courses on roadways
are subject to an especially high
degree of polishing in the long run
…and are based on a design that is
susceptible to polishing (e.g. asphalt
surface courses low in sand or fine
chippings) it is recommended that
aggregates or aggregate mixes with
an elevated PSV value (e.g. ≥ 53)
be used.”
䡲 The specifications are to provide
a separate ordinal number for
surface gritting.
䡲 Based on the 1998 edition
of the „Guidelines for laying porous asphalt surface
courses”, high-quality aggregates with a PSV value ≥ 55
should be used for the production of porous asphalts.
When using this design the surface
should not be gritted because the
aggregates would clog the voids of
the surface course and thus impair
the function of the porous asphalt.
It should therefore be kept in mind that
there will be a reduced level of skid
resistance until the binder film has
been abraded from the aggregate by
the tires, thus leading to exposed
aggregate surfaces. The authorities responsible for traffic
safety should therefore set
speed limits during this
period, if need be.
4. Measures
Mix design (type testing)
Skid resistance is a surface property
that cannot be influenced solely by
designing a specific mix or paving
method. Paving operations (e. g.
correct rolling and gritting), however,
can indeed have a significant impact
on initial skid resistance. During the
entire usable life of the road surface
skid resistance is influenced not only
by the mix design but also by a host
of other factors such as traffic loading
(particularly heavy traffic), weather,
environmental factors and local conditions (stacking space, uphill and
downhill sections, sharp bends).
All those factors should be considered during mix design and paving.
As long as appropriate prediction
(test) methods are not available as
part of extended type testing (see
also page 21), one should rely on the
experience obtained, e. g. through
skid resistance investigation and
evaluation.
Several factors are decisive to
achieve permanent skid resistance:
䡲 Ensure that the microtexture has
a sufficient degree of roughness
which can be influenced by the
amount and angularity of the sand
component and by high PSV
aggregates. As they have a higher
proportion of edges, aggregates
that are resistant to polishing will
have a much greater effect on
small particle sizes (approx. 0.5 to
5.6 mm) when added to the mix
than is the case when adding
the same amount to the coarser
fraction of the asphalt mix design.
!
䡲 The provisions in ZTV Asphalt-StB 01
stipulate that street surface courses
designed for Class I and II, heavy
traffic and special loads must have
a minimum PSV of 50. Investigations
on test sections have demonstrated
that in special cases aggregates
with an even higher PSV value might
be required for the traffic classifications and loads cited above.
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8
Measures
䡲 Aggregates which contain different minerals enhance the resistance to polishing because the
minerals exhibit different behaviours when polishing occurs.
This means that the microtexture
(roughness) of aggregates that
is required for skid resistance is
restored.
In many cases a single aggregate
does not attain all the optimal values
for PSV, strength, and resistance to
frost. Aggregates with a relatively high
PSV might exhibit relatively unfavorable strength behavior and sometimes unsatisfactory frost resistance.
0
20
80
60
60
13
30
80
20
9
0,25
Mesh size
0,71
2
5
8
31,5
0,09
100
22,4
0
60
27
16
20
40
40
40
Square mesh size in mm
Grading curve of SMA 11 S
Retained fraction in % by weight
100
90
100
11,2
Passing fraction in % by weight
Stone mastic asphalt SMA 11 S
Certain types of greywacke, quartzite, granite, or quartz-porphyry,
depending on what is available in
the quarry, can exhibit a good resistance to polishing.
The following points should be taken
into account when designing the mix
for asphalt surface courses:
1. Mineral aggregates
䡲 coarse aggregates
It is recommended to use
aggregates that have both
a high PSV and sufficient
mechanical strength – impact
value (SZ8/12)/Los Angeles
Coefficient (LA).
The individual aggregate
is subjected to more polishing
when using gap-grades
asphalt mixes (e. g. SMA).
It is thus a good idea to use
high PSV aggregates.
In certain cases (e. g. for more
reflective surface courses) the
use of various aggregates with
a varying PSV might be useful.
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9
Technique to predict resistance to skidding
In this case aggregates that tend
to polish should be supplemented
with aggregates exhibiting a
higher resistance to polishing.
Aggregates with a lower PSV
are able to meet skid resistance
requirements when mixed with
high PSV aggregates provided
that preferably smaller sizes are
used for the latter and the calculated PSV value (PSVcalc) meets
the specifications.
Polishing
Measurement
Aggregates exhibiting less resistance to polishing must have a
PSV > 43!
PSVcalc =
Aggregates contentA• PSVA
Total aggregates content
Methods used to predict the
resistance to skidding help to
improve the aggregate blend
as well as the behavior of a
specific asphalt mix with regard
to the resistance/susceptibility to
polishing. Unfortunately, there are
only a few testing devices available in Germany as yet. There
are, however, no standardized
instructions for executing the tests.
+
Aggregates contentB • PSVB
Total aggregates content
+
Aggregates contentC • PSVC
Total aggregates content
䡲 fine aggregates (sand)
Due to its angularity crushed
sand should generally be
used instead of natural sand
(observe the flow coefficient!).
In terms of resistance to polishing, quartz and silica sands
are better than carbonate sand.
Top: Details of the
Wehner-Schulze
testdevice
Bottom:
Principle of the
PGM testdevice
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10
Measures
䡲 Filler
Increasing the filler content
reduces the void content.
Too much filler might impair
the resistance to skidding.
2. Binders
Harder binder types may have a
favorable impact on skid resistance
behavior due to their elevated ring
and ball softening point. Polymer
modified Bitumen PmB 45 A is
recommended for SMA surface
courses on roads categorized
as heavy traffic roads (class SV,
I to III with special loads).
If the binder content is too high,
the surface course might lose its
skid resistance (fatting up).
3. Mixture
Surface courses with void contents
in the middle to upper range of
the specified values exhibit a better
resistance to skidding. Against this
background it is vital to apply volumetric criteria when analyzing and
evaluating the type test results.
Other requirements of the construction contract (e. g. resistance to deformation and ageing) must also be
considered when designing the mix.
Mix production
The mixture is produced on the basis
of the type test. Any deviations from
the varying aggregate sizes used
for the mixture might change the skid
resistance behavior of the road. The
same applies for excessive binder.
This is why effective self-monitoring
is so important. The production temperature for the asphalt used for
the surface course and the related
paving and compaction temperatures have to be set at the optimal
level to avoid „fatting up” of the road
surface during paving operations.
The mix temperature of 180 °C
should not be exceeded when using
binder types 70/100, 50/70 and
PmB 45.
Paving and compaction
Paving, compaction and gritting also
have an impact on the road surface
skid resistance.
䡲 Heavy static and/or vibratory
rollers should be used for heavy
duty road surfaces where the
mix is difficult to compact.
䡲 Compaction operations should
be monitored with appropriate
measures (e. g. rolling pattern,
compaction measurements).
䡲 Fat spots on the surface have an
adverse effect on skid resistance
and should therefore be avoided.
Fat spots are caused e. g. by the
following factors:
䡲 Excessive mix temperatures
䡲 Use of pneumatic-tyred roller
or combination rollers for all
mix types
䡲 Excessive vibration – especially
at excessive mix temperatures
and high outside temperatures
䡲 Low voids in the surface course,
causing displacement/rutting
under trafficking
䡲 Low binder viscosity
Uniform application of gritting
䡲 Initial skid resistance
䡲 Initial skid resistance is
mainly influenced by the
selection and use of rollers,
as well as by the gritting
method
䡲 With the exception of
porous and permeable
asphalt, all surface courses
require gritting to increase
initial skid resistance.
It should be noted that
noise emissions of tyres
will increase if coarse
aggregates are used.
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11
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12
Measures
䡲 For Rolled Asphalt:
Gritting is carried out by applying
an even, regular layer of dry, dedusted, blank or bitumen-coated
crushed aggregates of 1 to 3
or 2 to 5 mm size which are
then rolled into the asphalt layer.
The table specifies the type and
amount of aggregates to be
applied depending on the maximum aggregate size used for the
surface course.
Hot mix asphalt
surface before
and after gritting (detail)
䡲 The aggregates should be
evenly spread on the surface
of the hot layer, i. e. with a
spreader and in a timely
fashion, so as to ensure that
the aggregates are set into
the layer during rolling which
should not occur, however,
before the second roller pass.
Type and
amount of
aggregates
(Rolled Asphalt)
Gritting
Maximum aggregate size of surface course
material
(without oversize material)
up to and including 8 mm
larger than 8 mm
1/3
ca. 1 kg/m2
ca. 1 kg/m2
2/5
unsuitable
ca. 2 kg/m2
䡲 For mastic asphalt
The mastic asphalt surface
course is gritted with blank or
precoated high-quality aggregates that should be dry, free
of dust and easy to spread.
The spreader should be right
behind the screed where it
applies the aggregates to
the hot layer.
䡲 The application rate for
aggregates to be spread
on rolled mastic asphalt is
15 – 18 kg/m2. Usually,
crushed aggregates with
particle sizes 2 to 5 and/
or 5 to 8 mm are applied
to the surface.
The aggregates are pressed
into the layer with pneumatictyred rollers. The surface is
then smoothed out with smooth
drum rollers.
䡲 If the mastic asphalt surface
course has to meet noise
emission requirements the
aggregates are placed
at an application rate of
10 – 12 kg/m2 without
the aggregates being
embedded with rollers.
Cubic aggregates with
particle sizes 2 to 3 or 2
to 4 have been shown to
work well for this purpose.
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13
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14
Measures
Opening to traffic
䡲 A freshly placed layer should
be opened to traffic only after
the surface course has sufficiently
cooled. Otherwise, the surface
might be subjected to deformation
and the level of skid resistance
might decline due to the deplacement of aggregates and fat spots
on the surface.
䡲 Allow the surface course to cool
for at least 24 hours, and if
paving the binder and surface
course in a single pass, at least
36 hours (compact asphalt).
Cooling might take longer at
higher temperatures. If the client
wishes to reduce the cooling time
it is recommended that the contractor puts down his concerns in
writing in accordance with §4 (3)
of the German Contractual Rules
for Building Performances (VOB/B).
As a rule, there should always
be one night between paving
operations and opening to traffic.
䡲 If 4 + 0 traffic routing is used
(the roadway for one direction
is closed while the two lanes of
the other roadway take up traffic
in both directions) and/or if half
the width of the road is paved,
the slow moving traffic is routed
over the part of the surface course
that has already been completed.
This causes the danger of fat
spots on the surface.
䡲 When these measures are taken,
the increased traffic load compared to normal traffic routing
also subjects the pavement to
much more intensive polishing.
䡲 In the event of a premature
opening to traffic, the contractor should request partial
acceptance in accordance
with VOB/B §12(2) and
ZTV Asphalt-StB 01
Sections 1.7.1 and 1.8.3.
5. Testing
Self-monitoring activities
Mix production:
The mix temperature should be monitored at all times and limited to the
value cited on Page 10. Causes of
fatting of the mixture should be identified without delay and eliminated.
䡲 Type and
In addition to the provisions of
ZTV Asphalt- StB 01 the following
should be kept in mind: if different
aggregates with varying PSV values
are used for the surface course, an
additional self-monitoring test should
be conducted, so as to verify whether
the actual and target composition are
the same.
䡲 Amount and uniform
Paving:
The following tests should be
performed:
It is not possible to technically measure the skid resistance of the surface
course during paving. Even shortly
after paving and without any traffic
impact, neither the combined skid
resistance measurement SRT/outflow
meter nor SKM nor any other measuring method will yield results that
would allow conclusions to be drawn
as to the skid resistance at the point
of acceptance or during the usable
life of the pavement.
䡲 Temperature of the mix upon
delivery
䡲 Texture of the surface course
(visual inspection). If the mix
plant should be informed and
the surface course gritted more
thoroughly fat spots occur.
appearance
of the gritting
material (delivery
note control and visual
inspection)
application of gritting
material
䡲 Point in time when
gritting begins
(i. e. after which
rolling pass)
Fat spots on
the surface
The results should
be documented
on a daily basis
using the sample
table on the next
page.
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15
Documentation of self-monitoring activities Annex to Interim Advice Note No. 2/2002
Documentation of self-monitoring activities
to ensure initial skid resistance of rolled asphalt surface courses
er
Motorway BAB A9 km 18.317-22.090
Sample BG
Type of surface course:
SMA 11 S
st
Construction project
Contractor:
Exact position in km
Direction of travel/lane
M
u
19.720
Berlin-Munich
Tests conducted during paving
Paving date
Weather (sunny, cloudy, humidity, temperature)
Target values of contractor
Mix temperature [oC ]
160 – 170 °C
Appearance of mix
Difficult to compact
Paver, high-compaction screed
Paving equipment
(see work instructions)
Compaction equipment
Surface temperature
[oC ] during gritting
Regular
Following work
instructions
Roller spreader
t
s
u
M
120 °C
Diabas PSV > 53
BS/SP 1/3
Blank
Application rate for gritting material
Spreading of
gritting material
Uniform
Inspected by
r
e
Following work
instructions
Regular
No fat spots
> 100 °C
Gritting material
• Type of aggregate
• Size fraction
• Blank
• Precoated (with bitumen)
Actual values determined by contractor
165 °C
Mat shine
Tandem roller+heavy static roller
Rolling pattern
Follow work instructions
Spreader gritting/method Roller spreader
Appearance of surface
before applying chippings
• Regular
• Segregation
• Fat spots
19.07.02
Cloudy 18 °C
OK
OK
OK
[kg/m2]
0,8
0,9
Uniform
(Name)
Smith
(Signature)
Smith
Tests conducted after paving
Actual values determined by contractor
Target values of contractor
Remove
excess material
Appearance of surface
after gritting
No residual material
Little
material left
Regular
Regular
(regularity)
Embedment of
gritting material
Comments
(e. g. minimum cooling time prior
to opening to traffic)
Inspected by
(Name)
(Signature)
Firm embedment
24 hours
M
t
s
r
e
Firm
u
24 hours
Smith
Smith
Testing
Compliance tests
1. Upon acceptance
䡲 The client should carry out the
compliance tests within 4 to 8
weeks after the surface course
has been opened to traffic.
䡲 Notwithstanding the provisions
contained in the TP Griff-StB (SKM)
specifications, compliance testing
can also be carried out from
November until the end of April,
provided that the air temperature
and the road surface temperature
are not below + 5 °C while conducting measurements.
䡲 If the measured value is more
than 0.03 lower than the MSKM
threshold value specified for
acceptance, the contractor may
request a repeated compliance
test. Pursuant to TP Griff-StB (SKM)
this test is to be carried out in
May or June of the year following
the opening to traffic. The result
of such test will replace the original compliance test result. The
contractor is to assume the costs
for the repeated compliance test.
䡲 If the measured value is more
than 0.06 below the skid resistance threshold value, the defect
has to be remedied by taking
action to improve skid resistance.
2. Until the period of liability for
defects expires
䡲 Action to improve skid resistance
also has to be taken if the value
measured in a repeated compliance test conducted during
the period of liability for defects
is more than 0.03 below the
threshold value applicable during
that period. In such case repeated compliance testing is not
provided for.
The specifications set forth
in sections 1.6.4.2 (repeated compliance test) and
1.6.4.3 (arbitration review)
of ZTV Asphalt-StB 01 shall
not be affected by the aforementioned provisions.
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Testing
Test-methods
and devices
1. SKM method
SKM and the combined measuring method
SRT pendulum/outflow meter test are
the methods used to
determine the resistance to skidding
during compliance
testing. Pursuant to
ZTV Asphalt-StB 01
the Stuttgart Friction
Tester is not to be
used for compliance
testing.
䡲 Skid resistance measurements are
SKM apparatus, Detail:
test wheel and water
jet equipment
䡲 The SKM survey is conducted
µ-SKM
Individual values adjusted to 60 km/h
1,00
0,90
0,80
0,70
0,60
0,50
0,40
0,30
0,20
0,10
0,00
usually carried out in the right side
wheel track of the respective lane
by keeping a specified constant
distance to the hard shoulder
(+/- 0.15 m). The standard temperature for measuring the road
surface is 20 °C. The measured
value has to be adjusted if the
temperature deviates from 20 °C.
While taking the measurements
the temperature of the road surface temperature should be no
lower than +5 °C and no higher
than +50 °C
47,923
48,063
48,203
48,343
48,483
48,623
48,763
48,903
49,043
49,183
49,323
49,463
49,603
49,743
49,883
50,023
50,163
50,303
50,443
50,583
50,723
50,863
51,003
51,143
51,283
51,423
51,563
51,703
51,843
51,983
52,123
with a tyre that is set at 20
degrees to the direction of travel
and applied to the road surface
under known load.
A controlled flow of
water wets the road
surface immediately in
front of the test wheel.
When the vehicle
moves forward at the
target speed, the test
wheel slides in a forward direction on the
wet road surface. The
km
Measurement record of a 4 km section measured with the SKM van
Maximum permissible speed (v)
for the road
[ km/h ]
v>
– 100
Measuring speed
[ km/h ]
80
70 <– v < 100
60 oder 80
50 <– v < 70
40 oder 60
v < 50
40
䡲 SKM requires two surveys, each of 䡲 The table above shows at which
which should cover a minimum distance of 2000 m. When using this
measurement method it is possible
to inspect large sections of the surface course without having to interrupt measurement activities. The decisive 100 m-value is calculated as
an average of the values attained for
5 continuous 20 m section making
up this 100 m section. It is only this
specific decisive 100 m-value that
is used for follow-up evaluations.
䡲 The measurement speed may be
adjusted to a maximum speed deviation of +/- 4 km/h. Measurement
on roads that are wet due to rain
are not accepted. Skid resistance
values obtained for bends with a
radius smaller than 35 m should be
excluded from the evaluation.
speeds the measurement can be
performed, depending on the maximum permissible speed on the respective road.
䡲 The 2001 edition of the TP Griff-StB
(SKM) specifications provides a description of the SKM method.
䡲 Every SKM apparatus has to be
calibrated with a reference device
provided by the Federal Highway
Research Institute (BASt) and is then
granted a one-year operating license.
䡲 The functions and calibration of the
measuring devices shall be verified
at least once per month as stipulated
by TP Griff-StB (SKM), Section 8.2.
„Self-monitoring of measuring devices.” The results should be recorded
and retained.
SKM speed
during
measurement
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Testing
2. Combined measuring method SRT pendulum/
outflow meter:
䡲 The combined measuring method
䡲 The outflow or leaking test isused
SRT pendulum/outflow meter test
is a method where punctual measurements are carried out on
small sections.
to measure the macrotexture of the
surface course. The outflow time of
water between the two float switches of a vertical cylinder is verified with a stop watch at the measurement points used for the SRT
measurements. This measuring
method is described in the 2004
edition of the TP Griff-StB (SRT)
provisions.
䡲 The pendulum measures the friction/resistance (microtexture) that
a rubber slider meets on the road
surface.
䡲 Five measuring points located
on a measuring line at a distance
of 5 m to each other are used
to obtain the measurement values
which are processed into an
average. This average value is
the decisive measuring result.
The pendulum test should be
carried out five times for each
measuring point. The measured
result is displayed in SRT units.
䡲 The SRT pendulum tester and the
outflow meter should be calibrated by the BASt on an annual
basis.
Evaluation of skid resistance
measurements
For the values obtained with the
SKM method and the combined SRT
pendulum outflow meter method
threshold values are specified in
ZTV Asphalt-StB 01 in order to evaluate the skid resistance of the surface course.
䡲 The test results – SKM or SRT/outflow meter – reflect the condition
of the surface course in terms of
skid resistance at the time the measurements were made. Skid resistance is not a constant parameter.
It is subject to seasonal variations
which are specified with up to
0,1 µ SKM-units (see Huschek
„Assessment of road skid resistance under wet condition”,
published in the magazine Strasse
und Autobahn 3 (1995), p. 121
– 131). The test result is also significantly influenced by temperatures (e. g. road surface, water used
for pre-wetting, sliding rubber).
䡲 Typically, skid resistance values
seem to be higher right after the
winter season than in early fall.
Worse test results might be obtained during dry spells because
the road is covered, for instance,
with dust and pollen, while being
wetted. This, however, is not applicable for the test method SRT pendulum/outflow meter because the
area to be measured is cleaned
prior to measuring.
䡲 There is no known precision with
statistical validation yet for the
two measuring techniques. For
this reason – independent from
the speed – an overall tolerance
of µ SKM = ± 0,03 has been
specified for the evaluation of the
100 m test results obtained with
the SKM method.
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6. Future activities
The current level of
knowledge that ensures that skid resistance is achieved
and is demonstrated
to meet the specifications should be
complemented with
follow-up activities
focusing on the following points:
Laboratory
apparatus used
to predict skid
resistance
1. Review test and evaluation
methods used to demonstrate that
skid resistance meets the values
specified in ZTV Asphalt-StB 01.
2. Quantify the impact that factors
such as traffic, weather and environment have on skid resistance
at the point in time when skid
resistance is measured.
3. Precise description as to how to
calibrate and operate the skid resistance measurement methods
SKM SRT pendulum/outflow
meter approved in accordance
with ZTV Asphalt-StB 01, and
their statistical validation.
4. Evaluate skid resistance measurements*) carried out both as
specified in construction contracts and those by the Highway
Administration or the BASt to
survey the actual condition of
the road network. These evaluations are made to learn more
about the impact of mix properties (e. g. aggregate properties,
mix design) and the type and
peculiarities of pavement, compaction and gritting.
5. Develop or provide predictive
methods to make reliable skid resistance predictions during the road’s usable life, depending on the
polishing effect to be expected
under trafficking.
6. Verify any correlations between
the different methods used to
measure skid resistance.
7. Identify correlations between the
properties of the aggregates and
the evolving skid resistance of the
road surface.
*)...See also the BMVBW note, p. 26/
38.56.60 - 10/1 Va 2001, dated
January 26, 2001
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Deutscher Asphaltverband e.V.
www.asphalt.de
DIE DEUTSCHE
BAUINDUSTRIE
Hauptverband der Deutschen Bauindustrie e. V.
www.bauindustrie.de
Zentralverband des Deutschen Baugewerbes e. V.
www.zdb.de
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Germany
Fon +49 7967 152 297 • Fax +49 7967 152 500 151
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Deutscher Asphaltverband e. V. · Schieffelingsweg 6 · 53123 Bonn · Germany
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E-Mail dav@asphalt.de · Internet www.asphalt.de