(ECC) building components - Poelman Partners

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29 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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1

Toward
s

a
new production process of E
ngineered Cementitious Composites

(ECC)
building components


Lukien Hoiting

Technical University of Delft, Faculty of Architectur
e

Wim Poelman


University of Twente
, Faculty of Engineering Sciences

Joop den Uijl


Techni
cal 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 conc
rete called PVA
-
ECC (Polyvinyl A
lcohol Engineered C
ementitious
Composite).
Self
-
c
ompacting PVA
-
ECC is invented by V.C. Li and H. J. Kong (US Patent No.
6,809,131. Issued on Oct
ober
26, 2004).

ECC is a class of ultra ductile fibre reinforced
cementitious composites developed for applications in large materi
al 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 oppor
t
unity for developing

new
innovative
concrete applications
for

building industry.
However,
these new applications
can

not

be creat
ed without
new
production

methods.
Currently ECC mixture with a
PVA fibre content of 2 vol
. %
.
is

suitable
for common industrial production methods like s
praying, extruding and casting (Li 2003)
.

This research project will explore the possibility of injec
tion 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 mou
ld instead of poured.

Injection moulding

of concrete components

has the following advantages:



E
liminat
ion of

weather influences



I
ncrease

of

the quality of the component



Better
working conditions (for employees)



H
igher building speed

and
less
labour

intens
ive and therefore cheaper



E
conomic use of resources (centralizes work and tools)



C
reat
ion of
less waste


Next to the advantages of
industrialization

this
process

has
a

unique
design advantage
; it
does not need reinforcing steel.

Common concrete component
s

always

need steel
reinforcement to
resist

tensile stresses but i
n ECC
compon
ents 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


2

complex shape
s
, preferably
three
-
dimensional ben
t
.
Figure 2 shows some examples of blob
objects.
















Figure
2
.
Ex
ample 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
properti
es of ECC.


Fig
ure 3 Outdoor furniture designed with ECC in mind

by N. Ve
e
nendaal 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 me
chanical propertie
s
. The absence of
reinforcing steel allows leaving out concrete where it has no mechanical function. Leaving
out concrete is a interesting opportunity to redu
ce the density of the component
.

A s
ide effect of
omitting
reinforcing steel is the possibility to

design
concrete
members
with a
thickness less than 60 mm.
Us
ually

concrete members have
a

minimum
concrete cover
to

3

prevent
reinforcing
steel from corrosion
. Corrosion
dependent
s

highly
on the environment

for
example

when salt and sand are
present
. PVA fi
bres are resistant to UV l
ight and can be
used in any corrosive environment.


Compared to common concrete, t
he 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 t
o 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 w
ere the pump would jam due to the fibres and high viscosity
of the mixture.
A major part of this

research has been spent
i
n
receiving

a

fluid

concrete mix
and insi
ght

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 t
he strain capacity duri
ng 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 str
ength

of 4 MPa

given in
Figure
4
.
These mechanical properties
where
fo
und

in
a
direct tensile test
on
dog bone shaped specimen
s

of 200 mm length.


1
2
3
4
1
2
3
4
5
6
0
Displacement
Tensile stress (MPa)
Test 1
Test 2


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 d
escribed 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

t
h
ixotropy.

Therefore
,

the
behaviour of ECC during pumping

is hard to predict
.
Mo
reover, the

risk of segregation in the fluid concrete

always

exist.
Segregation occurs when

pumping

EC
C in combination with high fric
tion
, 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

4

visually inspected during mixing
.

The used ECC mixture consisted of the ingredients

given in
Tables
1
:











Table 1:
I
ngredients PVA
-
ECC mortar


There ar
e

different types of PVA fibres and table 2 shows

the properties of the fibres used in
the experiment.


Length,

[mm]

Diameter

[ mm]

Strength


[MPa]

Elongation
[%]

8

0,04

1300

6

12

0,10

1100

10

Tab
le

2

Properties of PVA
fibre

used in ECC mix


The
most important components of the
set up
where the

pump a
nd 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
,

t
o make sure that the hose could

be disconnected from the mould.
O
therwise the concrete would h
arden inside the pump and hose
, after the te
st
.


Ingredient

Amount kg/m
3

Portla
nd cement

404

Quartz sand

[
<
0
,
16
mm
]

338

Fine s
and

[0,
125
-
0
,
25 mm]

122

Fly ash

752

Super
plasticizer

34,9

Water

305

PVA

fibre (8 mm

or

12 mm
)

26


5


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

Brand
/type

Specifications

Material

1

Computer


Common desk top


2

Frequency
generator

ABB ACS601


3 kW


3

Engine

SEW


1,5 kW


4

Eccentric
worm pump

Nemo
-
pump
type N40 B

Rotation speed


1400 rpm

Pressure

6
bar

Flow:
17

m
3
/hour

at

6
bar


5

Hose

Abraflex HD

Diameter


63 mm


PU with
steel wire

6

Mou
ld


H
e
igh
t

970

mm

Wi
d
th

60 mm

D
e
pt
h


10 mm

Plyw
ood


Table 3. The test
set up



Since
blocking of
the pump
was expected

-

as

happened a few time
s

-

much
attention was
paid to

the rheological properties

of the mixture
.
Traditionally

the
viscosity

of concret
e is
determined by the slump

test
.
However,

ECC is a
highly
-
flowable
mix

and is better

6

characterized

by a slump spread.
The V
-
funnel
test is used to
evaluate the narrow
-
opening
-
passing ability and
predict whether there is a chance for blocking.

A moderate
viscosity is
required to minimize the funnel flow time (Takada
, 2004;

Gr
ü
newald
,
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

PVA
fibre

length

12

12

Spread

in mm

240

175

Segregation

Moderate

Large

V
-
test in sec

12,3

45

Moulding speed in sec

50

0

rpm

700

700

Power

35%

0

Remark

Plywood mould
declined and glass
pane
brook

Pump unable to move
concrete mix

Tab
le

4. Rheological properties of mix compared to

moulding properties



With the chosen setup it was possible to create a thin concrete slab within
approximately 40
seconds
, as shown in figu
r
e

5



test 1 rpm
-100
0
100
200
300
400
500
600
700
800
1
4
7
10
13
16
19
22
25
28
31
34
37
40
43
46
49
52
55
58
61
64
67
test 1 rpm

Figure

7
:
Time in seconds versus rotations per
minute



After hardening the sla
b turned out to have a high surface quality (very shiny and smooth).
The slab showed some enclosed air
b
ubbles

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 mou
ld 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.



7

5. Discussion

To get a better insight in the possible success of ‘injection moulding’ with PVA ECC furthe
r
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 ex
tremely 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 sh
ould 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 insufficien
t 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 prod
uce fairly large (1 m
3
) 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 mo
rtar 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
r
equirements
.
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
.
T
able

5 show
s

the charact
eristics 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.
W
ith p
lastics
,

hardening takes only a few
seconds.


Production

Injection moulding of ECC

Future
possibilities

Function

Geometry:
shape and
dimensions

Thin walled minimum 10 mm.

Complex and double bend

Probably 5 mm


Economic
batch size
(parts / time)

Low, min
imum 6 hours before mould
can be removed

Using calcium
aluminate cement or
calcium chloride


Colour and
graphics

Grey and red, yellow and black


Texture possible
with inlay and mould
finishing. Coating is
possible






Costs

Cost per part
(consumer
pri
ce)

3 x traditional concrete



8


Investment

Simple machine needed because of
low pressure, but several moulds
necessary

Using moulds from
ceramic industry


Turn around


Long, several hours before part can be
handled



Safety
personnel

Protection needed fr
om fine sand and
fly ash



Environment

Composite of plastic and concrete but
not a problem for reuse as debris







Quality

Tolerance

Not known yet



Roughness




Homogeneity
(defects or
pollution)

Entrapped air

Segregation

Mixing without air or
non
-
foam agent


Stability (intern
stresses)

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 in
jection moulding and ECC properties


9

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
ht
tp://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