Ettringite

Definition

Ettringite is a crystalline mineral that forms during the hydration of Portland cement, specifically when calcium aluminate reacts with gypsum in the presence of water. This compound plays a critical role in the development of strength and durability in cement-based materials, making it essential in the production of concrete. Its formation is an indicator of effective hydration and influences the overall performance of concrete structures.

5 Must Know Facts For Your Next Test

1. Ettringite is composed of calcium, aluminum, and sulfate ions, typically represented by the formula 3CaO·Al2O3·3CaSO4·32H2O.
2. The formation of ettringite occurs during the initial stages of cement hydration and continues for several days as long as sulfate is available.
3. Inadequate sulfate levels can lead to delayed ettringite formation, which may cause expansion and cracking in concrete over time.
4. Ettringite contributes to the strength development in concrete by filling voids and enhancing the microstructure, thus improving durability.
5. High temperatures can destabilize ettringite, causing it to decompose into other phases that can affect the performance of concrete.

Review Questions

• How does ettringite formation impact the strength and durability of concrete?
  • Ettringite formation is crucial for enhancing the strength and durability of concrete as it fills voids within the matrix and contributes to a denser microstructure. This mineral helps in binding other components together, effectively increasing load-bearing capacity. The presence of ettringite also indicates successful hydration, which is essential for achieving optimal performance in concrete structures.
• Discuss the consequences of inadequate sulfate levels on ettringite formation and overall concrete performance.
  • Inadequate sulfate levels can lead to delayed ettringite formation, which may result in a phenomenon known as delayed expansion. This delayed formation can create stresses within the concrete as it continues to cure, potentially leading to cracking and reduced structural integrity over time. Ensuring appropriate sulfate levels is vital for maintaining the desired properties and longevity of concrete structures.
• Evaluate the role of ettringite stability at high temperatures and its implications for concrete used in varying environmental conditions.
  • Ettringite stability at high temperatures is critical because its decomposition can lead to changes in the microstructure of concrete, negatively impacting its mechanical properties. When exposed to elevated temperatures, ettringite may transform into other mineral phases that are less desirable for structural integrity. This transformation poses significant implications for applications such as fire-resistance and durability under thermal stresses, making it essential to consider environmental conditions when designing concrete mixes.

Related terms

Portland Cement:

A type of cement commonly used in construction, made by grinding clinker produced from limestone and clay, which undergoes a series of chemical reactions during hydration.

Calcium Aluminate: A group of compounds formed from the reaction between lime and aluminum oxide, which are key ingredients in Portland cement and contribute to the formation of ettringite.

Hydration: The chemical reaction that occurs when water is added to cement, resulting in the hardening and development of strength in concrete through the formation of various compounds, including ettringite.