Experimental Study On Shrinkage Behavior Of Engineered Cementitious Composite With Polyvinyl Alcohol Fiber

The application of cement-based materials is limited because of its low tensile strength,easy cracking and difficulty in controlling cracks after cracking.With the continuous improvement of people's structural and functional requirements,the demand for improving the crack resistance of cement-based materials is increasingly strong.Under this demand,modified cement-based materials emerge as the times require.In recent years,in the research and application of modified cement-based materials,more and more attention has been paid to fiber-reinforced cement-based composites.Engineered Cementitious Composites with Polyvinyl Alcohol Fiber(PVA-ECC)is one of them.Polyvinyl alcohol(PVA)fiber has many advantages,such as high strength,high elastic modulus,acid resistance and alkali resistance.Adding it to cement-based materials can greatly improve the properties of the base material,improve its crack resistance,impermeability,impact toughness,durability,high temperature resistance and corrosion resistance,so it has attracted the attention of engineers in recent years and has become an engineering material.Material research is one of the hotspots,and has been applied in practical engineering in the United States,Japan and other countries.Shrinkage performance is an important performance of cement-based materials,which affects the deformation and durability of structural members.Meanwhile,the formulation of deformation calculation of structural members,non-linear finite element analysis,calculation of prestress loss and prediction of long-term shrinkage strain all depend on the research results of material shrinkage performance.However,the research on PVA-ECC materials by domestic and foreign scholars mainly focuses on mechanical properties,durability,corrosion resistance and so on,while the research on its long-term shrinkage performance is still scarce.Based on this,the effects of volume fraction of PVA fiber,water-binder ratio,sand-binder ratio,curing environment,base material strength and sealing time on shrinkage strain and mass change rate of PVA-ECC were studied through 12 groups of specimens with different mix ratios.At the same time,the cubic compressive strength,prism compressive strength,splitting tensile strength and their relationships at different ages of PVA-ECC were also studied.Conversion relationship,draw the following conclusions:(1)The incorporation of PVA fibers can improve the deformation properties of ECC substrates,improve the compressive toughness of ECC,prevent the spalling of ECC substrates,and make ECC "broken but not dispersed" when subjected to compression.(2)Within the scope of this test,the compressive strength of PVA-ECC cube and prism decreases with the increase of volume fraction and water-binder ratio of PVA fibers,and increases with the increase of sand-binder ratio.The splitting tensile strength of specimens can be significantly improved by adding PVA fibers.The conversion relationship between the cubic compressive strength of PVA-ECC material and the compressive strength of prism and splitting tensile strength of PVA-ECC material at the curing age of 7 days and 28 days is proposed.(3)The addition of PVA fibers inhibits the shrinkage of ECC substrates,but the effect is not obvious.Within the test range,the shrinkage strain of PVA-ECC decreases with the increase of volume fraction of PVA fiber,increases with the increase of water-binder ratio,and decreases with the increase of sand-binder ratio.(4)The shrinkage of PVA-ECC is greatly affected by different curing environments.The lower the humidity of surrounding media,the greater the shrinkage strain.Although different environmental conditions have great influence on shrinkage strain,the law of development of shrinkage strain is the same,and the form of shrinkage strain-time curve is similar.(5)The shrinkage strain of PVA-ECC increases with the increase of sealing time under different sealing time.The shrinkage strain decreases with the increase of sealing time,but the trend of shrinkage strain-time curve of the sealing group is the same as that of the non-sealing group.(6)By regression analysis of experimental data,a shrinkage estimation model of PVA-ECC material is given.The calculated value of the model agrees well with the experimental value.The research results in this paper can lay a foundation for the follow-up study of PVA-ECC materials,and provide theoretical basis and reference for the practical engineering application of PVA-ECC materials.