Behavior of Mortars with Different Dosages of Shrinkage Reducing Admixtures

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Title: Behavior of Mortars with Different Dosages of Shrinkage Reducing Admixtures

Author(s): A. Bettencourt Ribeiro, A. Carrajola, and A. Goncalves

Publication: Special Publication

Volume: 239

Issue:

Appears on pages(s): 77-92

Keywords: shrinkage; shrinkage reducing admixtures; surface tension

Date: 10/1/2006

Abstract:
To analyze the performance of two shrinkage reducing admixtures (SRA), tests have been performed, in order to evaluate the influence of increasing dosages of the admixtures. Shrinkage, compressive strength and weight loss have been measured. The efficiency of the admixtures in controlling autogenous and drying shrinkage was evaluated using sealed and unsealed specimens. As the accepted mechanism of action of these products is the reduction on surface tension of the capillary liquid of concrete, surface tension of water solutions was also determined to compare the shrinkage reduction with the decrease of surface tension. Mixtures with four different dosages of each SRA were prepared. The results indicate that shrinkage reduction is not proportional to the decrease of surface tension. Secondary effects such as changes in the evaporation rate and in the compressive strength of specimens have to be considered. Results of sealed specimens are not fully consistent with the accepted main mechanism of action of these products.