The crystallization and salt expansion characteristics of a silty clay

Abstract

To investigate mechanisms and principle for the salt expansion, theoretical analysis, micro-fabric observation and salt expansion tests are conducted to a silty clay containing sodium sulfate. Equations are provided to calculate the crystalized sodium sulfate through theoretical analysis. Long strip crystal bridges and bulky crystal are found in the micro scanning images of saline soil. When these crystals grow upon cooling, soil is supposed to expand. In salt expansion tests, the effects of compaction effort, water content, and salt content of soil are considered. Three compaction levels, i.e. 0.85, 0.90, and 0.95 are used. Three water contents, i.e. 13.2, 15.2 and 17.2% are used. Both pure Sodium sulfate soil and soil containing Sodium sulfate and Sodium chloride are used. The salt expansion data demonstrate that the volumetric content of crystal seems to have a unique relation with the volume strain of saline soil. A unified formula is established and can be used to predict the salt expansion strain for silty clay containing Sodium sulfate and Sodium chloride with any water content, salt content and dry density. Because the salt expansion tests used in this study use small sample and are without water supply, the salt and moisture migration in these tests is insignificant and the tests can be regarded as element tests. The unified formula can help to build constitute models for salt expansion.