Calcium carbonate and calcium sulfate in the aerated portland cement were structurally studied by infrared absorption method, differential thermal analysis, X ray diffraction method and chemical analysis. The aerated cements were produced by the four different conditions, that is, putting the cement in the 23-25°C, 40-45% relative humidity (low humidity room), putting in the 20°C, 90% relative humidity (high humidity room), putting in the chemical analysis room for 28 days, and grinding mechanically in the open air for 24 hrs. The results obtained are summarized as follows,
(1) Calcium carbonate was calcite type in the cement aerated in the high humidity room, but it was aragonite type in the cement aerated in the low humidity room. In the aeration in the chemical analysis room, calcium carbonate was detected as mostly aragonite type and a little amount of calcite type.
(2) The rate of aeration of cement was higher in high humidity room than in the low humidity room, joudging from the variation of absorption bands of calcium carbonate in the infrared absorption analysis and loss of weight on ignition.
(3) When portland cement clinker was mechanically ground in the open air by the dry method, it was forcedly aerated, and varied to the amorphous compound containing the amorphous calcium carbonate and structurally disordered clinker minerals.
(4) Calcium sulfate dihydrate in portland cement varied to the high sulfate form of calciumsul-foaluminate hydrate (ettringite) by the aeration of cement in high humidity room, but did not change by the aeration in the low humidity room. Calcium sulfate hemihydrate in portland cement varied to the calcium sulfate dihydrate via unknown state by every conditions of aeration.

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