Abstract: Described herein are cementitious composite materials incorporating carbon nanostructures (e.g., nanotubes, nanoplatelets, nanoribbons) that are employed as amendments (i.e., admixtures or additives) to cementitious waste forms as a means to enhance radionuclide and hazardous waste (e.g., heavy metals, toxic organics) retention wherein the incorporation of well-dispersed carbon nanostructures yields more effective waste forms through the resulting modification of the cementitious composite nano-, micro-, and meso-structure (e.g., hindering the infiltration of oxygen and the leaching of waste), and the chemical interactions between chemically-affine waste molecules and the amended cementitious composite.