Effect Of Hybrid Fiber On Creep Behavior Of High-performance Concrete

High-performance concrete(HPC)can effectively improve the workability,mechanical properties and durability of concrete,but mineral admixtures added in HPC also negatively increase the brittleness of concrete.Previous studies have shown that the incorporation of fiber can improve ductility and toughness of concrete.At present,fiber reinforced concrete has been widely used in construction projects.Hybrid fiber-reinforced concrete(HFRC)is usually mixed with fibers of the same type but different in size or type,which enables the fibers to complement each other and effectively improve the performance of the concrete.Creep is the inherent deformation performance of concrete,and it is no exception for fiber concrete.Creep can be two to four times larger than the elastic strain,thus it may result in significant serviceability problems and even structure failure.There has formed a relatively complete theoretical system of the creep of ordinary concrete,however,there are few studies on creep properties of fiber concrete,especially hybrid fibers.And it is a lack of theoretical basis in practical engineering applications.Therefore,it is necessary to systematically reserarch the creep of fiber concrete.A total of eight mixtures were used to investigation the creep of steel fiber-reinforced concrete(SFRC),polypropylene fiber-reinforced concrete(PPFRC)and hybrid steelpolypropylene fiber-reinforced concrete(S-PPFRC)in this passage.And this paper make the the concrete mix ratio constant and add fibers in same volume.The specific fiber content are: steel fiber(0.5%、1.0%、1.5%),polypropylene fiber(0.1%)and hybrid steel-polypropylene fiber(0.5%+0.1%、1.0%+0.1%、1.5%+0.1%).Each group of concrete was cured up to 28 d,and they were placed in the creep room for measurement after being loaded.The creep of each group of concrete during 1 year was compared,and the infulence of fiber on the creep of HPC was analyzed.The main research results are as follows:(1)The results of mechanical tests show that the addition of steel fiber in HPC could lead in the increase of compressive strength,compared to the reduction of compressive streng with polypropylene fiber added.In addition,the incorporation of fibers has little effect on the elastic modulus of HPC.(2)The results of creep tests show that polypropylene fiber has a little of effect on the creep of HPC,With the increasing of the content of steel fiber,the inhibition effect of steel fiber on the creep of HPC showed the tendency that is ascension first and then declining.And the hybrid steel-polypropylene fiber greatly restrained creep of HPC.(3)Combined with the fiber spacing theory,this paper has employed ultrasonic testing technology and SEM scanning analysis.It found that: steel fiber and incorporation of polypropylene fiber can change the internal structure of HPC.On the one hand it can improve the inherent defects of concrete,on the other hand it also increasee the microscopic defects.The fiber distribution will be uneven when the fiber content is too large,which lead to the increase of concrete defects,thereby reduce the inhibition effect of the concrete creep.