High Performance Concrete Overlay for ... - CONTEC ApS

REHABILITATION AND RETROFITTING
HIGH PERFORMANCE CONCRETE OVERLAY FOR
REHABILITATION AND STRENGTHENING OF ORTHO-
TROPIC STEEL BRIDGE DECKS
Peter Buitelaar
Contec ApS, Højbjerg, Denmark
René Braam
Delft University of Technology, Delft, The Netherlands
Niek Kaptijn and Henk Sliedrecht
Ministry of Transport, Public Works and Water Management, Structural Development
Department, Tilburg, The Netherlands
Abstract
Heavily and intensely loaded orthotropic steel bridges suffer from fatigue cracks in the
deck plate. Periodical repair is a costly measure that doesn’t solve the basic structural
problems. A heavily reinforced ultra high strength concrete overlay bonded to the deck
plate might reduce steel stresses because it increases the “plate factor” by monolithic
composite interaction. The service life of a bridge can thus be extended considerably.
Research projects were carried out to define the material properties of the overlay and to
calculate its steel stress reducing effect. FE-calculations demonstrated that stresses might
be reduced by a factor 4-5.
During the research a pilot project on a bridge was carried out. Ongoing research
resulted in the development of a new concrete mixture suited to be applied by a slipform
paver instead of the traditional vibration screed. This mixture demonstrated improved
properties since the intense compacting by the paver enabled a reduction of the
water/binder-ratio and an increase of the aggregate content. Moreover, the use of a paver
resulted in a considerable increase of the production capacity.
Full-scale rehabilitation projects on several bridges were executed. Both vibration
screeds and a slipform paver were used. On-site measurements and observations
demonstrated that controlled storage of the mixture’s material is crucial to obtain
This paper is part of the 7th International Conference on Short and Medium Span Bridges, Montreal, Canada, 2006.
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consistent fresh concrete properties. The demands with regard to the surface smoothness
are difficult to be met when a vibration screed is used. However, this could partly be
solved when applying an additional top layer to meet skid resistance demands. This top
layer also seems to be required when a slipform paver is used.
1. Introduction
High Performance Concrete (HPC, fc 100 – 150 MPa) and Ultra High Performance
Concrete (UHPC, fc 150 – >300 MPa) contain very densely packed cement and micro
silica particles. Despite their (very) low water/ binder ratios, as originally developed by
Hans Henrik Bache in 1978 and known under the acronym DSP, they have proven to be
very useful when combined with large amounts of reinforcement [1-3]. The
incorporation of large amounts of bar reinforcement and steel fibers, as based on the
theories and discoveries of Hans Henrik Bache in 1986 (CRC, Compact Reinforced
Composite), results in a composite material with a high ductility, good fatigue resistance
and high bending tensile strength [4-7]. This type of concrete is mainly used for heavily
loaded structures or objects, such as [8,9]:
• wear resistant components in hydraulic and pneumatic transport systems handling
abrasive materials (fly ash, cement, silica sand, glass, etc.),
• industrial floors and overlays in the heavy industry and food processing industry,
• security industry components (vaults, ATM’s),
• offshore structures (re-strengthening of platforms, offshore windmill foundations).
Contec ApS redesigned the original DSP mortars to make them more efficiently
applicable in industrial floors and ultra thin white toppings. Research was focused on the
workability, finishability and shrinkage reduction (autogenous and chemical). This
research resulted, among other things, in the development of the UTHRHPC overlay in
which a HPC or an UHPC is combined with the CRC technology. This overlay,
commercially marketed under the name Contec Ferroplan ® System, was during the last
ten years used in several 100.000 m 2 of industrial floors, industrial pavements and ultra
thin white toppings [10,11].
2. Project “orthotropic steel bridge decks”
After serious damage due to fatigue the bascule of the Van Brienenoord Bridge, a bridge
in one of the main highways in The Netherlands, was replaced since cracks had occurred
in the steel deck plate. A special Task Force was formed within the Civil Engineering
Division of the Dutch Ministry of Transport, Public Works and Water Management. Its
aims were to investigate the cause of the damage and to understand and control the
fatigue mechanism of the total of 80 steel fixed and movable bridges in The Netherlands
and to develop practical solutions for cost effective rehabilitation and renovation
[12-14]. Various alternatives were experimentally investigated in cooperation with the
Delft University of Technology and TNO Building and Construction Research. First,
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esearch focused on re-strengthening of the deck plate. One of the alternatives
investigated was to cast a steel fiber reinforced HPC overlay. This was done earlier on a
orthotropic bridge deck in Canada. Contec ApS was consulted because of their specific
knowledge of HPC and UHPC overlays in which high amounts of bar reinforcement are
applied. Different tests and calculations showed that an un-reinforced HPC overlay will
deteriorate very fast due to the high tensile stresses introduced by the traffic loads. This
supported the idea to use an UTHRHPC overlay.
3. Research
During the period 1999 – 2005 the properties of a specific HPC and UTHRHPC overlay
were investigated. These were required to design a rehabilitation technique and to
develop new and check existing calculation methods. Furthermore, information about
the durability of the material and its behaviour under traffic loads were required to
predict the extension of the service life [15,16]. Besides research on relatively small
samples, also full-scale structural elements were tested under different loading
conditions. Also FEM calculations and calculations on specific details were performed
[17]. The latter has to be performed for each individual bridge project since the
UTHRHPC overlay changes the properties of the orthotropic deck which will result in a
relocation of stresses.
Time-dependent deformations of the UTHRHPC overlay caused by shrinkage are
restrained by the steel bridge structure to which the concrete overlay is connected by
means of an intermediate epoxy layer with sprinkled in aggregates. The tensile stresses
introduced in the overlay might cause cracking of the concrete. Whereas reducing the
water/binder ratio results in a reduction of the drying shrinkage it also results in an
increase of another component of shrinkage, the so-called autogenous shrinkage [18,19].
This shrinkage component is not found for normal strength traditional concretes since
these have such a water-binder ratio (> 0.4), that there is always an overdose of water
present. This overdose evaporates from the concrete when it is allowed to dry, causing
the well-known ‘traditional’ (drying) shrinkage. HPC and UHPC, however, have a
water-binder ratio that low, that there is less water present in the mixture than required to
hydrate all binder material. During the hardening process the internal demand for water
is higher than the amount of water available. This is called ‘internal’ drying and causes
the concrete to shrink (‘autogenous shrinkage’), even when it is sealed to prevent
evaporation. When placing the HRHPC overlay in a traditional way, i.e. with a vibration
screed, only a limited area can be resurfaced within a certain period of time. This method
also has its limits regarding the required consistency of the HPC. A much more stable
HPC mix can be required since in most cases the bridge deck will be sloped and because
vibrations can not be avoided since the bridge can not be closed completely for traffic.
After the execution of a pilot project other placing methods were investigated. By using
a slipform paver it was possible to further reduce the water binder/ratio and to apply a
higher percentage of “large” aggregates (2-4 mm). Even a “zero slump” HPC could be
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applied because of the combined action of intense vibrating by high frequency poke
vibrators and the pressure of the paver’s extrusion pan. A test area (300 m²) was placed
with a large slipform paver to test this placing method on a large scale. The speed of
placing and the compressive strength development (70 MPa in less than 24 hours) and
compacting of the material were very promising.
In a test series is was investigated whether the higher amount of large aggregates and the
lower amount of binder resulted in a reduction of autogenous shrinkage despite the
reduction of the water/binder ratio. It was assumed that the very rigid “skeleton” of stiff
aggregates and reinforcement is glued together by a thin layer of binder and silica sand
such that shrinkage is hardly possible to occur. The shrinkage behaviour of three HPC
mixtures were investigated: The standard when placing with a vibration screed
(figure 1); a mixture specially designed for placing by slipform paver (figure 2) and a
standard for placing with vibration screed but including a so called internal curing
compound which is premixed in the dry binder (figure 3).
shrinkage deformation [10 -3 ]
0,45
0,4
0,35
0,3
0,25
0,2
0,15
0,1
0,05
screeding beam mixture
0
0 7 14 21
concrete age [d]
28 35 42
Figure 1: Deformation of the screeding beam mixture prisms.
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autogenous + drying
autogenous - 3 d
autogenous - 7 d
autogenous
The weight of the sealed prisms was also measured to check whether the sealing
functioned correctly (e.g. no mass loss due to evaporation of water). The figures contain
the results of the deformation measurements. The shrinkage presented is the mean of six
individual measurements (3 prisms, 2 measurements per prism). Shortening of the
specimens is presented as a positive value. The horizontal axis presents the time elapsed
since the moment of casting, i.e. the concrete age. When the measurements started all

prisms had an age of 1 day. The lines denoted as ‘autogenous – 3 d’ and ‘autogenous –
7 d’ refer to originally sealed prisms of which the sealing was removed at an age of 3
and 7 days, respectively. The prisms that remained sealed are denoted ‘autogenous’,
whereas the prisms originally not sealed are called ‘autogenous + drying’ since they
were subjected to both drying and autogenous shrinkage over the entire measuring
period.
The results presented in figure 2 demonstrate, as expected, that the highest shrinkage is
found for the specimens that remained unsealed. The highest values observed for this
combination of autogenous and drying shrinkage is 0.39‰ at an age of 28 d (registration
period of 27 d) for the screeding beam mixture. The mixture with the lowest waterbinder
ratio, being the slipform paver mixture, demonstrated the lowest shrinkage,
namely 0.33‰. The results for the screeding beam mixture with the internal curing was
in between these two: 0.36‰. It must be noted that the slipform paver mixture exhibits
the lowest autogenous shrinkage, even though it has the lowest water-binder ratio:
0.19‰ deformation at 28 d of age. Also now, the screeding beam mixture has the
highest shrinkage (0.26‰) and the result for the screeding beam mixture with internal
curing is again in between the both mentioned before (0.22‰). If it is assumed that
drying shrinkage is total shrinkage minus autogenous shrinkage, all three mixtures have
an almost identical drying shrinkage, namely 0.13-0.14‰. Here it should be noted that a
permanently sealed prism will exhibit a different autogenous shrinkage than a prism that
is also subjected to drying: both have different internal moisture gradients which will
affect internal processes that cause deformations to occur.
shrinkage deformation [10 -3 ]
0,45
0,4
0,35
0,3
0,25
0,2
0,15
0,1
0,05
slipform paver mixture
0
0 7 14 21
concrete age [d]
28 35 42
Figure 2: Deformation of the slipform paver mixture prisms.
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autogenous + drying
autogenous - 3 d
autogenous - 7 d
autogenous

Figure 2 clearly demonstrates that the shrinkage accelerates if the sealing is removed.
The deformation of an unsealed prism is, however, an upper bound value that is not
reached by the other prisms. The results from the weight measurements (not shown here)
indicated that the sealing functioned well: continuously sealed prisms didn’t exhibit any
mass loss.
shrinkage deformation [10 -3 ]
0,45
0,4
0,35
0,3
0,25
0,2
0,15
0,1
0,05
screeding beam mixture with internal curing
0
0 7 14 21
concrete age [d]
28 35 42
4. Pilot project
Figure 3: Deformation of the prisms from the screeding beam mixture
with internal curing compound.
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autogenous + drying
autogenous - 3 d
autogenous - 7 d
autogenous
All the tests showed that the application of an UTHRHPC overlay is a very promising
solution to rehabilitate orthotropic steel bridge decks and to extend the service life of the
total structure. Both the durability and strength of the UTHRHPC overlay were proven
to be adequate. Therefore, in the period from April 29 th - May 4 th 2003 a pilot project
was executed on the Caland bridge. It also aimed at testing the logistic aspects on a
relatively small scale project before other more complex and much larger projects would
be executed. The bridge area concerned were two traffic lanes with a total width of
6.70 m and a length of 80 m in one traffic direction. During this period the entire project
had to be executed, including re-routing the traffic, removal of the asphalt wearing
course, inspection and repair of the deck plate and the application, finishing, hardening,
curing and shot blasting of the UTHRHPC overlay [20,21]. All this was executed (from

the first step up to re-opening to traffic) within five days. The information gathered was
very useful for the larger projects executed in 2005 - 2006.
Steel strain measurements on the re-surfaced Caland bridge demonstrated a reduction
with a factor 4 - 5 in the fatigue critical structural details. This was in accordance with
the reduction factors measured on small test samples and as derived from FEM computer
simulations [22].
5. Moerdijk and Hagestein bridges
In May 2005 the first phase (direction Breda – Rotterdam, 2 times 2 driving lanes, each
approx. 1,000 m long) ) of the rehabilitation of the largest orthotropic bridge in the
Netherlands, the Moerdijk bridge, started [23]. The total area to resurface was
32,000 m 2 . The Moerdijk bridge on the highway A16, is part of the mayor connection
between the ports of Rotterdam in the Netherlands and Antwerp in Belgium. It is
believed to have the most intense traffic spectrum of Western Europe. Rehabilitation was
necessary since every 4 – 6 years fatigue cracks in the deck plate had to be repaired.
These repairs have financial impact due to their high direct costs (welding several
thousands of metres of cracks and applying a new asphalt wearing course) but also a
high environmental impact because they create large streams of wasted materials and
cause air pollution because of the large traffic jams caused by the closing of several
lanes. The steel deck plate of the Moerdijk bridge is uneven. Therefore, the overlay was
applied in a varying thickness, ranging from 47 to 100 mm. The very dense
reinforcement had to be positioned very accurately to provide a constant concrete cover
of 20 – 25 mm on the rebars. Extra reinforcement was applied if the layer thickness was
over 60 mm. Placing of the concrete was complicated since no transport was allowed on
the mesh reinforcement. Therefore, two transport lanes were used: one to transport the
mixture from a nearby batching plant to the site by truck mixer, one to spread it using a
small crane. In repeated cycles 20 parts each 100 m in length (from expansion joint to
joint) were cast. All activities took place in a large tent to make them independent of the
weather conditions.
A total area of 4,200 m 2 (340 m long and approx. 12 m in width) on one of the two
Hagestein bridges on the A27 (direction Breda – Almere) had to be resurfaced within a
strict time schedule of maximum 14 days in July 2005. The overlay had a constant
thickness of 60 mm, so the standard rebar mesh configuration of three layers of
reinforcement of ø 8 mm could be used. This enabled transport of the mixture over the
reinforcement after covering them with plywood plates in the driving route of the mixer
trucks. The overlay was cast in two days, each casting being over the full width of the
bridge. The original idea was to apply the overlay by using a slipform paver but the use
of the traditional vibration screed was found to be profitable for this relatively small job,
Also here a large tent placed over the whole working area. As soon as the required
concrete compressive strength of 50 MPa was reached (within 24 h after casting) the
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idge was re-opened for traffic again. A special water spreading tube was positioned
along the barrier to cure the overlay for 7 d without disturbing the traffic streams.
6. Conclusions
In the Moerdijk bridge project it was concluded that the contractor was not able to obtain
the required smooth surface, which implied maximum vertical surface tolerances of
3 mm over a measuring length of 3 m. Also the skid resistance was lower than expected.
The complexity of the job (the bridge still in use, causing vibrations) in combination
with the relatively new method of rehabilitation made placing and finishing more
difficult than foreseen. A very thin wearing course on top of the RHPC might be
required to obtain the required smoothness and surface skid resistance. Very fine
transverse cracks (width 0.1 mm) are, as predicted, present each 0.2 – 0.3 m. The
maximum crack depth is equal to the thickness of the concrete cover. In a small area of
approximately 30 m 2 compaction was proven to be insufficient since some of the
reinforcement at the bottom of the layer was not fully encapsulated by the concrete.
Injecting was required to completely fill this area.
Results from laboratory experiments performed showed promising results for placing
with a slipform paver instead of a vibration screed. Therefore, in 2005 an overlay was
placed on the viaduct Voorst (A1/E30) in the Netherlands to re-strengthen the existing
structure and to upgrade its capacity from 2 times 2 traffic lanes to 2 times 3 traffic
lanes; a hard shoulder becoming a rush-hour lane. The overlay was here for the first time
placed on an actual job with the use of a slipform paver. Placing proved to be more
efficient and the quality of the overlay increased.
In all projects carried out special attention must be given to the storage of the aggregates
used in the mixture. Already minor variations in their water content result in a
considerable change in the consistency of the mixture. This might cause problems during
placing, especially when the overlay is relatively thick, such as was the case at the
Moerdijk bridge, and when the overlay is placed using a slipform paver.
Despite several problems, partly related to the lack of experience at all parties involved,
there is great interest in continuing the re-strengthening of orthotropic steel bridge decks
in the near future. Even when it is necessary to afterwards place a thin wearing course on
top of the UTHRHPC overlay to cope with skid resistance and smoothness problems
[24], it is up to now the most promising method available. Steel stresses in the fatigue
critical structural details of the orthotropic steel bridge deck might be reduced with a
factor of 4 – 5. Other countries facing similar fatigue problems have shown their interest
in the rehabilitation method developed in a unique cooperation between the civil
engineering division of the Ministry of Transport, a technical university, the supplier of
the UTHRHPC overlay and contractors.
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New applications for the UTHRHPC in combination with a “back plate” consisting of
various materials will be developed in the near future to re-strength offshore platforms,
supply vessels and dry docks.
7. References
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3. Buitelaar, P. Ultra High Strength Concrete, Congresso del Concreto 1995,
AVICOPRE, Caracas Venezuela.
4. Bache, H.H. Compact Reinforced Composite. CBL Report no. 39. Cement and
Concrete laboratory Aalborg Portland.
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concretes (in Dutch). Cement 1999 nr. 7.
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orthotropic steel bridge decks in the Netherlands. Proceedings Structural Faults and
Repair. United Kingdom 2003.
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Stevinlaboratory, Delft University of Technology.
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17. Pover, J., 2002. Draft Internal report Ministry of Transport; Analyses of various
solutions for life time extension - PSR-project (in Dutch). April 2002.
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materials. Dissertation, Delft University of Technology, 1997.
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changes of the microstructure. Faculty of Civil Engineering and Geosciences, Delft
University of Technology, report 25.5-99-05, 2001
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overlay system for steel bridges. 5 th. CROW workshop Istanbul, Turkey.
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Concrete Overlay System for Rehabilitation and Strengthening of Orthotropic Steel
bridge decks. Proceedings ASCE/ SEI Orthotropic Bridge Conference. Sacramento,
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engineering Issue No. 40 Third Quarter 2005. United Kingdom.
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orthotropic steel bridge decks. German Federal Highway Research Institute (Bast)
19 October 2005. Bergisch Gladbach, Germany.
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