Civil Engineering Reference
In-Depth Information
The reactivity of MK depends on the temperature conditions under
which it is obtained, its surface area, and types of other materials contained
in it.
[64][65]
Ambroise, et al.,
[66]
examined the pozzolanic activity of four
clays of different compositions, by reacting them with lime. The consump-
tion of lime was followed by DTA (Table 8). The most reactive mixtures
were Nos. 1 and 2, containing 92% kaolinite, and the peak areas correspond-
ing to lime in these samples are 6 and 0 respectively. Samples 3 and 4, which
contained illite, quartz, carbonate, and only 19-29% kaolinite, reacted only
to a limited extent with lime, as evident from large areas for the lime peak.
The mortars with mixes 1 and 2 show higher compressive strengths than the
others.
Table 8.
Dependence of Clay Composition on Reactivity and Strength
Clay Composition
DTA Peak Area
Compressive Strength
(mm
2
)
(MPa)
1.
Kaolinite (92.5%)
6.0
25.9
2.
Kaolinite (92%)
0.0
24.1
3.
Kaolinite (19%),
Illite (37.5%),
Quartz (29%),
Carbonate (8%)
500.0
10.7
4.
Kaolinite (29%),
Illite (30%),
Quartz (18%),
Carbonate (11%)
630.0
12.0
Metakaolin reacts with lime to yield calcium silicate hydrate.
[60]
Metakaolin may also be activated by other materials such as alkali metal
hydroxides, water glass, etc. Activation leads to a polycondensation prod-
uct with cementing properties. The type of MK, composition, temperature
at which it is produced, surface area, etc., determine the strength develop-
ment characteristics of the product.
[67][68]
In conduction calorimetry, an
exothermic peak results by the reaction of MK and the activator. A strong
asymmetric peak in calorimetry is associated with an amorphous inorganic
