Microstructural behaviour of reactive powder concrete under different heating regimes

Reactive powder concrete is an ultra-high-performance concrete which has good mechanical properties and durability. The major difference between reactive powder concrete and conventional concrete is that no coarse aggregate is involved in reactive powder concrete, but crushed quartz and quartz sand are used instead, with a high dosage of silica fume. Heat treatment is a well-known method that can further improve the performance of reactive powder concrete. This paper examines the optimal duration under heat treatment with each pre-determined temperature for reactive powder concrete. Heat treatment with temperatures of 100°C, 150°C, 200°C and 250°C and durations of 8 h, 16 h and 24 h are used for testing. It is found that when the heat-treatment temperature increases, the optimal duration for maximising compressive strength will be longer. The heat-treatment temperature is also positively correlated with the compressive strength of reactive powder concrete. The microstructural behaviour of the effect on heat-treatment temperature and the duration on compressive strength is explored by scanning electron microscope and energy dispersive X-ray spectroscopy. It is shown that the heating duration has a positive effect on the quality and quantity of crystal formation while heating temperature affects the types of crystal formed.