Mitigation of Microcracking in Alkali-Activated Combined Slag and Fly Ash Concretes for Good Performance in Winter Conditions

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Title: Mitigation of Microcracking in Alkali-Activated Combined Slag and Fly Ash Concretes for Good Performance in Winter Conditions

Author(s): Alexandre Rodrigue, Josée Duchesne, Benoit Fournier and Benoit Bissonnette

Publication: Special Publication

Volume: 320

Issue:

Appears on pages(s):

Keywords: Alkali-activated concrete; autogenous shrinkage; cracking

Date: 8/1/2017

Abstract:
Concerns regarding the higher shrinkage and early cracking of alkali-activated binders can become a major issue for resistance to de-icing salts scaling, freeze-thaw cycles and/or chemical attacks. Using the Damage Rating Index (DRI) method, cracking has been quantified in concrete samples using a slag/fly ash binder activated with a combined sodium hydroxide and sodium silicate solution. The decrease of the added water dosage and the fly ash content results in an increase in the DRI values in the presence of slag/fly ash binder. Alkali-activated pastes with the same binding phase characteristics were tested using the ASTM C1698 for the evaluation of the autogenous volume changes to explain the observed cracking. With a constant activator-to-binder ratio of 0.35, different added water-to-binder ratios (0.12, 0.14 and 0.16) and fly ash contents (20, 30, and 40 %) were investigated. Autogenous shrinkage was found to decrease with increasing water dosage and fly ash content.