Experimental Study On Creep Properties Of PVA Fiber Reinforced Cementitious Composites

Polyvinyl alcohol fiber is a kind of high strength,high elastic modulus,water soluble fiber,which added to cement-based materials to form PVA-Engineered Cementitious Composites(abbreviated PVA-ECC).PVA-ECC has good ductility,crack resistance,impact toughness and the characteristics of strain hardening,which ultimate tensile strain can reach 3%.The addition of PVA fiber can prevent material fracture and flaking off,improve the poor crack tensile property and fragility of traditional cement-based materials,increase the impervious performance,frost resistance and carbonation resistance of cement-based materials,improve the durability of components.As a consequence,PVA-ECC attracts more and more attention from the engineering community and becomes research hotspot in recent years.Creep is an important mechanical property of cement materials,it has an great influence on mechanical behavior of component.Simultaneously,the deformation computation of component and nonlinear finite element method rely on the research results of materials.At the moment,most of research on PVA-ECC is about short-term mechanical behavior,studies on its creep performance are rarely reported in literatures.In this,the 20 group compression tests,5 group compressive elastic modulus and Poisson ratio tests,5 group shrinkage experiment and 13 group compressive creep tests are taken to research the compressive behavior,constitutive relation and creep performance of PVA-ECC.The follow conclusions can be made:(1)In the process of compression,PVA fiber can increase the specimens' deformation behavior,improve the specimens' compressive ductility and prevent material flaking off.The specimen has the characteristics of broken and not scattered in the destruction.(2)The compressive elastic modulus of PVA-ECC are 19.512~22.800 GPa in test condition,reducing with the increase of fiber volume fraction.Numerous concrete elastic modulus computational formula are not appropriate for PVA-ECC,the article proposes the reduction formula between elastic modulus and compressive strength.Composite elastic modulus calculation models are corrected through the test results,and the calculation models for PVA-ECC are given.(3)PVA fiber has little effect on the Poisson ratio of specimens,Poisson ratiosare 0.19~0.20 in test condition.(4)The addition of PVA fiber reduce the shrinkage compared with fibrous specimens.Shrinkage is more sensitive to temperature and humidity changes in the surroundings compared with creep.(5)The creep of PVA-ECC is rising with the increase of loading time,while the rising rate of creep is reducing with the increase of loading time.The creep of PVA-ECC is rising with the increase of fiber volume fraction and load stress,reducing with the increase of loading age on the whole.(6)By means of regression analysis of test data,Nelder hyperbolic power function model for PVA-ECC creep calculation has been obtained,the model calculation value agrees well with the experimental value.The results of this study provide theoretical basis and references for the use of PVA-ECC in engineering.