4th WCSET-2015 at Japan
Plenary Session:
Title:
Mitigation of Delayed Ettringite Formation in New and
Old Concrete
Authors:
Amde M. Amde, Richard A. Livingston
Abstract: The
effects on delayed ettringite formation (DEF) of
partially replacing the Portland cement by different
amounts Class F fly ash or using mix water conditioners
(MWC) are discussed. Recent studies have shown that DEF
may be associated with deterioration problems in
concrete. Many countries have reported deterioration of
concrete structures where the main cause of distress has
been identified as DEF. Partially replacing the Portland
cement with Class F fly ash decreased the expansion,
with specimens showing larger reductions as the
percentage of fly ash increased. The SEM results
correlated with the observed expansions. The effect of
using MWC was found to be similar to using 10% fly ash
with respect to expansion but not with respect to
compressive strength. The short term and long term
effects on compressive strength were also investigated.
The study also investigated whether the growth of DEF in
existing concrete can be mitigated with commercial
products. Externally applied water repellents and
crystal growth inhibitors were tested. The research
required casting laboratory specimens for expansion and
weight measurements, for strength testing, and for
scanning electron microscope (SEM) investigations. The
testing consisted of four products: ChimneySaver, Radcon
Formula #7, Dequest 2060S, and Noveon Good-Rite K752.
Three of the four products, ChimneySaver, Dequest 2060S,
and Good-Rite K752, reduced concrete expansion and
weight change when compared to the control set. The
study indicates that ettringite may have to be
identified and mitigated early to prevent deleterious
effects.
Keywords: Concrete
Durability, Crystal Growth Inhibitors, Delayed
Ettringite Formation, Ettringite, Fly Ash, Mix Water
Conditioner, Sulfate Attack
Pages:
005-006