Procedia Engineering 15 (2011) 5333 – 5337

1877-7058 © 2011 Published by Elsevier Ltd.doi:10.1016/j.proeng.2011.08.989

Available online at www.sciencedirect.com

Available online at www.sciencedirect.com

Procedia

Engineering Procedia Engineering 00 (2011) 000–000

www.elsevier.com/locate/procedia

Advanced in Control Engineering and Information Science

Interface Resistance between Carbon Fiber and Cement

Jiang Cuixiang, Zhong Dongwang, hen Hao College of Science, Wuhan University of Science and Technology, Wuhan 430065, P. R. China

Abstract

The interface resistance between carbon fiber and cement was studied by single fiber pull-out testing. The variation of electrical resistance between fiber and matrix with displacement was obtained. Single fiber electromechanical testing was also conducted by measuring the electrical resistance under static tension. Comparison of the results shows that the interface resistance increasing during single fiber pull-out is mainly due to the changes at the interface. The interfacial shear stresses cause the change of interfacial structure, which produce an effect on conductive network of the complex, and lead to the change of interface resistance between fiber and matrix. © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of [CEIS 2011] Keywords: Carbon Fiber; Cement; interface; resistance

1. Introduction

The smart concrete material containing short carbon fiber can provide the capability of real-time structural health monitoring [1][2]. It gives information on the time and load condition and allows study of the damage evolution, thereby enabling timely repairing and other hazard precaution measures. Damage sensing is made possible by the effect of damage on the volume electrical resistivity of the cement-based material [3-5]. It has been reported [6][7] that the electrical sign was attributed to the slight fiber pull-out and the resulting increase in the contact electrical resistance between the fiber and the matrix. This interface

* Jiang Cuixiang. Tel.: (86)13627285798 E-mail address: jiangcuixiang@sina.com

Open access under CC BY-NC-ND license.

Open access under CC BY-NC-ND license.

5334 Jiang Cuixiang et al. / Procedia Engineering 15 (2011) 5333 – 53372 Jiang Cuixiang et al/ Procedia Engineering 00 (2011) 000–000

resistance increases in turn resulted in an increase in the volume electrical resistivity of the composite. It’s necessary to study the conductive mechanism of the material. Damage in cement-based materials causes the slight fiber pull-out and this behaviour involves the deformation of the interfacial structure between carbon fiber and matrix. The paper presents the research on mechano-electric behaviour between the fiber and the matrix by the single fiber pull-out.

2. Experiment

2.1. Raw Materials and Equipments

Raw materials: Portland cement with grade of 42.5, PAN carbon fibers, the properties as shown in table 1; conductive carbon black YT-1P; disperser CH-12B (provided by Shanghai Sanzheng Polymer Material Co., Ltd.). Equipments: INSTRON 5848 MicroTester, Keithley 2700 Multimeter/data acquisition system.

Table 1. Properties of Carbon Fibers

Filament diameter /[μm]

Tensile strength /[ GPa]

Tensile modulus /[ GPa]

Elongation at break /[%]

Electrical resistivity /[Ω·cm]

6.5 4.0 240 1.4 25×10-5

2.2. Preparation of Specimen

The single carbon fiber was disparted from a bundle under light microscope. The carbon fibers have been surface treated at room temperature for 24h in H2O2 (30% reagent). The length of the fiber prepared for the experiment was 55mm.

Cement, carbon black, disperser, water were prepared in a proportion of 100:1.1:2.2:30. Firstly the disperser was added in water and stirred. Then the carbon black and cement were mixed with this mixture. After stirred 3 minutes, the mix was poured into mould. One end of the single fiber was embedded in the mix (the embedment length L about 2mm) to form specimen. It was demoulded after 1d and then allowed to cure at room temperature in air for 20d.

The cement used in the matrix was poor conductivity. The electrical resistivity of this material was the grade of 109Ω·cm. The addition of carbon black (1.1% by weight of the cement) to the cement paste significantly decreased the resistivity to the grade of 103Ω·cm.

2.3. Test Procedure.

The resistance was measured by using the four-probe method, using silver paint for the electrical contacts. The outer two contacts were for passing a current; the inner two contacts were for voltage measurement. One current contact and one voltage contact were on the matrix, while the other voltage and current contacts were on the fiber (Fig. 1). Prior to vertical tension application, the paper was cut horizontally along the diagonal of the rhombus. The tension was under load control.

5335Jiang Cuixiang et al. / Procedia Engineering 15 (2011) 5333 – 5337 000–000 3Jiang Cuixiang et al / Procedia Engineering 00 (2011)

MatrixSilver paint

Carbon fiberL

A

V

Fig.1 Configuration for single fiber pull-out testing

2.4. Results and Discussion

Fig.2 shows the variation of the fractional change in resistance ( ) with displacement during single fiber testing. Where

0/R RΔ

0R R RΔ = − , R0 is the resistance prior to pull-out testing. increased linearly with increasing displacement, and increased

0/R RΔsharply when the interface debonding was

completed.

ΔR

/R0

ΔR/R

0

Fig. 2 Plot of fractional change in resistance ( 0/R RΔ ) Fig.3 0/R RΔ vs. strain obtained during static tension of a Displacement(mm)

vs. displacement during single fiber pull-out testing bare single fiber

Fig. 3 shows the variation of fractional increase in resistance ( ) with strain obtained during

static tensile testing up to failure. The resistance of the single carbon fiber increases under tension due to

the dimensional change.

0/R RΔ

The variation of fiber resistance under tension due to the dimensional change can be expressed as

121

1

0

−−

+=Δυεε

RR (1)

Where is the 0R0.27

initial value of resistance, , is the strain， is the Poisson's ratio, .

0RRR −=Δ ε υυ =

5336 Jiang Cuixiang et al. / Procedia Engineering 15 (2011) 5333 – 53374 Jiang Cuixiang et al/ Procedia Engineering 00 (2011) 000–000

The test results and the results obtained by equation (1) under different strain condition are shown in table 2. The results show that there is a good consistency between the test results and theory calculation results.

Table 2 The fractional change in fiber resistance under different strain condition

strain（%） 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0

RRΔ (10-3) test results 5.03 6.24 7.58 8.44 10.18 11.57 13.3 16.2

obtained by equation (1) 4.63 6.17 7.78 9.36 10.89 12.46 13.9 15.5

The fractional change in resistance of the sample and the fractional change in resistance of the single fiber caused by dimensional change during single fiber pull-out are shown in table 3.

Table 3 The influence of single fiber dimensional change on the sample fractional change in resistance during single fiber pull-out

bonding force

（mN） s

s

RR

01

Δ=δ （10-3）

f

f

RR

02

Δ=δ （10-3） 2

1

δδ

（%）

23.87 125 5.03 4.02

27.86 135 5.45 4.04

31.84 149 6.24 4.18

39.18 165 7.58 4.59

43.77 178 8.08 4.54

47.02 188 8.44 4.49

54.86 264 10.18 3.86

62.70 650 11.57 1.78

Where s

s

RR

01

Δ=δ is the sample fractional change in resistance during single fiber pull-out, and

f

f

RR

02

Δ=δ is the fiber fractional change in resistance caused by the dimensional change.

The testing results show that the resistance increasing during single fiber pull-out is mainly due to the changes at the interface. The variation of resistance caused by the fiber dimensional change contributes slightly to the and can be neglected. 0/R RΔ

The changes of interface resistance between fiber and matrix are attributed to following reasons: the interfacial debonding effects on the conductive network; the deformation of the interfacial structure causes the change of conductive network; the change of fiber dimensional leads to the increase of resistance, which contributes slightly to

0/R RΔ and can be neglected. The changes in conductive network result in the change of resistance.

5337Jiang Cuixiang et al. / Procedia Engineering 15 (2011) 5333 – 5337Jiang Cuixiang et al / Procedia Engineering 00 (2011) 000–000 5

3. Summary

The single fiber testing was carried out to study the interface resistance between carbon fiber and matrix. The interfacial shear stresses cause the change of interfacial structure, which produce an effect on conductive network of the material, and lead to the change of resistance. The change of fiber dimensional leads to the increase of resistance slightly and can be neglected. The variation of the electrical resistivity is able to sense the strain in the materials.

Acknowledgements

This work was supported by the Project Fund of Wuhan University of Science and Technology Research Center of Green Manufacturing and Energy-Saving & Emission Reduction Technology(B0925),the Hubei Province Key Laboratory of Systems Science in Metallurgical Process of Wuhan University of Science and Technology (C201002) and Science and Research Foundation of Hubei Provincial Department of Education (B20081104).

References

[1] D. D. L. Chung. Damage in cement-based materials, studied by electrical resistance measurement. Mater Sci Eng Rev 2003; 42(1): 1–40.

[2] P. W. Chen, D. D. L. Chung, Carbon fiber reinforced concrete for smart structure capable of non-destructive flaw detection. Smart Mater Struct. 1993; 2:. 22-30.

[3] Q. Z. Mao, B. Y. Zhao, Z. Q. Li. Resistance changement of compression sensible cement specimen under different stresses. J Wuhan Univ Tech 1996; 11(3): 41-45.

[4] Y. Wu, C. Bing, W. Keru. Smart characteristics of cement-based materials containing carbon fibers. Mech Mater Eng Sci Exp 2003: 172–175

[5] S. H. Wen, D.D.L. Chung. Damage monitoring of cement paste by electrical resistance measurement. Cem Concr Res. 2000; 30(12): 1979-1982.

[6] X. L. Fu, D. D. L. Chung. Contact electrical resistivity between cement and carbon fiber: its decrease with increasing bond strength and its increase during fiber pull-out. Cem Concr Res. 1995; 25(7): 1391-1396.

[7] C. X. Jiang, Z. Q. Li, X.H. Song. Mechanism of functional responses to loading of carbon fiber reinforced cement-based composites. J Wuhan Univ Tech (Mater Sci) 2008; 23(4): 571-573