Abstract
The freeze drying process for hardened cement consists of a freezing step by liquid nitrogen and a drying step by vacuum. Since the use of liquid nitrogen involved the risk of cracking due to heat impact, the authors made improvement to existing freeze-drying equipment to minimize heat impact on specimens and tested various freezing conditions and drying temperatures in the current study. The specimens used in this experiment were hardened bodies of hauyne-containing cement with ettringite which was susceptible to structural destruction by drying. The authors determined from a comparative study the optimum drying conditions non-altering to ettringite where peak area measured by the powder X-ray diffraction remained almost unreduced. The pore size distribution of the specimens prepared by the proposed method was found to differ significantly in major pore diameter and total pore volume from those of the specimens dried by commonly used D-drying or drying at 105℃. The pore size distribution results were also interpreted to represent the extremely fresh condition in which most of ettringite remained intact.
