The various factors affecting the performance of admixture are as given below :
1. Type of super-plasticizer: The admixture will be more effective if molecular weight of the super-plasticizer is high.
2. Dosages: The quantity of admixture should be optimum. Excess of admixture may cause segregation or bleeding. It may also cause excessive retardation. The optimum dose should be estimated by trials.
3. Compatibility with cement: All admixtures may not produce same results with different cements. Therefore before using any admixture, its compatibility with cement has to be established. Properties of cement like fineness, chemical-composition, C3A content etc. affect the performance of admixture. Therefore, trials have to be made before finalizing an optimum dose of admixture.
4. Mix Design: All the constituents of mix affect the performance of the super-plasticizer as given below:
(a)Water: More water in the mix improves the physical interaction and dispersion of admixtures.
(b)Coarse Aggregate: Proportion and grading of CA influence the performance of admixture.
(c)Fine Aggregate: Proportion, grading and silt content also influence the performance.
(d)Cement: Its fineness, C3A content influence the performance. Higher C3A reduces efficiency of admixture.
(e)Other Admixtures: Presence of other admixtures also influence the performance of super-plasticizers.
Therefore proper trials before actual use are very vital for effectiveness of admixture.
5. Other factors: Certain other factors like temperature and humidity at the time of concreting also affect the performance of the super-plasticizers. High temperature and less humidity lower the efficiency of admixture. Drum mixers are not considered ideal for mixing admixtures, instead we should use pan or compulsive shaft mixers.