Effects of elevated temperature and water re-curing on the compression behavior of hybrid fiber reinforced concrete

Over the past decades, the effect of elevated temperatures on the mechanical properties of concrete has received significant attention because of the importance for fireproof design, safety evaluation and repair of fire damaged constructions. However, very few researches have been dedicated to the consequences of water re-curing of a thermally damaged concrete. In this paper, the effect of elevated temperatures and water re-curing on the mechanical response of two hybrid fiber reinforced concretes was investigated. For the first hybrid reinforced mix, long hooked-end and medium hooked-end steel fibers were adopted, as well as high strength short wave shaped steel fibers. In the second mix, polypropylene fibers substituted the short-wave shaped steel fibers. The mechanical behavior in compression was studied by measuring the stress-strain response. The elevated temperatures above 200 °C decreased: Young's modulus, compressive strength and toughness of the hybrid fiber reinforced concretes. The stable crack growth stage was reduced with the increase of the temperature above 200 °C, with an extension of the unstable crack growth stage for both kinds of hybrid fiber reinforced concrete. Water re-curing partially recovered Young's modulus, compressive strength, toughness, and extended the stable crack growth. An existing model was modified for predicting the stress-strain response of thermally damaged hybrid fiber reinforced concrete.