Slump Retention Admixture: Types and Characteristics

Introduction to Slump Retention Admixture

Slump retention admixture is a type of chemical additive used to extend the slump retention time of concrete. It is primarily used in high-temperature environments, for long-distance transportation, or in large-scale concrete pouring projects, preventing concrete from losing its workability too quickly due to moisture evaporation or cement hydration.

Types and Characteristics of Slump Retention Admixture

Slow-release Polycarboxylate Superplasticizer

• Mechanism: Designed with a molecular structure that allows the superplasticizer to release slowly, continuously dispersing cement particles and extending slump retention time.

  
  

• Characteristics: High water reduction rate (20%–40%), slump retention in concrete for 2–4 hours, suitable for high-performance concrete (HPC).

Retarding Slump Retention Admixture

• Main Ingredients: Sodium gluconate, sodium citrate, molasses-based retarders, etc.

  
  

• Mechanism: Slows down the cement hydration rate, reducing slump loss.

  
  

• Characteristics: Low cost but may impact early strength development.

Composite Slump Retention Admixture

• Composition: Polycarboxylate superplasticizer + retarder + air-entraining agent (e.g., rosin soap).

  
  

• Characteristics: Excellent comprehensive performance, suitable for pumped concrete and self-compacting concrete (SCC).

Usage Method and Precautions for Slump Retention Admixture

Dosage Control

• Recommended Dosage: Typically 0.1%–0.5% of the total weight of binder material (adjust based on trials).

  
  

• High-temperature Environments (>30°C): Increase dosage to 0.3%–0.6%.

Precautions

Cement Compatibility

• Different cements (e.g., high C3A content, sulfoaluminate cement) exhibit different adsorption properties towards slump retention admixture, requiring flowability tests with neat cement paste.

  
  

• Abnormal Phenomena: Rapid slump loss (high cement adsorption) or excessive retardation (overuse of retarder).

Temperature Influence

• High temperature (>30°C): Increase dosage or use in combination with a retarder.

  
  

• Low temperature (<10°C): Reduce the use of retarders to avoid excessively long setting times.

Compatibility with Other Admixtures

• With Superplasticizers: Typically add the superplasticizer first, then the slump retention in concrete.

  
  

• With Accelerators: Can counteract the slump retention effect, requiring dosage adjustment.

Storage and Shelf Life

• Liquid Slump Retention Admixture: Store in a sealed, light-proof container to prevent settling; shelf life of 6–12 months.

• Powdered Slump Retention Admixture: Store in a dry place to prevent clumping.