Abstract
Dry and wet cycle experiment was carried out on hardened cement paste to understand the drying shrinkage mechanism and the effect of Shrinkage Reducing Agent（SRA）on the pore size distribution determined by Low Temperature Thermo Porosimetry（LT-DSC）. In the specimen without SRA which was held at 20 degrees Celsius and relative humidity of 40％, the volume of Small Gel Pore（1.0 to 2.2 nm in radius）was reduced but it did not recover after dry and wet cycle experiment, while the volume of Large Gel Pore（2.2 to 6.0 nm in radius）did not change. Therefore, it could be clear that at this condition the main factor of the shrinkage and expansion was aggregation and dispersion of the C-S-H unit. On the other hand, in the specimen without SRA which was held at 40 degrees Celsius and relative humidity of 40％, the volume of C-S-H Gel Pore（1.0 to 6.0 nm in radius）was reduced but it did not recover after dry and wet cycle experiment, the pore structure became coarse and the volume of capillary pore increased. Thus, it could be clear that at this condition, the main factor of the shrinkage and expansion was aggregation and dispersion of the cluster of C-S-H. In contrast, in the specimen with SRA, the pore size distribution did not change after dry and wet cycle experiment. Therefore, it could be clear that SRA retain the C-S-H Gel Pore which contributes the shrinkage and expansion to reduce strain after dry and wet cycle experiment.
