The various factors which affect the performance of concrete admixtures are:
1. Type of super-plasticizer:
The admixture will be more effective if molecular weight of the super-plasticizer is high.
2. Dosage:
The quantity of admixture should be optimum. Excess of admixture may cause segregation or bleeding. It may also cause excessive retardation. The optimum does 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 does of admixture.
4. Mix Design:
All constituents of mix affect the performance of the super-plasticizer as given below:
- Water: more water in the mix improves the physical interaction and dispersion of admixtures.
- Coarse aggregate: proportioning and grading of coarse aggregates influence the performance of concrete admixture.
- Fine aggregate: proportioning, grading and silt content also influence the performance of concrete admixture.
- Cement: its fineness, C3A content influence the performance of admixture. Higher C3A reduces efficiency of admixture.
- Other admixture: presence of other admixtures also influences the performance of concrete admixtures.
Therefore, proper trials before actual use are very vital for effectiveness of admixture.
Other factors admixture performance:
Certain other factors like temperature and humidity at the time of concreting also affect the performance of the concrete admixtures.
Drum mixtures are considered ideal for mixing admixtures, instead we should use pan or compulsive shaft mixes.
