Microstructure Evolution During Hydration Process of Ultra-High Performance Concrete Containing Fly Ash and Silica Fume
WANG Qiannan1, GU Chunping2, SUN Wei1
1 School of Materials Science & Engineering, Southeast University, Nanjing 211189; 2 College of Civil Engineering and Architecture, Zhejiang University of Technology, Hangzhou 310014
Abstract: Ultra-high performance concrete (UHPC) is a promising material which exhibits extrodinary mechanical properties and durability. A UHPC paste containing fly ash and silica fume was prepared and its microstructure evolution during hydration was investigated with backscattered electron (BSE) images, thermogravimetry (TG) and nitrogen adsorption method. The results showed that the hydration of cement was fast at early ages, and it slowed down after 7 days. Due to its low activity, fly ash reacted slowly in the paste. The reaction degree of fly ash was only 7% by 28 days. The content of Ca(OH)2 increased quickly at first as the cement hydrated. After 3 days it started to decline due to the consumption by pozzolanic reactions of silica fume and fly ash. There was still some Ca(OH)2 existing in the paste by 28 days. Moreover, the specific surface area and the porosity of UHPC paste decreased as the curing progressed, resulting in a denser microstructure.
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2017, Vol. 31 
