Study On Dispersion Technology Of PVA Fiber Bundles In Cement-based Composites Based On Surface Action

Cement base material has many excellent physical and mechanical performance indexes,especially strong compressive ability.However,due to its significant shortcomings-low tensile strength and poor crack resistance in the use of actual engineering materials,it is subject to many restrictions.Fiber-reinforced cement-based composite materials greatly improve the strength and crack resistance of concrete.However,a large number of studies have shown that the effective crack resistance and toughness of the fiber depend on the dispersion of the fiber in the cement substrate.Therefore,how to improve the uniformity of fiber dispersion in the cement substrate and give full play to the fiber's crack resistance is the focus of research.Through the analysis of the surface effect of PVA fiber and powder dispersant,the powder material with higher surface energy is used as the dispersant to study the dispersion method of PVA fiber bundles,and through a large number of laboratory tests and theoretical analysis,it is proposed that PVA fiber is used in cement-based materials The distribution uniformity evaluation method and evaluation index,combined with the performance test of PVA fiber cement-based materials and the distribution uniformity test of PVA fiber,analyze and put forward the influence relationship of PVA fiber dispersion on the performance of cement-based materials.The main research conclusions of this paper are as follows:1)Based on the analysis of the surface characteristics and interaction of PVA fiber and powder,it is proposed to use higher surface energy powder as a dispersant,and add the powder to the PVA fiber bundle according to a specific mixing process to achieve PVA Fiber bundle dispersion technology;a new type of horizontal biaxial stirring disperser was developed,and the reasonable stirring time and the amount of dispersed powder were determined through simulation analysis and laboratory experiments.2)The gray matrix characteristic parameter method and the quality variation coefficient method are proposed to evaluate the dispersion uniformity of PVA fibers in the fiber and powder mixture;the angle second moment,entropy and quality variation coefficient are used as the evaluation indicators for the PVA dispersion uniformity;It is proposed to use scanning electron microscope image processing method to analyze the uniformity of fiber dispersion in cement-based composite materials.The relative dispersion coefficient and dispersion coefficient of PVA fiber distribution are used as the evaluation index of the dispersion uniformity of PVA fiber,and the evaluation index is verified by experiments.3)Through the PVA fiber dispersion test,the statistical analysis of the number of PVA fiber filaments in the cross section of the cement paste specimen shows that the number of PVA fiber filaments in each area of the cross section is normally distributed.The relative dispersion coefficient of PVA fibers is used as the PVA fiber in the cement paste test.The distribution uniformity index in the piece is evaluated.Through the PVA fiber dispersion test,the number of PVA fiber clusters in the cross section of the specimen is statistically analyzed,and the PVA fiber dispersion coefficient is proposed as the index of the dispersion uniformity of the PVA fiber in the cement paste specimen for evaluation.4)Based on the surface characteristics of PVA fiber and powder,through the PVA fiber dispersion technology test,combined with the surface free energy theory,the PVA fiber dispersion index(relative dispersion coefficient,dispersion coefficient)and the powder characteristic parameters(powder number average particle size)are analyzed.The correlation between fiber diameter,particle size distribution width index,and bonding ratio)reveals the exponential relationship between the fiber dispersion index and the powder number average particle size and particle size distribution width index,and the logarithmic relationship with the bonding ratio.5)Through the mechanical test of PVA fiber-reinforced cement-based composites,the correlation between the mechanical properties of fiber-reinforced cement-based composites(flexural strength,fracture toughness,fracture energy,and fiber dispersion index(relative dispersion coefficient dispersion coefficient),respectively,was analyzed.The exponential relationship between the flexural strength,fracture toughness and fracture energy of cement mortar specimens and the relative dispersion coefficient and dispersion coefficient of the fiber were revealed.