Effect of various water-reducing admixtures on the strength and workability of concrete
At the present time there are no ASTM specifications, and very little information in the ACI Committee 212 Report, concerning water-reducing admixtures. Therefore, the engineer must turn elsewhere for impartial information on the use of water-reducing admixtures. Once a source of information has "been selected, field tests still must he made to determine the suitability of a particular admixture for given job conditions. When such field tests are made, consistency is extremely important. One thing that should be determined is the effect of a change in the recommended amount of admixture on the results; also the effect of any other change on the results must be determined. All the admixtures tested by the writer, when used as recommended, reduced the amount of water required and increased the workability to some extent. For admixtures that entrained considerable amounts of air, the decrease in water required, and the increase in workability, were pronounced. For densifying admixtures, the decrease in water required, and the increase in workability and entrained air (if any), were much smaller. The strength of the stiff mixes, when used as recommended, compared favorably with plain mortar. The strength of the fluid mixes did not compare as favorably with plain mortar as did the others. However, if a constant workability had been maintained, all mixes probably would have compared favorably with plain mortar. An increase in the amount of admixture, over the recommended amount, increased the workability of all the mixes except one, which had a high workability with the recommended amount. The effect on the strength of the cylinders of increasing the amount of admixture over the recommended amount indicates that there is an optimum workability for maximum strength. This optimum workability can be obtained either by changing the amount of admixture or by changing the rate of agitation.
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