MICROSTRUCTURAL AND PHYSICAL ALTERATIONS OF REACTIVE POWDER CONCRETE AFTER HIGH TEMPERATURE EXPOSURE

Reactive powder concrete (RPC), which contains no coarse aggregate and has a higher proportion of fine particles (<600 µm), is categorized as an ultra-high performance concrete (UHPC). This paper presents the effect of high temperature exposure on RPC performance in terms of compressive strength and microstructural alteration. Our results indicated that the exposure progressively decreased the compressive strength of RPC and correlated to both the shrinkage and thermal characteristics of the aggregates and the matrix. At a temperature of 400 °C, the exposure induced mass loss from the hydrates by dehydroxylation, coarsening of the capillary pores, and induced micro cracks between unhydrated cement grains, hardened paste and aggregate. Exposure at 500 °C further increased mass loss and developed the micro cracks in terms of length and width. At 800 °C, hydrate mass loss sharply increased by 84 %, the C-S-H was substantially degraded, and extensive micro cracking appeared throughout the specimens including within the fine quartz aggregates