7/25/2019 Carbon Nanotube Reinforced Cement Composites Preparation, Characterization and Testing

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Carbon Nanotube Reinforced Cement Composites:

Preparation, Characterization and TestingYizheng Cao, Jason Weiss, Carol Handwerker

A study of the effects of carbon nanotubes (CNTs) concentration, superplasticizer content, ultrasonication and

undispersed silica fume (UDSF) on CNT dispersion and mechanical properties is performed. Dispersion of CNTs is

characterized by optical microscopy and scanning electron microscopy. AC-impedance spectroscopy (IS) is used to

investigate the fiber-reinforced composites dual arc behavior. The CNT-reinforced matrix shows a different IS behavior

than traditional macro conductive fibers, such as steel. Mechanical tests show an improvement in compressive strength

for UDSF-facilitated CNT-reinforced cement pastes. The ball on three ball (B3B) test was used to measure the flexural

strength of small disc samples of cement composites. CNT-reinforced cement pastes show an improvement of 25~45%.

Carbon Nanotubes

Youngs

modulus (GPa)

Tensile

Strength (GPa)

Density

(g/cm3)

CNT 1200 ~150 2.6

Steel 208 0.4 7.8

Image from S.V. Rotkin, S.

Subramoney, Applied Physics

of Carbon Nanotubes,

Springer, 2005

CNTs have extraordinary

mechanical properties shown

below. Data from Carbon

Nanotubes Science and

Applications, M. Meyyappan,

CRC Press LLC, 2005, p15

ue to van der Waals force, CNTs are tangled as bundles in

ature and are not ready to be used as a reinforcement.

ertain processing needs to be done to separate the bundles

nto single tubes. Ultrasonication and superplasticizer as

urfactant are used to achieve this goal.

Ultrasonication

1

2

4

3

After 3 hours ultrasonication with superplasticizer,

bundle 1 and 2 are close to a perfect dispersion, while 3

and 4 are still agglomerated, only part of which are

dispersed into single tubes.

Ball on Three Ball Flexural TestThe B3B device used in

this work for 2 inch

(diameter) disc samples.

Loading speed is set as

0.2 mm/min.

Left is a stress distribution of this

test.

Compared with traditional three

or four point bending, this B3B

test has several advantages: (1)

The ease to prepare testing

samples. (2) The complicated

stress distribution during test is

beneficial for detecting defects in

most directions. (3) The sample

surface and edge do not require

very good condition.

2( , , )

Ff

t

t

R a

R

R

F: applied force;

t: sample thickness;

v: Poissons ratio of the materialR: radius of the slice

Ra: support radius

Dispersion of CNTs

Undensified Silica Fume (SF)

7

7.5

8

8.5

9

9.5

10

0.00% 0.01% 0.10% 1.00% 10.0

CNT vol fraction

B3B

flexural

strength(MPa)

Group a

Group c

Group a

Group c

UDSF-Facilitated CNT-

Reinforced Cement Pastes

B3B flexural strength of Group a and Group c at the age

of 7 days

w /c Superplasticizer

Group a 0.365 0

Group b 0.3 0

Group c 0.25 0.3%

Both

SuperplasticizerDispersion mechanism of chemical

sufactants. Image from Pegel S,

Potschke P, Petzold G, Alig I, Dudkin

SM, Lellinger D, Polymer 49 (2008)

974-984

Due to their small size, SF

particles have the potential

to enter the CNT budles and

help the dispersion during

mixing [1].

[1]Florence Sanchez, Chantal Ince,Composites Science and

Technology 69 (2009) 13101318

AC-Impedance Spectroscopy (IS)

With varying frequency, the IS of composites is measured.

The IS conductive fiber reinforced cement composites has

two arcs rather than one due to insulating coating on the

fibers, which is explained with a switching model [1].

CNT-Reinforced Paste Results

9

10

11

12

13

14

15

16

17

0.00% 0.10% 0.20% 0.30% 0.40% 0.50% 0.60% 0.70%

B3Bflexuralstrength(Mpa)

CNTs volume fraction

Sonication of 2 m in

Sonication of 40 m in

Plain

The B3B flexural strength of 7-day cements pastes withdifferent volume fractions of dispersed CNTs

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50

Re(Z) (ohmm)

-Im(Z)(ohmm)

plain

0.78 volume %

1.56 volume %

3.12 volume %

4.68 volume %

0

10

20

30

40

50

0 10 20 30 40 50

Z' (ohm*m)

-Z''(oh

m*m)

0 min

10 min

1 h

3 h

15 h

With different volume

fractions of steel

fibers, the cement

pastes resistivity

decreases

With longer

ultrasonication, the

CNT-reinforced paste

IS curves shift to

lower resistivity. This

is because of a better

dispersion.

Compressive strength

of the three groups at

the age of 28 days

ConclusionWith ultrasonication and superplasticizer, the CNTs a

effectively dispersed. The fiber volume fraction a

dispersion can be characterized by AC-IS. The CN

reinforced pastes and SF-facilitated CNT-reinforced past(SCP) B3B flexural strengths are improved compared wi

plain pastes. The 28-day compressive strengths of SCP a

also effectively improved.

[1] Torrents JM, Mason

TO, Peled A. J Mater Sci

2001;36 (16): 400312.

The strength calculation

for this test [1].

[1] Brger A, Supancic P,

Danzer R, Journal of the

European Ceramic Society

22 (2002) 1425-1436