Foundation, Concrete and Earthquake Engineering

Dosage of Superplasticizers

In order to increase the workability of the concrete mix, the normal dosage of superplasticizers is between 1 and 3 litres per cubic metre of concrete, the liquid superplasticizer containing about 40 percent of active material. When superplasticizers are used to reduce the water content of the mix, their dosages is much higher: 5 to 20 litres per cubic metre of concrete. In the calculation of the water/cement ratio and of mix proportions in general, the volume of the liquid superplasticizer must be taken into account. 

It is worth noting that the concentration of solids in commercial superplasticizers varies so that any comparison of performance should be made on the basis of the amount of solids, and not on the total mass. For practical purposes, comparison should be made on the basis of the price for a given effect.
The effectiveness of a given dosage of a superplasticizer depends on the water/cement ratio of the mix. Specifically, at a given dosage of the superplasticizers, the percentage water reduction which maintains a constant workability is much higher at low water/cement ratio of 0.40, the reduction was observed to be 23 percent, and only 11 percent at a water/cement ratio of 0.55.

When superplasticizers are used in very low dosages to produce high workability normal-strength concrete, there are few problems in selecting an admixture-cement combination. At high dosages, the situation is significantly different in that the superplasticizers has to be compatible with the actual cement used, and is not enough for the superplasticizers and the cement separately to conform to their respective standards.  
FDN-A, B AND C Superplasticizer is a dry powdered admixture. It is produced through such a process: 1) sulphonating refined naphthalene with sulfuric acid, 2) condensing with formaldehyde, 3) neutralization, and 4) filtering. It conforms to GB8076-1997 and is mainly used for various high-strength concrete, steel concrete, prestressed concrete, large formwork concrete, slipforming concrete etc.

No comments:

Post a Comment