The leaching effect of cement hydration products

The barrier for low-level radioactive wastes repositories calls for the use of concrete. In a underground situation, the repository may be subject to intrusion of various elements from the external environment and may cause concrete deterioration and reduces its durability. This study focuses on the effect of leaching of concrete as simulated in the laboratory to assess the durability in long term use of concrete materials. The basic mixture of cement, mortar and concrete were used to produce test specimens that were exposed to different conditions such as pure water and substitute ocean water to simulate calcium loss under different circumstances. The possible mechanism of calcium loss and potential influence on concrete durability were then carefully examined. The results of the extensive laboratory experiments show that: (1) concrete materials has better resistance against calcium leaching as compared to mortar and cement paste based on the SEM-EDS measurements on the Ca/Si ratio; (2) the increase in duration of exposure of cement mortars resulted in increases in the porosity of the specimen as exhibited by the decreases of bulk density; (3) microstructural observation showed that mortar samples in ammonium nitrate solution experience accelerated leaching, resulting in the severe deterioration of the region near the exposed surface.