Effects of Polypropylene and Steel Fibers on Permeability of Ultra-high Performance Concrete at Hot State

Abstract

Permeability of concrete is identified as one of the key parameters controlling explosive spalling. Measurements of permeability were performed on ultra-high performance concretes (UHPC) at elevated temperature ranging from ambient temperature to 300 °C. The effects of polypropylene fibers and steel fibers were investigated. The results show that plain UHPC and UHPC with steel fibers exhibit steady increase in permeability with increasing temperature. UHPC with polypropylene fibers exhibits a sudden increase of permeability at 150 °C. The microstructure of UHPC before and after exposure to elevated temperature was investigated by conducting Field Emission Scanning Electron Microscope (FESEM) observation. The results confirm that both the channels caused by melted polypropylene fibers as well as the generated micro crack network are the major factors causing a significant increase in permeability