The new train station in Herstal, Belgium, stands as the new landmark of the city. Now connecting city
parts previously disconnected, the high tower of the station ensures visibility and is becoming the
symbol of the town. Beyond the strength of the architectural shape itself, the concrete building has
a solid, red colour.
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Self-compacting
and bri
g ht
red
Coloured self-compacting
concrete for the new train
station in Herstal
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Self-compacting and bright red 3 2017
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The new train station in Herstal, Belgium, stands as
the new landmark of the city. Now connecting city
parts previously disconnected, the high tower of the
station ensures visibility and is becoming the
symbol of the town. Beyond the strength of the
architectural shape itself, the concrete building has
a solid, red colour.
First phase: study on the construction method
The tower of the station connects visually all the different levels
of the project. It acts as a landmark for the city, allowing the
train travellers to directly find their bearings. The tower
contains the - direct - vertical circulations such as the elevator
and stairs.
The height of the tower (16 m) is defined by the height of the
surrounding landscape. Tower is peculiar because it does not
have floors on its upper part (last 9 m out of the 16 m), making
it more difficult to attain a satisfying structural rigidity.
Due to the high requirements on concrete quality and the
contractor's lack of experience in making high quality exposed
concrete, architectonic precast concrete first seemed as an
appropriate solution. Different studies with companies special-
ized in precast concrete were made.
Two main limitations were met:
Jean-Philippe Jasienski,
Abdelmajid Boulaioun
MULTIPLE architecture & urbanism
Nathalie Balfroid
FEBELCEM
Steve Conard
Holcim
1 The new train station in
Herstal, part of the
'Pôle Marexhe', 2016
credits: F. Dujardin2 Axonometry of the
'Pôle Marexhe'
credits: MULTIPLE
For its flexibility and in order to fulfil the structural and
aesthetics requirements of the tower of the new train station in
Herstal, ready-mix concrete has been chosen. In addition, the
self-compacting property of the concrete facilitated meeting
the aesthetic requirements for the concrete surface.
This paper redraws the main steps in the development, the
production and the pouring of a self-compacting red concrete
used for the construction of the building.
Architecture and landscape
The 'Pôle Marexhe', or the site of the urban renewal project,
was a dense and decrepit city block, lacking public space, and
hiding the green and hilly landscape in the background. This
old city block was demolished and is replaced by a set of city
spaces such as a new train station, four collective housing
buildings including shopping facilities located around a new
public square (fig. 2 and 4).
The new train station has been considered as the opportunity
to create a link between two different levels of the city: the
lower level valley (consisting of the square and the dense
urban/industrial fabrics) and the upper, green landscape level
(consisting of the hillsides and the park).
The concept of the building-square integrates two main stakes:
? generating an intermediate level, a belvedere;
? connecting the different levels of the public space.
Choosing the proper material was a key element of the project.
The station is built in red self-compacting concrete (photo 1).
The lateral sides of the building have a raw texture imprinted
by the timber formwork (photo 3 and 5). This sober and raw
expression character of the building is the inherent identity of
the project. The front facade is smooth and is facing to the
users of the public space.
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Self-compacting and bright red 3 2017
3 2017 140
05 1020 N Rue St Lambe rt
R u e H oyoux
Rue de la statio n
Rue Ma rexhe
thema
3, 5
The station is built in red
self-compacting concre -
te with a raw texture
imprinted by the timber
formwork
credits: F. Dujardin 4 Site plan credits: MULTIPLE
- The precast walls needed to have a high-quality finish on
both sides. Due to production procedure of precast concrete
element (i.e. horizontal casting), the companies could not
produce massive wall elements that have architectonic finish
on both faces.
- Due to the geometry of the tower (no intermediate floor on
more than 9 m height), it would be very difficult to assemble
massive precast wall elements and meet the structural
requirements (i.e. the lateral stability).
Another solution was to produce sandwich wall panels
composed of red architectonic concrete on both sides. These
4
3
elements would then be assembled and connected by casting
concrete between the two panels. This solution would easily
meet the structural requirements. Unfortunately, the precast
concrete industry is divided in two types of manufacturing
companies. On one hand, the companies that make architec-
tonic concrete do not build these specific structural elements.
On the other hand, the companies that build sandwich wall
panels could not meet the aesthetic requirements of the
projects (architectonic finish and colour). In addition, the
details (i.e. some angles and connections) would not attain the
targeted level of quality.
Finally it was decided to use ready-mix concrete.
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6 Tests at the CRIC lab; determination of
the colour and the texture
credits: J.P. Jasienski
7 Tests on self-compacting concrete:
(a) resistance to segregation,
(b) viscosity and flow velocity, and
(c) mobility and obstacles penetration
credits: J.P. Jasienski
Second phase: definition of the composition of the
concrete
The desired colour was intense and bright red. In order to reach
this colour, different tests (both in the laboratory and on-site) were
necessary. The first series of laboratory tests were mainly focused
on obtaining a satisfying colour (photo 6). The different type of
pigments, their percentage in the mix and the type of cement
(white or light grey) were tested. Based on experience and literature
(Lanxess, 2014), the percentage of pigment recommended before
saturation is around 6%. In this case, it was fixed to 5.5%, which
corresponds to one bag of pigment
(20 kg) per m
3 of concrete ? a simple measure that avoids
differences in production. This first test series helped to decide the
exact pigment to pick (some were either too orange or too scarlet),
but also the kind of cement. It appeared that the brightness of CEM
III/B (light grey) and white cement were very similar and both
satisfying. Therefore, the CEM III/B was further used.
The lateral faces of the station were textured. Different tests
were carried out with polyurethane-elastomers form liners and
wooden strips. The wooden strips were chosen due to their more 'organic' aspect and their ability to visually unify and
'correct' small imperfections in concrete itself (photo 6c and 6 d).
Results were still unsatisfactory due to bubbles at the surface.
It seemed that the concrete was sticking to the formwork.
Although the concrete was successfully fulfilling the usual tests
(density, segregation and air content), the problem was not
solved. Different types of formwork oils were tested but the
results were still unacceptable.
In order to solve the problem of the bubbles it was decided to
continue with self-compacting concrete. Moreover, considering
the contractor's lack of experience, a self-compacting concrete
appeared as a good way to minimize the impact of the concrete
pouring on the surface quality. A simpler pouring method and
the absence of a vibration process (the concrete self-places and
self-compacts) were key points to opt for this kind of concrete.
Tests with a modified composition including limestone filler
(instead of fly ashes that would damage the red colour) were
carried out to improve the self-compacting ability and the
concrete surface finish.
6a 6b
7a 7b 7c
6c 6d
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142
8 The two 1/1 scale on-site mock-ups (a and b), and the
resulting concrete, references for the reception on the
further works (c and d)
credits: J.P. Jasienski 9 Inside view on the new Herstal train stationcredits: F. Dujardin
reference that would stay on-site to serve as base for the
further works. Eventually this was used to train the workers
how to pour the concrete properly.
A strict building procedure was applied to avoid loss of
quality:
- A clear process for the formworks was established.
The formwork oil had to be applied within maximum
24 hours before casting, and the wood strips had to be
humidified. It was assured that the formwork could resist
very high pressure caused by the height of pouring (more
than 5 m).
- The concrete had to comply to established tests and reference
values (see Second phase - at the concrete mixer plant and
on-site). The details of the delivery note also needed to be
verified. The contractor had to work with a nearby concrete
mixer plant to ensure the workability of the fresh concrete
(less than 15 minutes in this case).
- During the mock-up tests, it appeared that it was better to set
the speed of the concrete pump to the minimum and pour
the concrete directly without any fall. Thus the extremity of
the pump had to be always dipped inside the concrete. Since
the handling of the head of the pump is not such an easy task,
the same worker did the pouring for all the concrete of the
building.
- A strict formwork stripping time of 48 to 72 h was defined
through the mock-ups. This value had to be respected to
secure the homogeneity of the hue.
- Due to different reasons (such as blemishes) some elements
have been demolished and re-built on the building site. Their
non-satisfactory aspect was easy to determine thanks to the
mock-ups used as references and to the CIB scale of the
standard PTV 21-601. For the main columns, an underesti-
mated value of the pressure of the concrete (almost 6 m
Due to lack of standards on self-compacting concrete, several
lab tests were performed (photo 7) and used subsequently as
base for the on-site casting (table 2).
Third phase: building site realization
Two 1/1 scale mock-ups were realized for three different
purposes (photo 8). First to verify that the same specifications
and quality of the approved samples made in the lab are still
valid in real conditions (outdoor, bigger scale, ready-mix
concrete from the concrete mixer plant, type of oil used for a
formwork, resistance of formwork panels, setting the speed of
the concrete pump?) and to approve the texture (soft and
wood-textured) and the final colour. Secondly, to validate a
Table 2
Tests executed in the labs and fixed values
Tests values
- MVh ? Density (NBN EN 12350-6) 2320kg/m 3*
- Concrete slump flow test ? Abrams cone (NBN EN 12350-8) 660 mm
T500 = 3,5 s
No segregation*
- Air content (NBN EN 12350-7) 2,6%*
- Mobility and fill rate ? L-box with 3 bars (NBN EN 12350-10)
- Viscosity and flow velocity - V Funnel test (NBN EN 12350-9) 0,9
15,0 s
- Resistance to segregation - Stability at sieve (NBN EN 12350-11)
% of laitance
Bleeding after 15 min 13 %
no
* these measures were tested both at the concrete mixer plant and on the work site.
Table 1
Main characteristics of the coloured Self-compacting concrete
Materials quantity
- CEM III/B 42,5N LA HSR 380 kg/m 3
- Limestone Filler L220 kg/m 3
- Water/cement ratio0,50
- Red pigments 20 kg/m 3
8a 8b 8c 8d
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height poured at one time) led to deformations of the form-
work that resulted in slightly bowed columns. The contractor
eventually removed them and re-casted them with more rein-
forced formwork.
Conclusions
Through the case study of the realization of Herstal train
station, this paper explained the methodology that was devel-
oped from the design process to the realization of the building
to achieve a high quality and uniformly coloured self-compact-
ing concrete structure.
? REFERENCES
1 Basic rules for achieving optimal results when colou-
ring building materials (2014). Concrete Plant Internati-
onal 5, Lanxess Deutschland GmbH, pp 80-90.
2 NBN EN 12350-6:2009. Testing fresh concrete -
Density.
3 NBN EN 12350-7:2009. Testing fresh concrete -
Air content: Pressure methods. 4
NBN EN 12350-8:2010. Testing fresh concrete -
Self-compacting concrete: Slump-flow test.
5 NBN EN 12350-9:2010. Testing fresh concrete -
Self-compacting concrete: V-funnel test.
6 NBN EN 12350-10:2010. Testing fresh concrete -
Self-compacting concrete: L box test. 7
NBN EN 12350-11:2010. Testing fresh concrete -
Self-compacting concrete: Sieve segregation test.
8 PTV 21-601:2016. Precast elements of architectural
concrete, PROBETON Technical Prescriptions.
Grand-Prix d'architecture de Wallonie 2015
The project was awarded Grand-Prix d'architecture de
Wallonie 2015. The jury highlighted that the project aims to
be both modest and very ambitious and sets a new frame for
public spaces to support urban life.
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