Ettringite delayed formation

In spite of numerous experimental works there are several unresolved questions and matty controversial opinions deahng with this problem. Some anthors support a view that the deterioration of concrete is the effect of alkah-aggregate reaction and the crystallization of ettringite occnrs later, in the microcracks thus produced [148]. 

There is a relatively good accordance as the chemical and phase composition, as well as the fineness of cement is concerned. Very well documented results in this field have been presented by Kelham [149,150]. Expansion increases with rise of alite and tricalcium aluminate content. The chemical composition of cement is of 

There is a commonly accepted view concerning the effect of heat treatment temperature. As higher temperature of thermal treatment, as higher and faster the expansion [151]. 

The question of expansion mechanism excites most controversies. There are the two contradictory hypotheses  

The effect of pessimum— the highest expansion at about 4% SO3 content in cement—is the further not quite clear phenomenon. The SO3 level corresponding to the highest expansion can vary for different cements [149], 

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Corrosion is not the only deterioration mechanism in reinforced concrete. Alkali-silica reactivity (ASR), sulphate attack, thurmasite attack, delayed ettringite formation, freeze thaw, thermal movement, settlement and other movement can all lead to concrete damage and their assessment must be included in the surveys. 

The thermal treatment of concrete can cause the detrimental effect of delayed ettringite formation, resulting in the deterioration of concrete elements. The problem of delayed ettringite formation belongs to the internal corrosion of concrete and will be discussed in the chapter relating to this corrosion. 

The delayed ettringite formation is rated among the internal corrosion of concrete, which is induced by a heat treatment of concrete, and thus occurring mainly during the precast concrete elements production. However, one carmot exclude the temperature rise up to 70 °C in the interior of massive concrete stracture, as a consequence of heat evolution process in hardened cement paste, and in this condition ettringite can be unstable. 

Fig. 6.29 Expansion of mortar from cement with high alkali content and granite aggregate vs time. Segment 3 results presumably from the delayed ettringite formation. (According to [85, 86])...

Fig. 6.37 Pre stressed concrete railway sleeper with cracks caused by the delayed ettringite formation...

The other stormy discussed problem refers to the role of anhydrite present in cement clinker, which slow dissolution is the cause of delayed ettringite formation [153]. In this case the delayed ettringite formation will be not linked with the heat treatment of concrete. 

The cause of delayed ettringite formation was elucidated based on the ettring-ite stability in concrete. As it is known, ettringite is stable at least at temperature 100 °C, in saturated water vapour [157]. However, Wieker et al. [151] found that ettringite is not stable at higher temperatures in the presence of alkalis. The results of these studies are presented in Table 6.2. 

Fig. 6.43 Famy s model of expansion meehanism, related to the delayed ettringite formation. Concrete treated at temperature > 70°C (Aeeording to [152])...

The thermal expansion coefficient for varions types of aggregate has a great impact on the expansion resulted from the delayed ettringite formation, as it has been pointed out in some reports. This problem was investigated by Grattan-Bellew et al. [179] who proved the relationship mentioned above (Fig. 6.46). 

Collepardi, M., Ogoumagh Olagot, J.J. In Scrivener, K., Skalny, J. (eds.) w Internal Sulphate Attack and Delayed Ettringite Formation. Proc. Int. RILEM TC 186-lSA Workshop, p. 212. Villars (2002)... 

Relationships of alkali sulfate to delayed ettringite formation (DBF) and reported expansion therefrom are unlikely, according to Miller and Tang (1996). 

Fu, Y., and Beaudoin, J.J. (1996) Microcracking as precursor to delayed ettringite formation in cement systems. Cement and Concrete Research 26,1493-1498. 

Lewis, M.C., Scrivener, K.L., and Kelham, S. (1995) Heat curing and delayed ettringite formation. Materials Research Society Symposium Proceedings 370,67-76. 

Risch et al. (1997) studied the possibility of using calcium aluminate cement alone or in combination with Poitland cement for the immobilization of inorganic wastes. They observed that the rate of leaching slowed down as the specimens became carbonated, producing a less permeable layer at the surface. However, delayed ettringite formation caused cracking of the test specimerts, associated with an errlargement of the teachable surface and a decrease of physical stabihty. 

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