Abstract:

In this paper,first,hybrid fiber-reinforced concrete was prepared by using the hybrid fiber of polyethylene fiber ( PE) and polypropylene plastic fiber ( HPP) .Then,the frost resistance of the reinforced concrete before and after the freeze-thaw process was investigated in terms of quality variation,dynamic elasticity modulus,compressive strength and flexural performance.Finally,the damage mechanism of the concrete was analyzed by using SEM analysis technique.The results show that ( 1) freeze-thaw cycles may cause obvious damage to plain concrete,and hybrid fiber can improve the integrity of concrete and decrease the surface damage; ( 2) the quality of plain concrete first increases and then decreases in the freeze-thaw cycle,while that of the hybrid fiber-reinforced concrete continuously increases; ( 3) the dynamic elastic modulus of the concrete with different proportions almost remains unchanged at first and then decreases; ( 4) after 300 freeze-thaw cycles,the relative dynamic elastic modulus of the concrete with a fiber content of 0. 8% + 1. 2% still keeps at 83. 63%; ( 5) the variation rule of compressive strength is similar to that of the dynamic elastic modulus; ( 6) the synergistic effect of fine-PE and coarse HPP fibers significantly improves the brittleness of concrete; ( 7) both the toughness index and the residual strength of hybrid fiber-reinforced concrete vary with the fiber content; ( 8) the prepared reinforced concrete is superior to the ideal elastic-plastic material when the hybrid fiber content is 0. 8% + 1. 2%; and ( 9) freeze-thaw cycles may result in certain damage to the flexural toughness,but still no brittle fracture appears,and the concrete still possesses good ductility.

Key words: cement concrete, hybrid fiber, frost resistance, flexural toughness, micro-structure