M E C H A N I C A L PROPERTIES OF C - A N D H O L L O W - T Y P E CARBON FIBER REINFORCED C E M E N T COMPOSITES

T J. Kim, B.J. Oh, Y.S. Lee*, B.S. Rhee* Ssangyong research center, POBox 12, Yuseong-Gu Taejeon, 305-345 Korea

,Dept. of Chem.Eng., Chungnam Nat'l Univ., Yuseoung-Gu, Taejon 305- 764, Korea

I n t r o d u c t i o n content was increased. Reinforcing effect of C-CFRC by shape factor was best. As the matrix becomes denser and

In the C and Hollow shape carbon fiber reinforcement, its stiffer, fibers tend to break in flexural stress rather than fiber retains the interfacial bonding force with matrix greater pull-out. Tensi le s t rength As shown in the Fig.4, the fiber than that of round-shape in rite contact area with matrix. So volume was increased, the tensile strength increased in this study, we studied the mechanical properties of cement proportionally, and Fig.5 shows the tensile strength is the composites(CFRC) randomly distributed with short non highest in fiber length 6-10mm(L/D; 250-300). If fiber length circular carbon fibers to investigate the effect of shape is too long, it is easy to form fiber ball and to become bad factors. The effect of carbon fibers shape, fiber volume fiber orientation. When fiber length is 3mm, fiber volume fraction, aspect ratio and cement based matrix were content is 2-3% then tensile strength of C-CFRC was experimentally examined by using tensile strez~th, fiexural increased 1.4 times than that of R-CFRC mtd increased strength, compressive strength, porosity in CFRC and 3-4times than that of plain(Vf=0) respectively fiber-matrix interface bond was observed by SEM. C o r l c l u s i o n

E x p e r i m e n t a l To investigate the effect of fiber shape factors; rite Mater ia ls ; Cement matrix; ordinary portland cement (OPC mechanical properties of cement composites randomly

Ssangyong cement).Light-weight aggregate;sirasu balloon distributed with short non circular carbon fibers were studied. (Calceed MSB301 Japan), mmro cell (Micro cell SL150 The results are following;Compressive strength:both round Austria). silica fume is added as the dispersent and filler of mtd non-circular(C& hollow)type carbon fiber reinforced cement matrix. Admixtures; highperformmme water reduction cement composites was decreased as increasing with fiber agent(Mighty 150 Japan), ethyl cellulose (BMC 324 German), length and content. But if fiber volume content 2-3%, fiber anti-forming agent(Agitan 803 German). Table 1 and Fig. 1 length 3-10ram C-CFRC was about 1.3-1.4 times high to shows the properties of mesophase pitch based carbon fibers R-CFRC in tensile strength, flexural strength and toughness. were made from AR mesophase pitch(MHI che. Japan) by But H-CFRC were decreased as increasing with fiber length. laboratory spinning machaine. Manufactur ing process of So the effect of reinforcing of C type carbon fiber was best. CFRC; 1)Mixng(table 2; dry mixing 5min and wet mixing Table 1 Properties of carbon fiber(by JIS R 7601) 5min by omni mixer). 2)Moulding(flexural testing:JIS R 5201, Tensile Elastic Elongat Cross Specific Surface tensile testing (Kajima con. method), Flow(JIS R 5201), Unit Fiber Lc doo2 Shape strength modulus ion D~a~ sectional Area weight (JIS Al106). 3)Curing(wet curing 2days (20°C,80%RH), . (K~e) (K~) (%) area (2) Gravity (m./.o) (,,) (A) autoclave (180°C,10atm,4hr), 14days in the room Tes t ing 574.0 methods" The center point load was applied at a constant c 9,220 1,024,400 0.9 OODi 40.222.8 openS= 1.76 2.3036 8.393.4839 displacement rate of 0.5mm/min cross head speed and the 120" load-deflection curve was recorded simultaneously, flexural Hollow 8,300 1,185,714 0.7 Do 36.1 589.8 1.78 2.8267 7.63 3.5014 toughness index was obtained by dividing the area under the oi 23.8

flexural load- displacement curve up to the maximum load with the area of the matrix(Vf=0) by ACI 544 method.

Results and discussion Propert ies of fresh CFRC; The fiber volume content and

fiber length are increased, flow and unit weight decreased almost linealy. But the decreasing rate among fiber shapes does not very so much. Compressive s t rength; In regard to all the shapes of carbon fibers, compressive strength would decrease a little as the fiber volume and length increased. Its seems to have occurred because the amount of entrained air content increased during rite mixing as the fiber volume increased. In addition, micro pore size distribution of R-CFRC or plain were narrowed and omnipresenced thml that of the C

Round 8,590 715,833 1.2 26.8 564,1 1.74 1.7545 9.80 3.4424

• KR 7,340 306,000 2.2 18.0 254.5 1.65 - - -

• ) Kureha chemical Co C-101S Table 2. Mixing ratios of CFRC

A~ greg a t e s Admixtures (wt. %) Carbon Cement S.Ball [M.C211[S.Fume BMC A-803 M-150 fibers W/C

OPC 0.15 [ 0.05 1 0.16 1-3 Vf% (1.0) l 0.25 0.5 3.0 3-25.4 mm 0.465

0.36 C,H,I~KR

OPC 0,3110.05 I - l-3Vf°~ (1.0) 0.25 0.5 3.0 3-25.4 mm 0.465

0.:36 C,H,R, KR

References or H-CFRC. Flexural s t rength; As shown in Fig.2, The flexural strength of CFRC was increased dramatically with 1. Y.Ohama, Carbon. vol 27, 1989,no 5 p729-737 increasing fiber volume content. When tile fiber length 3mm, 2. N.Bafia,I.Gonois ACI SP154-17, 1995,p315-333 the fiber volume content is added 2-3% then the flexural 3. A.Katz, A.Bentur, Cement and concrete research, strength of C-CFRC to R-CFRC more increased 1.3- 1994,vo1 24, no 2, p214-220 1.4times. Generally, the matrix with silica fume was well 4. P.W.Chen, D.D.L.Chung, Composites,1993,vol 24, penetrated and densificated into the groove or fiber shape. As no 1, p33-52, shown in Fig.3, characteristics of maximum flexural strength 5. A.Katz, V.C.Li, A.Kazmer, J.of materials in civil with increasing aspect ratio(L/D) have optimum point (L/D; eng. 1995, May, p125-128 150-250). On the other hand, when fiber length is short 6. T.J.Kim, B.S.Rhee etal, 3th TCIBC International (3mm), flexural strength of H-CFR was maximized because symposium, 1996, ply189-497 matrix penetrates easily into holes by capillary force. This 7. T.J.Kim, Thesis of doctor degree, chemical eng. phenomena mensioned above was observed by SEM.(Fig.6b) chungnam national univ. Korea 1997 Flexura l toughness Index; Fiexural toughness index was increased sharply according to fiber lrngth and fiber volume

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Fig. 1 Cross sectional area shapes of pitch based carbon fiber a) Round b) C- type c) Hollow-type

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Fiber voiume content ( % )

Fig. 2 The fiber volume vs flexural strength of CFRC added with or without silica fume according to fiber shapes. (fiber length -3ram), C :C-CF R: Round-CF H: Hollow-CF, KR: commertial CF, S: silica fume addtion

7O --~1,-- KRS

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Aspect ratio (L /D)

Fig. 3 Flexural strength vs aspect ratio of CFRC added with or without silica fume according

to fiber shapes.( V f - 2 % ) C: C - C F R:Round-CF H: Hollow-CF, KR:commetial CF S: silica fume addtion

75-

70 ~- ~ p ~ . - . ~ s I

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30 L~ ' ~ ' ' ~ " ' " ;' " ~ ~ ' ~ ' " - 0 100 200 300 40D 5 0 ~ 6 0 0 700 BZX) )09

Fiber voiurne content (%)

Fig. 4 The fiber volume vs tensile strength of CFRC added with or without silica fume according to fiber shapes. (fiber length -3ram), C :C-CF R: Round-CF H: Hollow-CF, KR: commertial CF, S: silica fume addtion

Aspea relio (UD)

Fig. 5 Tensile strength vs aspect ratio of CFRC added with or without silica fume according to fiber shapes.( Vf=2% ) C: C-CF

R: Round-CF H: Hollow-CF, KR:commetial CF S: silica fume addtion

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Fig. 6 Interfacial properties of fiber and matrix after flexural testing by SEM a) C-type b) Hollow-type

517