Study On Frost Resistance Of Fiber Concrete In Cold Regions

The essential reason why a concrete structure fails prematurely and fails to reach its service life is not usually a strength problem,but its durability is insufficient.As a new composite material,fiber reinforced concrete improves the shortcomings of insufficient strength,toughness and durability of concrete.In recent years,a large number of fiber reinforced concrete(FRC)were applied in project,especially the frost resistance of FRC attracted more and more attention from scholars.This paper summarized the classic theory of concrete's freezing and thawing destruction property and the mechanism about how fiber affect and improve the frost resistance of the concrete.Analysis and discussion on frost resistance of fiber reinforced concrete under the effect of single factor and double factor.On this basis,this paper carried out freeze-thaw cycle tests using freeze-thaw media,fiber types and fiber content as parameters,and the surface damage forms and relative motions of fiber concrete under the action of single-factor and double-factor through rapid freeze-thaw method.Elastic modulus,mass loss rate,compressive strength,flexural strength,and flexural toughness were analyzed.A loading-chlorine-freezing-thawing synchronously coupled loading device was developed and applied to the experimental study of frost-resistant durability of fiber concrete under the influence of multiple factors.Finally,based on experimental research results,the comprehensive durability evaluation of different types of fiber concrete in the water and salt solution environment under the environment of water and salt solution was evaluated by the grey correlation theory,and finally the optimal fiber content was obtained.The main research work in this paper and the results achieved are as follows:(1)The fiber strength and freezing resistance durability of fiber reinforced concrete were studied under the influence of single factor with fiber content and mixing mode as influencing factors.The test results show that: steel fiber can greatly improve the mechanical properties of concrete,while polypropylene fiber does not improve the compressive strength and flexural strength of concrete,but the incorporation of polypropylene fiber makes the morphology of the concrete block more complete.The fiber has a certain improvement effect on the mass loss rate and the relative dynamic modulus of elasticity during the freeze-thaw cycles of concrete,but the incorporation of fibers has a range.If too much fiber is incorporated,it will not be conducive to the improvement of the antifreeze performance of concrete.(2)In the environment of chloride salt-freeze-thaw coupling,the surface erosion and internal damage of fiber concrete are both severe when the fiber is frozen and thawed under thesame number of times.On the basis of the test,the mechanism of the resistance of the chlorideion to the frost-resistant durability of the fiber concrete was analyzed.It was concluded that the erosion of the chloride ions caused the mass loss rate and the relative dynamic elastic modulus of the concrete to decrease during the freeze-thaw cycle have changed,but the freeze-thaw damage mechanism of concrete has not changed.(3)Based on the original research,load-chlorine-freezing-thawing and synchronous coupling loading device was developed to study the frost resistance durability of fiber concrete under multiple factors.The test results show that when the concrete mass loss rate does not exceed 5%,its relative dynamic elastic modulus has dropped to zero.It shows that the chloride ion and the freeze-thaw cycle are the main factors that cause the surface of the fiber concrete to peel off and reduce the weight,and the load is the main reason that leads to the internal destruction of the fiber concrete.(4)Based on the research results of the previous experiments,a comprehensive evaluation of the durability of fiber reinforced concrete was carried out using the grey relational theory.It is considered that the anti-freeze durability of hybrid fiber reinforced concrete SPF1+40 is the best,which is in good agreement with the test results.