Surface Prehydration of Cement Clinker Phases Caused by Water Vapour

摘要

Industrial cements undergo some prehydration already during their manufacturing process. This is ft example due to reaction with water released by dehydration of gypsum which is ground together with clinker in the ba mill. Additionally, cement may pick up water during storage in the silo or later before use. Our study demonstrates thi the various cement clinker phases prehydrate very differently. Using a water sorption balance, the amount of chemical] and physically sorbed water and the relative humidity at which water sorption starts to occur on pure cement clinki phases were determined. It is shown that free lime acts as a desiccant in cement, and that C3A and the calcium sulphate absorb significant amounts of water whereas the silicates (C3S, C2S) show only minor sorption. The practici consequence of prehydration of cement is that prehydration causes a delayed set. Additionally, dosage and effectivene; of superplasticizers are greatly affected by cement prehydration.