Research Article
Open Access
Rheological and mechanical development of a
fiber-reinforced concrete for an application in civil
engineering
Henrik L Funke*, Sandra Gelbrich, Andreas Ehrlich and Lothar Krolls
Professur Strukturleichtbau und Kunststoffverarbeitung, Technische Universitat Chemnitz
*Corresponding author: Henrik L. Funke, Professur Strukturleichtbau und Kunststoffverarbeitung, Technische Universitat Chemnitz ,Reichenhainer
Straße 7009126 Chemnitz, Germany, Tel.: +49 -0- 371/531 38995; Fax: +49 -0-371 531 838995; E-mail:
Henrik.Funke@mb.tu-chemnitz.de
Received: July 09, 2014; Accepted: July11, 2014; Published: July 14, 2014
Citation: Funke HL, Gelbrich S, Ehrlich A, Kroll L (2014) Rheological and mechanical development of a fiber-reinforced concrete for
an application in civil engineering. SOJ Mater Sci Eng 2(2): 1-4. DOI:
http://dx.doi.org/10.15226/sojmse.2014.00111
In the course of revitalizing the Poseidon Building in Frankfurt,
an energetically optimized façade, made of an architectural concrete
was developed. The development of a fiber-reinforced architectural
concrete had to consider the necessary mechanical strength, design
technology and surface quality. The fiber-reinforced architectural
concrete has a compressive strength of 104.1 MPa and a 3-point
bending tensile strength of 19.5 MPa. Beyond that, it was ensured that
the fiber-reinforced high-performance concrete had a high durability,
which has been shown by the capillary suction of de-icing solution
and freeze thaw test with a weathering of abrasion of 113 g/m2 after
28 freeze-thaw cycles and a mean water penetration depth of 11 mm.
Keywords: fiber-reinforced concrete, rheology, CDF-Test, highperformance
concrete
Introduction
Apart from designing claddings, the focus in civil engineering
increasingly moves to sustainability and resource efficiency,
because future-oriented living and building is hardly viable
without a significant increase of resource efficiency. With
respect to resource efficiency, optimized building with low
input (material, energy, area) during the complete lifecycle
of a building means to meet the requirements of the residents
regarding indoor environment quality and home comforts.
A truly sustainable building has to meet individual design
requirements. It is to be built in the desired location within a
very short time and with little effort. It also has to be possible
to rebuild and remove the building easily at a future date[1].
Using the material and technologies that are currently available,
the practical implementation of these innovative ideas is rather
expensive and therefore reaches its limits easily. The application
of new high-performance materials which are inorganic-nonmetallic
offers more freedom for construction. Fiber-reinforced
concrete facilitates the production of thin-walled, single- and
double-curved free-form elements which are highly suitable for
lightweight construction and comply with design requirements
regarding surface quality[2-7].
The Poseidon Building, a multistory building in Frankfurt
which was built in the 1970s and 1980s, is an example for
construction in existing contexts. In 2008, the Poseidon Building
was planned to be replaced by a newly built skyscraper [8], but
a revitalization was preferred instead by reason of resource
efficiency and sustainability. In the course of revitalization, an
energetically optimized façade was going to be implemented to
get the Green Building "Gold" certification after LEED (Leadership
in Energy and Environmental Design).
The 13800 m2 three-dimensional façade consists of more
than 11500 elements. Of special importance in the course of
redesigning the façade was the replacement of the aluminum
elements with high-strength architectural concrete. That
architectural concrete was to be pure white, with perfect surface
quality. This means, it had to have a homogeneous coloring and
be absolutely non-porous.
This paper reports the devolpment of the architectural
concrete and an appropriate process technology for the
production of prefabricated façade elements. An important part
of this work is the testing of long-term behaviour and durability
aspects of the fiber-reinforced architectural concrete.
Method
Components of architectural concrete
The composition of the used concrete was dependent on the
requirements it had to meet respecting statics, color, surface
quality and element design. Based on these requirements, the
fine concrete in Table 1 was developed. Except from white
Portland cement CEM I 52.5 N (according to EN 197) it contained
amorphous aluminosilicate as pozzolan. Dolomite sand with a
grain size of 0 to 1 mm and dolomite powder with an average
grain size of 70 μm were used as aggregate and filler. The short
alkali-resistant (AR) glass-fibers (16 mass percent of ZrO2)
was 12 mm long and had a length weight of 45 g/km. A super
plasticizer based on polycarboxylate ether (PCE) was used with
a solid content of 30 mass percent. The water binder ratio was
0.35.
The fine grained concrete was mixed with the intensive
mixer Eirich R05T. The mixing parameters are shown in Table
2. The mixing time was 5 min in total. The fresh concrete was
tested according to DIN EN 12350. Air content and bulk density
of the fresh concrete were determined by means of an air content
testing device, following DIN 18555-2.
Rheological optimization by superplasticizer content
The optimization of the superplasticizer content was carried
out by rheological measurements of the fresh concrete of Table
2. For this, flow curves of the fresh concrete were measured with
various superplasticizers content using the rheometer Thermo
Scientific HAAKE MARS III Figure 1. The measurements were
carried out with the so-called material box. As a comparing
measurement variable, the torque was used at a shear rate of 10
s-1 in response to the superplasticizer content.
Determination of the hardened concrete characteristics
The samples for the tests to be performed on the hardened
concrete were stored dry, according to DIN EN 12390-2. The
compressive strength was determined by means of the Toni
Technik ToniNorm (load frame 3000 kN) following DIN EN
12390-3, with cubes having an edge length of 150 mm Figure 2a.
The pre-load was 18 kN. The span width set was 200 mm and the
load speed 100 N/s constant.
The 3-point bending tensile strength Figure 2b was
determined with samples which measured 225 x 50 x 15 m3
Table 1: Qualitative composition of the architectural concrete.
component |
explanation |
white cement CEM I 52.5 N |
white cement with high early strength |
amorphous aluminosilicate |
pozzolan to increase mechanical strength and durability, and as optical brightener |
dolomite sand 0/1 |
white aggregate |
dolomite powder (x50 = 70 µm) |
filler to improve processability of fresh concrete and as white pigment |
integral AR-glass fibers (12 mm) |
armoring for the fine-aggregate concrete matrix |
water |
for mixing the concrete |
high-performance plasticizer (30 M.-% PCE) |
electrosteric stabilizer |
Table 2: Mixing parameters for the production of fine concrete.
S. no |
component |
mixing principle |
mixing power in % |
mixing time in s |
1 |
binders + aggregates |
counter rotation |
15 |
60 |
2 |
75 % of water |
co-rotation |
50 |
90 |
3 |
super plasticizer |
co-rotation |
50 |
60 |
4 |
residual water |
co-rotation |
50 |
30 |
5 |
ar-glass fibres |
co-rotation |
60 |
60 |
Figure 1: Rheometer HAAKE MARS for rheological measurements (Origin:
Thermo Scientific).
Figure 2: Determination of compressive strength and 3-point bending
tensile strength.
length x width x height), based on DIN EN 12390-5 and ToniNorm
(test frame 20 kN).
To validate the durability of the architectural concrete,
the capillary suction of de-icing solution and freeze thaw test
(CDF-test) was measured by the Schleibinger Freeze-Thaw-
Tester Figure 3 with standard agent solution according to the
recommendations of RILEM TC 117-FDC. Beyond this, the water
penetration depth was determined.
Results
Optimization of superplasticizer content
Figure 4 shows the torque as a function of the superplasticizer
content at a shear rate of 10s-1. The torque decreases up to a
superplasticizer content of 3.5 mass percent due to the increasing
electrosteric stabilization of finely dispersed particles, such
as cement particles and silica fume. The point of saturation SP,
i.e. the complete stabilization of the finely dispersed particles,
is about 3.5 mass percent of the superplasticizer content. Over
the saturation point (> 3.5 mass percent) added superplasticizer
contents results in an increasing torque. The increasing of the
torque, and thus indirectly increases the dynamic viscosity, is due
to the viscosity of the plasticizer itself. Beyond this, the increased
entanglement of the steric PCE main and side chains results in an
increasing of the torque.
Fresh and hardened concrete characteristics
Table 3 shows the fresh and hardened concrete characteristics
after 28 days. With a high flow capacity (diameter of the resulting
flow table test: 650 mm) the fresh concrete complies with
the flow class F6. The air content tester showed an air volume
content of 2.0% and a geometric bulk density of 2.28 g/cm³ in
the fresh concrete. The total shrinkage deformation, determined
with a shrinkage channel, was 0.91 mm/m. The reasons for
this were first the high binder content, and the high chemical
shrinkage resulting from that. Second, autogenously shrinkage
increased due to the low water-binder ratio. Drying shrinkage
could be practically eliminated due to a two days aftertreatment
including humidifying and protection against draft. The high total
shrinkage deformation did not lead to shrinkage cracking and
was therefore not harmful.
The compressive strength was 104.1 MPa after 28 days
and already 38 MPa after 24 hours. Thus, the façade elements
were ready to be demolded after one day. The small variation
coefficient of 1.1% implied a homogenous microstructure of the
hardened concrete. The 3-point bending tensile strength was
19.5 MPa, so the static requirements were met.
Durability and recyclability
The results of the durability tests are listed in Table 4. The
developed architectural concrete displays a high durability, which
was validated in the CDF test (m28 = 113 g/m2and Ru,28 = 100%)
Figure 3: Determination of the capillary suction of de-icing solution and
freeze thaw test.
Figure 4: Torque as a function of superplasticizer content.
Table 3: Fresh and hardened concrete characteristics of fiberglassmodified
fine concrete after 28 days.
characteristic |
fresh concrete |
hardened concrete |
geometric bulk density |
2.28 g/cm³ |
2.21 g/cm³ |
flow spread |
650 mm |
- |
air content |
2.0 Vol.-% |
- |
linear shrinkage |
0.91 mm/m |
|
compressive strength |
- |
104.1 MPa |
3-point bending tensile strength |
- |
19.5 MPa |
Table 4: Examinations of the durability of architectural concrete.
test method |
test value |
CDF test |
m28 = 113 g/m²
Ru,28 = 100% |
water penetration depth |
11 mm |
after 28 freeze-thaw cycles and a water penetration depth of 11
mm. Thus, the architectural concrete meets the requirements
respecting building regulations and usability over a long period.
Due to its composition, the architectural concrete is completely
recyclable and can be used as aggregate or admixture in the
production of fresh concrete. Not using a steel reinforcement
facilitates and shortens recycling, including shredding, cleaning
and classifying. This ensures that the quality of the recycled
concrete is comparable to that of the original concrete.
Constructional implementation
Fifty out of the 11500 façade elements were produced per
day. The concrete elements were fixed to pedestals to ensure
their safe transport to the building site, where they were mounted
Figure 5.
Conclusions
This practical research work was concerned with an
applicable method to develop fiber-reinforced architectural
concrete for the redevelopment of the façade of the Poseidon
Building, in the course of its revitalization. It was demonstrated
that the developed fiber-reinforced architectural concrete
combines high strength with high surface quality, durability and
recyclability.
In building construction that requires lightweight
construction, the increasing use of innovative high-performance
materials which are fiber-reinforced and inorganic-non-metallic
facilitates the production of thin-walled, single- and doublecurved
free-form surfaces. This entails a larger design potential
for architects and planners, especially with regard to organically
formed buildings.
Acknowledgements
The successful implementation of the Poseidon project was
possible thanks to the close and always constructive collaboration
between Fiber-Tech and Hentschke-Bau. An individual
Figure 5: Mounted façade elements on the multistory building "Leo".
authorization could be gotten thanks to the examination of the
façade system by the Steinbeis Innovation Center FiberCrete in
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