Experimental Research of Crack Resistance of Hybrid Fiber Reinforced Concrete at Early Age

The mix proportions of hybrid fiber reinforced concrete with strength grades of CF40 and CF50 were designed according to the superposition mix design method,in which five levels of the polypropylene fiber content were selected in the range from 0.3 kg/m3 to 1.5 kg/m3 with the increment of 0.3 kg/m3 as the volume fraction of steel fiber was constant at 1.0%,and four levels of volume fraction of steel fiber were chosen in the range from 0.5% to 2.0% with the increment of 0.5% as the content of polypropylene fiber was kept in 0.9 kg/m3.The effects of different contents of fiber on the crack resistance of concrete at early age and the crack states variation of specimens were studied.The results showed that the hybrid of steel fiber and polypropylene fiber had coupling effects on improving the crack resistance of concrete at early age,and the crack resistance raised with the increase of fiber contents.The results also indicated that there were the rational and effective values of the volume fraction of steel fiber and the content of polypropylene fiber,and the fiber hybrid could collaboratively prevent and limit the cracks,which made thin and short cracks change into wide and long shape.