The use of cementitious materials for solidifying hazardous substances has recently shown considerable promise. The advantages of solidification, sometimes called stabilization, include: safer transportation and easier burial; less pollution of the environment caused by leaching and evaporating of hazardous constituents; improved physical properties of the wastes for easier handling; potential for recycling wastes into construction material; detoxification of substances for protection of workers. In the solidification process portland cement, proprietary additives and, in some cases, fly ash are mixed with the waste to produce a solidified mass for disposal. Solidification with portland cement is most applicable to inorganic wastes such as incinerator residue, road wastes, and heavy metal wastes. The high pH of the cement keeps metals in the form of insoluble hydroxide of carbonate salts. Low-level radioactive wastes and organic wastes can also be solidified using portland cement. Each waste material will react differently with the many possible combinations of cement and additives, depending on both the chemistry and the concentration of the waste. For proper stabilization to take place it is necessary to develop a laboratory mix design suitable for the specific hazardous waste.