Steel and PVA Fibres Reinforced UHPC Exposed to High Temperatures - Analysis of Residual Properties

Residual parameters of Ultra High Performance Concrete (UHPC) exposed to high temperatures were experimentally accessed. The UHPC was provided by hybrid fibre reinforcement based on polyvinyl alcohol (PVA) and steel fibres. Among the studied material properties, bulk density, matrix density, total open porosity, pore size distribution, water vapour transmission and liquid water transport properties were examined. The UHPC samples were exposed to the temperatures 400 °C, 600 °C, 800 °C, and 1000 °C respectively. For comparative purposes, the reference UHPC samples cured at laboratory temperature were tested as well. Based on the obtained results, correlation between concrete structural changes and tested parameters was found out. The applied temperature load highly affected the concrete porosity, pore size, and thus both liquid and gaseous moisture transport parameters. Disintegration of concrete structure, colour change, cracking, damage of steel fibres (melting), and failure of their cohesion was apparent from optical microscopy analysis.