Investigation of Early Stiffening of Concrete at Red River Lock and Dam Number 3.

摘要

Slump loss was experienced in a concrete used in construction of Red River Lock and Dam 3. A three-factor laboratory analysis was conducted to determine whether properties of the cement, the fly ash, or the mixing water,or some combination of these properties were responsible for this behavior. Results (ASTM C 359) indicated that the cement in combination with the project water was the primary cause of early stiffening behavior. The stiffening was die to false -set/ Increasing fly ash replacement and changing the mixing procedure tended to reduce the magnitude of the problem. This problem was solved by modifications in the manufacturing procedure of the cement so that formation of plaster of Paris was avoided. Following this modification, an apparent cement-admixture interaction was suspected as another cause of early stiffening. Some water-reducing admixtures (WRA's) were found to be associated with early stiffening. Recommendations were to use one of the WRA's that did not cause early stiffening or to avoid WRA's altogether. Keywords: Cement-admixture interaction; Slump loss; Workability. (SDW)