Impact resistance of fiber reinforced concrete at subnormal temperatures

One of the major advantages of reinforcing cement-based materials with randomly distributed fibers is in the improved resistance to dynamic loads. Unfortunately, however; this property of fiber reinforced concrete also happens To be the least understood. While this understanding is critical when designing structures subjected to impact and impulsively applied loads, it is also equally useful while developing better performing fiber reinforced cement composites. In this paper; impact resistance of fiber reinforced concrete was measured using a newly designed drop weight impact machine at two ambient temperatures of 22 degrees C and -50 degrees C. Two hammer approach velocities of 2.42 and 3.43 mis were investigated. Large, deformed macro-fibers of steel, and fine micro-fibers of steel and carbon were investigated at various fiber volume fractions of up to 2%. Hybrid composites with a combination of macro and micro fibers were also investigated Results indicate that at a given fiber volume fraction, macro-fibers of steel are far more effective in improving the toughness than micro-fibers, hut composites with a hybrid combination of macro and micro fibers are the toughest. Fiber reinforced composites are marginally more impact resistant at a higher hammer velocity, but absorb somewhat diminished amounts of impact energy at a subnormal temperature. Contrary to prevalent belief, however no particular reduction in the stress-rate sensitivity was observed at subnormal temperatures. (C) 1998 Elsevier Science Ltd. All rights reserved.