hi Mohamed Abd Ellatief
thank you for your intresting question
The AFt phase in cement concrete refers to one of the hydrous calcium sulfoaluminate phases, typically called ettringite. This compound is an important part of the chemistry of cement and plays a crucial role in the early stages of cement hydration and strength development.
When Portland cement reacts with water, it forms a variety of hydration products. Among these, ettringite (AFt phase) forms during the initial hydration of calcium aluminates in the presence of gypsum (calcium sulfate). The formula for ettringite is typically represented as 3CaO·Al2O3·3CaSO4·32H2O.
The formation of the AFt phase is important for several reasons:
1. Volume Expansion:** It contributes to the expansion of the cement paste, which can be beneficial in counteracting shrinkage during setting and hardening. However, excessive formation of ettringite can lead to deleterious expansion and cracking, especially if it forms at later stages (delayed ettringite formation).
2. Strength Development:** In the early stages of hydration, ettringite helps to develop the microstructure of the concrete, contributing to its initial strength.
3. Heat of Hydration:** The formation of ettringite is an exothermic process and contributes to the heat of hydration of cement. This is an important aspect in mass concrete construction where temperature control is critical.
4. Durability: Proper formation and stability of ettringite are also linked to the durability of concrete, especially in environments where sulfate attack might be a concern.
Understanding the formation and stability of the AFt phase is crucial for controlling the properties of cement-based materials, particularly in terms of their workability, strength development, durability, and resistance to various environmental factors.
AFT (Accelerated Carbonation Test): This is a laboratory test used to assess the carbonation resistance of concrete. Carbonation is a chemical reaction where carbon dioxide from the air reacts with the calcium hydroxide in concrete to form calcium carbonate. AFT helps in predicting how well concrete will resist carbonation over time. AFt (Alumina Ferric Tri-sulfate): In the context of cement, AFt is one of the phases that can form in certain cementitious systems. It is a hydrate phase that includes aluminum, iron, and sulfate. AFt is often associated with the hydration of Portland cements containing significant amounts of sulfate.
AFT =C4AcH11 C8Ac2H24
The AFt phase ettringite
Ettringite is a primary constituent of hydration of Portland cement concrete. Its formation plays an important role in the control of setting.
Hello,AFm and AFt phases: These are two groups of minerals that exist in cement and elsewhere. One of the most common AFm phases in hydrated cement is monosulfate, and by far the most common AFt phase is ettringite. The general definitions of these phases are somewhat technical, but for example, ettringite is an AFt phase because it contains three (t-tri) anhydride molecules, written as C3.A.3CaSO4.32HO2, and monosulfate is an AFm phase because it contains one ( m-mono) is an anhydride molecule when written as C3CaSO4H2O.
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