Dosage water-reduction

Admixture at normal dosage rate Average water reduction over w/c = 0.3-0.5 (%)... 

When high dosages of normal water-reducing and accelerating admixtures are used, to produce high water reduction and high workability. 

Many concrete producers use a combination of superplasticizer and a conventional water-reducing, set-modifying or air-entraining admixture to achieve the desired performance. The superplasticizer provides the major portion of the required water reduction and the conventional admixture is added to achieve one or more of the following objectives (1) further water reduction (2) admixture economy (3) the desired air content (4) increased workability and (5) extension of set and workability. Coimnercial conventional admixture formulations used for this purpose are usually based on sodium lignosulfonates, hydroxycarboxylic acids or processed carbohydrates. Such combinations, besides reducing the dosage of the... 

Previous work on superplasticized Portland cement concrete containing fly ash or blast furnace slag has shown that such mixes require 10% less admixture than reference Portland cement concrete to attain the same workability. Therefore, a given dosage may produce higher water reduction. The reason for the reduced admixture requirement has not been determined. It is probably due to the lowering (dilution) of the C3A content... 

More substantial increases in the rate of strength development are obtained by the use of superplasticizers. As mentioned previously, because of the dramatic water reduction that can be achieved by the use of higher dosage of the superplasticizers, significant cement reduction or a change in the type of cement (from a high early Type 111 to a normal Type 1) is possible (Tables 7.28, 7.29 and 7.7). 

At normal dosage of admixture water reductions for constant workability of 8-12% can typically be obtained. 

At equal dosages, all water reducers are effective in producing concrete of equal or higher compressive strength than that of reference concrete. At equal cement content, air content, and slump, the water reducers increase the 28 day strength by about 10-20%. Table 9 shows the influence of lignosulfonate type admixture on the compressive strength of concrete.Water reduction varies between 5 and 8%. 

The amoimt of water reduction achievable with a particular superplasticizer depends on the dosage and initial slump. Some results are given below (Table 10).I There is evidence that beyond a particular dosage, further water reduction is not possible. In all types of cements, water reduction occurs to different extents. 

Demulsifiers (specifically, oil spill demulsifiers) can be applied to oil spills in low concentrations. They prevent mousse formation for significant periods of time and cause a large reduction in oil-water interfacial tension. The best of these was found to prevent emulsification at dosages as low as 1 part inhibitor to 20,000 parts of fresh oil at 20° C [273]. At dosages of 1 1000, at temperatures higher than 10° C, the chemical also results in significant and rapid dispersion of the oil. For very low temperatures or highly weathered oil, the performance of the chemical falls off sharply. 

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