Influence Of Fiber Type And Dosage On The Mechanical Properties And Permeability Of Concrete

Fiber can improve the mechanical properties,durability and the ability to withstand harsh environments of concrete.There are few studies addressing the effect of macro polyvinyl alcohol fiber on the properties of fiber reinforced concrete.Based on the current research status,this thesis takes three different macro fiber types(Steel fiber,modified polypropylene fiber and macro polyvinyl alcohol fiber)and macro fiber reinforced concrete with five different fiber dosages(0.6%,0.9%,1.2%,1.5%and 1.8%)as research objects.The research results in this thesis can provide references for the mixture design of concrete with macro fiber,and provide experimental support for the practical application of the electrical resistivity method to evaluate the permeability of fiber reinforced concrete.The main parts are as follows:(1)Applying variance analysis to study the essential influence of the types and dosages of macro fiber on fresh concrete's workability,hardened concrete's mechanical properties and permeability.The results indicate that:for the three types of macro fiber,steel fiber has a relatively prominent influence on various properties of concrete;for the two types of synthetic fibres in this thesis,there is a fairly weak influence on various properties of concrete,but the fiber dosages have a relatively big influence on most properties of the concrete.(2)Taking compressive test to concrete of different ages,getting different compressive strengths of fiber reinforced concrete of different ages and investigating the influences of different types and dosages of fiber on compressive strength of concrete.The results indicate that:steel fiber and macro polyvinyl alcohol fiber can strengthen the compressive strength,and modified polypropylene fiber has trifling influence on the compressive strength of concrete.(3)In order to test the bearing capacity of the macro fiber reinforced concrete after cracking,adopting bending test together with deflection test and taking flexural test aiming at 117 macro fiber reinforced concrete rectangular specimens of 100mm×l00mm×400mm,measuring the load-deflection curve of macro fiber reinforced concrete of different ages and analyzing the influence of different types and dosages of fiber on mechanical properties such as residual strength,toughness,and equivalent flexural strength ratio.The results indicate that:various mechanical property indexes of macro fiber reinforced concrete generally increase along with increasing fiber dosages.(4)Through rapid chloride migration test and electrical resistivity test for concrete of different ages,studying the influence of different types and dosages of fiber on concrete's permeability.The results indicate that:at early stage,macro fiber may decrease the permeability of concrete but it has little influence on permeability at later stage.(5)The experimental results are analyzed by fitting.The results indicate that:macro fiber dosages have relatively strong relationship with the workability of fresh concrete and part of the mechanical properties of hardened concrete.The relationship is a linear relation.There is a fairly strong relevance between macro fiber reinforced concrete electrical resistivity and chloride migration coefficients.