Entire and Partial Heating Tests of High Strength Concrete Small Columns

The objective of this research is to clarify the reasons for explosive spalling of high strength concrete exposed to high heat flux during fire. The effect of moisture content and non-uniform heating was examined by ISO 834 standard fire tests. The specimens were small columns-shaped specimens (100x100x400 mm) made of 100 MPa compressive strength concrete. Two types of concrete mix design were applied. One is, with fibre reinforcement at 1.5 kg/m3 and the other is without fibre reinforcement. The moisture content was adjusted by differing the curing conditions either in water or in air. Resultant moisture content was 2.7-4.2% by weight for specimens cured in air, 4.1-5.0% by weight for specimens cured in water. The conditioned specimens were heated either partially (by two surfaces) or entirely (by four surfaces). The degree of spalling, shape of failure surfaces and fragments were analysed. Experimental results showed that severe spalling took place in the specimens without fibre, especially in case of partial heating. In case of fibre reinforced specimens, spalling was limited only to a small portion of surfaces. By the analysis of volume and weight loss, the effects of partial / total heating and moisture content were examined. The effect of partial heating dominates the overall tendency, while the effect of moisture content is important in the range of moisture content over 4% by weight. The result implies that the effect of thermal stress is dominant rather than the porepressure created by the evaporation of moisture.