Effect of multi-scale polypropylene fiber hybridization on mechanical properties and microstructure of concrete at elevated temperatures

This paper presents results of an experimental study on the compressive and splitting tensile strength of plain concretes and concretes incorporated with macro, micro and hybrid polypropylene (PP) fibers at elevated temperatures (20 degrees C, 200 degrees C, 400 degrees C, 600 degrees C, and 800 degrees C). Nine series of concrete mixtures with different contents PP fibers were prepared and the optimum mixing proportion of different sizes of PP fibers was discussed. The results indicated that the multi-scale polypropylene fiber reinforced concrete (dropped with three different sizes of PP fibers into concrete) had the best positive hybrid effect on resisting to high temperature, when the total PP fiber content was 6 kg/m(3) and the macro PP fiber substitution was 80%. Meanwhile, the addition of macro PP fibers significantly enhanced the toughness of concrete. Compared with the value of plain concrete, the compressive and splitting tensile strength of the optimal multi-scale polypropylene fiber reinforced concrete at 800 degrees C increased 14% and 36% respectively.