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Shrinkage-Reducing Admixtures and Early Age Desiccation in Cement Pastes and Mortars.


pdf icon Shrinkage-Reducing Admixtures and Early Age Desiccation in Cement Pastes and Mortars. (1885 K)
Bentz, D. P.; Geiker, M. R.; Hansen, K. K.

Cement and Concrete Research, Vol. 31, No. 7, 1075-1085, July 2001.

Keywords:

cement paste; mortar; drying; humidity; shrinkage; surface tension

Abstract:

Fundamental studies of the early age desiccation of cement-based materials with and without a shrinkage-reducing admixture (SRA) 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 (RH), and autogenous deformation. Interestingly, although the SRA accelerates the drying of bulk solutions, in cement paste with a water-to-cement (w/c) 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 SRA maintains a greter internal RH and reduces the induced autogenous deformation. Thus, these admixtures should be beneficial to low w/c ratio concretes undergoing self-desiccation, in addition to their normal usage to reduce drying shrinkage.