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LESSONS LEARNED FROM LABORATORY AND FIELD EXPERIENCES ON THE USE
OF DOUBLE TWIST STEEL WIRE MESH AS A REINFORCEMENT FOR ASPHALT
PAVEMENTS
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INTRODUCTIONOne of the oldest interface systems used in flexible
pavement is steel reinforcement. The idea that appeared in the
early 1950s was based on the general concept that if hot-mix
asphalt (HMA) is strong in compression and weak in tension, then
reinforcement is definitely needed. Steel reinforcement was
abandoned in the early 1970s after tremendous difficulties were
encountered in the installation. The idea reappeared in the early
1980s with a new class of steel reinforcement products in Europe:
many of the early reported problems appear to be solved, and
successful experiences with the new class of steel reinforcement
were reported. Installation of wire netting in Ontario (1960)
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WHAT IS ROAD MESH?Road Mesh is manufactured from double twisted
steel wire mesh with transverse reinforcing rods evenly spaced 16
cm centres. The hexagonal mesh size is complying with EN 10223-3.
The wire has a zinc coating complying with EN 10244-2 Class A.
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WHAT IS ROAD MESH?
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MATERIALS FOR PAVEMENT REINFORCEMENT
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ROAD MESH APPLICATIONSFATIGUE: Crocodile \Alligator cracksRoad
Mesh is able to absorb the horizontal tensile stresses resulting
from existing cracks and traffic loads, thus increasing the
pavement life.
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ROAD MESH APPLICATIONSRUTTING: ChannelisationRoad Mesh is
installed at the base of the overlay (> 60 mm) thus intersecting
the shear slip circles, eventually reducing the surface rutting
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ROAD MESH APPLICATIONSTRANSVERSE CRACKS: Overlays on jointed
concrete pavementsThe active joint is a discontinuity which tends
to propagate to the road surface. Road Mesh is installed within the
overlay to absorb the tensile forces
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LABORATORY AND FIELD EXPERIENCES
The key objective of the next slides is to review the existing
worldwide experiences on the application of the double twist wire
mesh reinforcement in HMA.
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NOTTINGHAM UNIVERSITY (UK)The research investigated the
effectiveness of different interlayer systems (geogrid, steel
reinforcement and fiberglass grid) in preventing the reflection of
cracks in HMA overlays. A repeated load shear test was first used
to evaluate the interface shear strength and stiffness for
unreinforced and reinforced samples. Only steel reinforcement
provides interface shear stiffness comparable to the unreinforced
case; both geogrid and glass fibre caused a significant reduction
in the interface shear stiffness.
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NOTTINGHAM UNIVERSITY (UK)Pilot-scale pavement tests carried out
at the Nottingham Pavement Test Facility enabled the model to be
checked under realistic conditions: the pavement consisted of two
layers of asphalt with reinforcement between them, overlying
individual concrete slabs with air gaps between them. The gaps
acted as wide cracks, inducing reflection cracking in the overlying
asphalt
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NOTTINGHAM UNIVERSITY (UK)The test results have shown that steel
reinforcement improves the fatigue life by a factor up to 3, well
above the other materials performance
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CAGLIARI UNIVERSITY (I)The research investigated the crack
propagation process in the presence of steel reinforcement based on
a finite element (ANSYS) model. The figure shows the crack
development as a function of the load cycles at different
frequencies (10 and 20 Hz): by making reference to a crack 1 mm
deep, the reinforcement increases the pavement life by a factor
variable between 3 and 12 (at 20 Hz and 10 Hz respectively).
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The Smart Road was conceived by the Virginia DOT in conjunction
with Virginia Techs Transportation Institute and the Federal
Highway Administration and allows testing of various hypotheses on
pavement material performance and characteristics.
Pavement materials can be tested under different environmental
conditions using the All Weather Testing facility.
The flexible pavement portion of the Smart Road includes 12
sections 100 m long, closely monitored through a complex array of
sensors located beneath the roadway and embedded during
construction. SMART ROAD (USA)
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SMART ROAD (USA)All instruments were embedded in the pavement
section during construction and included pressure cells,
thermocouples and specially made HMA strain gages.
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SMART ROAD (USA) In Section I the steel mesh was installed on
top of a surface mix base layer (SM-9.5A) and underneath a BM-25.0
base mix layer to investigate its capability as a reinforcing
system
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SMART ROAD (USA) Results of the FE models were compared with
actual stress and strain measurements at the Smart Road. To
quantify the contribution of steel reinforcement to the pavements
service life, a classical fatigue law (Arizona DOT) was adopted:N =
9.33 10-7 et-3.84The improvement is pronounced at intermediate and
high temperatures and is approximately 140 % at the average
temperature of 25 C both in the transverse and in the longitudinal
direction.
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SMART ROAD (USA)The Smart Road has provided the design criteria
for the calculation of the design life of a Road Mesh reinforced
pavement.
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CATANIA UNIVERSITY (I)The research focused on the capacity of
non-destructive pavement measurement techniques to quantify the
increase in terms of resistance to deformation given to flexible
reinforced pavements by steel mesh, was carried out elaborating
data coming from a survey conducted with Falling Weight
Deflectometer (FWD) and Ground Penetrating Radar (GPR) on an
experimental section 250 meters long on a national road (SS 121) in
West Sicily.
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CATANIA UNIVERSITY (I)
Improvement of the pavements service lifeTo quantify the
contribution of steel reinforcement to the early stages of a
pavements service life, a classical fatigue law (Asphalt Institute)
was adoptedN = 0.0796 et-3.291 E-0.854
The presence of the Road Mesh reinforcement provides a service
life increase variable between
36 % (reinforcement at 15 cm depth) and 52 % (reinforcement at 8
cm depth)
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CONCLUSIONS- Nottingham Univ.: improvement factor 3;- Cagliari
Univ.: improvement factor 3 - 12- Smart Road: improvement factor
1.15 - 3.6- Catania Univ.: improvement factor 1.36 - 1.52
The performance of Road Mesh in asphalt pavement layers have
been thoroughly investigated in the last 10 years through a number
of research projects carried out by Universities and Road
Authorities around the world, finalised to develop an empirical
design methodology for reinforced pavements, validate FEM numerical
results with beam tests and field data and evaluate the working
life enhancement of a reinforced pavement.
The main results of the researches in terms of FATIGUE LIFE
IMPROVEMENT due to the Road Mesh are quite similar in terms of
reinforcements effectiveness:
The product Road Mesh is manufactured from double twisted steel
wire mesh with transverse reinforcing rods evenly spaced throughout
at approximately 16 cm centres, as depicted in table 1 and figure
1. The hexagonal mesh size is 80 by 100 mm (nominal) as defined in
EN 10223-3. Table 1: Mechanical characteristics of the Road MeshThe
wire is protected against corrosion by a zinc coating complying
with EN 10244-2 Class A. The thickness of the product varies
between the 2.2 mm wire diameter up to 8.3 mm where the transverse
rod passes through the double twist. The varying height of the
product strands, and distance between them, ensures that the
asphalt can encapsulate the wire, without developing a weak shear
zone at the product interface.Fig. 1: Geometrical characteristics
of the Road MeshOther reinforcing products, due to their geometry,
are able to absorb crack reflection stresses, but because they are
not able to integrate themselves into the aggregate matrix, they
contribute to reducing the rut resistance as well The product Road
Mesh is manufactured from double twisted steel wire mesh with
transverse reinforcing rods evenly spaced throughout at
approximately 16 cm centres, as depicted in table 1 and figure 1.
The hexagonal mesh size is 80 by 100 mm (nominal) as defined in EN
10223-3. Table 1: Mechanical characteristics of the Road MeshThe
wire is protected against corrosion by a zinc coating complying
with EN 10244-2 Class A. The thickness of the product varies
between the 2.2 mm wire diameter up to 8.3 mm where the transverse
rod passes through the double twist. The varying height of the
product strands, and distance between them, ensures that the
asphalt can encapsulate the wire, without developing a weak shear
zone at the product interface.Fig. 1: Geometrical characteristics
of the Road MeshOther reinforcing products, due to their geometry,
are able to absorb crack reflection stresses, but because they are
not able to integrate themselves into the aggregate matrix, they
contribute to reducing the rut resistance as well In a road, the
deflections range between 0,3mm for an excellent road to 1,5mm on a
poor quality road. For a reinforcement to impart any strength
resistance, the reinforcement needs to offer tensile resistance at
very low strains as indicated roughly by the green circle. It is
quite clear that the red line shows that the steel mesh is able to
by far provide the maximum benefit at the lowest strains. It is
then also apparent that the bigger the deflections in the pavement,
the greater the contribution of the reinforcement. This also makes
sense, as we know that with conventional road design, if the road
has low deflections in the order of 0,3mm, the pavement will
perform quiet satisfactory, and should last through to the end of
the next maintenance cycle. If it is a new road, then one could
consider allowing the road structure to be thinner, thereby
inducing higher design deflections, and incorporate the Road Mesh
to take up the increase in tensile strains at the bottom of the
asphalt as a result of the increase in deflections.Road Mesh is new
to the industry and therefore requires an explanation of how to
install the product. The theory is quite complex, and sometimes the
audience will believe that the installation will follow suite. This
is not the case as indicated in this presentation.N = Number of
cycles for crack initiation; and et = tensile strain at the bottom
of the HMA layers.
N = Number of cycles for crack initiation; et = tensile strain
in the HMA at the reinforcement level, E = elastic modulus of
HMA.
N = Number of cycles for crack initiation; et = tensile strain
in the HMA at the reinforcement level, E = elastic modulus of
HMA.
