Cement accelerator

Cement accelerators are shown in Table 10-12. The most common accelerators are calcium chloride and sodium chloride. Calcium chloride may be used in concentrations up to 4% by weight in wells with bottom-hole temperatures less than 50° C. Calcium chloride tends to increase the final strength under pressure conditions. 

The addition of sodium sulfate to Portland cement accelerates the cement hardening and increases mobility of the solution. Chloride-free accelerators... 

Toxicology LD50 (oral, mouse) 2700 mg/kg mod. toxic by ing. TSCA listed Hazardous Decomp. Prods. Heated to decomp., emits toxic vapors of SOx Uses Accelerator for pure-gum sundries and medical supplies, bathing shoes, bathing caps, novelties, and cold-cure cements accelerator for food-contact rubber articles for repeated use... 

Empirical CioHis02S4Zn Formula Zn(C4H90CS2)2 Properties Wh. powd. mod. sol. in benzene, ethylene dichloride si. sol. in acetone insol. in water, gasoline dens. 1.45 dec. when heated Uses Ultra-accelerator used in self-curing rubber cements accelerator in food-contact rubber articles for repeated use Regulatory FDA 21CFR 177.2600 Zinc carbonate... 

An accelerator is a chemical additive that is used to speed up the normal rate of the reaction between cement and water (7). This shortens the time of thickening of the cement. Further, an accelerator increases the early strength of cement. Accelerators do not increase the ultimate compressive strength of cement but promote a rapid strength development. However, in a higher concentration the accelerator may act as a retarder. Accelerators may also interact with other additives, such as dispersants. 

E.M. Al-Mutlaq, Use of non-chloride cement accelerator and electric arc furnace dust in cement, US Patent 9278888, assigned to Saudi Basic Industries Corporation (Riyadh, SA), March 8,2016. 

Rubber accelerator Rubber antioxidant Rubber bearings Rubber blends Rubber cements Rubber chemicals... 

Silica and Alumina. The manufacture of Pordand cement is predicated on the reaction of lime with siUca and alumina to form tricalcium sihcate [12168-85-3] and aluminate. However, under certain ambient conditions of compaction with sustained optimum moisture content, lime reacts very slowly to form complex mono- and dicalcium siUcates, ie, cementitious compounds (9,10). If such a moist, compact mixture of lime and siUca is subjected to steam and pressure in an autoclave, the lime—silica reaction is greatiy accelerated, and when sand and aggregate is added, materials of concrete-like hardness are produced. Limestone does not react with siUca and alumina under any circumstances, unless it is first calcined to lime, as in the case of hydrauhc lime or cement manufacture. 

In concrete, triethanolamine accelerates set time and increases early set strength (41—43). These ate often formulated as admixtures (44), for later addition to the concrete mixtures. Compared to calcium chloride, another common set accelerator, triethanolamine is less corrosive to steel-reinforcing materials, and gives a concrete that is more resistant to creep under stress (45). Triethanolamine can also neutralize any acid in the concrete and forms a salt with chlorides. Improvement of mechanical properties, whiteness, and more even distribution of iron impurities in the mixture of portland cements, can be effected by addition of 2% triethanolamine (46). Triethanolamine bottoms and alkanolamine soaps can also be used in these type appUcations. Waterproofing or sealing concrete can be accompUshed by using formulations containing triethanolamine (47,48). 

The recovery of sand from foundry molds and cores is much easier when binders made water soluble by use of sodium alumiaate are used ia place of iasoluble resin binders (35,36). Sodium alumiaate acts as a setting accelerator for Portiand cement (qv) (37). In similar appHcation, addition to concrete provides a longer gel time before fully curing (38). 

Potassium alum, which also occurs naturally as the mineral kalinite [7784-24-9], KAl(SO 2 12H20, sp gr 1.75, is used ia tanning skins, as a mordant ia dyeiag, and ia the pharmaceutical and cosmetic iadustries (see Pharmaceuticals Cosmetics). It is used as a styptic pencil and as a hardening agent and set accelerator for cement and plaster. The ACGIH threshold limit value TWA is 2 mgAl/m (1 ). 

Aluminide and sUicide cementation coatings such as TaAl on tantalum and MoSi2 on molybdenum oxidize at slow rates and possess some inherent self-repair characteristics. Fine cracks that appear and are common to these coatings can be tolerated because stable, protective oxides form within the cracks and seal them. Thermal cycling, however, accelerates faUure because of thermal expansion mismatch that ultimately dismpts the protective oxide coating. 

Minor and potential new uses include flue-gas desulfurization (44,45), silver-cleaning formulations (46), thermal-energy storage (47), cyanide antidote (48), cement additive (49), aluminum-etching solutions (50), removal of nitrogen dioxide from flue gas (51), concrete-set accelerator (52), stabilizer for acrylamide polymers (53), extreme pressure additives for lubricants (54), multiple-use heating pads (55), in soap and shampoo compositions (56), and as a flame retardant in polycarbonate compositions (57). Moreover, precious metals can be recovered from difficult ores using thiosulfates (58). Use of thiosulfates avoids the environmentally hazardous cyanides. 

Retarders and Accelerators. Materials that control hardening of cement may be either organic or inorganic. Retarders are often incorporated in oil well cementing and hot-weather concrete appHcations, whereas accelerators may be useful for cold-weather concrete appHcations in which higher rates of reactivity are desirable. In most cases, these admixtures are used in low concentrations, suggesting that they act by adsorption. 

Concrete, Mortar, and Plaster. Citric acid and citrate salts are used as admixtures in concrete, mortar, and plaster formulations to retard setting times and reduce the amount of water requited to make a workable mixture (172—180). The citrate ion slows the hydration of Portland cement and acts as a dispersant, reducing the viscosity of the system (181). At levels below 0.1%, citrates accelerate the setting rate while at 0.2—0.4% the set rate is retarded. High early strength and improved frost resistance have been reported when adding citrate to concrete, mortar, and plaster. 

FIG. 17-73 Normal (perpendicular) rapping efficiency for various precipitated dust layers having about 0.03 g diist/cm (0.2 g diist/in ) as a function of maximum acceleration in multiples of g, Curve 1, fly ash, 200 or 300°F, power off. Curve 2, fly ash, 70°F, power off also 200 or 300°F, power on. Curve 3, fly ash, 70°F, power on. Curve 4, cement-ldln feed, 300°F, power off. Curve 5, cement dust, 300°F, power off. Curve 6, same as 5, except power on. Curve 7, cement-ldln feed, 300°F, power on. Curve 8, cement dust, 200°F, power off. Curve 9, same as 8, except power on. Curve 10, cement-ldln feed, 200°F, power off. Curve 11, same as 10, except at 70°F. Curve 12, cement-ldln feed, 200°F, power on. Curve L3, cement-ldln feed, 70°F, power on. °C = (°F — 32) x %. [Spioull, Air Polliit. Control Assoc. J., i.5, 50 (1965).]... 

Obviously, too, the rate will depend on the total surface area of cement grains available for reaction, and thus on the fineness of the powder. So hardening is accelerated by raising the temperature, and by grinding the powder more finely. 

Class H Intended for use as a basic well cement from surface to 8,000 ft (2,440 m) depth as manufactured, and can be used with accelerators and retarders to cover a wide range of well depths and temperatures. No additions other than calcium sulfate or water, or both, shall be interground or blended with the clinker during manufacture of Class H well cement. Available in moderate and high- (tentative) sulfate-resistant types. 

It is often necessary to either accelerate, or retard the thickening and setting time of a cement slurry. 

For example, when cementing a casing string run to shallow depth or when setting a directional drilling kick-off plug, it is necessary to accelerate the cement hydration so that the waiting period will be minimized. The most commonly... 

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