ABSTRACT
High-strength concrete (HSC) columns were found to be more prone to explosive spalling due to their low permeability and high brittleness. Adding polypropylene fibers to the mix could be a solution since the fibers melt during the early stages of heating and create channels in the concrete. Hence, the water vapor finds an escape without causing spalling. Coating of concrete members with special mortars, e.g. perlite and vermiculite rendering, could be another solution since the coating works as an insulation, which prevents heat from penetrating to the heart of concrete. Previous researchers pointed out that the data on the effect of fire on the behavior of HSC loaded columns is scarce. In addition, the authors did not cite any literature on the effect of cooling regime on the fire behavior of HSC loaded columns. This paper presents an experimental program on the behavior of HSC columns with or without polypropylene fibers and/or those coated with perlite or vermiculite mortar under fire. The research includes testing seventeen reinforced HSC columns heated to 750°C for one hour under three loading levels (30%, 40% and 50% of the control specimen's ultimate load). To study the effect of cooling regime, the columns were left to cool in air or quenched by water. The results indicated that a preload level, not more than 40% of the columns' ultimate load, leaving the column to gradually cool in air, inclusion of polypropylene fibers and coating with perlite mortar greatly improved the residual capacity after fire. The column with the above specification had a capacity almost identical to the control column, which was not heated.
