| The uniformity of the carbon fiber in the cement-based material determines the excellent performance of the carbon fiber cement mortar composite.The uniformity of the carbon fiber network is closely related to the spatial distribution of the fiber.Research and engineering use requires a dispersion evaluation method that can accurately express the spatial relative position of carbon fibers,guide the analysis of carbon fiber dispersion and material properties quantitatively,optimize the dispersion coefficient of carbon fibers,and improve the utilization of carbon fibers.In this paper,the nearest-neighbor distance statistical method is used to evaluate the distribution of carbon fibers in the cement base,and the mean distance dispersion coefficient and mean distance uniformity coefficient are established to synergistically compare the dispersion uniformity of carbon fibers.Based on the dispersion coefficient,the effects of different dispersion time,dispersant,volume ratio of coarse silica sand,and silica fume content on the dispersion of carbon fibers were explored.The main research work and conclusions are as follows:(1)A dispersion quantization algorithm was developed to express the spatial relative position of carbon fibers,and the mean distance dispersion coefficient and mean distance uniformity coefficient were established.The applicability of the method in evaluating the dispersion of carbon fibers in cement-based materials was verified by the results of different dispersion time experiments.(2)The effects of different dispersion times on the dispersion uniformity of carbon fiber were compared.The results show that the process resistivity,resistivity growth value,mean distance dispersion coefficient and mean distance uniformity coefficient are the best when silica sand,cement and carbon fiber are mixed for dry dispersion for 3minutes and water reducing agent and defoamer are added for continuous dispersion for3 minutes.(3)The dispersion quantification method was used to compare the effect of 1.5g /L carboxymethyl cellulose,methyl cellulose and hydroxyethyl cellulose on carbon fiber dispersion.Methylcellulose is better than hydroxyethyl cellulose.However,the change of resistivity and resistivity growth value indicated that after the surface modification of dispersant,the resistance of the carbon fiber interface changed and the action proportion of each conductive form of the matrix changed.(4)The volume ratio of coarse silica sand to fine silica sand increases,the mean distance dispersion coefficient increases,and the mean distance uniformity coefficient decreases.Moreover,the resistivity and resistivity stability also indicate that the carbonfiber dispersion effect is increased,and the results are optimal when the coarse silica sand completely replaces the fine silica sand.Comparing the change in compressive strength and flexural strength,the strength is more closely related to the dense uniformity of the material.(5)5% cement quality silica fume optimizes the average dispersion coefficient and variance dispersion coefficient of carbon fibers,while improving the flexural and compressive strength.The optimization of the electrical and mechanical properties of5% silica fume and coarse silica sand carbon fiber cement mortar is most obvious. |
