This paper presents an experimental investigation on mechanical properties (including compressive strength, tensile splitting strength and fracture energy) of ultra-high performance concrete (UHPC) with recycled steel fiber, compared with none fiber and industrial steel fiber reinforced UHPC. Moreover, the microscopic observation of fracture energy was carried out. All specimens were prepared at 0.18 water /binder (W/B) ratio and the dosage of steel fiber was controlled at 60 kg/m3. The results indicate that recycled steel fiber has a significant effect on enhancing strength and toughness of UHPC. And owing to the crimped shape, higher tensile strength (1800-2000 MPa) and appropriate diameter (1 mm) of recycled steel fiber, the steel fibers of UHPRSFRC will not immediately be pulled off and necking phenomenon is distinct.

Recycled steel fiber processed from waste tires were used to prepare ultra-high-performance concrete. Ultra-high-performance concrete with normal industrial steel fiber and plain concrete without any steel fiber were also prepared for comparison. Experimental investigations were conducted to determine the mechanical properties of ultra-high-performance concretes, including compressive strength, splitting tensile strength, fracture energy and elastic modulus. Additionally, explosive spalling of concretes exposed to high temperature up to 800 °C was also tested. The recycled tire steel fiber could improve the fracture energy of concrete more significantly than normal industrial steel fiber. The splitting tensile strength of the recycled tire steel fiber reinforced concrete was also the highest among these concretes with various steel fibers. Moreover, the recycled steel fiber presented better behavior to resist the explosive spalling of the ultra-high-performance concrete. It is concluded that the recycled tire steel fiber help ultra-highperformance concrete possess higher toughness in terms of fracture energy and higher cracking resistance, so as to have higher resistance to thermally explosive cracking.Fourth International Conference on Sustainable Construction Materials and Technologies http://www.claisse.info/Proceedings.htm ** The data inside the brackets is the amount of the total specimens for each condition. That outside the brackets is the number of specimens suffered explosive spalling.

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