What are the main components of concrete retarder?

The types of cement retarder can be divided into two categories: inorganic retarder and organic retarder according to their chemical composition. From the perspective of molecular weight or synthesis method, they can be divided into two major categories: organic compounds and polymers. The most studied organic compounds are mainly organic phosphonic acids (salts). The polymers used as retarders are usually oligomers with molecular weights generally in the thousands. They are mostly produced through copolymerization. The most studied polymers are polymers containing carboxyl groups, phosphonic acid groups, and sulfonic acid groups. Relatively speaking, the dosage of organic retarder such as hydroxycarboxylic acid (salt) and organic phosphonic acid (salt) is small, but they are more sensitive; while the dosage of polymer retarder is larger, but the dosage is related to thickening. The time linear relationship is better.

Inorganic retarder

1) Phosphate and metaphosphate retarder

Phosphate and metaphosphate retarder are the most studied inorganic retarder. The retarding effect of orthophosphoric acid (H3PO4) is not great, but the retarding effect of various phosphates is strong. At the same dosage, sodium pyrophosphate (Na2P2O7) has the strongest retarding effect among phosphate retarders.

2) Borax (Na2B4O7·10H2O)

Highly hygroscopic and easily soluble in water And glycerin, the aqueous solution is weakly alkaline and easy to weather slowly in dry air.

3) Sodium fluorosilicate (Na2SiF6)

White crystalline substance, density 2.68g ·cm, slightly soluble in water, insoluble in ethanol, and corrosive. The general dosage is 0.1-0.2% of the cement dosage.

Organic retarder

Organophosphonic acid (salt)

There are many types of organic phosphonic acids (salts), many of which are suitable for use as oil well cement retarder.

Example 1: Methylenephosphonic acid derivatives are used as ultrafine cement retarder, and the service temperature can reach above 116°C.

Example 2: Mixing methylenephosphonic acid derivatives and borax at a mass ratio of (0.025-0.2):1 as a high-temperature retarder. The phosphonic acid derivative is selected from ethylenediaminetetramethylenephosphonate calcium, ethylenediaminetetramethylenephosphonate sodium, and ethylenediaminepentamethylenephosphonic acid. The applicable temperature of this retarder is 121-260℃ (BHST), and it is suitable for high-temperature deep well cementing in long sealing sections.

Example 3: Organic phosphonic acid (salt) and inorganic phosphoric acid (salt) are compounded in a certain proportion to be used as retarder. In addition, retarder can also be added. Condensation enhancer to expand application temperature range. A recommended retarder composition is as follows: 10-15% sodium calcium ethylenediaminetetramethylenephosphonate, 40-45% phosphoric acid and 40-50% retarder enhancer. The effective use temperature of this retarder is 70-140℃.

Example 4: Synthetic hydroxydiamine methylenephosphonic acid is used as a high-temperature retarder, with a use temperature range of 50-170°C. Example 2: An unsaturated amine compound is reacted with phosphorous acid and formaldehyde to generate an alkylene phosphonate as a retarder. The operating temperature range is 40-170°C, and the overall performance is excellent

Polymer retarder

Polymer retarder is the most researched type of retarder at home and abroad in recent years. Since a variety of different functional monomers can be combined together through polymerization technology, and the length of the molecular chain, molecular weight size and distribution can be controlled, this type of retarder can use molecular design ideas to guide its synthesis and be comprehensive. Retarder with ideal performance.

The main ingredients are polyhydroxy compounds, hydroxycarboxylate and its derivatives, and high-sugar lignosulfonate. Because of its water-reducing effect, it is also It is called retarding water reducing agent. In addition, some inorganic salts such as zinc chloride, borate, and various phosphates also have a retarding effect. ⑤ Admixtures to improve durability: air-entraining agents, waterproofing agents, anti-rust agents, etc. The dosage is 0.1~0.6% of the cement dosage. Retarder is suitable for continuous pouring of concrete, large volume concrete, ready-mixed concrete and pumped concrete under high temperature conditions.

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