Calcium sulfoaluminate clinker hydration at different alkali concentrations

• Published in: Cement and concrete research 2020-12, Vol.138, p.106251, Article 106251
• Main Authors: Padilla-Encinas, P., Palomo, A., Blanco-Varela, M.T., Fernández-Jiménez, A.
• Format: Article
• Language: English
• Subjects: 27Al MAS-NMR; Alkalinity; Aluminum; Calcite; Calcium aluminate; Calcium aluminum silicates; Calcium carbonate; Calcium sulfoaluminate clinker; Carbonation; Clinker; Crystal structure; Crystallinity; Ettringite; Hydrates; Hydration; NaOH concentration; NMR; Nuclear magnetic resonance; Pastes
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2020.106251

This paper discusses the effect of alkalis on strength development and hydration products in a commercial calcium sulfoaluminate clinker (KCSA). KCSA pastes were hydrated with water and 0.1 M, 1 M, 2 M, 4 M and 8 M NaOH. The hydration products were characterised at 3d, 28d and 90d, by XRD, SEM, DTA/TG and 27Al MAS-NMR. With 0.1 M, 1 M and 2 M, the main hydration products were similar to those observed in the water-hydrated pastes: ettringite, AH3 and calcium aluminate hydrates such as CAH10; 27Al MAS-NMR analysis revealed different degrees of crystallinity in AH3. With 4 M and 8 M, ettringite was not detected, AH3 crystallinity rose and siliceous hydrogarnet, calcium carboaluminate hydrates, thenardite and calcite were formed at higher alkalinity. Sample carbonation, which grew more intense with time and at higher alkalinity, yielded calcium carbonate and an aluminium hydroxide gel inducing cracking. •Hydration of a commercial calcium sulfoaluminate clinker (KCSA) with water and 0.1 M, 1 M, 2 M, 4 M and 8 M NaOH.•KCSA hydration is slightly delayed at 0.1 M, 1 M and 2 M, The main hydration products are ettringite, CAH10 and AH3.•At 4 M and 8 M, AFt was not detected; AH3 crystallinity rose and C3ASH4, thenardite and calcite were formed•27Al MAS-NMR analysis revealed different degrees of crystallinity in AH3 as function of time and pH.