Main categories of water reducing agents

The appearance form is divided into water agent and powder. The solid content of liquids is generally 20%, 40% (also known as mother liquor), and 60%, and the solids content of powders is generally 98%.
According to the water-reducing and enhancing capabilities of water-reducing agents, they are divided into ordinary water-reducing agents (also known as plasticizers, the water-reducing rate is not less than 8%, represented by lignosulfonates [2]), high-efficiency water-reducing agents ( Also known as superplasticizer, the water reduction rate is not less than 14%, including naphthalene series, melamine series, sulfamate series, aliphatic series, etc. [2]) and high-performance water reducing agents (water reduction rate is not less than 25 %, represented by polycarboxylic acid-based water reducing agents [2]), and are divided into early-strength type, standard type and retardant type.
According to the composition materials, it is divided into: (1) lignosulfonates; (2) polycyclic aromatic salts; (3) water-soluble resin sulfonates.
Naphthalene series superplasticizer, aliphatic superplasticizer, amino superplasticizer, polycarboxylic acid superplasticizer, etc.
According to the chemical composition, they are usually divided into: lignosulfonate-based water-reducing agents, naphthalene-based high-efficiency water-reducing agents, melamine-based high-efficiency water-reducing agents, sulfamate-based high-efficiency water-reducing agents, and fatty acid-based high-efficiency water-reducing agents. Aqueous agents, polycarboxylate-based high-efficiency water-reducing agents.
Lignosulfonate
Lignosulfonate is a by-product of sulfite pulping. [4] The molecular weight of lignosulfonate is 2000~5000, and the sulfonate group is 1.25~2.5mcq/g. It is soluble in aqueous solutions with various pH values and insoluble in organic solvents. The functional group is phenolic hydroxyl group. [5] Its raw material is lignin, which is generally extracted from coniferous trees. Lignin is polymerized from three lignin monomers: p-peranyl alcohol, coniferyl alcohol, and sinapyl alcohol, including: calcium lignosulfonate, Sodium lignosulfonate, magnesium lignosulfonate, and lignosulfonate water-reducing agents are commonly used ordinary water-reducing agents. They are anionic surfactants and can be used directly or as raw materials for compound admixtures. First, because it is cheap, it is still widely used. When used in mortar, it can improve workability, fluidity, strength, and water reduction rate of 8%-10%.
Preparation method: Generally, there are two main methods for extracting lignin to make water-reducing agent.
(1) Neutralize the sulfite waste liquid with alkaline solution, remove sugar substances through biological fermentation, and evaporate and dry it into powdered water-reducing agent.
For example, the products of Jilin Kaishantun Chemical Fiber Pulp Mill adopt this method. It uses the waste liquid from the production process of chemical fiber pulp made from the plant's sulfite-cooked wood (more than 75% of which is white pine). It first undergoes biological fermentation to remove sugar and extract alcohol, and the remaining alcohol waste with a concentration of about 10% is used as raw material. The liquid is concentrated to about 50% by an evaporator, then transported to a sprayer for drying, and then spray-dried with hot air at 200°C. Its pH=4.5-5.5. Different types of materials and different cooking processes have a greater impact on the chemical composition of sulfite pulp waste liquid and the resulting lignosulfonate, thus affecting the performance of the water-reducing agent.
(2) For alkali lignin or sulfate lignin, use acidification and precipitation to separate the lignin, and then perform sulfonation to generate lignin sulfonate in an alkaline medium. The lignin in the alkaline pulping black liquor exists in the form of alkali lignin. When the effective alkali content in the black liquor is >1.14%, the alkali lignin is completely dissolved in the black liquor and becomes a hydrophilic gel without precipitation. When the effective alkali content is <0.71%, the alkali lignin colloid is partially destroyed. Precipitation occurs. Due to the presence of alkali lignin hydrophilic groups, the black liquor has a certain activity, but the effect is unstable. Therefore, to produce water-reducing agent from alkaline pulp waste liquid, it is necessary to introduce anionic surface active groups such as sulfonic acid group, amine group, and carboxyl group for modification. Lignin easily reacts with sulfonating agents such as sulfurous acid and sulfite to form lignosulfonate. The principle of the reaction is: the addition of sulfurous acid to the enol group in the molecule molecule introduces a sulfonic acid group. The reagent for introducing the sulfonic acid group is Na2S03. Since Na2S03 is hydrolyzed to generate H2SO3, the addition reaction can proceed in an alkaline medium. Produces lignosulfonate.
Application status: Domestic lignosulfonate water-reducing agents mainly have three options: 1) Used alone as a water-reducing agent to prepare coagulation; 2) Used in various early-strength agents, early-strength water-reducing agents, retarder-reducing agents, etc. Preparation components of composite admixtures such as water agent, retarding superplasticizer, pumping agent, waterproofing agent; 3) For export. According to the survey, for concrete below C30, 30% of the technical content of sulfonate is exported.
Abroad, lignosulfonate is regarded as an environmentally friendly product. South Korea imports 160,000 tons of liquid lignosulfonate from China every year. The United Kingdom, the United States, Japan, etc. also import lignosulfonate from China. It is mainly used as a water-reducing agent alone or as a raw material for compound water-reducing agent products.