Slag‐fly ash and slag‐metakaolin binders: Part II—Properties of precursors and NMR study of poorly ordered phases

Abstract

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.

Bone ash reinforced geopolymer composites

“…Alkali‐activated cement containing large amounts of calcium was initially developed by Glukhovsky in Ukraine during the 1950 s 13 . It can be made from waste materials of Class F fly ash and ground granulated blast furnace slag 13‐18 . These materials contain a cementitious binder phase of calcium silicate hydrate (CSH), which is the binder phase in cements.…”

“…In nuclear magnetic resonance, the silicate tetrahedra share linkages with two or sometimes three other tetrahedra, denoted as Q 2 or Q 3 (mAl) in Magic Angle Spinning nuclear magnetic resonance (MAS NMR). Alkali‐activated cements are often confused with geopolymers originally pioneered by Davidovits using calcium‐free systems based on metakaolin and possessing an X‐ray amorphous structure of tetrahedral alkali aluminosilicate frameworks (Q 4 (mAl) where m = 1‐4) 1,7,12,14‐17 . In geopolymer, the Al is four‐coordinated, creating a negative charge imbalance which is compensated for by the presence of Group I monovalent cations such as Na + or K + 1,7,12,14‐17 .…”

“…1,7,11 Alkali-activated cement containing large amounts of calcium was initially developed by Glukhovsky in Ukraine during the 1950 s. 13 It can be made from waste materials of Class F fly ash and ground granulated blast furnace slag. [13][14][15][16][17][18] These materials contain a cementitious binder phase of calcium silicate hydrate (CSH), which is the binder phase in cements. In nuclear magnetic resonance, the silicate tetrahedra share linkages with two or sometimes three other tetrahedra, denoted as Q 2 or Q 3 (mAl) in Magic Angle Spinning nuclear magnetic resonance (MAS NMR).…”

“…Alkali-activated cements are often confused with geopolymers originally pioneered by Davidovits using calcium-free systems based on metakaolin and possessing an X-ray amorphous structure of tetrahedral alkali aluminosilicate frameworks (Q 4 (mAl) where m = 1-4). 1,7,12,[14][15][16][17] In geopolymer, the Al is four-coordinated, creating a negative charge imbalance which is compensated for by the presence of Group I monovalent cations such as Na + or K + . 1,7,12,[14][15][16][17] Geopolymers possess a nanoporous microstructure, with the characteristic pore size related to the alkali cation.…”

“…1,7,12,[14][15][16][17] In geopolymer, the Al is four-coordinated, creating a negative charge imbalance which is compensated for by the presence of Group I monovalent cations such as Na + or K + . 1,7,12,[14][15][16][17] Geopolymers possess a nanoporous microstructure, with the characteristic pore size related to the alkali cation. 19 Kriven et al [19][20][21][22][23][24][25] have made geopolymer composites by combining water-glass containing 11 moles of water reacting with 1 mole of 1.2 μm-sized metakaolin particles.…”