What is the formula for ettringite?
The chemical formula for ettringite is [Ca3Al(OH)6. 12H2O]2.2H2O or, mixing notations, C3A. 3CaSO4.
What causes delayed ettringite formation?
Internal sulfate attack occurs when there is an excess of sulfate in the original mixture. Delayed ettringite formation, or DEF, is a form of internal sulfate attack that can happen with steam-cured and mass concrete when internal concrete temperatures exceed 70°C.
What is delayed ettringite formation in concrete?
Delayed ettringite formation (DEF) may be defined as the formation of ettringite in a cementitious material by a process that begins after hardening is substantially complete and in which none of the sulfate comes from outside the cement paste.
How ettringite forms and what it causes to concrete?
Gypsum and other sulfate compounds react with calcium aluminate in the cement to form ettringite within the first few hours after mixing with water. Most of the sulfate in the cement is normally consumed to form ettringite at early ages.
When the content is low most ettringite will be formed in the plastic state?
3. When the ____________ content is low, most ettringite will be formed in the plastic state. Explanation: When the C3A content is low, most ettringite will be formed in the plastic state.
How can delayed ettringite formation be stopped?
DEF can be prevented by limiting the internal concrete temperature to 70oC during its very early life. This can be achieved either by direct specification, or indirectly by limiting the cement content or specifying the use of low or very low heat cement.
Is ettringite good 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 the range of water in M10?
34 to 36 liters
What is the range of water in M10? Explanation: The range of water for M10 (1:3:6) is 34 to 36 liters with a weight of 226kg of cement.
Why is fly ash used in cement?
Generally, fly ash benefits fresh concrete by reducing the mixing water requirement and improving the paste flow behavior. The resulting benefits are as follows: Improved workability. The spherical shaped particles of fly ash act as miniature ball bearings within the concrete mix, thus providing a lubricant effect.
At what percentage gypsum is added to cement?
The cement manufacturing industry is the major consumer of gypsum, which is added to the clinker in a percentage of 3–5 wt% [1], [2], [3].
How is C3S clinker calculated?
The most important consequence of the occurrence of impurities in the lattices of matrix clinker compounds is a disagreement between the calculated and real amount of phases in clinker. C 3 A = 2.65 × ( % Al 2 O 3 − ( 0.469 × % SO 3 + 0.15 ) ) − 1.692 × % Fe 2 O 3 .
Is ettringite soluble in water?
Ettringite is a hydrous calcium aluminium sulfate mineral with formula: Ca6Al2(SO4)3(OH)12·26H2O….
| Ettringite | |
|---|---|
| Solubility | Partially soluble in water |
| Alters to | Partially dehydration on atmospheric exposure, becomes opaque |
| References |
What is the ratio of M10?
1 : 3 : 6
Different types of concrete grades and their uses
| Concrete Grade | Mix Ratio (cement : sand : aggregates) | Compressive Strength |
|---|---|---|
| M10 | 1 : 3 : 6 | 10 MPa |
| M15 | 1 : 2 : 4 | 15 MPa |
| M20 | 1 : 1.5 : 3 | 20 MPa |
| Standard Grade of Concrete |
What is the minimum curing period of concrete?
What is the minimum curing time for concrete? For the majority of structures, the curing time at temperatures above 5º C (40º F) should be at least 7 days or until 70% of the specified compressive or flexural strength is attained, whichever is longer.
Why 2% gypsum is added in the cement?
Gypsum is often added to Portland cement to prevent early hardening or “flash setting”, allowing a longer working time. Gypsum slows down the setting of cement so that cement is adequately hardened.
What is delayed ettringite formation (DEF)?
Delayed Ettringite Formation (DEF): Hardened concrete that has been subjected to high-temperature heat curing or high internal hydration heat temperature may suffer from expansion and cracking during subsequent exposure to moisture. DEF is diagnosed by the presence of gaps around aggregate particles.
Is delayed ettringite formation harmful to precast concrete?
Delayed ettringite formation (DEF) could be deleterious and reduce the serviceability of structures built with precast concrete elements subjected to a short-term heat curing regime. Over 3 decades of research many characterization techniques have been developed to study the impact of DEF in cementitious systems.
How is ettringite formed in concrete?
Ettringite is normally one of the earliest phases formed during cement hydration. However, when the concrete temperature is higher than approximately 65 °C (150 °F), ettringite is unstable and the formation of the primary ettringite is halted. The constituents of ettringite are dispersed as monosulfate and calcium silicate hydrates.
How does temperature affect alkalinity of ettringite?
In addition to the loss of water from ettringite structure, high temperature increases the dispersion of cement potassium (K) and sodium (Na) ions into pore solution increasing the alkalinity [81] ( Fig. 11 ).