Study On Preparation And Performance Of Circularly Aligned Steel Fiber Reinforced Cement-based Pressure Pipes

Concrete pipes are widely used in municipal water supply and drainage engineering.Since concrete is brittle material and is easy to crack.When concrete pipes buried underground in the process of using once cracking,corrosive sewage,such as sewage and industrial waste water,which are transported by pipe may cause leakage and pollute the surrounding soil.And it is a threat to environment security.Therefore,it has great significance to improve the bearing capacity and ductility of the concrete pipe in order to prevent leakage.Compared with concrete pipe,steel fiber reinforced concrete pipe(SFRC)has high bearing capacity and ductility.However,in ordinary SFRC pipes,randomly distributed steel fibers have arbitrary orientation and location.Among all fibers,only a few fibers have circular direction along the pipe,and it can not bear circular tensile stress effectively caused by the external and internal load.The fibers cannot give full play to strengthening and toughening.In this study,in order to improve the strengthening and toughening efficiency of steel fibers,an external circularly uniform magnetic field was applied to the process of preparing SFRC pipe specimen to make the fibers circularly distributed along the pipe.And then the circularly aligned steel fiber reinforced cement-based(ASFRC)pipe is prepared.The external and internal load test are carried out to investigate the external and internal mechanical properties of ASFRC and SFRC pipes.The main research work and achievements are as follows:(1)Investigated the preparation method of the ASFRC pipe.An external circularly uniform magnetic field was applied to the freshly mixed steel fiber reinforced cementitious composite to make the steel fiber along the pipe when the mold filled with cementitious composite was compacting on the vibration table.The ASFRC pipe was prepared when the matrix hardened.So the steel fiber orientation is in accordance with the force direction in the actual application process,which improves the reinforcing and toughening effect of the steel fiber.(2)Through the external and internal load test,the effect of fiber orientation,fibercontent,fiber type and matrix strength on the external and internal mechanical properties of ASFRC and SFRC pipe were analyzed quantitatively.The results show that,with increase of the fiber content and the matrix strength,the external and internal mechanical properties of ASFRC and SFRC pipes improve gradually.The reinforcement and toughening of the hooked steel fiber to the cementitious composite is larger than that of the cylindrical steel fiber.(3)Through the force analysis of the pipe under the action of external and internal load,the relationship between the external and internal load and the section stress of the pipe section are obtained,respectively.And the stress-strain constitutive relation of axial tension model and the flexural tensile strength model of ASFRC is obtained by the investigation of the pullout model of a single fiber,and combine with few steel fibers.The external load bearing capacity model and internal load-strain relationship model of ASFRC and SFRC pipe are established after combining the force analysis results and considering the fiber orientation efficiency factor,The applicability and accuracy of the model was verified by the comparison between the test results and the model results.