Effect of lithium nitrate on the reaction between opal aggregate and sodium and potassium hydroxides in concrete over a long period of time

Abstract

Abstract. Alkali-silica reaction (ASR) is a reaction between amorphous or poorly crystallized siliceous phase, present in aggregates, and sodium and potassium hydroxides in the pore solution of concrete. Chemical admixtures such as lithium compounds are known to have high potential of inhibiting ASR. The aim of this study was to determine the effect of lithium nitrate on ASR in mortars containing high reactive opal aggregate over a long period of time. Mortar bar expansion tests were performed and microstructures of mortar bars were observed by scanning electron microscopy coupled with an energy dispersive X-ray microanalyser. Results from this study showed that effectiveness of lithium nitrate in mitigating ASR was limited over a long period of time. A larger amount of ASR gel which was formed in the presence of lithium nitrate indicated that the deterioration processes intensify within longer periods of time, which so far has not been observed in literature. Microscopic observation confirmed the presence of alkali-silica gel and delayed ettringite in mortars with lithium nitrate.Key words: alkali-silica reaction, lithium nitrate, ettringite formation, expansion, SEM/EDS. Effect of lithium nitrate on the reaction between opal aggregateand sodium and potassium hydroxides in concrete over a long period of time J. ZAPAŁA-SŁAWETA * and Z. OWSIAK Kielce University of Technology eses have been put forward to explain the role of lithium ions in the reaction. These include, but are not limited to, a hypothesis of reduced silica reactivity caused by the formation of a layer of lithium silicate crystallites or lithium ion-rich amorphous products on the silica surface. This layer on the surface of the aggregate prevents the reaction of silica with sodium and potassium hydroxides [12,13]. Recent years have brought more reports on the modified composition and properties of sodium-potassium-calcium silicate gels with lithium ions. Sodium and potassium ions in gels are exchanged for lithium ions, which makes them less swellable [14,15]. Gels with lithium ions are more compact, which limits the diffusion of hydroxyl, sodium and potassium ions into reactive grains [16]. Studies of the alkali-aggregate reaction have often indicated the presence of delayed ettringite [17,18]. The coexistence of aggregate reaction products with ettringite has been widely observed, especially in concrete railway sleepers in Finland, Sweden, Australia, Germany, South Africa, United States and China [19][20][21][22][23]. According to the current state of knowledge, the delayed ettringite crystallizes in the microcracks generated by the aggregate reaction with sodium and potassium hydroxides, but is not the primary source of the cracks [24,25]. Ettringite is not produced in strongly alkaline environments. However, when the concentration of sodium and potassium hydroxides decreases as a result of reacting with reactive aggregates, the conditions for its crystallization become favourable [26,27].Data on the simultaneous effects of lithium ions on alkali...

Chemical corrosion of external stairs – case study

“…4a, c), the presence of which was suggested by a high background exhibited on the XRD pattern. The X-ray microanalysis reveals a significant silicon content typical for the alkaline silica gel formed as a result of the alkali-silica reaction with sodium and potassium [14,15,16,17]. The presence of chlorine and even single crystals of sodium chloride are also detected (Fig.…”

“…The occurrence of the alkali-aggregate reaction could be prevented by using mineral additives or chemical admixtures during the production of concrete [1,14,19,20,21]. They would increase the tightness of concrete and counteract the alkali-aggregate reaction by binding the sodium and potassium ions in the C-S-H phase [1].…”

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“…The texture can reveal, for example, some specific distribution of reactive and unreactive phases in aggregate. The case in which the whole aggregate particle contains only one reactive mineral phase is very rare in nature [ 17 , 18 ]. However, those cases are usually considered in model tests [ 19 , 20 , 21 , 22 , 23 , 24 ].…”

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“…Choosing the right amount of lithium nitrate, which would limit concrete expansion caused by the alkali aggregate reaction, depends on the amount of the alkali in the cement as well as the type, the amount and the location of reactive minerals in the aggregate [10,11]. Lithium nitrate is introduced into the concrete mix together with mixing water and the amount of the lithium ions introduced corresponds to the molar ratio of Li to [Na+K].…”