Alkaline Activation of Blends of Metakaolin and Calcium Aluminate

Abstract

The present paper reports the preliminary results obtained and analyzed in the framework of a joint Spanish–Japanese project on the behavior of blends of alkali‐activated metakaolin (MK) and calcium aluminate cement (CAC). In these experiments, the materials were activated with an 8M solution of NaOH, poured into molds, and subjected to brief thermal curing (2 or 20 h at 85°C). The hardened pastes were tested for mechanical strength and characterized for mineralogy and microstructure by a number of techniques (XRD, FTIR, BSEM, and MAS‐NMR). The results showed that under the above conditions, the Al and Ca in the CAC were taken up into the aluminosilicate formed as the main product of the alkali activation of MK. None of the CAC hydration compounds (CAH10; C2AH8; C3AH6; AH3) normally formed were detected in any of the cases studied.

Influence of calcium additions on the compressive strength and microstructure of alkali‐activated ceramic sanitary‐ware

“…The results exhibited by the alkali‐activated CSW/CAC blended mortars differ from those previously reported by Fernández‐Jiménez et al for alkali‐activated metakaolin/CAC blended pastes prepared with 20% CAC, where strength values close to 13 MPa were reported after 20 curing hours at 85°C. The strength of the CSW/CAC mortars significantly improved with up to 20 wt% CAC substitutions and generally decreased with further additions.…”

Effect of Sodium Silicate on Calcium Aluminate Cement Hydration in Highly Alkaline Media: A Microstructural Characterization

“…2, while Table III lists the main phases detected. C 3 AH 6 formed in the absence of silica (SN8), while in the presence of this compound the most intense diffraction lines were observed to split, providing evidence of the interaction between part of the additional silica and the C 3 AH 6 to form Ca 2.93 Al 1.97 (Si 0.64 O 2.56 )(OH) 9.44. These are the phases that normally appear during water hydration of this cement.…”

“…9 According to the results of that research, under the experimental conditions used (thermal curing for 2 or 20 h at 851C), the Al and Ca from the CAC were taken up in the aluminosilicate gel, the main reaction product forming in the alkali activation of metakaolin. 9 According to the results of that research, under the experimental conditions used (thermal curing for 2 or 20 h at 851C), the Al and Ca from the CAC were taken up in the aluminosilicate gel, the main reaction product forming in the alkali activation of metakaolin.…”

“…4,5,[9][10][11] Ferna´ndez-Carrasco and colleagues [12][13][14] showed that CAC hydration under moderately alkaline conditions favors the conversion of hexagonal into cubic hydrates. 4,5,[9][10][11] Ferna´ndez-Carrasco and colleagues [12][13][14] showed that CAC hydration under moderately alkaline conditions favors the conversion of hexagonal into cubic hydrates.…”

Evaluation of blends bauxite-calcination-method red mud with other industrial wastes as a cementitious material: Properties and hydration characteristics

“…As the Si-O stretching modes for the SiQ n units display infrared absorption bands located around 850, 900, 950, 1100 and 1200 cm −1 for n = 0, 1, 2, 3 and 4, respectively [29,31], the band at 991 cm −1 indicates a distribution of the SiQ n units centered around SiQ 2 and SiQ 3 units for the hydrated RSFC2 samples at 3 and 28 days. The position of this band suggests that the C-S-H gel formed is similar to the gel-type aluminosilicate found in the alkali-activated systems [20,29,32,33]. It is thus believed that the C-S-H gel formed in the hydrated RSFC2 has high polymerization of SiO 4 tetrahedra with a part of silicon substituted by aluminium.…”