1. The analysis of the results of the determination of pozzolanic
activity with Portland cement shows that even at the lowest
calcination temperature tested (400 C), the values obtained
are similar to those of the reference mixture. The optimal pozzolanic
activity index was obtained with a calcination temperature
of 700 C for 30 min. However, this value is only 3.5%
higher than the value obtained with a calcination temperature
of 600 C for 1 h, which requires less energy. As a result, using
a temperature of 700 C is not economical.
2. The analysis of the results of determination of the concentration
of fixed calcium hydroxide – Chapelle method – showed that
the best results are obtained with a calcination temperature
of 700 C for 30 min. However, this value is very close to the
one obtained with a calcination temperature of 600 C for 1 h,
which requires less energy. The resulting value is more than
twice the limit required to classify a material as having low pozzolanic
activity.
3. The concentration of kaolinite (% – dry weight) was 37%, which
is below the minimum desired level for calcined clays (50%).
The amount of associated quartz should be low, which is not
the case with this material.
4. For identical w/b ratios, the concrete mixes prepared with WTP
sludge ash showed increases in strength ranging from 3% to
30%, depending on the w/b ratio and the concentration of substitution
used. The fact that improved strength is already present
after 7 days means that the flow of operations in
construction sites is not affected.