Optimum dosage of PP fiber for the spalling control of high strength reinforced concrete columns

Spalling is defined as damages to concrete exposed to high temperature during fire, causing cracks and localized bursting of small pieces of concrete. As the concrete strength increases, the degree of damage caused by spalling becomes more serious due to impaired permeability. It has been reported that polypropylene(PP) fiber has an important role in protecting concrete from spalling, and the optimum dosage of PP fiber is 0.2%. However, this result was based on the fire test of non-reinforced concrete specimens. The high-temperature behavior of high-strength reinforced concrete columns with various concrete strength and various quantity of PP fibers is investigated in this study. The results revealed that the ratio of unstressed residual strength of columns increased as the concrete strength increased and as the quantity of PP fiber increased from 0% to 0.2% the residual strength of columns increase. However, the effect of PP fiber quantity on residual strength of column was barely above 0.2%.