Alkali-silica reactions

Some types of aggregate can react with Na, K and OH ions in the pore solution, giving rise to detrimental expansion. The principal reactions can take place with aggregate containing certain forms of amorphous or poorly crystalline sihca (alkah sihca reaction, ASR) and with dolomitic hmestone aggregate (alkali carbonate reaction). 

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. 

Diamond (D50) described the types of silica that can take part in ASR. They include quartz if sufficiently strained or microcrystalline, tridymite, cristobalite and glass or other amorphous forms, which occur in varying combinations in opals, flints, cherts and other rock types. Opals are especially reactive. Macroscopic, unstrained crystals of quartz appear to be Linreactive but are possibly not completely inert. Some silicate minerals and volcanic glasses may undergo reactions similar to ASR. 

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Potential volume change of cement—aggregate combinations Accelerated detection of potentially deleterious expansion of mortar bars due to alkali-silica 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,... 

Lithium hydroxide is effective in reducing the expansion caused by alkali-silica reactions. Mixes containing 1.0% LiOH have shown decreased... 

The mechanism of the inhibitive action of LiOH proposed by Stark et al. [7] is attributed to the formation of lithium silicate that dissolves at the surface of the aggregate without causing swelling [7], In the presence of KOH and NaOH the gel product incorporates Li ions and the amount of Li in this gel increases with its concentration. The threshold level of Na Li is 1 0.67 to 1 1 molar ratio at which expansion due to alkali-silica reaction is reduced to safe levels. Some workers [22] have found that when LiOH is added to mortar much more lithium is taken up by the cement hydration products than Na or K. This would indicate that small amounts of lithium are not very effective. It can therefore be concluded that a critical amount of lithium is needed to overcome the combined concentrations of KOH and NaOH to eliminate the expansive effect and that the product formed with Li is non-expansive. 

Hobbs, D.W. (1988). Alkali Silica Reaction in Concrete, Thomas Telford Ltd., London. 

Wang, H. and Gillott, J.E. (1992). 9th International Conference on Alkali Silica Reaction, London, 1090-99. 

AR = alumina ratio (alumina modulus). ASR = alkali silica reaction. LSF = lime saturation factor. SR = silica ratio (silica modulus). C, = analytical (total) concentration of x, irrespective of species, [x] = concentration of species x. x = activity of species x. RH = relative humidity. =... 

Rodrigues, F,A, Monteiro, P.J.M., and Sposito, G., The alkali-silica reaction. The surface charge density of silica and its effect on expansive pressure. Cement Concrete Res., 29, 527, 1999,... 

Fire-, blast-, and earthquake-resistant materials and systems Crosscutting innovations Constituent materials New materials Smart systems for design of fire-, blast-, and heat-resistant alternative reinforced structures Survivability reserach Concrete as part of multimaterials systems Noncorroding steel reinforcement Concrete with predictable performance Materials with reduced shrinkage and cracking Reduction of alkali-silica reactions in concrete... 

Alkali-silica reaction is an expansive reaction in concrete that can occur when a solution of sodium or potassium hydroxide reacts with a siliceous aggregate to form a gel of hydrated alkali silicate. 

Alkali-silica reaction in the Netherlands Experiences and current research , Heron, 2002, 47 (2), 81-86. 

H. M. Visser, R. B. Polder, Alkali-silica reaction in concrete penetration of alkalis (in Dutch), TNO Building and Construction Research report 2000-BT-MK-R0207, 2000. 

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