The failure process of mortars during sulfate attack
Keywords:
concrete structure, sulfate environment, damage process, ettringite, gypsumAbstract
External sulfate attacks on concrete structures may
cause serious damage and it has attracted a wide
range of attention from numerous researchers over
the past decades. However, many studies have been
concentrated on the sample which has been already
destroyed. This paper investigated the entire
deterioration process of mortars that were
immersed in Na2SO4 solution containing 3 gSO42-/L
and 33.8g SO42-/l at 20 oC up to 600 days. The study
on time-varying regularity of expansion, cracks,
compressive strength and mineral phases was
investigated. Back scattered electron image was
used to further examine the evolution of
microstructures of the mortars during the attack
process. The results showed that damage process of
mortars can be described as induction stage,
surface damage, bulk damage and then completely
damage stage. Fine ettringites that were formed in
restricted spaces, approximately 2-5 ?m, result in
surface damage. At the bulk damage stage,
cracking was the main characteristic of mortar
which leads to obvious expansion. In this stage,
some large ettringite crystals (>20?m) were just
deposited in the formed cracks. At the later stage,
gypsum can be easily formed at interfacial
transition zones as the consumption of calcium
hydroxide, which mainly contributed to completely
strength failure rather than expansion.
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