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中南大学学报(英文版)

Journal of Central South University

Vol. 27    No. 6    June 2020

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Effect of sodium sulfate on strength and microstructure of alkali-activated fly ash based geopolymer
LV Qing-feng(吕擎峰), WANG Zi-shuai(王子帅), GU Liu-yang(谷留杨), CHEN Yi(陈臆), SHAN Xiao-kang(单小康)

Key Laboratory of Mechanics on Disaster and Environment in Western China, Ministry of Education,Lanzhou University, Lanzhou 730000, China

Abstract:The main objective of this paper focuses on the changes that occur in the strength and microstructural properties of sodium silicate activated fly ash based geopolymer due to varying the sulfate salt and water content. A series of tests including X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, physical adsorption and unconfined compressive strength were used to investigate this effect. The results indicate that the higher water content has an adverse effect on the alkali activation and microstructural properties of geopolymer, so the optimum mass ratio of sodium sulfate in alkali-activated geopolymer under different water-to-binder ratios shows a “peak shifting” phenomenon, i.e., the higher the water-to-binder ratio, the higher the optimum mass ratio. Lower presence of sodium sulfate has no significant effect on the alkali-activated geopolymer systems; higher addition of sodium sulfate, however, could cause the symmetrical stretching vibration of Si—O and the symmetrical stretching vibration of Si—O—Si and Al—O—Si, and promote the formation of N-A-S-H gels. Furthermore, the cement effect of the gel and sodium sulfate aggregate could improve the integrity of pore structure obviously. The maximum strength of geopolymer curing at ambient temperature was 52 MPa. This study obtains the rule that the strength properties of alkali-activated geopolymers vary with the water-to-binder ratio and sodium sulfate content. The feasibility of geopolymer co-activated by sodium sulfate and sodium silicate was investigated, and reference for engineering application of alkali-activated geopolymer in salt-bearing areas was provided.

 

Key words: geopolymer; microstructure; fly ash; sodium sulfate; water-to-binder ratio

中南大学学报(自然科学版)
  ISSN 1672-7207
CN 43-1426/N
ZDXZAC
中南大学学报(英文版)
  ISSN 2095-2899
CN 43-1516/TB
JCSTFT
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