Set Control Concrete Admixtures – Accelerators & Retarders

Why Use Accelerating Admixtures?

Accelerating admixtures are used to speed up the set time and increase the early strength of concrete. Accelerators are most frequently used in the winter months to allow final finishing operations to take place within a reasonable time after the concrete is initially poured.

Main Types of Accelerators:

ASTM Classifications

  • Type C: Accelerating
  • Type E: Water Reducing & Accelerating
    • Chloride
    • Non-Chloride
    • Sub-Freezing

Benefits of Accelerating Admixtures:

  • Speed Up Set Time & Project Schedule
  • Reduce Bleed Water
  • Increase Early Strength
  • Reduce the Duration of Required Weather Protection

Why Use Retarding Admixtures?

Retarding admixtures are used to slow down the set time and allow adequate time to finish the concrete. Retarding admixtures are most often applied during the summer months to reduce the chance of concrete hardening before finishing operations are completed.

Main Types of Retarders:

ASTM Classifications

  • Conventional
  • Hydration Controlling
    • Type B: Retarding (Rarely Used)
    • Type D: Retarding & Water Reducing (Most Common)
    • Type G: Retarding, Water Reducing, & High Range

Benefits of Retarders:

  • Aids Finishing Operations
  • Allows increased transportation time for long shipments to construction sites.
  • Reduces Cold Joint Potential