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Open AccessArticle

Preparation of a New Type of Cemented Paste Backfill with an Alkali-Activated Silica Fume and Slag Composite Binder

by Qi Sun 1, Tianlong Li 1 and Bing Liang 2,*
1
School of Civil Engineering, Liaoning Technical University, Fuxin, Liaoning Province 123000, China
2
School of Mechanics and Engineering, Liaoning Technical University, Fuxin, Liaoning Province 123000, China
*
Author to whom correspondence should be addressed.
Materials 2020, 13(2), 372; https://doi.org/10.3390/ma13020372
Received: 18 December 2019 / Revised: 4 January 2020 / Accepted: 7 January 2020 / Published: 13 January 2020
(This article belongs to the Section Construction and Building Materials)
A new type of cemented paste backfill (CPB) was prepared using sodium hydroxide (NaOH) as the activator, slag and silica fume (SF) as the binder, and tailings as the aggregate. The effects of proportion of replacement of 0%, 5%, 10%, 15%, and 20% silica fume on the properties of CPB were studied. The strength formation mechanism of CPB was explored through a combination of scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and Fourier transform infrared (FTIR) spectroscopy. The SEM images were analyzed by IMAGE J software, and the porosity of CPB with different silica fume contents was obtained. The results show that as the amount of silica fume increases, the unconfined compressive strength (UCS) increases first and then decreases. When the amount of silica fume was approximately 5%, CPB with a larger UCS can be obtained. When the silica fume content increased from 0% to 5%, because silica fume has good activity and small particles, more calcium silicate hydrate (C–S–H) gels and Mg-Al type layered double hydrotalcites (LDHs) were generated in CPB, which made it denser and improved its strength compared with the non-silica fume group. C–S–H gels were the main source of CPB strength. With a further increase in the amount of silica fume, thaumasite produced inside of CPB, reducing the content of C–S–H gels. Moreover, due to the expansion of thaumasite, it is easy to generate a large number of micro cracks in CPB, which weakens the strength of CPB.
Keywords: cemented paste backfill; alkali-activated silica fume and slag composite binder; strength formation mechanism; microstructure cemented paste backfill; alkali-activated silica fume and slag composite binder; strength formation mechanism; microstructure
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MDPI and ACS Style

Sun, Q.; Li, T.; Liang, B. Preparation of a New Type of Cemented Paste Backfill with an Alkali-Activated Silica Fume and Slag Composite Binder. Materials 2020, 13, 372.

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