Influence of Cement Particle-Size Distribution on Early Age Autogenous Strains and Stresses in Cement-Based Materials.
Influence of Cement Particle-Size Distribution on Early
Age Autogenous Strains and Stresses in Cement-Based
Bentz, D. P.; Jensen, O. M.; Hansen, K. K.; Olesen, J.
F.; Stang, H.; Haecker, C. J.
Journal of the American Ceramic Society, Vol. 84, No.
1, 129-135, January 2001.
cements; particle size distribution; autogenous
shrinkage; cement paste; eigenstress; hydration; pore
size distribution; relative humidity
The influence of cement particle size distribution
(PSD)on autogenous strains and stresses in cement pastes
of identical water-to-cement ratio is examined for
cement powders of four different finenesses.
Experimental measurements include chemical shrinkage to
quantify degree of hydration, internal relative humidity
development, autogenous shrinkage, and eigenstress
development using a novel embedded spherical stress
sensor. Because the latter three measurements are
conducted under sealed conditions, while chemical
shrinkage measurements are made under "saturated"
conditions, the National Institute of Standards and
Technology cement hydration and microstructure
development model is used to separate the effects of
differences in hydration rates (kinetics) from those
caused by the different initial spatial arrangement of
the cement particles. The initial arrangement of the
cement particles controls the initial pore-size
distribution of the cement paste, which, in turn,
regulates the magnitude of the induced autogenous
shrinkage stresses produced by the water/air menisci in
the air-filled pores formed throughout the hydration
process. The experimental results indicate that a small
autogeneous expansion (probably the result of ettringite
formation), as opposed to a shrinkage, may be produced
and early age cracking possibly avoided through the use
of coarser cements.