Question: What problems will occur if excessive sodium methallyl sulfonate is added during polycarboxylate superplasticizer synthesis?
Answer: Over-dosed SMAS causes concrete bleeding & segregation, severe over-retarding, low early strength, poor initial slump, high salt efflorescence risk, unstable mother liquor and increased production cost.
- Excessive SMAS introduces a large number of hydrophilic sulfonate groups on the polymer molecular chain, which leads to overly strong water retention capacity. The finished polycarboxylate superplasticizer will cause serious concrete bleeding and segregation during construction, especially obvious when using manufactured sand or low-fineness modulus sand.
- Too much sodium methallyl sulfonate will significantly extend the setting time of cement paste, resulting in severe over-retarding. The early strength of concrete drops sharply, which seriously affects the turnover efficiency of precast components and the construction progress of cast-in-place engineering.
- High SMAS dosage changes the molecular weight distribution of copolymer. The molecular chain becomes too hydrophilic and flexible, reducing the initial dispersion performance. The initial slump of concrete cannot reach the design standard, even if the total admixture dosage is increased.
- SMAS itself contains inorganic salt impurities such as sodium sulfate. Excessive addition raises the total salt content of the mother liquor, increasing the risk of concrete surface efflorescence, and accelerating corrosion of steel bars in reinforced concrete structures.
- Excess unreacted sodium methallyl sulfonate monomer remains in the mother liquor, reducing the storage stability of polycarboxylate admixture. Long-term storage is prone to stratification, flocculation and yellow discoloration, shortening the shelf life of the product.
- The cost of raw materials rises obviously. SMAS is a relatively expensive functional monomer; excessive dosage directly increases the comprehensive production cost of polycarboxylate superplasticizer without bringing corresponding performance improvement.
