Civil Engineering Reference
In-Depth Information
steep increase occurs in the CLS uptake up to an initial concentration of
about 1 g/L. This is due to the formation of a large amount of C-S-H (of high
specific surface) formed in the presence of low amounts of lignosulfonate.
DTA curves show large endothermal effects below 200°C and one between
400 and 500°C for the formation of lime. At CLS concentrations between
1 and 3 g/L there is a decrease in the uptake of CLS as the degree of
hydration of C
3
S is reduced. At a concentration above 3 g/L, there is again
a gradual increase in the amount of CLS uptake, although the hydration of
C
3
S is minimal. Therefore, the gradual increase in the adsorption of CLS
above a concentration of 3 g/L, may either be due to a better dispersion of
C
3
S particles which increases its surface area and/or to the penetration of
CLS molecules between the interlayer position of C-S-H phase. On the
desorption branch, at low concentration levels, there is complete irrevers-
ibility of adsorption, indicating that CLS is strongly adsorbed on the
hydrated C
3
S as complex.
Figure 4.
Rate of hydration of C
3
S as a function of the concentration of CLS by conduction
calorimetry.
