Civil Engineering Reference
In-Depth Information
Retarders such as salicylic acid retard C
2
S hydration especially at
higher w/s ratios,
[40]
but commercial lignosulfonates (at about 0.125%)
have a better retarding effect.
In general, retarders are effective in the very early hydration of
cement. For a given percentage, Na gluconate, citric acid, or sucrose are
better retarders of initial set of a normal low alkali cement than lignosul-
fonate, salicylic acid, Na heptonate, or boroheptonate.
[40]
At a constant w/c, the addition of commercial lignosulfonate
results in lower strength cement mortars, but later strengths are higher, as
can be seen in Fig. 9.
[73]
Sometimes lignosulfonate addition may not cause
an increase in strength at later ages due to the entrainment of air.
Figure 9.
Compressive and flexural strengths of portland cement mortars at a given w/c
ratio with lignosulfonate.
