High-Range Water-Reducing Admixtures in Precast Concrete Operations

Abstract

The minimum acceptable reduction of water requirement is proposed to be 12 percent, incontrast to a minimum acceptable reduction of water requirement of 5 percent for chemical admixtures Types A, D, and E (conventional water-reducing admixtures). Two classes of high-range., water-reducing admixtures are proposed, namely, Types F and G, denoting normal-setting and retarding admixtures, respectively. ented as a concrete admixture as early as 19351 Nevertheless, they did not come into real commercial use until the 1960s. They have been used in Japan for about 15 years and in Western Europe3 for nearly 10 years. A few other countries such as Australia4'5 have also used them commercially (especially in the precast concrete industry) producing apparently favorable results. H-R admixtures have been used in North America for only about 5 years and to a much lesser extent than in Europe or Japan. Nevertheless, they have been found particularly advantageous in precast concrete applications. In addition to improving the workability of the concrete mix and the attainable compressive strength of the product, H-R admixtures substantially reduce the time required to achieve stripping strengths. This, of course,