Civil Engineering Reference
In-Depth Information
In the first few hours of the test, the pozzolanic materials raised the heat
of hydration as a result of the filler effect (Taylor, 1997), which favours
hydration and pozzolanicity. Between 5 and 12 hours, however, the reactions
were highly exothermal and the upward slope on the curves was very steep,
with the base cement exhibiting greater heat of hydration than the blended
materials. Over time, the pozzolanic activity of the material was instrumental
in the development of heat of hydration.
This effect is shown more clearly in Fig. 4.4 which depicts the variation in
heat of hydration in mixed mortars normalised to the base mortar (assigned
a value of 0) in the first 14 hours of the trial. Note that the heat of hydration
declined with rising addition pozzolanicity. Hence, opaline lowered the heat
of hydration less than the other additions. Given its high pozzolanicity, the
MK blend even exhibited greater heat of hydration than the control due to
its specific reactions with calcium hydroxide, for the formation of aluminium
hydrate compounds plays an important role in the development of the heat
released (Frías et al., 2000).
4.4.2 Mechanical properties
The existing European Standard (EN 197-1, 2011) lists the mechanical
specifications (compressive strength) to be met by commercial Portland
100
Cement
Pumice
Tuff
Opaline rock
Diatomaceous earth
Limestone filler
Metakaolin
80
60
40
20
0
0
2
4
6
8
10
12
14
-20
-40
-60
-80
-100
4.4
Incremental heat of hydration in mortars with different additions
(cement : addition ratio, 70 : 30) referred to base cement (100 : 0).
