The specific surface area of hardened plaster paste was measured by an improved method and apparatus, and the reproducibility of the measurement was examined. The methods for estimation of some characters of the hardened bodies were studied on the basis of the measured specific surface area. The results obtained are as follows :
(1) The average value of the specific surface area was 0.896 m²/g for the hardened paste with W/P= 0.70, and its standard deviation was 0.015 m²/g.
(2) The average heat of adsorption calculated from the measured surface area was 1992 cal/mol, and its standard deviation was 20 cal/mol.
(3) On the assumption that the crystals in the hardened bodies were rectangular parallelepipeds, shape factor (φ), diameter (d_sp), for specific surface area and number of crystals per unit volume (N_v) were given as follows : φ=ds·s/v, d_sp=φ/ρ_p·s_w, N_v=Sw/6·d_sp²V_twhere s, v, ds, Sw, ρ_p and V_t are the surface area, volume and surface mean diameter of a crystal, and the specific surface area, density of particles and apparent specific volume of hardened plaster paste, respectively.

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