Nordic workshop final report

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Durability aspects of fly ash and slag in concrete Pore Solution after 24 h (with portland cement) • Essentially alkali hydroxide solutions: Na + , K + , OH - . • The solution is also saturated with respect to Ca 2+ , but its solubility is low in alkali solutions due to common ion effect. • Unless leaching or moisture movement (or some other ionic ingress) occurs, the alkali hydroxide solution concentrations remain relatively constant over time. 13 Pore Solution after 24 h (with portland cement) • Essentially alkali hydroxide solutions: Na + , K + , OH - . • The solution is also saturated with respect to Ca 2+ , but its solubility is low in alkali solutions due to common ion effect. • Unless leaching or moisture movement (or some other ionic ingress) occurs, the alkali hydroxide solution concentrations remain relatively constant over time (but with SCM’s the pore solution alkalinity changes over time as alkalis get taken up in hydrated phases). 14 Page 100 of 299 Nordic workshop, Oslo, Norway, February 15-16, 2012 7
Durability aspects of fly ash and slag in concrete Role of Alkalis Effect of the pH of the alkali solution on the solubility of amorphous silica pH of Concrete is 13-14 Dissolved Silica (mM/L) . 70 60 50 40 30 20 10 0 Solubility Curve of Amorphous Silica (Tang & Su‐fen, 1980) 8 9 10 11 12 13 pH Crystalline silica solubility is low at high pH at ambient temperatures 15 How do SCMs Mitigate ASR? • The main factor appears to be a reduction in pore solution alkalinity due to incorporation of alkalis into the lower Ca/Si C-S-H which is also increased by presence of Al 2 O 3 in SCMs to form low Ca/SI C-A-S-H. Page 101 of 299 Nordic workshop, Oslo, Norway, February 15-16, 2012 8
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Durability aspects of fly ash and s
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Nordic workshop final report

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