Sodium Lignosulfonate in Concrete

When an appropriate amount of sodium lignosulfonate is mixed into concrete, the free water in the cement slurry flocculation structure is released due to the adsorption, dispersion, electrical activity, surface free energy reduction, and other factors of sodium lignin sulfonate. The influence of sodium lignin sulfonate on concrete is as follows:

1. Improve the performance of concrete: when the dosage and slump of cement are close to the benchmark concrete, adding sodium lignosulfonate in concrete can reduce water dosage by about 10%, concrete 3-28d strength increased by about 15%, and the later strength also will be increased.
2. Save cement: it can save about 10% of cement while keeps the concrete strength and slump close to the benchmark concrete.
3. Improve the workability of concrete: the water retention, cohesiveness, and pumpability of concrete mixed with sodium lignin sulfonate are significantly improved.
4. Lignin has a retarding effect: after adding 0.25% lignin water reducing agent, the initial setting time of ordinary cement is delayed by 1-2 hours when the slump of the concrete is basically the same, and the initial setting time of slag cement is 2 4 hours.
5. It can reduce the early hydration heat of cement: the appearance of the exothermic peak of the concrete mixed with sodium lignosulfonate is later than that of the unmixed concrete.
6. Certain air permeability: when the content of sodium lignosulfonate is 0.25%, the air content of concrete increases by 2%~3%, thus improving the properties of concrete such as impermeability and freeze-thaw resistance.
7. Reduced bleeding rate: Under the condition that the slump of concrete is basically the same, the bleeding rate of concrete mixed with lignin is lower than that of normal concrete by more than 30%. While keeping the water-cement ratio constant and the slump increased, the bleeding rate of concrete with lignin will be decreased due to the hydrophilicity of lignin and the introduction of air.
8. It can improve the compactness of concrete and improve the impermeability of concrete.
   Sodium lignosulfonate does not contain chloride salts and has no corrosion hazard to steel bars.

When using lignin sodium sulfonate, the dosage must be strictly controlled, otherwise, the early strength of concrete will be affected. After exceeding the dosage, the setting time may be significantly prolonged, or even not hardened. According to different application requirements, the actual dosage can be determined through the proportioning test with reference to the following dosage range, combined with local actual conditions.

• When lignin is used as a water-reducing agent raw material, the dosage selection range is 0.1-0.20%;
• When used as a raw material for retarding and air-entraining water reducer, the dosage range is 0.20-0.30%
• When used as a composite water reducer raw material, the dosage range is 0.05-0.20%

The retardation effect of lignin products increases significantly with the decrease of temperature, and the lower the temperature, the slower the strong growth. It is suitable for concrete with a daily minimum temperature above 5℃. Not suitable for steaming concrete alone.

Lignin products are easily soluble in water (hot water is better) and can be made into 1%-50% aqueous solution. When dissolving, first put water into the container, and add sodium lignosulfonate while stirring. Remember to pour a lot of water quickly to avoid clumping or prolong the dissolution time. After being formulated into a solution, it should be used up within 10 days to prevent mildew.

Lignin products may have a false setting for cement with anhydrite or fluorogypsum as a regulator. The suitability test of cement varieties is required before use. Before being used as a concrete water-reducing agent, a mix ratio test must be carried out, and it can be used in engineering only if it meets the technical requirements.

For the concrete with specified air-entraining volume, when the air-entraining volume is too large, the appropriate vibrating time must be selected, or other defoaming measures must be adopted to ensure that the air-entraining volume meets the technical requirements.

When the concrete with lignin needs to be steam-cured, technical measures such as prolonging the resting time or compounding other additives, reducing the content of sodium lignosulfonate and other technical measures can prevent the occurrence of phenomena such as strength drop or looseness.