Overview of Water Reducing Agent
Water reducing agents or water reducers are a kind of concrete admixture that can reduce the water consumption under the condition of keeping the slump of concrete basically unchanged.
According to the chemical composition, water reducing agent is usually divided into lignosulfonate type of water reducing agent, naphthalene series of high-efficient water reducing agent, melamine series of high-efficient water reducing agent, amino sulfonate series of high-efficient water reducing agent, fatty acid series of high-efficient water reducing agent, polycarboxylate series of water reducing agent.
Introduction to Lignosulfonate
Lignosulfonate is a by-product of sulfite pulping. The molecular weight of lignosulfonate is 2000~5000, the sulfonate group is 1.25~2.5mcq /g. Lignosulfonate is soluble in water solutions of various PH values, insoluble in organic solvents, its functional group is phenolic hydroxyl. It is made from lignin, which is usually extracted from conifers. Lignin is composed of three kinds of lignin monomer polymerization, including calcium lignosulfonate, sodium lignosulfonate, and magnesium lignosulfonate. Lignosulfonate water reducer is a common type of water reducer, belonging to anionic surfactants. It can be used directly, but also as one of the compound admixture raw materials. Because of the cheap price, it is widely used worldwide. Used in mortar it can improve construction, fluidity, increase strength, and water reduction rate by 8%-10%.
Preparation method of Lignosulfonate
There are two main methods of delignification to manufacture water reducing agents.
(1) The sulfite waste liquid is neutralized with an alkaline solution, the saccharides are removed by biological fermentation, and the powder water reducing agent is evaporated and dried.
The waste liquid in the production process of chemical fiber pulp cypress made from sulfite cooking wood (more than 75% white pine) was used as raw material. Alcohol was extracted from the waste liquid by biological fermentation treatment and desaccharification. The alcohol waste liquid with about 10% concentration was concentrated to about 50% by an evaporator and then sent to the sprayer for drying. The pH = 4.5 to 5.5. Different wood types and cooking processes have a great influence on the chemical composition of the waste sulfite pulp liquid and lignosulfonate, thus affecting the properties of water reducing agent.
(2) Alkali lignin or sulfate lignin with the acidification precipitation method will be separated, and then sulfonated, in the alkaline medium to generate lignosulfonate. Lignin in alkaline pulping black liquor exists in the form of alkali lignin. When the content of effective alkali in black liquor is greater than 1.14%, alkali lignin is completely dissolved in black liquor, forming a hydrophilic gel without precipitation. However, when the content of effective alkali is less than 0.71%, the colloidal part of the alkaloid is destroyed and precipitation occurs. Because of the hydrophilic group of alkali lignin, black liquor has some activity, but the effect is not stable. Therefore, it is necessary to introduce the sulfonic acid group, amine group, carboxyl group, and other anionic surface-active groups to produce water reducing agent from alkali pulp waste liquid. Lignin is easy to react with sulfite and other sulfonating agents to generate lignosulfonate. The reaction principle is that the sulfonic acid group is introduced into the addition of the enol group in sulfonic acid and the sulfonic acid group is introduced into the reagent with Na2S03. Because Na2S03 is hydrolyzed to generate H2SO3, the addition reaction can be carried out to generate lignosulfonate in an alkaline medium.
Applications of Lignosulfonate
Lignosulfonate superplasticizer is mainly used as a superplasticizer alone in the preparation of coagulation, or used as raw materials for compound water reducing agent products. In addition, it can be used to make a variety of early strength agents, early strength water reducing agents, slow setting water reducing agents, slow setting high efficient water reducing agents, pumping agents, water-proofing agents, and other compound additives preparation components.
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