Civil Engineering Reference
In-Depth Information
effects at 300° and 300-500°C represent dehydration effects of the cubic
C
3
AH
6
phase. In the absence of lignosulfonate, even at 15 minutes, a large
endothermal peak occurs at 300°C due to the presence of the cubic phase.
In the presence of 0.1% sugar-free lignosulfonate, there is a slight retarda-
tion effect in the early periods, but at 1 day the cubic phase predominates.
At 0.5% addition, there is a significant retardation effect as evidenced from
the presence of a large amount of the hexagonal phase. Complete conver-
sion of the hexagonal to the cubic phase occurs only at 28 days. Further
retardation is observed at 1-3% additions of Na lignosulfonate. Thermo-
gravimetric analysis and XRD investigations confirmed the results ob-
tained from DTA. It also appears that sugar-free Ca and Na lignosulfonates
are nearly as effective as the commercial lignosulfonate in delaying the
setting characteristics of cement (Table 2).
[15]
Figure 11.
DTA of C
3
A hydrated in the presence of sugar-free Na lignosulfonate.
