Research On The Performance Of Hybrid Fiber Modified Desulfurized Gypsum-based Composite Cementitious Material

Desulfurization gypsum-based composite cementitious material(DGCCM)is an effective way to consume gypsum,but shortcomings such as poor toughness and water resistance limit its application.Adding fiber is an effective method to improve the toughness and water resistance of DGCCM.Most of the existing researches focus on the influence of single fiber on the mechanical and physical properties of gypsum,but lack the durability of gypsum and the properties of hybrid fibers gypsum.Basalt fiber(BF)and Polyvinyl alcohol fiber(PVAF)have good mechanical properties,corrosion resistance,and good bonding properties to matrix.Compared with PVAF,BF is rigid fiber,while PVAF is flexible fiber,with different performance.Therefore,in this paper,BF and PVAF were used to prepare fiber-desulphurized gypsum base composite cementitious material,and the effects of single BF or PVAF and mixed BF and PVAF on the mechanical properties,water resistance,and durability of the desulphurized gypsum-base composite cementitious material were studied.The main research contents are as follows.(1)Three lengths and five mixtures of BF or PVAF were used to set up a single factor test to explore the effect of single fiber on the mechanical properties,water resistance,and durability of DGCCM and the mechanism of action,and to analyze the macroscopic failure modes of samples after dry-wet cycles and freeze-thaw cycles.The results showed that the mechanical properties of DGCCM were not affected by BF of 6 mm,but were enhanced or improved by fibers of other lengths.The addition of BF or PVAF improved the internal structure of the matrix,made the structure more dense,the water absorption of the sample decreased,and the fiber could effectively inhibit the generation of a large number of cracks after the dry-wet cycle and freezethaw cycle.(2)The BF and PVAF with different length and content were mixed,and the orthogonal test of four factors and three levels was designed to study the influence of hybrid fibers length and content on the properties of DGCCM.The results showed that DGCCM exhibited good mechanical properties,water resistance,and durability when the both fibers were 12 mm.The influence of fiber content on the properties of DGCCM was higher than that of fiber length.(3)The orthogonal test of two factors and four levels was designed to study the influence of hybrid fibers content on the properties of DGCCM.The results showed that PVAF had a highly significant effect on the absolute dry flexural strength of DGCCM,but BF had no significant effect on it.Both PVAF and BF had highly significant effects on the absolute dry compressive strength of DGCCM.BF had a highly significant effect on the softening coefficient of DGCCM,PVAF had no significant effect on the softening coefficient of DGCCM,and BF had a significant effect on the freeze-thaw dissolution rate of DGCCM.