Study On The Performance Of Fiber Regenerated Concrete Under Freeze-thaw Cycle

With the vigorous development of China's construction industry,concrete,as the building foundation material with the largest amount and the widest range of application,has produced a large amount of waste concrete.However,due to the defects of the waste concrete itself,the use scope is limited.The research and improvement of the waste concrete is a key step.China has a vast territory,and buildings in the north are affected by cold current all the year round.In this paper,the content of recycled aggregate was set at a constant value of 50%.The content of polypropylene fiber and steel fiber was the main factor of the study.The content of polypropylene was the mass fraction of 0kg/m~3,0.6kg/m~3,0.9kg/m~3,1.2kg/m~3,1.5kg/m~3and1.8kg/m~3.The content of steel fiber is 0%,1.2%,2%,2.8%and 3.6%of volume fraction.In order to solve the deformation performance of regenerated concrete caused by internal damage,this paper proves that regenerated concrete has better deformation performance under different freezing-thawing cycles by adding fiber to improve the density through experiments.The test block(150mm×150mm×150mm)and the test beam(80mm×160mm×900mm)were made respectively.The mass,dynamic elastic modulus,cube compressive strength,deflection,cracking moment,yield moment and freeze-thaw damage variables of the test block were analyzed under 0,25,50,75,100,150 fast freeze-thaw cycles.It provides a theoretical basis for the research on the deformation of fiber regenerated concrete under different freeze-thaw cycles.This paper mainly conducts the following research:(1)the variation rules of the mass,dynamic elastic modulus and compressive strength of the regenerated concrete test block under different polypropylene fiber and steel fiber content without freeze-thaw cycle.Polypropylene fiber recycled concrete has better deformation performance and steel fiber recycled concrete has higher strength.The theoretical and experimental values of deflection,cracking moment and yield moment of steel fiber regenerated concrete test beams are compared.The calculated value of deflection is close to that of test value,and the calculated value of cracking moment and yield moment is about 15%larger than that of test value.(2)under 150 times of rapid freeze-thaw cycle,the mass loss rate of recycled concrete exceeds 5%,exceeding the specification requirements.The maximum mass loss rate of steel fiber recycled concrete is 1.21%,and the maximum mass loss rate of polypropylene fiber recycled concrete is 3.42%,meeting the specification requirements.The dynamic elastic modulus of recycled concrete and fiber-recycled concrete both meet the"relative dynamic elastic modulus of the test block reaches 60%"in the specification.The loss rate of compressive strength of recycled concrete test blocks is greater than that of steel and polypropylene fiber test blocks.The cracking moment loss rate of regenerated concrete test beams is 79.5%,and the maximum cracking moment loss rate of polypropylene fiber and steel fiber regenerated concrete is 81%and 81.4%,which all meet the requirements of"the cracking moment should not be lower than 75%before freezing and thawing"in the code.The relative yield moment loss rates of recycled concrete and fiber-recycled concrete also meet the requirements of the code.(3)based on the test values of the fiber recycled concrete,the Aas-jakobeen damage model was determined.With the increase of the number of freeze-thaw cycles,the material parameters and linear regression were obtained to calculate the factors A,B,C,affecting the and the corresponding trend chart of material parameters was obtained.The theoretical study is consistent with the experimental conclusion,and the method can be used to analyze freeze-thaw damage.