Sage-Tips

What is concrete Ettringite?

Ettringite is a primary constituent of hydration of Portland cement concrete. Its formation plays an important role in the control of setting. Minor amounts of secondary ettringite are often encountered in air voids of hardened concretes, regardless of the type of cement used.

Is Ettringite bad for concrete?

Delayed ettringite formation (DEF) is a chemical reaction with proven damaging effects on the mechanical properties of hydrated cementitious composite (concrete). Ettringite crystals can cause cracks and the widening of cracks due to pressure on the crack walls caused by the positive volume difference in the reaction.

What is delayed Ettringite?

Delayed ettringite formation (DEF) is expansion and cracking of concrete associated with the delayed formation of the mineral ettringite which is a normal product of early cement hydration. DEF is a result of high early temperatures (above 70oC – 80oC) in the concrete which prevents the normal formation of ettringite.

Why gypsum is added in cement?

Hint: Gypsum slows down the hydration process of cement once it is mixed with water. Complete answer: In the cement manufacturing process clinkers are formed, these cement clinkers are cooled down and added with a small amount of gypsum, after that mixture is sent to the final grinding process.

How can you increase the durability of concrete?

Ways To Improve Durability Of Concrete Structures

1. Mix Design.
2. Construction Joints.
3. Prevent Premature Moisture Loss During Placing.
4. Low Permeability.
5. Proper Curing.
6. Protect Concrete From De-icing Salts After Curing.
7. Concrete Placement.

What does Ettringite look like?

Ettringite is a hydrous calcium aluminium sulfate mineral with formula: Ca6Al2(SO4)3(OH)12·26H2O. It is a colorless to yellow mineral crystallizing in the trigonal system. The prismatic crystals are typically colorless, turning white on partial dehydration.

Where is Portlandite found in nature?

Occurrence. Portlandite occurs in a variety of environments. At the type location in Northern Ireland it occurs as an alteration of calc–silicate rocks by contact metamorphism of larnite–spurrite. It occurs as fumarole deposits in the Vesuvius area.

What is CSH gel?

Calcium-silicate hydrate (C-S-H) is the main binder in cement and concrete. C-S-H nanoscale building blocks form a cohesive gel, whose structure and mechanics are still poorly understood, in spite of its practical importance.

What is the purpose of gypsum?

Gypsum is widely used to manufacture wallboards that are used to cover walls and ceilings. It’s also used to make plaster which is used in the construction of homes as well as mixed into a patching compound for wallboard repair.

What affects concrete durability?

Other factors affecting durability of concrete are: Cement Content, Aggregate Quality, Water Quality, Concrete Compaction, Curing Period, Permeability, Moisture, Temperature, Abrasion, Carbonation, Wetting and Drying Cycles, Freezing and Thawing, Alkali-Aggregate Reaction, Sulfate Attack, Organic Acids.

What is the function of ettringite in concrete?

Ettringite is a primary constituent of hydration of Portland cement concrete. Its formation plays an important role in the control of setting. Minor amounts of secondary ettringite are often encountered in air voids of hardened concretes, regardless of the type of cement used.

What is delayed ettringite formation (DEF)?

Massive secondary ettringite is often denominated as delayed ettringite formation, DEF. Originally, this term was reserved for secondary ettringite formed in concretes that are heat or steam cured above 70 °C (Taylor et al.2001).

What are the disadvantages of ettringite hydration?

Ettringite, monosulfate aluminate and other minor compound constitute 15–20\% volume in hydration products. Extremely sensitive to alkaline environment. Its will effect the durability of concrete because at high temperature ettringite is the very unstable product.

What are the characteristics of ettringite?

Microscopically, this ettringite takes the form of massive aggregates or bands at the aggregate–cement paste interface, causing debonding, or filling cracks, accompanied by air voids (almost) completely filled by ettringite (Fig. 8.19). The majority of the individual ettringite crystals in the aggregates cannot be distinguished.