*2.6. BET Specific Surface Area Test Method (BET) and Thermogravimetric Analysis (TGA)*

To evaluate the mechanisms of additives treatment, BET and TGA (DSC200F3, NETZSCH-Gerätebau GmbH, Germany), analyses were conducted on attapulgite-amended, diatomiteamended, dual-additives-amended, and unamended compacted clay specimens. The specimens were prepared according to the procedures as follows. First, the attapulgiteamended, diatomite-amended, dual-additives-amended, and unamended clay powders were mixed thoroughly to prepare the dry mixture. The dosages of additives were all designed as 5% (dry weight basis) and the ratio of dual-additives was 4 (dry weight of attapulgite 4% to dry weight of diatomite 1%). Then, the powder mixtures were frozen using liquid nitrogen for 5 min at a temperature of −120 ◦C. Sublimation of water was conducted at a temperature of −80 ◦C for 24 h in a vacuum freeze-drying unit at −18 N (Nanjing Xianou Instruments Manufacture Co., Ltd., Nanjing, China). Then, the specimens were subjected to BET and TG analyses, respectively.
