Retarders/water reducers

When a normal, accelerating, or retarding water-reducing admixture is utilized to increase the workability of a concrete mix by direct addition, it would be reasonable to assume that the extent of the effect would be markedly affected by changes in mix design parameters such as cement content, aggregate size, shape and grading, and the water-cement ratio. A study of many hundreds of results, however, indicates that this is not the case and Fig. 

Method A. Using a normal or retarding water reducer, the water-cement ratio is reduced 6-10% at the same cement content and slump. 

When concrete is specified by compressive strength and workability, normalsetting and retarding water-reducing admixtures (both normal and mid-range types) are widely used as a means of attaining the required properties at lower cement contents than mixes which contain no admixture. Although the use of admixtures... 

Retarding and retarding water-reducing admixtures 11 Durability... 

Retarding water-reducing BS 5075 Part 1 ASTM C.494-D IB Type VZ... 

Retarding water-reducing admixtures also incorporate water-reducing properties and most commercially available retarders are of this type. 

Retarding water-reducing admixtures are also dependent on aggregate type and grading. 

Retarding water-reducing admixture - strength gain. 

Hydroxy carboxylic Acids The hydroxycarboxylic acids have hydroxyl (OH) and carboxyl (COOH) groups attached to a carbon chain. Glnconic, citric, tartaric, mucic, malic, salicylic, heptonic, saccharic, and tannic acids can be nsed as retarding and retarding water reducing admixtures. For use as normal WRA they are mixed with accelerating admixtures [23]. Hydroxycarboxylic acid-based WRA are mostly used as aqueous solutions of sodium salt. However, they may occasionally be found as salts of ammonia or triethanolamine. 

Ramachandran, V. S., Effect of Retarders/ Water Reducers on Slump Loss in Superplasticized Concrete, Developments in the Use of Superplasticizers, Am. Conor. Inst SpecialPubl, 68 393-407 (1981)... 

The versatility of the thermal analysis techniques such as TG, DTG, DTA, DSC, and conduction calorimetry for evaluating the role of admixtures in concrete is demonstrated in Chs. 5 through 8. The actions of accelerators, retarding/water-reducing admixtures, superplasticizers and supplementary cementing, and other admixtures are described in Chs. 5,6,... 

Dry mix mortars often exhibit a quite complex mix composition, especially if they are rapid setting and/or rapid hardening. In the latter case, they generally contain binary or ternary binders based on calcium aluminate or calcium sulfoaluminate cements in blends with calcium sulfate without and with portland cement. Isothermal calorimetry is an efficient method to use for optimising mix designs of such mortars with respect to the hydration kinetics. As only small cement mortar or paste samples are used, the influence of the binder composition as well as of different combinations of accelerators, retarders, water reducers, plasticisers, etc. can quickly be tested. Two examples of how the amount of calcium sulfate addition is able to influence hydration kinetics are shown for blends of calcium aluminate cement with hemihydrate (Figure 2.22) and ternary binders based on port-land cement, calcium sulfoaluminate cement and anhydrite (Figure 2.23). 

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