Sodium lignosulfonates having perfect technical characteristics are commonly used in construction. The main advantage of this unique product is that it is eco-friendly for environment and human health, have high surface activity and stabilizing properties.
Lignosulfonates are used for concrete, cement slurry and plaster blends manufacture, help to produce workable and flowable slurry and increasing mechanical strength of the final product by controlling of plaster blends and concrete setting time. It improves final resistance of products and makes it more durable.
Lignosulfonates (often abbreviated as LS) were one of the first dispersants added as an admixture to concrete. Lignosulfonates have been used since the 1930s as plasticizers or water reducers. Mixed with concrete, their use has afforded the beneficial effects of retarding the setting time and reducing the amount of mixing water required.
Furthermore, greater workability of plastic concrete during its placement in formworks and increased air entrainment have resulted from their use. As by-product of the pulping industry, lignosulfonates are of low price and despite their limited performance they find a large field of applications for improving the quality of concrete.
Lignosulfonates retard the setting of cement. While this retardation can occasionally be advantageous, under certain weather conditions (e.g. in cool weather) the setting time may be extended to an impractical length of time. Approximately a quarter of the total solids in spent liquor is sugars, which can cause a strong retarding effect.
Therefore, the removal of some or all of the sugars is usually desirable. Different methods such as precipitation, alkaline heat treatment or ultrafiltration are used to reduce the sugar content in the spent sulfite liquor.
This purification reduces the retarding effect. However, it does not disappear as sugar-free lignosulfonate shows retarding effects. In short, commercially available lignosulfonates show retardation, which is due to the lignosulfonates themselves, possibly but not always incremented by retardation from residual sugars.