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Slag‐fly ash and slag‐metakaolin binders: Part II —Properties of precursors and NMR study of poorly ordered phases
Author(s) -
Sankar Kaushik,
Sutrisno Andre,
Kriven Waltraud M.
Publication year - 2019
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.16224
Subject(s) - metakaolin , fly ash , geopolymer , materials science , ground granulated blast furnace slag , curing (chemistry) , portland cement , sodium silicate , slag (welding) , metallurgy , chemical engineering , composite material , cement , engineering
Sodium silicate‐activated slag‐fly ash binders ( SFB ) and slag‐metakaolin binders ( SMKB ) are room‐temperature hardening binders that have excellent mechanical properties and a significantly lower carbon footprint than ordinary Portland cement ( OPC ). The aim of this study was to use nuclear magnetic resonance ( NMR ) spectroscopy to study the nanostructure of poorly ordered phases in SFB by varying slag/fly ash ratio, curing time, and curing temperature. Fly ash was completely substituted with metakaolin and the effect of this substitution on the poorly ordered phases was studied. It was observed that the proportion of geopolymer was generally higher in SMKB when compared to SFB . Although C–N–A–S–H and geopolymer coexisted in SFB and SMKB , C–N–A–S–H was the major product phase formed. The mean chain length ( MCL ) and the structure of C–N–A–S–H gel were estimated as a function of time, temperature, and slag/fly ash ratio. The MCL was found to have a negative correlation with slag/fly ash ratio and Ca/(Si+Al) ratio, but positive correlation with curing temperature. The average Si/Al atom ratios for geopolymers were also estimated. Lastly, the increased proportion of five‐coordinated aluminum (Al(V)) in metakaolin resulted in the decreased unreacted metakaolin in the hardened binder but did not increase the geopolymer content.