Effect of chemical admixtures on workability and strength properties of prolonged agitated concrete

A lignosulfonate-based water reducer, a dextrin-based water reducer, and a gluconate-based retarder were used in concretes which were mixed continuously in the drum of a truck mixer, and the slump measurements were carried out at certain time intervals. It was found that at any time, the slump loss in gluconate-based retarder and combined lignosulfonate and gluconate mixes was less than those of other mixes. The setting times of samples taken after prolonged mixing, as well as after retempering, were also compared with those of initial ones. Compressive and flexural strengths of samples taken initially and after different agitation times were determined. The strength change obtained after prolonged agitation was slight, but retempering by water to bring the workability to the initial level reduced the strengths; however, the strength loss in gluconate retarder-added mixes was smaller than those of others. The bond strength between reinforcing bar and reference mix was also compared with that of gluconate retarder mix. (C) 1998 Elsevier Science Ltd.