Experimental Study On Mechanical Properties And Durability Of Whisker-toughened Hybrid Fiber Concrete

In view of the harsh service environment of concrete buildings and structures in northwestern China,the environment in which chloride ions and sulfate ions exist in large quantities and vary in concentration,concrete service in this environment is prone to swelling,cracking and other damage,resulting in strength loss and ultimately leading to concrete damage.At the same time,the northwest of China is located in the high latitude area,concrete will also be subject to freeze-thaw erosion damage,resulting in more complex concrete damage mechanism.Therefore,this paper chooses to carry out the study of mechanical properties,frost resistance degradation law,degradation mechanism and service life of plain concrete(PC),single fiber concrete(XC,WC),mixed fiber concrete(XWC),whisker-toughened mixed fiber concrete(JXWC2)concrete under the joint action of freeze-thaw cycles and chloride salt and sulfate erosion.This paper adopts the analysis method of macroscopic test to analyze the laws and microscopic test to get the basis to study the mechanical strength of different concrete and the mode of fiber action respectively;the degradation law,degradation mechanism and service life of concrete under the coupled salt and frost environment are studied;the prediction model of service life of concrete under chloride salt and sulfate attack is established by combining with Webb distribution.The main contents of the study are as follows.1.Concrete with strength grade C30 and water-cement ratio of 0.42 was prepared as a reference group,on the basis of which single fiber concrete(basalt fiber concrete(XC)and reticulated polypropylene fiber concrete(WC)with 0.6% volume admixture),and mixed fiber concrete(XWC with 0.6% basalt and 0.6% reticulated polypropylene fiber by volume admixture)were prepared.JXWC was subsequently prepared by adding whiskers with 2.0%,2.5%,3.0%,and 3.5% doping into XWC.damage morphology,composition,microscopic morphology,and pore structure changes of PC and JXWC were analyzed by means of Hopkinson pressure bar,nuclear magnetic resonance,field emission scanning electron microscopy,and thermogravimetric-differential thermal test;and on the basis of gray model based on the pore structure parameters and pore size percentage distribution,a concrete strength prediction model was established.2.The concrete groups after curing were compared horizontally to study the mode of action of fibers in concrete,and the mode of action of various fibers in concrete was analyzed with the help of Hopkinson pressure bar,nuclear magnetic resonance,field emission scanning electron microscope,etc.The influence factors on the pore distribution were analyzed,and the fiber action model of concrete was obtained with the help of Monte Carlo random distribution model.3.This paper simulates the actual working conditions with 7 kinds of solutions,based on the freeze-thaw durability test under the action of different kinds of salt and different concentrations of salt solution,and systematically studies the damage law and mechanism of PC and JXWC2,and comprehensively analyzes the influence of different kinds of salt,different salt concentrations and different number of freeze-thaw cycles on the mass loss rate and relative dynamic elastic modulus of two kinds of concrete,and obtains the relationship between the deterioration of concrete performance with the concentration of salt solution and The relationship between the salt solution concentration and freeze-thaw cycles was obtained.Based on the freeze-thaw test,the service life of concrete in the salt-freezing environment in Northwest China was predicted based on the Webb distribution based on the damage principle.