What is cement retarder? It is easy to understand to delay the cement hydration reaction, thereby extending the setting time of commercial concrete, so that fresh commercial concrete can maintain plasticity for a longer period of time, facilitate pouring, improve construction efficiency, and at the same time, Admixtures that will not cause adverse effects on the later performance of commercial concrete.
Types of retarder
There are many types of retarder, the commonly used ones are: lignosulfonate and its derivatives, low molecular weight cellulose and its derivatives, hydroxycarboxylic acid Acid (salt), organic phosphonic acid (salt), boric acid (salt), complex, etc. At home and abroad, continuous improvements have been made to address the shortcomings of the original retarder, and some new retarders have also been developed. Specific substances that can be used as retarder include: dextrin, various types of starch, casein and certain protein-containing substances; as well as sucrose, glucose, calcium or sodium salt of lignosulfonate, carboxymethylcellulose Sodium (CMC), carboxyethyl cellulose (CHC) and their mixtures; in addition, tartaric acid, potassium tartrate, calcium tartrate, calcium sulfate dihydrate, calcium sulfite, ferrous sulfate, boric acid, mixtures of boric acid and tartaric acid, Mixture of tartaric acid and sodium bicarbonate, sodium hexametaphosphate, phosphoric acid, disodium phosphate, trisodium phosphate, tetrasodium phosphate, disodium hydrogen phosphate, sodium pyrophosphate, alkyl phosphate ester, disodium ethylenediaminetetraacetate, each Plant humic acid, etc.
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 operating temperature can reach above 116°C.
Example 2: Methylenephosphonic acid derivatives and borax are compounded at a mass ratio of (0.025-0.2):1 as a high-temperature retarder. The methylenephosphonic acid derivatives are selected from ethylenediaminetetramine. Calcium methylenephosphonate, sodium ethylenediaminetetramethylenephosphonate, 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 as a retarder. In addition, a retardation enhancer can also be added to expand the 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℃.
Cement retarder is widely used in concrete summer construction and pumping construction. According to the different chemical compositions, concrete retarder for commercial concrete is divided into two types: inorganic concrete retarder and organic concrete retarder. At present, lignin sulfur salt is a retarder with large output and wide application. In addition, molasses, hydroxycarboxylic acid and a few inorganic salt retarder are also commonly used. Therefore, combining different types of retarder, the retarding mechanism of retarder is discussed. </p
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