Study the influence of alkali leaching on internal sulfate attack by delayed ettringite formation

Abstract

    The primary ettringite formation in the initial stage of the hydration is considered as a positive effect because it enables the setting regulation of cement, a damaging role is often attributed to the ettringite formation in cement matrix (so-called delayed ettringite formation). Delayed Ettringite Formation (DEF) is an internal sulfate attack caused by early age heating to a temperature of over about 70°C. The high temperature during the hydration process will be decomposed and/ or prevented the normal (primary) ettringite formed during the initial hydration of cement. The ettringite is re-crystallized at later ages in cement matrix exposed to moist environment and causes expansion or cracking. In concrete elements which were affected by natural climate changes during service life, the composition of the pore solution inevitably changes due to the influence of storage. This research has been experimented to determine the longitudinal deformation of the mortar specimens and concentration of Na+ and K+ of the immersion solution in two conditions (immersion water was not changed during the experiment and was changed regularly)during the period of about 700 days. The experimental results in this paper showed that the leaching of alkali ions (Na+ and K+ ) into surrouding storage solution which plays a significant role in the mechanism of expansion by delayed ettringite formation