Study On The Mechanical Properties And Plastic Deformation Mechanism Of Fiber Spherical Aggregate Concrete

The cement-based material represented by concrete has excellent mechanical strength,low cost and simple preparation method,but the material is brittle and porous,low toughness,which is easy to crack and damage,and short service cycle.As the main material to provide rigid support in concrete,stone itself does not have any elastic and plastic deformation ability,is the main reason for the brittle performance of concrete.In this thesis,a kind of fiber-cement spherical aggregate with plastic deformation ability was prepared by the method of fiber granulation.Through the mechanical anchorage of the fiber inside the spherical aggregate and the integration of the bond interface between the spherical aggregate and the concrete matrix,the multi-scale strengthening of the dual interface bonding property of "fiber-plasticized aggregate and concrete matrix" was achieved.The plastic spherical aggregate is used to replace the traditional rigid aggregate,and the flexible energy dissipation and rigid support function of the spherical aggregate are given full play to realize the cooperative optimization of the mechanical strength and deformation performance of concrete.This thesis carries out innovative research in the following aspects:(1)Research on the development and plasticizing mechanism of fiber spherical aggregateBased on fiber dispersion,cylinder compression strength,failure morphology and deformation capacity of fiber spherical aggregate,fiber spherical aggregate with both stiffness and deformation capacity was developed to replace traditional coarse aggregate based on the basic requirements of 1h water absorption,bulk density and porosity of fiber spherical aggregate.The results showed that the dispersion of polypropylene fiber(PP)and polyvinyl alcohol fiber(PVA)in spherical aggregate was good,and the prepared polypropylene fiber spherical aggregate(PPA)and polyvinyl alcohol fiber spherical aggregate(PVAA)had excellent mechanical properties and plastic deformation ability.Therefore,PPA and PVAA are selected in this chapter to replace the traditional coarse aggregate.(2)Study on strengthening and toughening mechanism of fiber spherical aggregate concreteUsing PPA and PVAA to prepare fiber spherical aggregate concrete PPAC and PVAAC,the flexural strength and compressive strength of fiber spherical aggregate concrete under different fiber size and dosage were studied.It is found that the 28 d flexural strength of fiber spherical aggregate concrete is significantly improved compared with ordinary concrete: the flexural strength of PPAC and PVAAC increases by 11.75 MPa and 10.54 MPa,respectively,when the dosage is ≥1.5%.Compared with ordinary concrete,the compressive strength of PVAAC also improved slightly: the compressive strength of Pv Aac gradually increased with the increase of fiber size.The compressive strength of PPAC increased greatly when the fiber content was more than1.0%,and the growth rates were 15.78%,11.17% and 18.1%,respectively.(3)Study on the strengthening and toughening mechanism of the dual interface of "fiber-plasticized aggregate-concrete matrix"SEM was used to compare and observe the anchorage of fiber in aggregate and the morphology of the bonding interface between fiber spherical aggregate and concrete matrix.The strengthening and toughening mechanism of fiber on aggregate and the strengthening and toughening effect on concrete strength combined with interface integration were studied.The results show that there is a strong mechanical adhesion between PP and aggregate matrix,and PVA can overcome the problem of rapid crack expansion mainly through sliding friction resistance and its own tensile toughness,which can significantly improve the toughness and deformation ability of concrete.There is no obvious interface between the spherical aggregate and the concrete matrix,and the integrated bonding interface strengthens the bonding strength between the aggregate and the concrete matrix,so that the aggregate and the matrix can cooperate to deform when the concrete is bending.(4)Study on plastic deformation mechanism of fiber spherical aggregate concreteBy studying the stress-strain curve of fiber spherical aggregate concrete,the energy loss,peak stress,residual stress,peak strain and residual strain in the compression process of fiber spherical aggregate concrete are analyzed,and the influence of fiber spherical aggregate on the plastic deformation capacity of concrete is studied.It is found that the stress-strain curve of fiber spherical aggregate concrete has a plateau section at the peak point,and the descending section is more gentle and the extension stage is longer.The ultimate deformation capacity of concrete is consistent with the change law of energy dissipation in the whole process.The plastic deformation capacity of PPAC and PVAAC reaches the optimal value at 1.5% content in both the peak failure stage and the post-peak deformation stage of concrete.(5)Study on failure mode and extrusion deformation mechanism of fiber spherical aggregate concreteBy observing the final failure mode of ordinary concrete and fiber spherical aggregate concrete and the failure form of internal aggregate,the plasticizer mechanism of plastic aggregate to achieve compressive deformation of concrete is analyzed.The results show that the ductile aggregate concrete has a large deformation during the failure process,and the aggregate and matrix still maintain an integrated structure during the failure.The fiber transfers the energy gathered at the aggregate contact point to the fiber tip,and the aggregate contact point becomes a local plastic extrusion surface.It overcomes the problem that the brittle fracture of rigid aggregate causes the rapid destruction of the whole concrete structure and makes concrete have the capacity of plastic compressive strain.There are 57 figures,27 tables and 100 references.