Preparation And Performance Study Of High Bulk Rate Glass Fibre Reinforced Cementitious Materials

Glass fiber reinforced cement-based composites（GRC）,as a relatively mature composite material,has the advantages of light weight,high strength,high plasticity and convenient processing,and has been widely used in various fields.With the continuous improvement of building quality and engineering requirements,GRC materials increasingly need to improve the strength,crack resistance,toughness and other properties,and increasing the fiber content is one of the effective ways.Glass fiber,as a reinforcing material with excellent performance,is used in various composites.In glass fiber reinforced resin matrix composites,the fiber volume ratio can reach 50%or even higher,while in cement-based materials,the fiber volume ratio usually does not exceed 5%.Therefore,it is necessary to consider the preparation process,macro performance and other factors to explore the maximum volume content of glass fiber in cement-based materials.This paper aims to explore the maximum volume fraction of glass fiber in cement-based materials,prepare new high-performance GRC materials,and study their properties.In this paper,the forming process of GRC material with high fiber volume fraction is designed;The flexural strength and compressive strength of GRC are determined through orthogonal test mix design.The effects of water binder ratio,cement sand ratio and fiber volume ratio on the basic mechanical properties of GRC materials are analyzed,and the optimal mix ratio is obtained.On this basis,the effects of glass fiber volume ratio and length on the basic mechanical properties of cement-based materials are deeply studied;The toughness including bending toughness and impact toughness was analyzed;Study the durability change rules of high fiber volume ratio GRC materials,such as frost resistance,chloride ion permeability resistance,carbonation resistance,etc.,improve the impact of high fiber volume ratio on the durability of GRC materials,and provide data support and theoretical reference for the subsequent practical engineering application of high fiber volume ratio GRC materials.By analyzing the fluidity of the mixture prepared by each fiber feeding sequence and the change law of the flexural and compressive strength of the test block after forming,the appropriate fiber feeding sequence is obtained.There is little difference in the fluidity of the mixture prepared by the fiber post mixing method and the water mixing method,but the mixing process of the fiber water mixing method is complex,so the fiber feeding sequence of the post mixing method as the GRC material with high fiber volume ratio is determined.The pressing method is used to assist the forming of high fiber volume ratio GRC materials.6 Mpa is determined as the forming pressure of the pressing method of high fiber volume ratio GRC materials by analyzing the bending strength,compressive strength and pore size distribution of the test block.The effects of water binder ratio,cement sand ratio and fiber volume ratio on the basic mechanical strength of GRC materials were studied by orthogonal test.The significance of each factor was explored by range analysis and variance analysis,and the optimal ratio of GRC materials was determined.The results show that the optimum mix proportion is water binder ratio 0.35,cement sand ratio 1:0.8 and glass fiber volume ratio 7%.The addition of high volume fraction glass fiber can significantly improve the basic mechanical properties of GRC materials;Among them,the maximum flexural strength can reach 38.6mpa,which is 2.4 times that of ordinary GRC materials,and the maximum compressive strength can reach 55.7 Mpa,which is1.4 times that of ordinary GRC materials.Through four point bending test and impact test,the influence of high volume fraction glass fiber on the toughness of GRC material was investigated.The results show that increasing the volume fraction of glass fiber can increase its bending toughness and impact toughness.When the fiber volume ratio is 0%,3%,5%,7%and 10%,the bending toughness index can reach I5,I10,I20,I30 and I30 respectively.The average value of i30 of GRC material with 7%fiber volume ratio can reach 47.82,and the ultimate strength can reach 11.73 Mpa,which is about 1.63～1.98 times that of traditional GRC material.Its bending toughness performance is the best.Under the impact load,the cracking and failure resistance of high fiber volume ratio GRC material has been significantly improved,and the impact toughness has been greatly improved.The average number of final crack failure of GRC material with 7%fiber volume ratio is 196.17 times,which is 3.2～17.8 times that of traditional GRC material.The impact ductility index is 48.04,which is about 3.8～33.4 times that of traditional GRC material.Its impact toughness performance is the best.Through freeze-thaw cycle test,electric flux test and carbonization test,the influence of high volume glass fiber on durability was explored.The results show that increasing the volume fraction of glass fiber can improve the durability of GRC materials,such as frost resistance,chloride ion penetration resistance and carbonation resistance.When the fiber volume ratio is7%,the mass loss rate of GRC material during freeze-thaw cycle is only 0.35%,the relative dynamic modulus is 92.4,the total electric flux in 6h is 976.23C,the carbonization depth in 28d is 1.13mm,and the drying shrinkage value in 56d is 683.47×10^-6,GRC material has the best durability performance..