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Volume 11, Issue 1
(July 1989)
ISSN: 0149-6123
Behavior of Cement-Reduced and “Flowing” Fresh Concretes Containing Conventional Water-Reducing and “Second-Generation” High-Range Water-Reducing Admixtures Fresh concretes were prepared using cements of high and moderate C3A contents and having a cement content of 323 kg/m3 (545 lb/yd3) and a water-to-cement ratio of 0.50. Conventional water-reducing agents based on lignosulfonates and carboxylic acids were used to reduce water and cement contents by 8 to 9%. Second generation high-range water-reducing admixtures (HRWR) were used to reduce cement and water contents by 15 to 16%. Testing included slump loss, air loss with time, setting time, and bleeding. Similar tests were carried out on flowing concretes, where cement and water contents were maintained constant and HRWR was added to increase initial slump levels to 200 to 300 mm (8 to 9 in.). In this series, testing was carried out at both 23°C (73°C) and 32°C (90°F). Use of chemical admixtures to reduce both water and cement contents resulted in accelerated rates of slump loss and shorter working times compared to controls. When used to produce flowing concretes, working times were equivalent to those for mixes not containing the admixtures. In general, setting times were increased from 1 to 2 h at 23°C (73°F) and by lesser amounts at 32°C (90°F). Bleeding of flowing concretes was greater than that of control mixtures, especially when a copolymer-type HRWR was used. Rate of air loss was significantly greater in cement-reduced mixtures containing HRWR compared with controls; however, air loss rates in flowing concretes were roughly equivalent for all mixtures tested.
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Paper ID: CCA10099J | ||
