Reference: Cement and Concrete Research, 31 (7), 1075-1085, 2001.
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SHRINKAGE-REDUCING ADMIXTURES AND EARLY AGE DESICCATION IN CEMENT PASTES AND MORTARS





D.P. Bentza M.R. Geikerb, and K.K. Hansenb

aBuilding and Fire Research Laboratory
100 Bureau Drive Stop 8621
National Institute of Standards and Technology
Gaithersburg, MD 20899-8621 USA
bTechnical University of Denmark
Building 118
DK-2800 Lyngby
DENMARK


ABSTRACT

Fundamental studies of the early age desiccation of cement-based materials with and without a shrinkage-reducing admixture have been performed. Studies have been conducted under both sealed and drying conditions. Physical measurements include mass loss, surface tension, X-ray absorption to map the drying profile, internal relative humidity, and autogenous deformation. Interestingly, although the shrinkage-reducing admixture accelerates the drying of bulk solutions, in cement paste with a water-to-cement ratio of 0.35, it actually reduces the measured drying rate. Based on the accompanying X-ray absorption measurements and a simple three-dimensional microstructure model, an explanation for this observation is proposed. In sealed systems, at equivalent hydration times, the shrinkage-reducing admixture maintains a greater internal relative humidity and reduces the induced autogenous deformation. Thus, these admixtures should be beneficial to low water-to-cement ratio concretes undergoing self-desiccation, in addition to their normal usage to reduce drying shrinkage.

Keywords: Cement paste (D); drying (A); humidity (A); shrinkage (C); surface tension.


 
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