Page 182 - Handbook of Thermal Analysis of Construction Materials

166 Chapter 4 - Introduction to Concrete Admixtures

Retarders such as salicylic acid retard C S hydration especially at
2
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.