As a water-reducing and plasticizing admixture, it improves the workability of fresh concrete without adding extra water.
The lignosulfonate polymer adsorbs onto the surfaces of cement and aggregate particles through electrostatic and hydrogen bonding.
This creates electrosteric repulsion between particles, dispersing them and preventing agglomeration.
The workability is increased as the inter-particle forces are reduced, allowing concrete to be placed and finished more easily.
It also functions as an air entrainment agent, entrapping microscopic air bubbles that increase frost resistance of hardened concrete.
Sodium lignosulfonate retards the setting time of concrete, providing more time for transporting, placing and finishing fresh concrete.
The strength of concrete is enhanced over time as hydration is slowed down, allowing for more complete hydration.
It is used in dosages ranging 0.1-2.0% of cement weight depending on required workability and set time.
Lignosulfonates improve both the plastic and hardened state properties of concrete in a cost-effective manner.
Their renewable and low-toxicity nature make them a sustainable concrete admixture option.
The typical dosage ranges used for sodium lignosulfonate as a concrete admixture are:
- Water Reduction/Plasticizing: 0.10-0.15% by weight of cement.
This dosage range is effective in increasing the workability and slump of fresh concrete without using extra water.
- Setting Time Retardation: 0.15-0.30% by weight of cement.
This range provides moderate retardation of initial and final set, allowing longer workability retention.
- High Range Water Reducer (HRWR): 0.30-1.50% by weight of cement.
At higher dosages it acts as a powerful water reducer and plasticizer for concrete with low water-cement ratio.
- Extra High Range Water Reducer: 1.50-2.00% by weight of cement.
Required for high-strength, self-consolidating concrete mixtures with very low water content.
- Air Entrainment: 0.05-0.10% by weight of cement.
Provides 5-8% of entrained air voids at these rates, improving frost resistance.