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 deformation, 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 NIST cement hydration and microstructure development model is used to separate the effects of differences in hydration rates (kinetics) from those due to 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 by using coarser cements, a small autogenous expansion (due to ettringite formation) as opposed to a shrinkage may be produced and early age cracking possibly avoided.
Keywords: Autogenous deformation; Cement paste; Eigenstress; Hydration; Particle size distribution; Pore size distribution; Relative humidity.