Microstructural changes in high and ultra high strength concrete exposed to high temperatures environments

Abstract

A concrete exposed to environments of high temperature or directly to fire undergoes microstructural changes that result in loss of mechanical properties. The present paper deals with the study of high-performance concretes (HPC) and ultra high-performance concretes (UHPC) resistance to high temperatures. Microstructural changes are followed up to temperatures of 700°C. Changes on residual permeability and porosity, together with weight losses, due to moisture, binding water, aggregates and fibre transformations, are considered. The study, performed on a wide variety of concretes, indicates that UHPC seem to be less resistant at high temperatures than HPC, but the addition of fibres improves the fire resistance of UHPC.