The role of lithium compounds in mitigating alkali-gravel aggregate reaction

Bulletin of the Polish Academy of Sciences Technical Sciences

2017

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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...

Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Bulletin of the Polish Academy of Sciences Technical Sciences

2017

Self Cite

“…A long-term method as set out in the ASTM C227 [9,10] was used to evaluate the effect of chalcedony dust on the reaction of alkalis with the reactive aggregate in cement mortars. The method consists in measuring linear changes in the cement mortar bars of 25 x 25 x 250 mm.…”

Section: Testing Methodsmentioning

confidence: 99%

The Evaluation of the Effect of Chalcedony Dust on the Reaction of Alkalis With Reactive Aggregate in Cement Mortars

Mazur

2018

SAE

A b s t r a c tChalcedony dust can be used as a mineral additive in cements and concretes. This material can act as a pozzolan and prevent the expansion caused by the alkali-silica reaction. The paper presents the examination of cement mortars with reactive opal aggregate and various quantities of chalcedony dust conducted using a long-term method as set out in the ASTM C227. A petrographic analysis as well as tests of potential reactivity of opal aggregate were carried out by chemical method as specified in the ASTM C289. The microstructure of cement mortars with chalcedony dust and opal was also examined. The tests showed a positive effect of the chalcedony dust additive on the reduction of the expansion caused by the alkali-silica reaction compared to the mortars without the additive. The addition of 20% of chalcedony dust to cement mortars lowers the expansion to a safe level that does not exceed 0.1% after 360 days (as set out in the ASTM C227). S t r e s z c z e n i eMączka chalcedonitowa może być wykorzystywana jako dodatek mineralny do cementów oraz betonów. Surowiec ten może działać jak pucolana i zapobiegać ekspansji wywołanej reakcją alkalia-krzemionka. W referacie przedstawiono badania zapraw cementowych z reaktywnym kruszywem opalowym oraz różną ilością dodatku mączki chalcedonitowej metodą długoterminową wg ASTM C227. Wykonano analizę petrograficzną oraz badania potencjalnej reaktywności kruszywa opalowego metodą chemiczną zawartą w normie ASTM C289. Przeprowadzono również badania mikrostruktury zapraw cementowych z mączką chalcedonitową i opalem. Badania wykazały pozytywny wpływ dodatku mączki chalcedonitowej na ograniczenie ekspansji wywołanej reakcją alkalia-krzemionka w stosunku do zapraw bez tego dodatku. Dodatek mączki chalcedonitowej do zapraw cementowych w ilości 20% obniża ekspansję do bezpiecznego poziomu, nieprzekraczającego po 360 dniach 0,1% (według normy ASTM C227).Słowa kluczowe: reakcja alkalia-krzemionka, mączka chalcedonitowa, dodatek mineralny, kruszywo reaktywne, skład cementu

“…In some cases the destruction of concrete was incorrectly attributed to other deterioration processes, excluding the reaction with alkalis [4]. In Poland, no cases of destructive alkaline reaction have been reported so far, however, the presence of reactive aggregates has been found in the regions of north-eastern and south-west Poland [5][6][7]. It is further necessary to take into account that concretes in road structures are highly exposed to AAR, which results from the limited possibility of protecting them from moisture.…”

Section: Introductionmentioning

confidence: 99%

The use of lithium compounds for inhibiting alkali-aggregate reaction effects in pavement structures

IOP Conf. Ser.: Mater. Sci. Eng.

2018

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Abstract. Internal corrosion of concrete caused by the reaction of reactive aggregate with sodium and potassium hydroxides from cement is a threat to the durability of concrete pavements. Traditional methods for reducing the negative effects of the reaction include the use of unreactive aggregates, low alkali cements, mineral additives or chemical admixtures, incorporated during mixing. Lowering the relative humidity of the concrete below 80% is another measure for limiting the destructive reaction. The incorporation of lithium compounds, in particular lithium nitrate and lithium hydroxide, to the concrete mix is a method of limiting alkali-silica reaction effects. The challenge is to reduce the negative effects of aggregate reactivity in members in which the reaction has occurred because the aggregate happened to be reactive. The paper presents ways of limiting the deterioration of ASR-affected concrete in road pavements and other forms of transportation infrastructure, mainly through the use of lithium compounds, i.e. lithium nitrate. Impregnation methods that allow the penetration of lithium ions into the concrete structure were characterized, as was the effectiveness of the solutions applied.