Effect Of Fiber On Creep Behavior Of Concrete

A variety of fiber reinforced concretes (FRC) are widely used in practical engineeringsince fibers can play a positive effect of ordinary concrete on the strengthening,toughening and crack arresting. As an inherent long-term deformation performance ofconcrete, creep exerts an important effect on concrete structure, particularly on prestressedconcrete structure. However, less work has been done about the effect of fibers, especiallyon horizontal contrast between different fibers, on creep behavior of concrete. And there isno research on predicting the long-term creep behavior by short-term performanceparameters of fiber and FRC. In order to improve the creep theory of FRC, thecompressive creep behavior of several kinds of FRC after1a had been comparativelystudied in this paper. The commonly used fibers selected in this paper, including steel fiber,polypropylene (PP) fiber, polypropylene macro-fiber, polyvinyl alcohol fiber and basaltfiber, have different elastic modulus. All the specimens are in the same test environment:controlled temperature (20±2)℃and humidity (60±5)%. By the use of ultrasoundtechnology and image processing method, the influence mechanism of fiber on creepbehavior was also analyzed.The results show that two aspects should be considered when we research the creepbehavior of FRC. They are the elastic modulus of fiber and internal defect of concrete. Thenew internal defect of concrete by the incorporation of fiber can increase creep of concrete.For concrete, fibers with elastic modulus lower than the contrast concrete will increase itsinternal defects, then increase creep deformation of concrete; while the creep would beinhibited by those fibers with a higher elastic modulus. But large amounts of interfacelayer between fiber and concrete matrix will weaken inhibition effect of fiber on creep,when the fiber is excessive. The test results also prove that steel fiber with a higher elasticmodulus can decrease the creep of concrete effectively. Compared to the contrast concrete,the specific creep of concrete with a steel fiber volume fraction of2%is decreased by25.1%after1a. When the steel fiber volume fraction is changed from2%to3%, theinhibition ability to creep of fiber becomes weaker instead of stronger. While as fiber content is7.5kg/m3, PP macro-fiber with a lower elastic modulus has a great influence oninternal defects of concrete. Compared with the contrast concrete, the specific creep of PPmacro-fiber reinforced concrete, increases by17.0%after1a.In addition,28d elastic modulus of FRC is the macroscopic reflection of variousfactors affecting concrete creep. And there is a high negative correlation between28delastic modulus and specific creep after1a of concrete. The higher28d elastic modulusof FRC is, the lower its long-term creep deformation is, and vice versa. Based on thispoint, comparing the short-term performance (28d elastic modulus) of FRC and contrastconcrete, the long-term creep behavior of FRC can be predicted.