Civil Engineering Reference
In-Depth Information
2.4
OPC3
FA3
2.0
1.6
1.2
0.8
0.4
0.0
0
4
8
12
16
40
60
80
100
Time (days)
17.14
Activated fly ash (FA3) and traditional OPC (OPC3) mortar
expansion (%) over time (García-Lodeiro et al., 2007).
(main reaction product), while the rest remain in the liquid housed in the
pore system (criado et al.,
2005; Kovalchuk et al.,
2007). When the curing
temperature and humidity are unsuitable, the excess alkalis spread across the
pore system, precipitating as salts on the surface of the material (Temuujin et
al., 2009; van deventer
et al.,
2010). recent studies conducted by Pacheco-
Torgal and Jalali (2010) show that sodium efflorescence is especially prevalent
in alkali-activated aluminosilicate binders burnt at a temperature below the
dehydroxylation temperature and containing sodium carbonate additions as
a source of sodium cations.
Kani et al. (2011) recently showed that efflorescence can be reduced either
by adding alumina-rich admixtures or by hydrothermal curing at temperatures
of 65 °c or higher.
Frost resistance
The excellent resistance to extreme environments, and in particular to frost,
exhibited by traditional Portland cement concretes and mortars is based on the
degree of saturation and pore system of the hardened paste. if the concrete
never becomes saturated, the risk of freeze/thaw-induced deterioration is
nil. if the concrete expands beyond its stress resistance as a result of the
presence of ice, however, it will be damaged. The information available on
geopolymer expansion in response to frost is contradictory. according to
Zhang and Wei (2006) alkali-activated fly ash concrete can withstand 2.2
times more freeze-thaw cycles than concrete made from oPc with the same
compressive strength. Škvára (2007) reported that alkali activated fly ash-
