Accelerated hardening

Bensted, J. 1977. Chloroaluminates and the role of calcium chloride in accelerated hardening of Portland cement. World Cement Technology, 8, 171-175. 

Polymers blended with non-polymeric additives form subclass Bl. It can be distinguished into subgroup Bll, the plasticized or "soft" PVC and subgroup B12, the filled polymers, with fillers such as carbon black, silica, zinc oxide, etc. A filler usually is cheaper than the polymeric main component it can constitute as much as 40% by weight of the material. Other additives, such as pigments, accelerators, hardeners, stabilisers, flame-retardants, lubricating agents, etc. are used in much lower concentrations (functional composites). 

Solidification of minerals in carbonate rocks or in sea shells, or that of silica and alumina in lateritic or desert soils, is a very slow process. It takes years and centuries and even geological time to consolidate some minerals. Unfortunately, little is known on the exact chemical reactions and the resulting hardening process. As a result, the chemical hardening in nature cannot be translated into technological applications where accelerated hardening and solidification are desired. 

Use Rubber accelerator, hardening agent for resins, rodenticides, fungicides. 

To obtain a sufficiently high rate of cure at molding temperatures, it is usual to add about 0.2-2.0% of an accelerator (hardener)—a latent acid catalyst which decomposes at molding temperatures to yield an acidic body that will accelerate the rate of cure. Many such materials have been described, the most prominent of them being ammonium sulfamate, ammonium phenoxyacetate, trimethyl phosphate, and ethylene sulfite. A stabilizer such as hexamine is often incorporated into the molding powder to improve its shelf life. 

Storage-stable one-pack polyester stoving enamels can be formulated with poiyisocyanate resins that are thermoreversibly blocked. Tin catalysts (e.g., dibutyl tin dilaurate) are particularly suitable for accelerating hardening with hydroxypolyester resins. 

Catalysts are used to accelerate hardening. Phosphoric acid and organic phosphates are generally used in practice. These compounds also improve adhesion of the resol-epoxy resin to the metallic substrate. 

Uses Carrier in inks hard resin additive in overprint varnishes reactive polyol in melamine- and urethane-cured coatings for wood and metal intermediate for polyester and alkyd coatings cure accelerator, hardener, gloss aid, chem. resist, aid in coatings Properties Wh. pastilles sol. ( 25% solids) in Arcosolv soivs., butanol, NMP insol. in water, propylene glycol, and ethylene glycol m.w. 2500 (wt. avg.) bulk dens. 5.556 Ib/gal acid no. < 0.1 hyd. no. 255 VOC 0.10%... 

See also accelerator, hardener, catalyst and cross-linking. 

Silicone diaphragm free of natural latex rubber. Manufacturer (Tel. +1-773-7365500) declined to specify accelerants, hardeners, etc... 

Supersulphated cement is obtained from blast-furnace slag (80-85%), calcium sulphate (10-15%) and lime or Portland cement klinker (approximately 5%). After hardening, the strength comparable to that of ordinary Portland cement may be obtained with a considerably lower heat of hydration. Supersulphated cement may be used in various special concrete structures, particularly in situations where the action of acid fluids, sea water and oils should be expected e.g. for foundations and harbour structures. Mixing supersulphated cement with Portland cements and special treatment, such as accelerated hardening, is not possible. 

Sources of chloride ions and diffusion into concrete. The harmful chloride ions leading to rebar corrosion damage either originate directly from the concrete mix constituents or diffuse into the concrete from the surrounding environment. The use of seawater or aggregate that has been exposed to saline water (such as beach sand) in concrete mixes creates the former case. Calcium chloride has been deliberately added to certain concrete mixes to accelerate hardening at low temperatures, mainly before the harmful corrosion effects were widely known. 

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