At present, high-efficiency water-reducing agents mainly include lignin-based, naphthalene-based, resin-based, molasses-based and polycarboxylate water-reducing agents. Each type also includes air-entraining water-reducing agents. 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) Lignosulphonatewaterreducer
The main variety is wood Calcium sulfonate is a brown powder obtained by evaporating, sulfonating, concentrating, and spray drying wood pulp waste liquid after alcohol extraction. There are also sodium lignin and magnesium lignin type water-reducing agents. The suitable dosage is 0.2% to 0.3%, and the water reduction rate is about 10%. If the water is not reduced, the slump can be increased by about 250px, and the 28d strength of the concrete can be increased by 10% to 20%. If the strength is kept unchanged, savings can be made. 10% cement; however, wood calcium has a retarding effect on concrete. Generally, the retarding effect is 1 to 3 hours. The retarding property is stronger at low temperatures. If the dosage is too much, the retarding will be serious. In addition, wood calcium is an air-entraining water-reducing agent, which increases the air content of concrete from 2% when not added to 3.6%. This has an impact on the strength of the concrete, but is beneficial to the frost resistance of the concrete.
(2) Naphthalene formaldehydewaterreducer
Naphthalene formaldehyde water reducer It is made from naphthalene and naphthalene homologues fractionated from coal tar as raw materials. It is formed by sulfonation and condensation. It has a strong dispersing effect on cement, so its water reduction, strengthening, and durability improvement effects are better than those of lignin, and it is a high-efficiency water-reducing agent. Generally, the water reduction rate is above 15%, the early strength is significant, and the concrete is strengthened by more than 20% in 28 days. 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 is more suitable for preparing high-strength concrete and fluidized concrete.
(3) Molasses-based water-reducing admixture
Molasses-based water-reducing admixture is made of The waste liquid left over from refining sugar during the sugar factory production process is used as raw material, and is neutralized with lime to form salt substances, which are brown powdery solids or paste liquids. In addition to the functions of general water-reducing agents, they also have significant It has a retarding effect, so it is a retarding water reducing agent. Generally, the initial setting and final setting time should be extended by more than 3 hours. The suitable dosage is 0.2% to 0.3%, the water reduction rate is 6% to 10%, and the strength of concrete is enhanced by 15% to 20% in 28 days. If the original strength is kept unchanged, about 10% of cement can be saved.
(4) Polycarboxylate superplasticizer
Polycarboxylate superplasticizer It has a special comb-like structure that 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 and tensile resistance. , flexural strength and elastic modulus, improve 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, improve concrete compactness and other effects to improve Durability of concrete. The effective dosage is 0.1% to 0.2%. The polycarboxylate water-reducing agent has strong dispersion, low dosage, small concrete slump loss, good compatibility with different cements, and does not cause obvious retardation or micro-intrusion. gas. </p
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