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