Retarders of setting

The effectiveness of each admixture may vary, depending on its concentration in the concrete, the time of addition in the mixing cycle and various constituents of the concrete. Although each class of admixture is defined by its main effect (i.e. water reduction, set acceleration), it may have one or more secondary effects (retardation of set, increased bleeding, air entrainment) and its use may result in side effects. Side effects are those modifications of properties produced in the concrete that, even though unsought, are both inevitable and independent of an admixture s main function. Prior to selecting an admixture for an intended application, these... 

Most of the charaeteristics of conventional water reducers are shown also by superplasticizers, at least qualitatively thus, they are more effective if added a few minutes after mixing, retard setting and increase slump loss. Retardation of set is slight with SMF but more marked with SNF. Slump... 

An alternative explanation for the retardation of setting by deamination, dinitrophenylation, anion adsorption, and sulfation is provided by the... 

The set and hardening retarders are commonly used in practice. At the retardation of setting process the application of ready mix concrete or injection woiks are easier. 

Metal oxides PbO, ZnO 0.4-0.5 Strong retardation of setting reduction of initial strength, unchanged 28 days strength... 

There are many organic retarder of setting (see Table 4.3). Among them the lig-nosulphonates, hydroxyl-carboxylic and carboxylic acids arrd their salts, amines, amino acids, carbohydrates of general formula C (H20), and the products of their oxidation that is acids and their salts can be mentioned. 

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. 

Water absorption by cement, especially if the latter has a high C3A content, furthermore causes retardation of setting (because of diminished reactivity of the C3A) and, depending on how much water is absorbed, also causes loss of strength (in consequence of pre-hydration of the C3S in the cement). Besides, false set - temporary early stiffening of the cement when mixed with water - may also be due to causes associated with silo storage (see Section V.3). 

Currell BR, Grzeskowlak R, Midgley HG, Parsonage JR. The acceleration and retardation of set high alumina cement by additives. Cement Concrete Res 1987 17 420-432. 

J. R. HiU and J. Plank. Retardation of setting of plasterof Paris by organic acids Understanding the mechanism through molecular modeling. J. Comp. Chem. 25 (12), 2004,1438. 

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