Civil Engineering Reference
In-Depth Information
The conduction calorimetric curve of cement with 45% diatomite
shows that the pozzolan modifies considerably the heat generated in the
samples (Fig. 30).
[2][76]
Not only does the main exothermic peak appear
earlier, but it is also of greater intensity than that exhibited by the reference
cement. This indicates that the tricalcium silicate phase of the cement is
accelerated by diatomite.
Figure 30.
Heat generation in the portland cement-diatomite mixture.
Thermal analytical techniques have been applied to investigate the
causes leading to the deterioration of concrete subjected to various environ-
mental factors. A mortar nearly two thousand years old obtained from El
Tajan near Mexico City was analyzed by TG and electron microscopy.
[77]
TG analysis was done on samples taken from different areas and depths.
The loss of water below 100°Cwas caused by the adsorbed water from the
volcanic tuff, while the endothermal effect at >700°C corresponded to the
carbonated lime and carbonated silicates and aluminates derived from the
pozzolan. The extent of the reaction of lime with pozzolan was computed
to be 6.91%.
8.0
RELATIVE EFFECTS OF POZZOLANS
AND THEIR MIXTURES
The role of individual supplementary cementing materials and
additives has been described in the previous sections. The effect of these
materials, viz., silica fume, slags, rice husk ash, fly ash, metakaolinite, or
natural pozzolans on the properties of concrete such as workability, setting,
rate of hydration, strength development, heat, durability, etc., is known to
