EXPERIMENTAL STUDY ON FIRE RESISTANCE OF 200-300 MPA HIGH STRENGTH CONCRETE WITH SYNTHETIC FIBER AND STEEL FIBER

Abstract

High strength concrete columns are largely used for high-rise reinforced concrete buildings. Such concrete with low water to cement ratio has a dense structure and may experience explosive cover spalling when subjected to fire. The decrease of column cross-section could cause the steel reinforcements exposed to a high temperature at an early stage, and consequently, reduce the load-carrying capacity of the column. For 80 – 150MPa high strength concrete, we developed a method of suppressing the spalling behavior by adding a small number of synthetic fibers in 2000. Moreover, in 2009, we applied hybrid fibers of synthetic fibers and steel fibers to 120 – 200MPa high strength concrete. It is now common knowledge that adding both synthetic and steel fibers is indispensable for improving the fire resistance of the concrete with compressive strength more than 150MPa. However, there is a lack of study concerning the effects of fiber content and fiber geometry. This study carried out several heating tests on 200 – 300MPa high strength concrete using the ISO834 standard fire curve, in which various fiber types and fiber contents were considered. The effects of fiber type, fiber content, and geometry of both synthetic fiber and steel fiber on spalling depth were discussed. The following conclusions can be derived from this study.