Table 10.6 Loss tangent (tan ,0.002)of cement pastes.Refer to Note in Table 10.2 Formulation With as-received silica fume (Hz) With silane-treated silica fume (Hz) 0.2 1.0 2.0 0.2 1.0 2.0 A 0.082 0.030 <10-4 0.087 0.032 <10-4 4+ 0.102 0.045 <10-4 0.093 0.040 <10-4 A 0.089 0.033 <10-4 0.084 0.034 <104 0.085 0.043 <10-4 0.084 0.032 <104 AK 0.079 0.039 <10-4 0.086 0.035 <10-4 AS 0.076 0.036 <10-4 0.083 0.033 <10-4 Table 10.7 Storage modulus(GPa,+0.03)of cement pastes.Refer to Note in Table 10.2 Formulation With as-received silica fume (Hz) With silane-treated silica fume (Hz) 0.2 1.0 2.0z 0.2 1.0 2.0 A 12.71 12.14 11.93 16.75 16.21 15.95 + 11.52 10.61 10.27 15.11 14.73 14.24 A+F 13.26 13.75 13.83 17.44 17.92 18.23 AO 14.14 14.46 14.72 18.92 19.36 19.57 AK 15.42 16.15 16.53 19.33 19.85 20.23 A+S 17.24 17.67 15.95 21.34 21.65 21.97 Table 10.8 Drying shrinkage strain(104,+0.015)different curing ages Formulation With as-received silica fume (days) With silane-treated silica fume(days) 1 4 8 19 4 8 19 B 1.128 3.021 3.722 4.365 1.013 2.879 3.623 4.146 BF 0.832 2.417 3.045 3.412 0.775 2.246 2.810 3.113 BO 0.825 2.355 3.022 3.373 0.764 2.235 2.793 3.014 BK 0.819 2.321 3.019 3.372 0.763 2.232 2.790 3.010 BS 0.812 2.316 2.976 3.220 0.752 2.118 2.724 2.954 Notes B:cement waterwater reducing agent silica fume methylcellulose defoamer. BF:B+as-received fibers BO:B+O:-treated fibers. BK:B+dichromate-treated fibers. BS:B+silane-treated fibers. Further addition of carbon fibers decreases the loss tangent.The loss tangent decreases in the following order:as-received fibers,ozone-treated fibers,dichromate-treated fibers and silane-treated fibers,at least for the case of as-received silica fume at 0.2 Hz.The storage modulus(Table 10.7)is decreased by the addition of methylcellulose.Further addi- tion of carbon fibers increases the storage modulus,such that the modulus increases in the ©2003 Taylor&Francis
Table 10.6 Loss tangent (tan , 0.002) of cement pastes. Refer to Note in Table 10.2 Formulation With as-received silica fume (Hz) With silane-treated silica fume (Hz) 0.2 1.0 2.0 0.2 1.0 2.0 A 0.082 0.030 104 0.087 0.032 104 A 0.102 0.045 104 0.093 0.040 104 AF 0.089 0.033 104 0.084 0.034 104 AO 0.085 0.043 104 0.084 0.032 104 AK 0.079 0.039 104 0.086 0.035 104 AS 0.076 0.036 104 0.083 0.033 104 Table 10.7 Storage modulus (GPa, 0.03) of cement pastes. Refer to Note in Table 10.2 Formulation With as-received silica fume (Hz) With silane-treated silica fume (Hz) 0.2 1.0 2.0 z 0.2 1.0 2.0 A 12.71 12.14 11.93 16.75 16.21 15.95 A 11.52 10.61 10.27 15.11 14.73 14.24 AF 13.26 13.75 13.83 17.44 17.92 18.23 AO 14.14 14.46 14.72 18.92 19.36 19.57 AK 15.42 16.15 16.53 19.33 19.85 20.23 AS 17.24 17.67 15.95 21.34 21.65 21.97 Table 10.8 Drying shrinkage strain (104 , 0.015) different curing ages Formulation With as-received silica fume (days) With silane-treated silica fume (days) 1 4 8 19 1 4 8 19 B 1.128 3.021 3.722 4.365 1.013 2.879 3.623 4.146 BF 0.832 2.417 3.045 3.412 0.775 2.246 2.810 3.113 BO 0.825 2.355 3.022 3.373 0.764 2.235 2.793 3.014 BK 0.819 2.321 3.019 3.372 0.763 2.232 2.790 3.010 BS 0.812 2.316 2.976 3.220 0.752 2.118 2.724 2.954 Notes B: cement water water reducing agent silica fume methylcellulose defoamer. BF: B as-received fibers. BO: B O3-treated fibers. BK: B dichromate-treated fibers. BS: B silane-treated fibers. Further addition of carbon fibers decreases the loss tangent. The loss tangent decreases in the following order: as-received fibers, ozone-treated fibers, dichromate-treated fibers and silane-treated fibers, at least for the case of as-received silica fume at 0.2 Hz. The storage modulus (Table 10.7) is decreased by the addition of methylcellulose. Further addition of carbon fibers increases the storage modulus, such that the modulus increases in the © 2003 Taylor & Francis
order:as-received fibers,ozone-treated fibers,dichromate-treated fibers and silane-treated fibers. Table 10.8 gives the drying shrinkage strain of ten types of cement paste as a function of curing age.The drying shrinkage is decreased by the addition of carbon fibers,such that it decreases in the following order:as-received fibers,ozone-treated fibers,dichromate-treated fibers,and silane-treated fibers.The drying shrinkage is decreased by the use of silane- treated silica fume in place of as-received silica fume,whether fibers are present or not. 3 Thermal behavior Table 10.9 shows the specific heat of cement pastes(Xu and Chung,1999b,2000).The spe- cific heat is significantly increased by the addition of silica fume.It is further increased by the further addition of methylcellulose and defoamer.It is still further increased by the still further addition of carbon fibers.The effectiveness of the fibers in increasing the specific heat increases in the following order:as-received fibers,O3-treated fibers,dichromate-treated fibers and silane-treated fibers.For any of the formulations,silane-treated silica fume gives higher specific heat than as-received silica fume.The highest specific heat is exhibited by the cement paste with silane-treated silica fume and silane-treated fibers.Silane treatment of fibers is more valuable than that of silica fume for increasing the specific heat Table 10.10 shows the thermal conductivity.It is significantly decreased by the addition of silica fume.The further addition of methylcellulose and defoamer or the still further Table 10.9 Specific heat (Jg-K-1,0.001)of cement pastes.The value for plain cement paste (with cement and water only)is 0.736Jg-K-.Refer to Note in Table 10.2 Formulation As-received Silane-treated silica fume silica fume A 0.782 0.788 A+ 0.793 0.803 A+F 0.804 0.807 AO 0.809 0.813 AK 0.812 0.816 A+S 0.819 0.823 Table 10.10 Thermal conductivity (Wm-K-,0.03) of cement pastes.The value for plain cement paste (with cement and water only)is 0.53 Wm-K-.Refer to Note in Table 10.2 Formulation As-received Silane-treated silica fume silica-fume A 0.35 0.33 A+ 0.34 0.30 A 0.35 0.34 AO 0.38 0.36 AK 0.39 0.37 AS 0.34 0.32 ©2003 Taylor&Francis
order: as-received fibers, ozone-treated fibers, dichromate-treated fibers and silane-treated fibers. Table 10.8 gives the drying shrinkage strain of ten types of cement paste as a function of curing age. The drying shrinkage is decreased by the addition of carbon fibers, such that it decreases in the following order: as-received fibers, ozone-treated fibers, dichromate-treated fibers, and silane-treated fibers. The drying shrinkage is decreased by the use of silanetreated silica fume in place of as-received silica fume, whether fibers are present or not. 3 Thermal behavior Table 10.9 shows the specific heat of cement pastes (Xu and Chung, 1999b, 2000). The specific heat is significantly increased by the addition of silica fume. It is further increased by the further addition of methylcellulose and defoamer. It is still further increased by the still further addition of carbon fibers. The effectiveness of the fibers in increasing the specific heat increases in the following order: as-received fibers, O3-treated fibers, dichromate-treated fibers and silane-treated fibers. For any of the formulations, silane-treated silica fume gives higher specific heat than as-received silica fume. The highest specific heat is exhibited by the cement paste with silane-treated silica fume and silane-treated fibers. Silane treatment of fibers is more valuable than that of silica fume for increasing the specific heat. Table 10.10 shows the thermal conductivity. It is significantly decreased by the addition of silica fume. The further addition of methylcellulose and defoamer or the still further Table 10.9 Specific heat (Jg1 K1 , 0.001) of cement pastes. The value for plain cement paste (with cement and water only) is 0.736 J g1 K1 . Refer to Note in Table 10.2 Formulation As-received Silane-treated silica fume silica fume A 0.782 0.788 A 0.793 0.803 AF 0.804 0.807 AO 0.809 0.813 AK 0.812 0.816 AS 0.819 0.823 Table 10.10 Thermal conductivity (Wm1 K1 , 0.03) of cement pastes.The value for plain cement paste (with cement and water only) is 0.53 Wm1 K1 . Refer to Note in Table 10.2 Formulation As-received Silane-treated silica fume silica-fume A 0.35 0.33 A 0.34 0.30 AF 0.35 0.34 AO 0.38 0.36 AK 0.39 0.37 AS 0.34 0.32 © 2003 Taylor & Francis
addition of fibers has little effect on the density.Surface treatment of the fibers by ozone or dichromate slightly increases the thermal conductivity,whereas surface treatment of the fibers by silane has negligible effect.For any of the formulations,silane-treated silica fume gives slightly lower(or essentially the same)thermal conductivity as as-received silica fume. Silane treatments of silica fume and of fibers contribute comparably to reducing the thermal conductivity. 4 Electrical behavior Figure 10.1 gives the volume electrical resistivity of composites at seven days of curing.The resistivity decreases much with increasing fiber volume fraction,whether a second filler (silica fume or sand)is present or not (Chen and Chung,1995b).When sand is absent,the addition of silica fume decreases the resistivity at all fiber volume fractions except the high- est volume fraction of 4.24%;the decrease is most significant at the lowest fiber volume fraction of 0.53%.When sand is present,the addition of silica fume similarly decreases the resistivity,such that the decrease is most significant at fiber volume fractions below 1%. When silica fume is absent,the addition of sand decreases the resistivity only when the fiber volume fraction is below about 0.5%;at high fiber volume fractions,the addition of sand even increases the resistivity due to the porosity induced by the sand.Thus,the addition of a second filler(silica fume or sand)that is essentially non-conducting decreases the resis- tivity of the composite only at low volume fractions of the carbon fibers and the maximum fiber volume fraction for the resistivity to decrease is larger when the particle size of the filler is smaller.The resistivity decrease is attributed to the improved fiber dispersion due to 1.000,000 100,000 g (wo 10,0001 g 1,000 11 (c) (d)i: 100 (a) 10 (b) 0 2 3 4 5 Vol.%fibers Figure 10.I Variation of the volume electrical resistivity with carbon fiber volume fraction(Chen and Chung,1995b).(a)Without sand,with methylcellulose,without silica fume; (b)Without sand,with methylcellulose,with silica fume;(c)With sand,with methyl- cellulose,without silica fume;(d)With sand,with methylcellulose,with silica fume. ©2003 Taylor&Francis
addition of fibers has little effect on the density. Surface treatment of the fibers by ozone or dichromate slightly increases the thermal conductivity, whereas surface treatment of the fibers by silane has negligible effect. For any of the formulations, silane-treated silica fume gives slightly lower (or essentially the same) thermal conductivity as as-received silica fume. Silane treatments of silica fume and of fibers contribute comparably to reducing the thermal conductivity. 4 Electrical behavior Figure 10.1 gives the volume electrical resistivity of composites at seven days of curing. The resistivity decreases much with increasing fiber volume fraction, whether a second filler (silica fume or sand) is present or not (Chen and Chung, 1995b). When sand is absent, the addition of silica fume decreases the resistivity at all fiber volume fractions except the highest volume fraction of 4.24%; the decrease is most significant at the lowest fiber volume fraction of 0.53%. When sand is present, the addition of silica fume similarly decreases the resistivity, such that the decrease is most significant at fiber volume fractions below 1%. When silica fume is absent, the addition of sand decreases the resistivity only when the fiber volume fraction is below about 0.5%; at high fiber volume fractions, the addition of sand even increases the resistivity due to the porosity induced by the sand. Thus, the addition of a second filler (silica fume or sand) that is essentially non-conducting decreases the resistivity of the composite only at low volume fractions of the carbon fibers and the maximum fiber volume fraction for the resistivity to decrease is larger when the particle size of the filler is smaller. The resistivity decrease is attributed to the improved fiber dispersion due to Figure 10.1 Variation of the volume electrical resistivity with carbon fiber volume fraction (Chen and Chung, 1995b). (a) Without sand, with methylcellulose, without silica fume; (b) Without sand, with methylcellulose, with silica fume; (c) With sand, with methylcellulose, without silica fume; (d) With sand, with methylcellulose, with silica fume. 1,000,000 100,000 10,000 1,000 100 Volume resistivity ( Ωcm), log scale 10 1 012 (b) Vol.% fibers (a) (d) (c) 345 © 2003 Taylor & Francis