Experimental study on spalling risk of concrete with 115~120MPa subject to ISO834 Fire

Abstract

[EN] High strength concrete encased columns are being developed for erecting high-rise buildings as their higher load bearing capacity and smaller cross section size than normal concrete encased column. At ambient temperature, high strength concrete is always mixed with steel fibers to improve its ductility to match the material properties of high strength steel while constructing concrete encased columns. However, for high strength concrete at elevated temperature, spalling usually can be observed due to different thermal properties of various materials mixed such as siliceous aggregate, cement, silica fume, grit and moisture. Most of previous studies present that pore vapor compression induces high strength concrete spalling and propylene fiber can prevent it from spalling. The aim of the present experimental study is to discover the minimum propylene fiber ratio to prevent spalling of 115~120MPa concrete with aggregate and steel fiber. The experimental study carried out on 17 specimens with different water-binder ratio, steel fiber ratio and monofilament propylene fiber ratio exposed to ISO834 fire. The test results that 0.15% by volume of propylene fibers can prevent 115/120MPa high strength concrete with aggregate from spalling. It is worth noting that propylene fiber mixture ratio of 0.15% is lower than that of EN 1992-1-2 proposed up to 0.22%. Lower propylene fiber mixture ratio has been soak to improve the workability of 115~120MPa high strength concrete with steel fibers.