Towards a new production process of Engineered Cementitious Composites (ECC)
building components
Lukien Hoiting
Wim Poelman
Joop den Uijl
Technical University of Delft, Faculty of Architecture
University of Twente, Faculty of Engineering Sciences
Technical University of Delft, Faculty of Civil Engineering and
Geosciences
1. Introduction
This article is about a new production process using a closed mould technology for this
plastic-fibre reinforced concrete called PVA-ECC (Polyvinyl Alcohol Engineered Cementitious
Composite). Self-compacting PVA-ECC is invented by V.C. Li and H. J. Kong (US Patent No.
6,809,131. Issued on October 26, 2004). ECC is a class of ultra ductile fibre reinforced
cementitious composites developed for applications in large material volume usage, cost
sensitive construction industry (Li 2003). ECC most outstanding feature is its mechanical
behaviour under tension. While regular fibre reinforced concrete (e.g. glass fibre or steel
fibre) tends to break brittle, PVA-ECC behaves more like a metal in a ductile way as shown
in figure 1.
Figure 1. Ductile behaviour of ECC
This ductile behaviour is an opportunity for developing new innovative concrete applications
for building industry. However, these new applications can not be created without new
production methods. Currently ECC mixture with a PVA fibre content of 2 vol. %. is suitable
for common industrial production methods like spraying, extruding and casting (Li 2003).
This research project will explore the possibility of injection moulding with ECC. Injection
moulding is one of the highly developed production processes in industry for processing
polymers. The production process in this article is called “injection moulding of concrete”
because the material is pressed in the mould instead of poured.
Injection moulding of concrete components has the following advantages:
 Elimination of weather influences
 Increase of the quality of the component
 Better working conditions (for employees)
 Higher building speed and less labour intensive and therefore cheaper
 Economic use of resources (centralizes work and tools)
 Creation of less waste
Next to the advantages of industrialization this process has a unique design advantage; it
does not need reinforcing steel. Common concrete components always need steel
reinforcement to resist tensile stresses but in ECC components the PVA-fibres take up
tensile stresses. The elimination of steel for reinforcement provides an enormous impact to
freedom of design. Because of this so called “form freedom” the technology is appropriate for
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complex shapes, preferably three-dimensional bent. Figure 2 shows some examples of blob
objects.
Figure 2. Example of blob lamp by Karim Rashid and blob architecture by Saha Hadid
Typical applications of ECC could be: steps of a staircase, cladding for blob architecture,
urban furniture or a small dome for example for a bus shelter. Figure 3 shows an example of
urban furniture designed for ECC. This elegant design is possible because of the unique
properties of ECC.
Figure 3 Outdoor furniture designed with ECC in mind by N. Veenendaal for ipv Delft.
Form freedom can be used to improve the aesthetic qualities of a product but more
important, it supports optimizing the product towards mechanical properties. The absence of
reinforcing steel allows leaving out concrete where it has no mechanical function. Leaving
out concrete is a interesting opportunity to reduce the density of the component.
A side effect of omitting reinforcing steel is the possibility to design concrete members with a
thickness less than 60 mm. Usually concrete members have a minimum concrete cover to
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prevent reinforcing steel from corrosion. Corrosion dependents highly on the environment for
example when salt and sand are present. PVA fibres are resistant to UV light and can be
used in any corrosive environment.
Compared to common concrete, the price of an ECC component will be higher. but because
of the ductile behaviour, ECC can also replace plastics. Compared to plastics the price of
ECC will be less, while properties like heat resistance and chemical inertia are better in ECC
than plastics.
To explore the possibility of moulding with ECC a series of experiments was performed. The
goal of the first test was to proof the possibility to pump ECC in a closed mould using an
electrical worm pump. The mould had a relatively narrow cavity (10 mm) in order to create a
thin slab. Expected problems were the pump would jam due to the fibres and high viscosity
of the mixture. A major part of this research has been spent in receiving a fluid concrete mix
and insight in rheological properties.
2. Theoretical Background
Special about ECC is its ductile behaviour due to the fact that the load, that can be
transmitted over a crack, is larger than the load at which the crack is initiated. As a
consequence, under increasing deformation many very fine and shortly spaced cracks are
formed. These cracks are called micro cracks and appear at an increasing load. After the first
crack the strain capacity during strain-hardening is about 5%, roughly 500 times more than
typical fibre reinforced concrete (Kuraray, 2007]. In our research, we found a strain capacity
of about 1% with a tensile strength of 4 MPa given in Figure 4. These mechanical properties
where found in a direct tensile test on dog bone shaped specimens of 200 mm length.
Tensile stress (MPa)
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Test 1
Test 2
5
4
3
2
1
0
1
2
3
Displacement
4
Figure 4: Tensile stress versus elongation (%) of ECC with 8 mm PVA
Before hardening ECC behaves like a non-Newtonian fluid. This means a fluid which flow
properties are not described by a single constant value of viscosity. This behaviour leads to
challenges with respect to moulding technology. One has to deal with parameters like, shear
rate and thixotropy. Therefore, the behaviour of ECC during pumping is hard to predict.
Moreover, the risk of segregation in the fluid concrete always exist. Segregation occurs when
pumping ECC in combination with high friction, the water is pressed out of the concrete.
3. Test
The ingredients for the PVA-ECC were mixed in a concrete mixer (Eirich, type R09/T). They
were added one by one, starting with the dry parts and finishing with the fibres. The mix was
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visually inspected during mixing. The used ECC mixture consisted of the ingredients given in
Tables 1:
Ingredient
Portland cement
Quartz sand [< 0,16 mm]
Fine sand [0,125-0,25 mm]
Fly ash
Super plasticizer
Water
PVA fibre (8 mm or 12 mm)
Amount kg/m3
404
338
122
752
34,9
305
26
Table 1: Ingredients PVA-ECC mortar
There are different types of PVA fibres and table 2 shows the properties of the fibres used in
the experiment.
Length,
Diameter
Strength
[mm]
[ mm]
[MPa]
8
0,04
1300
12
0,10
1100
Table 2 Properties of PVA fibre used in ECC mix
Elongation
[%]
6
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The most important components of the set up where the pump and the closed mould.
We used a eccentric worm pump with a 1.5 kW engine and a frequency generator to control
the rotational speed of the pump. A cross section is shown in figure 5. The pump was filled at
the topside funnel using a bucket and connected to the mould with an industrial water hose.
Figure 5: Cross-section of an eccentric worm pump
The mould was build using regular formwork plywood panels (figure 6).
The front side of the mould was closed with a glass pane so the rise of the concrete could be
monitored during pumping. The topside of the mould was open. A slide valve was placed in
the inlet of the mould, to make sure that the hose could be disconnected from the mould.
Otherwise the concrete would harden inside the pump and hose, after the test.
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Figure 6 Overview of the set up in the concrete laboratory
The mould and glass pane were greased with formwork oil to facilitate cleaning. Table 3
shows the specifications of the components.
Device
Computer
Frequency
generator
Engine
Eccentric
worm pump
Brand/type
5
Hose
Abraflex HD
6
Mould
1
2
3
4
Specifications
Common desk top
ABB ACS601
SEW
Nemo-pump
type N40 B
Material
3 kW
1,5 kW
Rotation speed 1400 rpm
Pressure
6 bar
Flow: 17 m3/hour at 6 bar
Diameter
63 mm
Height
Width
Depth
970 mm
60 mm
10 mm
PU with steel wire
Plywood
Table 3. The test set up
Since blocking of the pump was expected - as happened a few times - much attention was
paid to the rheological properties of the mixture. Traditionally the viscosity of concrete is
determined by the slump test. However, ECC is a highly-flowable mix and is better
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characterized by a slump spread. The V-funnel test is used to evaluate the narrow-openingpassing ability and predict whether there is a chance for blocking. A moderate viscosity is
required to minimize the funnel flow time (Takada, 2004; Grünewald, 2004). A V-funnel test
and the slump spread of a cone test where each time carried out, just prior to the pumping.
4. Results
Test 1
Test 2
12
12
240
175
Moderate
Large
12,3
45
50
0
700
700
35%
0
Plywood mould
Pump unable to move
declined and glass
concrete mix
pane brook
Table 4. Rheological properties of mix compared to moulding properties
PVA fibre length
Spread in mm
Segregation
V-test in sec
Moulding speed in sec
rpm
Power
Remark
With the chosen setup it was possible to create a thin concrete slab within approximately 40
seconds, as shown in figure 5
test 1 rpm
800
700
600
500
400
test 1 rpm
300
200
100
0
-100 1
4
7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67
Figure 7: Time in seconds versus rotations per minute
After hardening the slab turned out to have a high surface quality (very shiny and smooth).
The slab showed some enclosed air bubbles and some dried out spots which are points of
attention. The fibres seemed to have been evenly spread throughout the slab. Expected
problems like blocking up of the hose or mould did not seem to be an issue if the concrete
mix did not segregate in the pre-test and had a high speed in de V-test.
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5. Discussion
To get a better insight in the possible success of ‘injection moulding’ with PVA ECC further
testing is necessary. This preliminary test has proven the used setup can give a better insight
in the workability of ECC, in combination with a (worm) pump. A few variables of moulding
ECC will be discussed.
Fly ash: Tests have shown that the mix is extremely sensitive for the kind of fly ash. To
create a more robust mix it would be useful to add some VMA (viscosity modifying
admixture).
Air: In this first test the mixture has not been vibrated to let out the enclosed air. Vibrating the
mixture before or after it is pumped (in the mould) could be applied to see if it results in a
more homogeneous slab.
Inserts: Besides creating a slab it would be necessary to get insight in how the concrete
flows when obstacles are placed in the mould. The obstacles should represent the distance
keepers (to keep e.g. the insulation core in place), inserts and other details like ribs which will
be present in the mould for advanced building components.
Pump: The concrete pump used in this test proved to have insufficient power. For future tests
either a stronger engine is needed or a different pump (e.g. centrifugal pump). Besides
pumps, it might be interesting to look into ways of using pressure vessels to ‘pump’ the
mortar. Using this method Lafarge has managed to produce fairly large (1 m3) 25 mm thin
shell elements (Vicenzino, E. et al 2005).
Rheology: Besides tests concerning the used tools and mould, a better insight about the
rheology of ECC in this application is needed. Especially the optimal fluidity of the mortar in
relation to the strength of the hardened concrete is of importance.
After discussing the variables, it is clear there are many future challenges for moulding ECC.
It is known there is a strong relation between material properties and production
requirements. Since it is possible to adjust the properties of concrete, this research is not
only about a production method but also about “tuning and adjusting” material properties
towards the requirements for injection moulding. Table 5 shows the characteristics of ECC,
given the general characteristics of production methods. The development of the production
method is not yet finished. Most important is the hardening time of ECC, which is significant
longer than time needed for injection moulding. With plastics, hardening takes only a few
seconds.
Production
Function
Geometry:
shape and
dimensions
Economic
batch size
(parts / time)
Colour and
graphics
Injection moulding of ECC
Thin walled minimum 10 mm.
Complex and double bend
Future possibilities
Probably 5 mm
Low, minimum 6 hours before mould
can be removed
Using calcium
aluminate cement or
calcium chloride
Texture possible
with inlay and mould
finishing. Coating is
possible
Costs
3 x traditional concrete
Cost per part
(consumer
price)
Grey and red, yellow and black
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Investment
Turn around
Safety
personnel
Environment
Quality
Tolerance
Roughness
Homogeneity
(defects or
pollution)
Stability (intern
stresses)
Simple machine needed because of
low pressure, but several moulds
necessary
Long, several hours before part can be
handled
Protection needed from fine sand and
fly ash
Composite of plastic and concrete but
not a problem for reuse as debris
Using moulds from
ceramic industry
Not known yet
Entrapped air
Segregation
Mixing without air or
non-foam agent
Depends on segregation
Using a VMA
(Rheomix) to
improve robustness
Smooth and shiny surface but air
holes. Depends on segregation and oil
used for unloading
Table 5: Link between production requirements for injection moulding and ECC properties
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References
Grunewald, S. (2004). Performance-based design of self-compacting fibre reinforced
concrete. University of Technology, Delft.
Kuraray PVA fibre division, (2007, December 3), retrieved December 4 2007, from
http://www.kuraray-am.com/pvaf/pva-ecc.php
Li, V., “On engineered cementitious composites (ECC): a review of the material and its
applications”, Journal of advanced concrete technology Vol. 1, No.3 215-230 November
2003
Richard R., “Industrialised building systems: reproduction before automation and robotics”,
Automation in Construction 14 (2005), p. 443
Takada, K. (2004).Influence of admixtures and mixing efficiency on the properties of self
compacting concrete. University of Technology, Delft.
Vicenzino, E., “First use of UHPFRC in thin precast concrete roof shell for Canadian LRT
station”, in PCI Journal, September – October 2005
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