Dynamic Leach Testing of Low and Medium pH Injection Grouts to be used in Deep Repositories: Master's Thesis

The work comprised of two parts. The literary part reviews the characteristics of cement chemistry and durability aspects of cementitious materials. Also the influences of cementitious materials to the groundwater and barrier systems, such as bentonite are discussed. The long-term safety of materials is essential in deep geological repository. The experimental part of the work concentrates on the dynamic leach testing of two injection grouts, one low-pH grout and one medium-pH grout. Leach testing was performed in a glove-box (N2 atmosphere) in order to avoid the interference of atmospheric CO2. Two simulated groundwater solutions, fresh ALL-MR and saline OL-SR, were used as leachates. The object of the work was to evaluate the influence of the water flow on leaching of grout samples. Two flow rates were chosen, higher flow rate of 7.5 mL/h and a lower one of 0.625 mL/h. The pH value of each leachate sample was measured, but the amount of total dissolved organic carbon was determined only for some leachates. Rather expected results were gained. The faster decrease of pH values was noticed in the case of the higher flow rate experiment. A similar decrease was detected in both low- and medium-pH grout leachates. The difference in the pH values between the two grouts was greater in the saline leachates for both flow rates The low-pH leachates reached the target pH < 11 in all tests. The medium-pH grout leachates also showed decreasing trend in both solutions at the faster flow rate. However, only a minor decrease was observed at slow flow rate. The chemical and mineral composition of the grout samples was analyzed by using X-Ray Diffractometry (XRD), thermal analysis (TG/DTA), X-Ray Fluorescense (XRF), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). According to the XRD results all the analyzed grout samples were mainly amorphous and, thus, only relatively small amounts of crystalline compounds were detected. The main compound in all the sample specimens was amorphous calcium silicate hydrate gel.