Alkali-aggregate reaction

The different types of admixtures, known to reduce alkali-aggregate reactions, can be divided into two groups those that are effective in reducing the expansion due to the alkali-silica reaction, and those that lower expansions resulting from the alkali-carbonate reaction. For the alkali-silica reaction, reductions in the expansion of mortar specimens have been obtained with soluble salts of lithium, barium and sodium, proteinaceous air-entraining agents, aluminum powder, CUSO4, sodium silicofluoride, alkyl alkoxy silane,... 

Fig. 6.2 Influence of air entrainment on expansion due to alkali-aggregate reaction (Ramachandran). 

The ions should not take part in the alkali-aggregate reaction to form other expansive materials. 

The aluminate-based admixtures undoubtedly provide the best wet-mix shotcrete, making it possible to build thick linings even in overhead work. The high alkali content and the consequent health hazard are the main constraints to their more widespread use. Furthermore, there is concern that the admixture may promote the alkali-aggregate reaction in concretes containing reactive aggregates, as well as sulfate attack [117]. 

Non-alkaline liquid accelerators are fairly new to the international market, therefore the bibliography on their use is still scarce. They were conceived to solve some classical problems stemming from the use of alkaline accelerators, such as caustic alkalis, hazardous conditions in underground work, risk of alkali-aggregate reaction, risk of handling conventional accelerators with extremely high pH level, and reduction of latter-age strength. 

Nomachi, H., Takada, M. and Nishibiyashi, S. (1989). 8th International Conference on Alkali-Aggregate Reaction, Kyoto, Japan, 211-15. 

Ohama, Y., Demura, K. and Wada, I. (1992). 9th International Conference on Alkali-Aggregate Reaction in Concrete, London, 420-31. 

Oberholster, R.E. and Westra, W.B. (1981). Proceedings 5th International Conference on Alkali-Aggregate Reaction in Concrete, Capetown, S. Africa, 10. 

Farbiarz, J., Schuman, D.C., Carrasquillo, R.E. and Snow, P.G. (1989). Proceedings 8th International Conference on Alkali-Aggregate Reactions in Concrete, Olso, Norway. 241-6. 

Gillot, J. E., Alkali-Aggregate Reactions in Concrete, Eng. Geol. Int. J. 

D51 Diamond, S., Barneyback, R. S. and Strublc, L. J., in Alkali-Aggregate Reaction in Concrete, Paper S252I22, CSIR, Pretoria (1981). 

Ozol, M. A., in Alkali-Aggregate Reaction—Preventive Measures, p. 113. Icelandic Building Research Institute, Reykjavik (1975). 

Freeze-thaw Alkali-aggregate reactions Fire Acid attack... 

ALkah sihca and alkali aggregate reactions are a significant cause of damage to concrete structures in many countries around the world, for instance in the UK, Denmark, Norway, France, Belgium, The Netherlands, Canada and the USA. As concrete is usually made with aggregate from local sources, the experience in each of these countries is based on a particular range of aggregates, see e. g. 

P- Nixon, C. L. Page, Pore solution chemistry and alkali aggregate reaction in ACI SP-100 Concrete Durability, ). M. Scanlon (Ed.), American Concrete Institute, Vol. 2, 1833-1862, 1987,... 

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