A long-term investigation on microstructure of cement-stabilized handan clay

Abstract

In order to better understand the mechanisms of cement treatment on the expansive clay, this study presents a long-term study on the micro-structure evolution of the cement-treated highly expansive clay (Handan clay) over a curing period of one and an half years through scanning electronic microscope (SEM) tests and X-ray diffraction analyses. A series of unconfined compression tests were also conducted on cement-modified clay. SEM testing results revealed the microstructure change and cement hydration process during cement treatment of the highly expansive clay. Cement added to the expansive clay generally experiences a hydration, initial setting to form a gel membrane, final setting to form a semi-solid gel and eventual solidification process. The microstructure of the highly expansive clay goes through a series of changes, from a dispersive structure before adding cement, to a flocculated and agglomerated structure after adding cement, further becoming a semi-solid and chained net structure due to the hydration and hardening of cement, and finally forming a stacked dense solid structure. Testing results indicated that the pozzolanic reaction happens very early after adding cement. However, well-crystallised pozzolanic products form at about 28 days in this study. The pozzolanic reaction continues more than one year in this study. The unconfined compressive strength increases with curing time and is closely related with the microstructure change of cement-treated clay. Void ratio estimated from SEM images also indicates that the cement-treated clay has a dense structure.