2012 Composites in Construction

7/31/2019 2012 Composites in Construction

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Composites in construction

Jan Wastiels

20 April 2012

Content

intro composite materials

(G)FRC and applications

ECC and applications

TRC and applications vubonite

tensile modelling

processing

vubonite applications


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Composite materials

strong and stiff fibres are embedded in a matrix

fibres are oriented following structural needs

with polymer matrix: high fibre fractions Vfarepossible

result: lightweight and strong materials

aerospace > aviation > transport > building

building applications ?

Comparison steel - flame retardant

polyester composite

E E/ f f/

Steel 205 26 250 32

Pol 2,5 1,7 50 35

Polc 16,5 11 270 175

E: stiffness modulus (GPa)

E/: specific stiffness

f: strength (MPa)

f/: specific strength

Pol: flame retardant polyester

Polc: polyester composite with 20wt% UD glass fibres

Conclusion:

the composite improves much when specific properties are considered:

absolute stiffness of the composite is poor, but specific stiffness is acceptable

absolute strength of the composite is OK, but specific strength is very good

BUT: drawbacks of polymer matrix: use of solvents, VOCs, bad fire resistance, high cost

price, hazardous waste

building applications ???


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CIF5 Newcastle July

10 20085

An absolute fire resistant matrix for composites:

vubonite

Polyester - glass composite0 sec 15 sec

30 sec 40 sec

CIF5 Newcastle July

10 20086


vubonite

M1 Polyester - glass composite

65 sec60 sec

20 sec 40 sec


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CIF5 Newcastle July

10 20087


vubonite

M1 Polyester - glass composite

65 sec60 sec

20 sec 40 sec

Cement matrix?

Polyester Cement C/P

E (GPa) 2.5 25 x 10

fc (MPa) 40 40 =

ft (MPa) 50 5 /10

mu()

20 0.2 /100

matrix fails in tension long before fibres!

composite stress at matrix cracking is very low!

behaviour in cracked stage is normal

E : stiffness modulus

fc : compressive strength

ft : tensile strength

mu : matrix tensile failure

strain


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Minimum amount of fibres

Vf crit = (mu / fu ).Vm

mu = 5 MPa

fu = 2 GPa

Vm 1 (> 0.95)

Vf crit = 0.25 %

Glass fibre reinforced cement (GRC)

Traditional production technology: short fibres

Typical 2 to 4%


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Fibre length effect Short fibres: critical length lc lc = (fu . r)/fu

fu 1 MPa

r = 7 m (fibre) lc = 14 mm

r = 0.1 mm (bundle) 200 mm

in practice always l < lc

pullout occurs

efficiency l = 0.03 to 0.5

Fibre orientation effect

efficiency of oriented fibres is lower than 1

different values for uncracked and crackedmatrix

dependent on distribution of fibres (2D-3D)

strongly dependent for cracked matrix onbending stiffness of fibres

values between 1/6 and 3/


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Combined efficiency

for 2D distribution: = 3/8 . 3/10 . l/lc

for individual fibres: = 0.11,

thus Vf crit = 0.25%/0.11 = 2.3%

for fibre bundles: < 0.01,

thus Vf crit = 25%

since Vf< 5%, pseudo plastic behaviour intension is hardly obtainable

Consequences of production technique

no tensile strength increase

limited ductility

hardly crack opening

control by fibres

no load bearing

applications


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Use of GRC: various

Engineered Cement Composites (ECC)

Vf= 2 % of short,

random PVA fibres

self compacting

cement Ductile and very

flexible, due to

tuned interaction

cement-fibres


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ECC: behaviour in bending high ductility compared to conventional GRC

however limited post-cracking stiffness

ECC: behaviour in tension

enormous ductility (3 to 7 %) and limited crack width

but nearly no strain hardening (post-cracking stiffness)


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Applications of ECC

mainly surface repair of retaining walls, bridgedecks and dams

Structural application needs

compressive strength: is provided by the matrix

ductility: can be solved (ECC)

tensile strength significantly higher than the cement itself:cu = fu Vf

significant post-cracking stiffness: Ec = EfVf enough fibres: Vf> Vf crit = (mu / fu).Vm controlled efficiency of fibres

strict crack width control (see later)

many strong, stiff and aligned fibres!

cost price: glass fibres


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Fibre Reinforced Cement TRCFRC - ECC

Short fibres

Distribution & orientation not

controlled

Low fibre content

Concrete processing:- Casting

- Pressure forming (plates)

- Shotcrete

Textile Reinforced Cement

24

TRCFRC - ECC

Short fibres Prefabricated textiles

Distribution & orientation not

controlled

Low fibre content

Concrete processing:- Casting

- Pressure forming (plates)

- Shotcrete

Carefully controlled orientation

and distribution

High fibre content possible

Composite processing:- Hand lay-up

- Pultrusion

- Calendaring


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TRC opportunities

25

- Lightweight constructions

- Freeform constructions

- High fibre volume fraction

- Flexible reinforcement

-Compressive AND tensile stresses

structural material

durability is very important issue

- Limited concrete cover

1. Felix Candela, Mexico,1958

2. Heinz Isler, UK

Applications of TRC: sandwich elements


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Applications of TRC: thin walled elements

Applications of TRC: diamond-shaped grid


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Applications of TRC: pedestrian bridge

Which cement?

Traditional:production technique leads to limited VfE-glass must be replaced by AR-glass ($) for

durability reasons

Hydration products cause embrittlement withtime, even with AR-glass

heavy coating is needed, so bad interaction cement-fibre

and low efficiency

Vubonite does not present these drawbacks


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CIF5 Newcastle July

10 200831


vubonite

Why (or what is) vubonite ?

Powder component: based on the calciumsilicatemineral Wollastonite (CaSiO3)

CIF5 Newcastle July

10 200832


vubonite



Liquid component: proprietary metal ion modified

phosphoric acid


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CIF5 Newcastle July

10 200833


vubonite



Liquid component: proprietary metal ion modifiedphosphoric acid

Acid-base setting reaction after mixing

CIF5 Newcastle July

10 200834


vubonite



Liquid component: proprietary metal ion modified

phosphoric acid Acid-base setting reaction after mixing

Fresh mixture is acidic (pH=1), but neutral (pH=7)after hardening: compatible with glass fibres


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CIF5 Newcastle July

10 200835


vubonite



Liquid component: proprietary metal ion modifiedphosphoric acid

Acid-base hardening reaction after mixing

Fresh mixture is acidic (pH=1), but neutral (pH=7)after hardening: compatible with glass fibres

Vubonite is always used in combination with fibresand/or fillers: it is a matrixor binderfor (fibre)composites, similar to organic resins like polyester

Tensile experimental data

0

20

40

60

80

100

120

0 0,4 0,8 1,2 1,6

strain(%)

stress(MPa)

0

10

20

30

40

0,0 0,4 0,8 1,2 1,6 2,0

strain (%)

stress(MPa)

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

5,5

0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0 11,0 12,0

Elongation in mm/m

Force in kN

E-modulus of the matrix

first crack in the matrix

starting point of the crack pattern

last crack in the matrix

E-modulus of the reinforcement

breaking point

Random E-glass 10% (vubonite)

UD E-glass 10% (vubonite)

UD AR-glass 2% (OPC)


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0

5

10

15

20

25

30

0 0.2 0.4 0.6 0.8 1

strain (%)

stress (MPa)

Stress-strain behaviour

static loading

matrixfibre

matrix

fibre

matrix-fibreinterface


static loading


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ACK theory (Aveston, Cooper, Kelly)

Three stages in tensile behaviour:

uncracked

multiple cracking

crack opening

Aligned UD

reinforcement

ACK Stage 1

Fibres and matrix linear elastic

Perfect adhesion fibres-matrix

Law of mixtures: Ec = EmVm + EfVf

The end of stage 1 is reached when c = mu(and m = mu) : the first crack appears at a

composite stress


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ACK Stage 2

At crack location: all load taken up by fibresVfmust be larger than Vf crit to avoid failure:

Deterministic material properties: not onlyone crack appears at mc , but all possible

cracksmultiple cracking stage

ACK Stage 2

Local high shear stress at interfacedebonding of fibre and matrix over length 0

diameter 2r


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ACK Stage 2 Constant frictional shear stress 0 at debonded

interface stress transfer from fibres to matrix

starting at crack after debonding length 0 the

matrix stress again reaches mu

In the debonded length no new crack can appear

ACK Stage 2


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ACK Stage 2

In the end, the crack spacing x is everywherebetween 0 and 20

mean crack spacing: x = 1.3370 the deformation increases due to the multiple

cracking:

with

ACK Stage 3

Fibres and matrix debonded over the wholelength everywhere frictional slip

stress in matrix remains unchanged during

loading all the extra load is taken up bythe fibres

stiffness : EfVf (adapted law of mixtures)


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0

5

10

15

20

25

30

0 0.2 0.4 0.6 0.8 1strain (%)

stress(MPa)

experimental

theory ACK

ACK-Theory versus experiment

mu1

mu2

mu3

EfVf


static loading


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Weibull distribution function for matrix tensile strength (Curtin 1998)

c

c

1

exp1:

=

0

m

R

cXxngcrackspaci

+=

xEc

cc

0

1

1

=

104

1

cff

ccE

x

VE

Stochastic Cracking Model

0

5

10

15

20

25

30

0 0.2 0.4 0.6 0.8 1strain (%)

stress(MP

a)

experimentaltheory stochastic crackingtheory ACK

Stochastic cracking model vs. experiment


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Example: glass fibre chopped mat 2%

0

5

10

15

20

25

30

0 0,5 1 1,5 2strain (%)

stress(MPa)

Vf= 2%

0

1

2

3

4

5

6

0 5 10 15 20 25

Vf (%)

X(mm)

ductility: no

strength: 7 MPa

post-cracking stiffness: 0.5 GPa


0

5

10

15

20

25

30

0 0,5 1 1,5 2strain (%)

stress(MPa)

Vf= 5%

0

1

2

3

45

6

0 5 10 15 20 25

Vf (%)

X(mm)

ductility: yes

strength: 16 MPa



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0

5

10

15

20

25

30

0 0,5 1 1,5 2strain (%)

stress(MPa)

Vf= 10%

0

1

2

3

4

5

6

0 5 10 15 20 25

Vf (%)

X(mm)

ductility: yes

strength: 33 MPa



0

5

10

15

20

25

30

0 0,5 1 1,5 2strain (%)

stress(MPa)

Vf= 20%

0

1

2

3

45

6

0 5 10 15 20 25

Vf (%)

X(mm)

Conclusion: Vf has an important effect on the stress-strain curve

ductility: yes

strength: 67 MPa



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Low Vf leads to large crack spacing and crack opening. For V f higher than 5%,crack spacing is dense, and average crack width is limited for all stress levels

vubonite composite: crack width and spacing

0

10

20

30

40

50

60

70

0 10 20 30stress (MPa)

crackwidth(m) Vf = 2%

Vf = 5%

Vf = 10%

Vf = 20%

0

10

20

30

40

50

0 10 20 30

stress (MPa)

x(mm)

Vf = 20%

Vf = 10%

Vf = 5%

Vf = 2%

1

m

m

no load 15% 30% max load

1mm

T

Textile fibre structures for

vubonite

Biaxial

Multiaxial Knitted

Leno-woven

Spacer with

varyingdistances

Spacer

Circular


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Composite processing

Cement composite processing

30 to 50% particles: non-Newtonian viscous

fluid with non-zero yield stress separation

and filtering

58


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CIF5 Newcastle July

10 200859


vubonite

Processing: hand lay-up

1 4

2 3

CIF5 Newcastle July

10 200860


vubonite

Processing: vacuum bagging

1 3

2


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CIF5 Newcastle July

10 200861


vubonite

Processing: pultrusion

CIF5 Newcastle July

10 200862


vubonite

Processing: pultrusion


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CIF5 Newcastle July

10 200863


vubonite

Processing: spray-up

Self compacting impregnator

Translation of the hand lay-up processing intoa mechanised and automatic process: well

controlled wetting and impregnation with

precise fibre volume

64


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Translation of the hand lay-up processing intoa mechanised and automatic process: well

controlled wetting and impregnation with

precise fibre volume

65


Feeding of textile fibre

structure (2 to 4 textiles)

66


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Continuously refreshed

matrix material

67


Grooves for controlled wetting

and impregnation of fibres

68


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Adjustable calendar pressure for

controlled impregnation

(pneumatic muscles up to 12 kN)

69


Adjustable pressure for

compaction (self weight 600N,

eventually increased to 3kN)

70


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Continuous process 300m/hour

through movable support

(thickness buildup)

71

1 min 5 min400C

14 min

After 120 min


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CIF5 Newcastle July

10 200873


vubonite

Applications

Intelli Fire Wall , used to separate high power transformers in case of calamity.

Each wall is composed of 24 lightweight panels and can be erected in very short time.

The walls are designed to withstand the forces of an explosion and the heat of a

transformer fire

CIF5 Newcastle July

10 200874


vubonite

Applications

Fire protective cable duct to be used in large buildings, industry, tunnels, etc.

This shape has been designed for pultrusion


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CIF5 Newcastle July

10 200875


vubonite

Applications

Thin composite mould for the thermoforming

of curved glass panels (size approx. 50 cm)

CIF5 Newcastle July

10 200876


vubonite

Applications

Protection of electricity and data transmissionpoles against bush fires in California


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CIF5 Newcastle July

10 200877


vubonite

Applications

Fire resistant piping

CIF5 Newcastle July

10 200878


vubonite

Applications

Thermal insulation forConstant volumecombustion chamber(UGent)


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CIF5 Newcastle July

10 200879


vubonite

Applications

Prototype bridge with sandwich panels

CIF5 Newcastle July

10 200880


vubonite

Applications

Sculptures


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CIF5 Newcastle July

10 200881


vubonite

Applications

Decoration of the main desk in the health center

of luxury hotels in Slovenia and Italy. Ivan Kisovec

CIF5 Newcastle July

10 200882


vubonite

Applications

Rubensplein Knokke Franz West


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Uplifting the roof of the operahouse Unter der Linden Berlin:

vubonite screen transparent to sound

Documents

2012 Composites in Construction