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tricalcium aluminate + ettringite → mono-sulfate aluminates (AFm) When it reacts with concrete, it causes the slab to expand, lifting, distorting and cracking as well as exerting a pressure onto the surrounding walls which can cause movements significantly weakening the structure.
AFm form inter alia when tricalcium aluminate 3CaO·Al 2 O 3, or C 3 A in CCN, reacts with dissolved calcium sulfate (CaSO 4), or calcium carbonate (CaCO 3). As the sulfate form is the dominant one in AFm phases in the hardened cement paste (HCP) in concrete, AFm is often simply referred to as Aluminate Ferrite monosulfate or calcium aluminate ...
Calcium aluminates can form complex salts in combination with different types of anions.Two series of calcium aluminates are known in cement chemistry: AFm and AFt phases, being respectively mono- or tri-substituted with a given divalent anion X (e.g. SO 2− 4, CO 2− 3, or hosting a divalent impurity such as SeO 2− 4 [3]...), or with two units of a monovalent anion, e.g. OH −, Cl − ...
Ettringite is the most common and prominent member of the AFt group (X in this case denoting sulfate), and often simply called Alumina Ferrite tri-sulfate (AFt). AFm: abbreviation for "alumina, ferric oxide, mono-substituted" or (Al 2 O 3 − Fe 2 O 3 − mono). It represents another group of calcium aluminate hydrates with general formula [Ca ...
When the temperature of concrete exceeds 65 °C for too long a time at an early age, the crystallization of ettringite (AFt) does not occur because of its higher solubility at elevated temperature and the then less soluble mono-sulfate (AFm) is formed. After dissipation of the cement hydration heat, temperature goes back to ambient and the ...
This reaction is expansive, and can disrupt mature concrete. Where concrete is to be placed in contact with, for example, sulfate-laden ground waters, either a "sulfate-resisting" cement (with low levels of tricalcium aluminate) is used, or slag is added to the cement or to the concrete mix. The slag contributes sufficient aluminium to suppress ...
Monocalcium hexa-aluminate, CaO·6Al 2 O 3 (CA 6) (occurring in nature as hibonite, a representative of magnetoplumbite group [6]) In addition, other phases include: Dicalcium aluminate, 2CaO·Al 2 O 3 (C 2 A), which exists only at pressures above 2500 MPa. [7] The crystal is orthorhombic, with density 3480 kg·m −3. The natural dicalcium ...
ASTM C1293: "Test Method for Concrete Aggregates by Determination of Length Change of Concrete Due to Alkali-Silica Reaction". It is a long-term confirmation test (1 or 2 years) at 38 °C in a water-saturated moist atmosphere (inside a thermostated oven) with concrete prisms containing the aggregates to be characterised mixed with a high-alkali ...