2018-11-14 · effects since the concrete in a fresh state is highly deformable. At high temperatures (above 70 0C) primary ettringite is not stable. It decomposes into monosulfate and SO 4 2-. In the thermally cured concrete or core of massive concrete sections, the temperature may rise more than 700C.Under this condition, C 3
“Late ettringite formation” is certainly more accurate in the practicai sense, since the “problem” normally surfaces several years after the concrete is case but it is not precise. Late can have many meanings and, as study of this report will show, the process by which ettringite formation causes the problem occurs over a long time span.
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 70 o C – 80 o C) in the concrete which prevents the normal formation of ettringite. 3. Ettringite in hardened concrete Scanning electron photomicrographs show that ettringite (3CaO ⋅ Al2O 3 ⋅ 3CaSO 4 ⋅ 32 H 2O) occurs in concrete in various forms, often as spherical clusters of ettringite crystals, felt-like or parallel needles of differing sizes. If ettringite crystallizes out without spatial obstruction, ettringite is reduced, there will also be a concomitant reduction of concrete expansion and cracking. If both ettringite formation and concrete deterioration are simultaneously reduced, then the case for ettringite induced expansion/cracking is strengthened. Our experiments used four commercial inhibitors – two phosphonates, a polyacrylic acid, Concrete Experts International has extensive, worldwide experience in diagnosing delayed ettringite formation (DEF) in concrete structures and with research regarding the nature and effects of DEF. Diagnosing DEF is an integrated part of our petrographic analysis of 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. An ettringite formation in hardened concrete does not in every case lead to a direct damage of the concrete structure. At present, there is still controversy whether different types of ettringite exist; whether the damage mechanism can be initiated by coarse- or fine-crystalline ettringite; whether the formation of large ettringite crystals in hardened concrete, which also occur without heat treatment, is the primary cause 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 70 o C – 80 o C) in the concrete which prevents the normal formation of ettringite.
In concrete chemistry ettringite is a hexacalcium aluminate trisulfate hydrate, of general formula: (CaO) 6 (Al 2 O 3)(SO 3) 3 ·32H 2 O. or (CaO) 3 (Al 2 O 3)(CaSO 4) 3 ·32H 2 O. Ettringite is formed in hydrated Portland cement system as a result of the reaction of calcium aluminate with calcium sulfate, both present in Portland cement.
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. At ambient temperature curing, ettringite forms as a part of the “normal” hydration process of portland cement. However, when concrete is exposed to excessive temperatures during curing, ettringite formation is hampered and forced to form at later ages.
Delayed ettringite formation (DEF) is commonly referred to as heat-induced internal sulfate attack, which affects the durability and strength of the concrete like in
The primary Ettringite is the mineral name for calcium sulfoaluminate. (3CaO•Al2O3•3CaSO4• 32H2O), which is normally found in portland cement concretes. Calcium sulfate However, there are few minerals in the process of cement hydration which are responsible for expansion and deterioration of cement and concrete. Ettringite is Delayed ettringite formation (DEF) is commonly referred to as heat-induced internal sulfate attack, which affects the durability and strength of the concrete like in 15 Feb 2010 The simultaneous occurrence of the delayed ettringite formation mechanism and the alkali-silica reaction in concrete structures is not well Ettringite Formation in Lime-Treated Soils: Establishing Thermodynamic Foundations The Solubility of Ettringite at 25°C. Cement and Concrete Research, Vol. 3 Feb 2020 Internal swelling reactions (ISR) are important degradation mechanisms for cement based applications.
This form of ettringite is not considered to be deleterious
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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 70 o C – 80 o C) in the concrete which prevents the normal formation of ettringite. The present paper reports a new method for converting ettringite and thaumasite in non-expansible and insoluble phases, for its application in the restoration of concrete artefacts subjected to
Delayed ettringite formation (DEF) can damage concrete that has experienced a temperature above about 70°C.
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Another example of harmless and usefulEEF is Type expansive K cement containing a calcium aluminate sulfate (C4A3S) which, under proper restraint, hydrates within a few days producing uniformly distributed ettringite peak temperatures in concrete are over about 65°C, the sulphates may be incorporated in other cement phases. After concrete hardening, the very slow formation of higher volume secondary ettringite may occur as water is taken into the crystal structure which can lead to potentially disruptive expansion. 2000-12-01 2012-04-01 of concrete elements. Delayed ettringite formation is not only related to heat treatment during curing of concrete elements [5].
It decomposes into monosulfate and SO 4 2-. Due to the hydration process, temperatures in concrete will increase during early stages and when the temperature exceeds 70 0 C, Delayed Ettringite Formation (DEF) can take place. DEF can have
Damage to the concrete occurs when the ettringite crystals exert an expansive force within the concrete as they grow. In normal concrete, the total amount of ettringite which forms is evidently limited by the sulfate contributed by the cement initially.
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This videos discusses various factors that influence the DEF mechanism in concrete. Also discussed are mitigation measures for the same.
If the supply of sulfate from the gypsum is Ettringite formation is considered to be the cause of most of the expansion and disruption of concrete structures involved in sulfate attack (ACI. Committee 201 A revised structure model of ettringite is presented, in order to provide quantitative X-ray diffraction (QXRD) of this mineral in cement pastes. The model is Unlike ordinary Portland cement (PC) based systems, where ettringite (C3A·3C$· H32) is a minor constituent, the hydrates in rapid-set concrete systems are In cement no- menclature ettringite is also referred to as AFt and monosulfate as AFm. Ettringite formation while the concrete is in a plastic state contributes to the For ESA, the sulfate ions diffuse from the exterior solution, and ettringite forms in the capillary pores.
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The large amount of ettringite detected in concrete affected by different failure mechanisms (alkali-silica reaction [ASR], freezing and thawing [FT], and wetting
DEF is a gradual reformation of ettringite (3CaO・ Al 2 O 3・3CaSO 4・32H 2 O, Fig. 1), following their original formation in concrete and subsequent decomposition in high temperatures. Ettringite is a normal product of early Ettringite Group. Although it is generally assumed that a solid solution series between ettringite and thaumasite exists, both species have different space groups and a possible discontinuity was identified, characterised by a gap in the a-dimension of the solid-solution phases (Barnett et al., 2000). Lou Z H, Xu X Y. Condition of Ettringite Formation and Its Role In Slag Portland Cement[J].Journal of the Chinese Ceramic Society, 1981, 9:295–301. Effects on Ettringite. Sodium Sulfate Experiments. 15.