Title: Durability of Alkali-Activated Slag/Fly Ash Pastes and Concretes: an Overview of Performance Regarding Freezing and Thawing, Surface Scaling, Shrinkage and ASR

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

Publication: Symposium Paper

Volume: 349

Issue:

Appears on pages(s): 508-521

Keywords: Alkali-activated concrete, ASR, de-icing salts, durability, freezing and thawing, scaling, shrinkage

DOI: 10.14359/51732768

Date: 4/22/2021

Abstract:
Alkali-activated slag/fly ash concretes activated with combined sodium silicate and sodium hydroxide show good mechanical and durability properties in general. When tested in terms of resistance to freezing and thawing cycling in watersaturated conditions, the concretes tested in this study show final values of relative dynamic modulus averaging 100% after 300 cycles. However, all tested concretes showed poor performance towards freezing and thawing in presence of de-icing salts with only one tested mixture showing a final average scaling value below 0.5 kg/m^². Early-age microcracking is observed on all tested concretes and is correlated to high values of autogenous shrinkage in equivalent paste mixtures. Increasing the fly ash content reduces both the observed autogenous shrinkage and early-age cracking. Low drying shrinkage values ranging from 470 to 530 μm/m after 448 days of measurements at 50% RH and 23°C are noted. The use of fly ash in these alkali-activated concretes reduces the expansion levels of concrete specimens incorporating alkali-silica reactive aggregates. With increasing fly ash contents (20, 30 and 40% replacement), decreasing expansions are observed for any given reactive aggregate. In general, the durability properties measured in this study were improved by partially substituting slag with fly ash as binder material.