Influence of dispersant structure and mixing speed on concrete slump retention

The relationship between rate of dispersant depletion from the aqueous phase and concrete slump retention was investigated by varying polycarboxylate dispersant structure and mixing speed. The influence of dispersant structure on the rate of slump loss was determined by testing two polycarboxylate-polyether dispersants that differed in charge density. The influence of mixing rate on slump loss was determined by changing mixer rotation speed. The rate of dispersant depletion was influenced by dispersant structure and mixing speed. A higher rate of dispersant depletion was observed at higher mixing speed and with a polymer of higher charge density. In comparing the different mixing procedures, a good correlation was found between slump value and the number of drum revolutions, while a poor correlation was found between slump value and time. Concrete slump retention was influenced by the rate of dispersant depletion and the rate of dispersant depletion was influenced by dispersant structure and mixing speed.