The rheological behavior of water-calcium sulfates and hydroxyapatite-calcium sulfates binary blends was considered in this study. These blends are to be used as permeable reactive barriers for groundwater remediation. The influence of gypsum and plaster on the rheological behavior of Ca-HA(Gel) has been studied. The results show that all blends and formulations exhibit a shear-thinning effect and thixotropic behavior. The viscosity also depends on the level of concentration of the solid and the reactivity of the blends. The hydration of plaster causes cohesion and agglomeration between particles due to electrostatic forces, while the hydration of gypsum leads to dispersion due to repulsive forces between particles. The zeta potential was used in this study to understand the interaction between particles and its effect on the global behavior of the blends. The dissolution in water of sulfate ions containing calcium sulfate leads to a change in the surface charge of the blend. This allowed the dispersion or agglomeration of the mixtures to be predicted.