Abstract
This paper analyses the effect of mineral additives on alkali - silica reaction. Amorphous SiO2 contained in concrete aggregate is known for reactions with Na2O and K2O that cause concrete expansion and cracking. Concrete expansion is the result of silicates reaction (ASR). Alkali silica gel is a reaction product having expanding properties. Expanding silica gel creates stress that causes concrete cracking. The paper investigates the elimination of the negative effect of ASR by using fly ash as active mineral additive. In the tests active mineral additive (fly ash) is expected to reduce the effect of alkali - silica reaction and volumetric strain. DOI: http://dx.doi.org/10.5755/j01.sace.6.1.6354
Highlights
alkalisilica reaction (ASR) i.e. reaction of alkali and silica gel in granular matrix composites, is destruction caused by adverse chemical reactions between the alkali present in hardened concrete (Na2O and K2O) and reactive silica or carbonate components present in the aggregates (Gumuliauskas, Navickas, 2007)
The effect of fly ash used as the mineral admixture was determined by analysing the relation between the average volumetric strain and the content of fly ash in concrete mix in the batch of specimens with the same content of the fly ash
The volumetric strain in specimens made of concrete mix with aggregate from this quarry and 0 % of fly ash was 0,0220, i.e. several times higher compared to specimens of the same composition with aggregates from Rizgonys and Zatyšiai quarries
Summary
ASR i.e. reaction of alkali and silica gel in granular matrix composites, is destruction caused by adverse chemical reactions between the alkali present in hardened concrete (Na2O and K2O) and reactive silica or carbonate components present in the aggregates (Gumuliauskas, Navickas, 2007) Such corrosion may even lead to structure failures; it is very important to find ways to reduce it and produce alkali - silica reaction resistant concrete. During cement hardening SiO2 reacts with Na2O and K2O and hydrosilicate crystals of alkali metals with variable content of crystalized water are formed on the surface of reactive aggregates Such corrosion of concrete becomes especially visible on the surface of concrete structures, where pieces of opal aggregates are pressed out from the surface layer (Balandis et al, 2006). Alkali – silica reaction is an acid-base reaction between calcium hydroxide (Ca(OH)2), otherwise known as Portlandite, and silicic acid (H4SiO4) or Si(OH4), otherwise known as pozzolanic reaction, schematically represented as follows: Ca(OH)2 + H4SiO4 → Ca2+ + H2SiO42-+2H2O → CaH2SiO4 ∙ 2H2O (Balandis et al, 2006)
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