Study On The Influence Of The Dispersion Of PVA Fibers On The Properties Of Cement-based Composites

As the most widely used basic engineering materials for large-scale engineering construction in China,cement-based materials have the characteristics of high strength,high rigidity,strong anti scour ability and good integrity,which can effectively bear and transfer external loads.However,cement-based materials lack of excellent ductility and crack resistance,which affects their service performance and life,enhances the toughness of cement-based materials,and improves their mechanical properties,crack resistance and fatigue performance.Adding PVA fibers into cement-based materials to make them composite is an effective way to improve the performance of materials,but the degree of dispersion uniformity of PVA fibers in cement-based materials has a significant impact on its mechanical properties,crack resistance and fatigue life.Therefore,it is very important to study the dispersion of PVA fibers in cement-based materials.In this paper,two kinds of inorganic dispersants,fly ash and cement,and different mixing time were used to disperse PVA fibers,and PVA fibers were separated by dry sieving and wet washing.Secondly,the gray level co-occurrence matrix image processing method and the mass average weight method are used to detect the PVA fibers.The image entropy and the angular second-order moment of the fibers surface texture are analyzed by MATLAB programming,and the image entropy and the angular second-order moment are used to characterize the dispersion degree of the fibers bundle.At the same time,the mass average weight method is used to study the influence of different mass ratios on the variation coefficient of PVA fibers mean,The dispersion degree of the fibers bundle was characterized by the coefficient of variation of the fibers mean.Then,the mathematical model of one-way ANOVA is established to test the significant influence of different factors and their levels on the dispersion degree of PVA fibers,and the relationship between the image entropy and the second-order moment of angle and the dispersion degree of PVA fibers is obtained;the relationship between the variation coefficient of PVA fibers mean and the dispersion degree is analyzed,and the gray level co-occurrence matrix image processing method is verified and analyzed;finally,the indoor co-occurrence matrix image processing method is used The relationship among compressive strength,flexural strength,fracture energy of cement mortar,compressive strength,splitting strength of cement stabilized macadam and PVA fibers dispersion was studied.The fibers dispersion test results show that fly ash can effectively promote the dispersion of PVA fibers,and the image entropy and angular second-order moment can effectively characterize the degree of fibers dispersion.The image entropy increases with the increase in the mass ratio of fly ash to PVA fibers.When the mass ratio is 50,the image entropy and the PVA fibers bundle are evenly dispersed in the cement-based material.The best setting parameters of the pure pulp agitator are obtained by research:the rotation speed of the stirring blade is,the revolution speed is,the stirring time and the mass ratio are 3 min and 50,respectively,at this time the image entropy=2.0963,the PVA fibers can Evenly dispersed.By studying the effect of the degree of dispersion of PVA fibers on the properties of cement-based composites,it is known that the fracture energy and flexural strength of cement mortar when PVA fibers are uniformly dispersed have increased by about 36.9%and 16.9%,respectively,compared to when the fibers are not uniformly dispersed,the ordinary cement mortar has increased by about 72.0%and 17.5%respectively.The compressive strength and splitting strength of cement stabilized crushed stone when the PVA fibers are uniformly dispersed have increased by about 5%and 5.5%,respectively,compared with that when the fibers are not uniformly dispersed.Cement stabilized macadam has increased by approximately 16.5%and 24.2%respectively.At the same curing age and when the entropy is the same,the compressive strength and splitting strength of cement stabilized macadam with the PVA fibers content of 0.9 kg/m~3 are better than The compressive strength and splitting strength of cement stabilized macadam with PVA fibers content of 0.6 kg/m~3.