with the particle size of the aggregate,as the flexural strength decreases with increasing par- ticle size (Kamakura et al.,1983). Effective use of the carbon fibers in concrete requires dispersion of the fibers in the mix. The dispersion is enhanced by using silica fume (a fine particulate)as an admixture(Ohama and Amano,1983;Ohama et al.,1985;Katz and Bentur,1994;Chen et al.,1997).A typi- cal silica fume content is 15%by weight of cement (Chen et al.,1997).The silica fume is typically used along with a small amount(0.4%by weight of cement)of methylcellulose for helping the dispersion of the fibers and the workability of the mix (Chen et al.,1997).Latex (typically 15-20%by weight of cement)is much less effective than silica fume for helping the fiber dispersion,but it enhances the workability,flexural strength,flexural toughness, impact resistance,frost resistance and acid resistance (Soroushian et al.,1991;Zayat and Bayasi,1996;Chen et al.,1997).The ease of dispersion increases with decreasing fiber length (Ohama et al.,1985). The improved structural properties rendered by carbon fiber addition pertain to the increased tensile and flexible strengths,the increased tensile ductility and flexural tough- ness,the enhanced impact resistance,the reduced drying shrinkage and the improved freeze- thaw durability (Kamakura et al.,1983;Ohama and Amano,1983;Akihama et al.,1984; Ohama et al.,1985;Lal,1990;Park and Lee,1990;Soroushian,1990;Park et al.,1991; Soroushian et al.,1992a,b;Park and Lee,1993;Toutanji et al.,1993;Chen and Chung, 1993a;Katz and Bentur,1994;Banthia et al.,1994a,b,1998;Banthia and Sheng,1996; Pigeon et al.,1996;Zayat and Bayasi,1996;Chen et al.,1997).The tensile and flexural strengths decrease with increasing specimen size,such that the size effect becomes larger as the fiber length increases(Urano et al.,1996).The low drying shrinkage is valuable for large structures and for use in repair (Chen et al.,1995;Ali and Ambalavanan,1998)and in joining bricks in a brick structure(Zhu and Chung,1997;Zhu et al.,1997). The functional properties rendered by carbon fiber addition pertain to the strain sensing ability (Chen and Chung,1993b,1995a,1996a,b;Chung,1995;Zhao et al.,1995;Fu and Chung,1996,1997a;Mao et al.,1996a,b;Fu et al.,1997,1998a,b;Sun et al.,1998,2000; Shi and Chung,1999;Wen and Chung,2000a,2001a,b,2002a,b)(for smart structures),the temperature sensing ability (Sun et al.,1998a,b;Wen and Chung,1999b,2000b-d),the damage sensing ability (Chen and Chung,1993b,1996b;Lee and Batson,1996;Bontea et al.,2001;Wen and Chung,20001f),the thermoelectric behavior (Chen and Chung, 1993b,1996b;Sun et al.,1998a,b;Wen and Chung,1999c,2000b-d),the thermal insulation ability (Shinozaki,1990;Fu and Chung,1999;Xu and Chung,1999b)(to save energy for buildings),the electrical conduction ability(Clemena,1988;Banthia et al.,1992;Chen and Chung,1993c,1995b;Fu and Chung,1995;Shui et al.,1995;Xie et al.,1996;Brousseau and Pye,1997;Hou and Chung,1997;Wang et al.,1998;Wen and Chung,2001c-f) (to facilitate cathodic protection of embedded steel and to provide electrical grounding or connection),and the radio wave reflection/absorption ability(Shimizu et al.,1986;Fujiwara and Ujie,1987;Fu and Chung,1997b,1998a,b)(for electromagnetic interference or EMI shielding,for lateral guidance in automatic highways,and for television image transmission) In relation to the structural properties,carbon fibers compete with glass,polymer,and steel fibers (Lal,1990;Mobasher and Li,1994,1996;Banthia et al.,1994a,b,1998;Banthia and Sheng,1996;Pigeon et al.,1996;Chen and Chung,1996c).Carbon fibers (isotropic pitch based)(Chen and Chung,1996c;Newman,1987)are advantageous in their superior ability to increase the tensile strength of concrete,even though the tensile strength,modu- lus and ductility of the isotropic pitch based carbon fibers are low compared to most other ©2003 Taylor&Franciswith the particle size of the aggregate, as the flexural strength decreases with increasing par￾ticle size (Kamakura et al., 1983). Effective use of the carbon fibers in concrete requires dispersion of the fibers in the mix. The dispersion is enhanced by using silica fume (a fine particulate) as an admixture (Ohama and Amano, 1983; Ohama et al., 1985; Katz and Bentur, 1994; Chen et al., 1997). A typi￾cal silica fume content is 15% by weight of cement (Chen et al., 1997). The silica fume is typically used along with a small amount (0.4% by weight of cement) of methylcellulose for helping the dispersion of the fibers and the workability of the mix (Chen et al., 1997). Latex (typically 15–20% by weight of cement) is much less effective than silica fume for helping the fiber dispersion, but it enhances the workability, flexural strength, flexural toughness, impact resistance, frost resistance and acid resistance (Soroushian et al., 1991; Zayat and Bayasi, 1996; Chen et al., 1997). The ease of dispersion increases with decreasing fiber length (Ohama et al., 1985). The improved structural properties rendered by carbon fiber addition pertain to the increased tensile and flexible strengths, the increased tensile ductility and flexural tough￾ness, the enhanced impact resistance, the reduced drying shrinkage and the improved freeze￾thaw durability (Kamakura et al., 1983; Ohama and Amano, 1983; Akihama et al., 1984; Ohama et al., 1985; Lal, 1990; Park and Lee, 1990; Soroushian, 1990; Park et al., 1991; Soroushian et al., 1992a,b; Park and Lee, 1993; Toutanji et al., 1993; Chen and Chung, 1993a; Katz and Bentur, 1994; Banthia et al., 1994a,b, 1998; Banthia and Sheng, 1996; Pigeon et al., 1996; Zayat and Bayasi, 1996; Chen et al., 1997). The tensile and flexural strengths decrease with increasing specimen size, such that the size effect becomes larger as the fiber length increases (Urano et al., 1996). The low drying shrinkage is valuable for large structures and for use in repair (Chen et al., 1995; Ali and Ambalavanan, 1998) and in joining bricks in a brick structure (Zhu and Chung, 1997; Zhu et al., 1997). The functional properties rendered by carbon fiber addition pertain to the strain sensing ability (Chen and Chung, 1993b, 1995a, 1996a,b; Chung, 1995; Zhao et al., 1995; Fu and Chung, 1996, 1997a; Mao et al., 1996a,b; Fu et al., 1997, 1998a,b; Sun et al., 1998, 2000; Shi and Chung, 1999; Wen and Chung, 2000a, 2001a,b, 2002a,b) (for smart structures), the temperature sensing ability (Sun et al., 1998a,b; Wen and Chung, 1999b, 2000b–d), the damage sensing ability (Chen and Chung, 1993b, 1996b; Lee and Batson, 1996; Bontea et al., 2001; Wen and Chung, 20001f), the thermoelectric behavior (Chen and Chung, 1993b, 1996b; Sun et al., 1998a,b; Wen and Chung, 1999c, 2000b–d), the thermal insulation ability (Shinozaki, 1990; Fu and Chung, 1999; Xu and Chung, 1999b) (to save energy for buildings), the electrical conduction ability (Clemena, 1988; Banthia et al., 1992; Chen and Chung, 1993c, 1995b; Fu and Chung, 1995; Shui et al., 1995; Xie et al., 1996; Brousseau and Pye, 1997; Hou and Chung, 1997; Wang et al., 1998; Wen and Chung, 2001c–f) (to facilitate cathodic protection of embedded steel and to provide electrical grounding or connection), and the radio wave reflection/absorption ability (Shimizu et al., 1986; Fujiwara and Ujie, 1987; Fu and Chung, 1997b, 1998a,b) (for electromagnetic interference or EMI shielding, for lateral guidance in automatic highways, and for television image transmission). In relation to the structural properties, carbon fibers compete with glass, polymer, and steel fibers (Lal, 1990; Mobasher and Li, 1994, 1996; Banthia et al., 1994a,b, 1998; Banthia and Sheng, 1996; Pigeon et al., 1996; Chen and Chung, 1996c). Carbon fibers (isotropic pitch based) (Chen and Chung, 1996c; Newman, 1987) are advantageous in their superior ability to increase the tensile strength of concrete, even though the tensile strength, modu￾lus and ductility of the isotropic pitch based carbon fibers are low compared to most other © 2003 Taylor & Francis