Syntheses, properties and solid solution of ternary lamellar calcium aluminate hydroxi salts (AF_m-phases) containing SO₄²⁻, CO₃²⁻ and OH⁻

Author: Pöllmann, Herbert

Source: Neues Jahrbuch für Mineralogie - Abhandlungen, Volume 182, Number 2, April 2006 , pp. 173-181(9)

Publisher: E. Schweizerbart'sche Verlagsbuchhandlung

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Abstract:

The addition of gypsum, hemihydrate or anhydrite to OPC is necessary for the control of setting and hardening. The reaction of the aluminate phase leads to the formation of AF_t (Ettringite) and AF_m-phases in the course of hydration. The primary Af_t-phase (ettringite) is transformed to AF_m-phases. A natural analogue of AF_m-phases containing sulfate ions was named Kuzelite.

In this investigation ternary solid solutions containing sulfate, carbonate and hydroxide of lamellar calcium aluminium hydroxi salts (AF_m phases) were synthesized and characterized.

The synthesis of ternary AF_m-phases containing SO₄²⁻, CO₃²⁻ and OH⁻ was performed using pure chemicals. The influence of temperature, water content and additional carbonate for carbonation reaction is discussed. The X-ray patterns of different hydration stages at 100 % r. h. and 35 % r. h. were studied. Transformation reactions of ettringites and lamellar salts can be caused by sulfate deficiency, carbonation reactions or transformation reaction with additional C₃A. The following ternary solid solutions of AF_m-phases with single phase compositions could be established:

Lamellar calcium aluminum hydroxi salts (AF_m-phases)

3CaO·Al₂O₃·(x)CaCO₃·(y)Ca(OH)₂·(z)CaSO₄·nH₂O

0.33 < x < 0.66

0.17 < y < 0.50 X + y + z = 1

0 < z < 0.17

Two new distinct ternary phases were determined:

1. 3CaO·Al₂O₃·1/6CaSO₄·1/2Ca(OH)₂·2/6CaCO₃·nH₂O

2. 3CaO·Al₂O₃·1/6CaSO₄·1/6Ca(OH)₂·4/6CaCO₃·nH₂O

Keywords: AFM-PHASES; SULFATE; CARBONATIZATION; TRANSFORMATION; SOLID SOLUTION; ETTRINGITE; KUZELITE; TERNARY PHASES; LAMELLAR PHASES

Document Type: Research article

DOI: http://dx.doi.org/10.1127/0077-7757/2006/0042

Publication date: 2006-04-01