Research On Mechanical Properties Of Hybrid Short Fiber Reinforced Concrete Slab

Ordinary concrete is a brittle material with low tensile strength.Concrete members are tend to cracking in early-age and serviceability states,and the mechanical properties of the reinforcements would deteriorate when exposed to aggressive environments,resulting in a decrease in the durability of the concrete structure.The maintenance and reconstruction of reinforced concrete structures will cause serious environmental pollution and waste a lot of resources.Under the background that our country vigorously advocates improving energy utilization efficiency and promotes the building materials industry to reach the peak carbon dioxide emissions as soon as possible,it is particularly important to improve the durability of reinforced concrete structures.Fibers limit the development of cracks through the bonding between fiber and matrix,share part of the tensile force on the fracture surface,improve the tensile strength and toughness of the concrete,and reduce the crack width,thus enhancing the durability of reinforced concrete structures.At present,the fibers used in fiber reinforced concrete are mainly inorganic fibers such as steel fiber and glass fibers,and synthetic fibers such as polypropylene fibers.Steel fiber has high strength and high modulus of elasticity,but its specific gravity is large,and it is not easy to disperse uniformly in concrete;it is easy to rust in humid environment and corrosive environment.Glass fiber and polypropylene fiber have lower modulus of elasticity,after being mixed into concrete,it can obviously limit the plastic shrinkage in the early stage of concrete pouring,and the toughness after cracking is significantly improved;but its specific gravity is small,and it is easy to form agglomeration in concrete;and the high temperature resistance is poor.Using micro fiber to limit the development of micro cracks and macro fibers to limit the development of macro cracks,hybrid fiber reinforced concrete can have higher cracking strength,residual tensile strength and toughness at the same time.The application of hybrid fibers to flexural concrete members can significantly improve their crack resistance and bearing capacity.The purpose of this paper is to study the flexural properties of hybrid fiber reinforced concrete and reinforced hybrid basalt fiber reinforced concrete slabs.The research contents mainly include:1)Research on flexural properties of basalt fiber reinforced concrete.The test results show that micro fibers mainly limit the development of micro cracks and improve the crack resistance of concrete;macro fibers mainly limit the development of macro cracks and improve the post cracking performance of concrete.Under the combined effect of the positive and negative effects of fibers on concrete,there is an upper limit on the improvement of the tensile properties of concrete.The optimal length and volume content of micro fiber are smaller.Within the range selected in this paper,the optimal value of fiber length and volume content of micro basalt is15 mm and 0.75%;the optimal value of macro basalt fiber length and volume content is 45 mm and1.75%.2)Influence of fiber modulus of elasticity on flexural properties of fiber reinforced concrete.The results indicate that,under the same fiber length and volume content,the restricting effect on the crack development rise with the increase of fiber modulus of elasticity.For the same volume content and fiber length,the growth of cracking strength rise with the increase of micro fiber modulus of elasticity.And for the same volume content and fiber length,the growth of equivalent residual strength rise with the increase of macro fiber modulus of elasticity.3)Study on flexural properties of hybrid fiber reinforced concrete by fiber modulus of elasticity.Compare the effects of micro fiber and macro fiber with different modulus of elasticity on the crack resistance and post-cracking properties of hybrid fiber reinforced concrete,the research shows that the effect of fiber modulus of elasticity on the flexural properties of single fiber reinforced concrete and hybrid fiber concrete are similar.With the increase of micro fiber modulus of elasticity,cracking strength of the hybrid fiber reinforced concrete increases;with the increase of macro fiber modulus of elasticity,equivalent residual strength of hybrid fiber reinforced concrete rise.4)Research on flexural properties of reinforced hybrid fiber reinforced concrete slabs.After replacing the full-section concrete of the reinforced slab with hybrid fiber concrete,the micro fiber can limit the development of micro cracks,cracking load of the reinforced concrete slab is increased by 30%～50%.The macro fiber have a bridging effect on macro cracks and share part of the tensile force on the fracture surface,stiffness of the reinforced concrete slab after cracking is increased,the yield load is increased by 51.19% and the ultimate load is increased by 30%～35%.