Retardants cement setting

The addition of STPP (1-7%) acted as a retarder and increased compressive strength (mortar II). Less heat and ammonia were evolved and the cement set more slowly in 10 minutes. The paste hardened in 30 to 60 minutes. Traces of ADP persisted for 30 minutes but no STPP was detected in the reaction products. Struvite, the main hydration product, schertelite and dittmarite all appeared within 5 minutes. Struvite continued to increase in amount as the cement aged schertelite disappeared after 3 hours and dittmarite after a week. Stercorite was found only during the first 7 hours. 

High-alumina cement is a rapid-hardening cement made from bauxite and limestone. It is comparatively resistant to chemical attack. Milling retards the setting of aluminous cement [1582]. On the other hand, setting accelerators such as lithium carbonate increase their effect by this treatment. 

Examples of retarders are shown in Table 10-11. They are added to prevent cement from setting too rapidly. These additives are also referred to as set retarders. Cements with retarders to prevent rapid setting may be used at the high-temperature and high-pressure environments of deep wells. Common retarders are lignosulfonate and certain carbohydrate derivatives, such as welan gum, xanthan gum, cellulose, and polyanionic cellulose. 

A mixture of lignosulfonates, alkali-treated brown coal, and minor amounts of organic silicon compounds (e.g., ethyl silicone) reduces the permeability of cements [1019]. The additives may interact with the crystallization centers of the cement slurry and form a gel system in its pores and capillaries, thus reducing the permeability of the cement and increasing its isolating capability. Furthermore, it is claimed that the additive retards the setting rate of cement up to 200° C and increases the resistance to corrosive media. 

I. Livsey and R. Shaunak. Cement setting retarding agents. Patent GB 2182031, 1987. 

K. A. Rodrigues. Cement set retarding additives, compositions and methods. Patent US 5341881, 1994. 

Lignosulfonates and lignosulfonate derivatives are used extensively as cement set time retarders (20, 21). Many of the same additives used in drilling muds are used in cement slurries and spacer fluids for similar purposes. 

High content of cement setting retarders like sulfates, halides... 

This procedure is Coveney, Whiting and co-workers synthesis of the hexaphos-phonic acid 61 by the Moedritzer-lrani reaction, the dodecasodium salt of which they investigated as a cement setting retarder. An attempt to synthesize the dodecaethyl ester of 61 using the Kabachnik-Fields reaction failed.128... 

The rapidity of the set of MAP cement can be ameliorated by the use of set retarders. Sodium tetraborate decahydrate (borax) can the used to decrease the rate of reaction between MgO and the acid phosphate salt. The normal set time for nonretarded cement is about 3 min, however, the addition of 20% borax can extend the set time to >20 min. It is thought that borax yields B402 ions, which then act as an Mg2+ cation acceptor. This complex precipitates on the surface of the MgO grains, forming a barrier that slows the release of further Mg2+ ions, retarding the set of the cement (Sugama and Kukacka, 1983a). 

Retarders enable setting time to be extended thereby preventing the formation of cold joints in large pours. Additionally, water-reducing retarders allow a reduction in cement content with a consequent reduction in maximum temperature rise. 

Polar parts of organic molecules are primarily adsorbed on Cj A and C AF phases, on cement grains. Therefore cement setting is retarded, unless the special accelerator is used simidtaneously. scosity decreases due to deflocculation and in some extend imder air bnbbles influence. The latter rednce also bleeding. 

Synonyms NaeDTPMP Properties Amber liq. m.w. 705 Uses Deflocculant, sequestrant, scale inhibitor for cooling water treatment, detergents, peroxide bleach stabilization, l l cleaners, geothermal, oil field applies. deflocculant, sequestrant, process additive for paper, textiles, and metals industrial and commercial formulations for cleaning various substrates cement modifier (retards concrete setting times)... 

The setting time of the binder will depend on the amount of calcitmi chloroaluminate present, on the form of SO3 that is present, and on the SO3/AI2O3 ratio. Usually the cement sets faster than Portland cement. If required, a hydroxyc oxylic acid, such as citric acid, may be added to retard the setting process (Takuma et al, 1997). 

Currell, B. R. et al. (1987) The aeeeleration and retardation of set of high alumina cement by additives. Cement and Concrete Research 17, 420-432. 

Introduction of phosphogypsum as an additive to cement accounts for about 4 million tonnes per annum. Portland cement usually contains about 5% gypsum, which is added to control (retard) the setting time. Phosphate, fluoride, and organic impurities in the phosphogypsum are undesirable and should be reduced to acceptable levels. Material from double crystallization phosphoric acid processes is satisfactorily employed in Belgium and Japan. 

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