Explosive Spalling of Concrete Columns with Steel and Polypropylene Fibres Subjected To Severe Fire

The exposure of concrete elements to high temperatures during fire can cause major risk to life safety and to the serviceability of a building. One of the main reasons for this is due to concrete spalling which caused by pore pressure and thermal stresses. Previous research has indicated that the inclusion of polypropylene fibres to concrete reduces explosive spalling. However, concrete containing polypropylene fibre can still be vulnerable to explosive spalling during fire. This paper presents the outcomes of a research investigating the effect of using steel fibres in addition to polypropylene fibres to reduce explosive spalling of concrete. The experimental part of this study evaluates the performance of six normal strength columns under a loading ratio = 60% of the design capacity and subjected to severe heating rate higher than ISO 834. The columns were cast using various dosages of steel and polypropylene fibres. Analyses of the main findings included evaluation of the measured concrete temperatures along with axial displacement recordings. The analysis demonstrates a clear assessment of the spalling levels of the various representative specimens. The study also compares the experimental axial displacement with theoretical predictions using DIANA. Conclusions drawn from the study indicate that adding steel fibresalong with polypropylene fibres can reduce the degree and severity of spalling if compared with concrete containing polypropylene fibres only. The spalling degree was reduced from 22.03% to 12.41% in best case and from 14.95% to 10.49% in average when steel fibres were used with polypropylene fibres.