A comparative study on the pore structure of alkali-activated fly ash evaluated by mercury intrusion porosimetry, N2 adsorption and image analysis
In this study, the pore structure of alkali-activated fly ash (AAFA) pastes characterized by different techniques, including mercury intrusion porosimetry (MIP), nitrogen adsorption and image analysis (based on backscattered electron images), was evaluated and compared critically. The degree of reaction of fly ash in AAFA pastes was derived from image analysis. It was found that due to a significant “ink-bottle” effect, the pore diameter of capillary pores derived from MIP was two orders of magnitude smaller than the size determined by image analysis. MIP and nitrogen adsorption results showed different peaks corresponding to the gel pores of AAFA pastes. Based on the experimental results, image analysis is regarded as a reliable technique for the characterization of large pores (> 1 μm) in AAFA pastes. Nitrogen adsorption is more suitable to characterize small pores (< 0.1 μm) in AAFA than MIP, and MIP data should be carefully interpreted, preferably in combination with other characterization techniques.
The authors thank the China Scholarship Council for the financial support to the first author’s study in The Netherlands. We also thank the National High Technology Research and Development Program (“863 Program”, SS2015AA030801), National Natural Science Foundation of China (51402057, 51561135012), Science and Technology Project of Guangdong Province (2016B05051004), Guangzhou Education Bureau Foundation (1201610460), State Key Laboratory of Silicate Materials for Architectures Foundation (SYSJJ2017-05), Pearl River S&T Nova Program of Guangzhou (201506010004) and Australian Research Council Discovery Project (1006016) for funding the project. We would like to thank Professor Klaas van Breugel for his ultimate support and guidance to the project.
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