At present, water reducing agents mainly include lignin series, naphthalene series, resin series, molasses series and polycarboxylic acid, etc., and various types are also divided into air-entraining agents and non-air-entraining agents. According to its influence on the setting and hardening speed of concrete, it can be divided into three types: ordinary type, early strength type and retarded type.
(1) Lignin-based water reducer (lignosulphonate water reducer)
The main variety is calcium lignosulfonate, which is a brownish-yellow powder obtained by evaporation, sulfonation, concentration, and spray drying of wood pulp waste after alcohol extraction. In addition, there are wood sodium and wood magnesium reduction Liquid. The suitable dosage is 0.2%～0.3%, and the water reduction rate is about 10%. If the water is not reduced, the slump can be increased by about 10cm, and the 28d strength of concrete can be increased by 10%～20%. If the strength remains unchanged, it can be saved. Cement 10%; but wood calcium has a retarding effect on concrete, generally retarded for 1 to 3 hours, and the retardation is stronger at low temperature, and if the content is too much, the retardation is serious. And wood calcium is an air-entraining water-reducing agent, which increases the air content of concrete from 2% when it is not mixed to 3.6%, which has an impact on the strength of the concrete, but is beneficial to the frost resistance of the concrete.
(2) Naphthalene formaldehyde water reducer
The naphthalene water reducer is the raw material of naphthalene and naphthalene homologues fractionated from coal tar. It is formed by sulfonation and condensation. It has a strong dispersing effect on cement, so its effects of reducing water, strengthening, and improving durability are better than lignin, and it is a superplasticizer. Generally, the water reduction rate is more than 15%, the early strength is significant, and the concrete 28d strengthens more than 20%. The suitable dosage is about 0.5% to 1.5%, and the PH value is 7 to 9. It is suitable for all concrete projects, and more suitable for preparing high-strength concrete and fluidized concrete.
(3) Molasses water reducer
Molasses water-reducing agent is made of waste liquid left over from sugar extraction in the production process of sugar mills. It is neutralized with lime to form salt substances. It is brown powdery solid or pasty liquid, except for general water-reducing agents. In addition to its functions, it also has a significant retarding effect, so it is a retarding type water reducer, and generally the initial setting and final setting time should be extended by more than 3h. The suitable dosage is 0.2%～0.3%, the water reduction rate is 6%～10%, the 28d strength of concrete is increased by 15%～20%, if the original strength remains unchanged, the cement can be saved by about 10%.
(4) Polycarboxylate Superplasticizers
In recent years, due to technological innovation, a new type of cement admixture—polycarboxylic acid water-reducing agent has been developed and used in large quantities.3-mercaptopropionic acid is mainly used in the production of polycarboxylic acid water-reducing agent to control molecular weight and adjust high performance It greatly improves the water reduction rate and slump retention performance of concrete.
The polycarboxylate superplasticizer has a special comb-like structure, which promotes the dispersion of cement particles through electrostatic effects and steric hindrance effects, improves the workability of concrete mixtures, can effectively reduce water consumption and improve various physical properties of concrete. Including concrete compression, tensile strength, flexural strength and elastic modulus, improving the frost resistance and impermeability of concrete; it can adjust the setting time of concrete and improve the construction performance of concrete; at the same time, it can also reduce bleeding and improve concrete density And other effects to improve the durability of concrete. The effective dosage is 0.1%～0.2%. The polycarboxylate water-reducing agent has strong dispersibility, low dosage, low concrete slump loss, good compatibility with different cements, and does not cause obvious retardation and micro-induction gas.