Hydration and leaching of the cement - zeolite composite

This study has examined the effect of harmful waste material-zinc saturated zeolite on hydration processes and the stabilization of such harmful waste in cement composites. Measurements were made on cement pastes with defined water/solid ratios, W/S, different contents (10-50%) of natural zeolite saturated by Zn^2+-ions, and the constant addition of 0.3% of plasticizer-type admixure relative to the mass of the solid sample. The hydration processes were traced by determining the heat effects of reactions by means of differential microcalorimetry and by measuring specific conductivity by means of conductometry. Stabilization after solidification was carried out by means of a leaching test and UV/Vis spectrophotometrical analysis was used to determine the zinc concentration in elutes. The results obtained indicate a direct effect of zeolite addition on hydration heat and relative hydration degree. The higher the addition, the lower the hydration heat and degree. Kinetic curves define individual hydration intervals and hydration rates during solidification. The effect of zeolite addition is directly related to the occurrence of the maximum hydration rate. Changes in specific conductivity and appearance of maximums on conductograms indicate that the addition of zeolite changes the electrolytic properties of the reaction system. When the content of saturated zeolite in cement pastes increases, specific conductivity decreases, and the recorded maximums appear at later hydration and solidification times. Zinc concentration in elutes after the leaching test depends on the duration of solidification, quantity of saturated zeolite and duration of rinsing after cement sample solidification. Low zinc concentration in elutes after leaching indicates that such wastes can be successfully stabilized by solidification processes in Portland cement composites.