- Author
-
Bentz, D. P.
|
Geiker, M. R.
|
Hansen, K. K.
- Title
- Shrinkage-Reducing Admixtures and Early Age Desiccation in Cement Pastes and Mortars.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
Technical University of Denmark, Lyngby
- Journal
-
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.