The aim of this research is investigating the influential factors governing the level of concrete spalling at a material level. From the former research on concrete spalling under the fire conditions, many available mechanisms have been provided and recently, the spalling damage of concrete has been explained as a result of high inner pressure due to the evaporation of the water in concrete microstructure. Based on the spalling mechanism, this study prepared various concrete specimens made with different water-to-binder ratios, air contents, moisture contents, aggregate sizes, aggregate types and supplementary cementitious material (SCM) to investigate the governing factors on spalling of concrete. From the investigation, the factors which can cause pore connectivity, easiness of cracking, and moisture content of the concrete microstructure were governing factors on spalling damage. Therefore, in this research, based on the results of the investigation it was possible to provide critical factors on spalling damage of the concrete, and it is expected that the data obtained from this study can provide useful information for the design of fire resistant concrete.

Keywords: Concrete microstructure, Spalling, fire resistance, Pore connectivity, Inner cracking, Moisture content.