is a Ca, Al-sulphate hydrate, which is formed by the chemical interaction of the anhydrite/gypsum and residual dehydroxylated aluminosilicate clays and/or Al-Si glasses [19, 41, 44-47].
It is known that cement concrete collapses in acid because of ettringite
produced in a reaction between calcium aluminate of cement and sulfate of acid.
As water is introduced to cement to make a paste, which hardens over time, the main microstructural phases in the hydrated cement paste are: (1) calcium silicate hydrate gel, C-S-H; (2) calcium hydroxide, CH; (3) ettringite
(a sulfoaluminate hydrate); (4) monosulfate; (5) unhydrated cement particles; and (6) air voids.
The cured material contains less than 5% by weight of ettringite
is formed with aluminate ions being supplied by monosulfate and un-reacted [C.
It also forms gypsum and ettringite
when exposed to sulfates.
During deposition, the composition of semicoke changes as unstable phases of minerals are replaced by a considerable amount of ettringite
(a Ca-Al-sulphate) (Motlep et al.
Excessive heat-would expose the concrete to DEF (Delayed Ettringite
Formation), produce thermal cracking, reduce the concrete ultimate strength and modulus of elasticity, he explained.
Therefore, fewer products of CSH and ettringite
were produced in the early stage of hydration, which leads to slow strength development and retards the setting time (Hewlett 2003).
3]A as well as formed ettringite
crystal whiskers film which slows the rapid coagulation of [C.
The very rapidly initiated reaction of the cement clinker component with sulfate to form ettringite
seems to be critical.
The pre-mixed cementitious powder includes conventional portland cement, silica fume and ettringite