Microstructural and mechanical effects of latex, methylcellulose, and silica fume on carbon fiber reinforced cement

The effect of methylcellulose, silica fume, and latex on the degree of dispersion of short carbon fibers in cement paste (with water-reducing agent in an amount varying from 0 to 3 percent by weight of cement) was assessed. This degree, as indicated by the ratio of the measured volume of electrical conductivity to the calculated value, and the effectiveness of the fibers in enhancing the tensile/flexural properties attained by using methylcellulose and silica fume were higher than those attained by using methylcellulose alone or latex. Methylcellulose was superior to latex in giving a high degree of fiber dispersion at fiber volume fractions < 1 perscent, as measured by this technique, but latex resulted in superior tensile-flexural properties and lower content and size of air voids than methylcellulose. With the fiber content fixed at 0.53 vol. percent, the degree of fiber dispersion, as measured by this technique, decreased with increasing latex-cement ratio from 0.05 to 0.30, while the void content aatained a minimum at an intermediate latex-cement ratio of 0.15. As a result of the former, the flexural toughness decreased monotonically with increasing latex-cement ratio. As a result of the latter, the flexural strength attained a maximum at an intermediate latex-cement ratio of 0.15. In contrast, both flexural toughness and strength increased monotonically with increasing latex-cement ratio when fibers were absent.