Evaluation of Cleaning and Coating Techniques for PCB-Contaminated Concrete

摘要

PCB-contaminated concrete is a significant environmental management issue for many industrial facilities. The U.S. EPA has authorized exposure control in operating facilities via encapsulation or use of physical barriers when complete PCB removal is not technically achievable and/or is not cost-effective. Achievement of effective encapsulation with epoxy coatings is challenging for PCB-contaminated concrete as oil and/or other chemicals are often present. This work involved experimental investigation of encapsulation via cleaning and epoxy-coating of PCB-contaminated concrete. Experimental studies were performed with three cleaning techniques for removal of PCBs, and three epoxy-coating systems for encapsulating PCBs. Resurfacing of oils and PCBs from concrete after cleaning, or "bleedback," was also studied. These tests were conducted using PCB/oil-contaminated concrete core samples from industrial plants. Results indicated that no cleaning system alone is effective as a long-term solution for PCB-contamination concrete, and that bleedback occurred within days after cleaning due to capillary rise, affected by changes in wetting temperature induced by heating, which affects the density of the oil. The presence of free oil on the concrete surface resulted in failure of the coating systems, which occurred faster if heating was applied. Where appropriate surface preparation was performed, the integrity of the coatings remained intact throughout the experimental period (eight months). In such cases, the coating system acted effectively as a barrier against diffusion of PCBs. This study demonstrated that, except in high-temperature areas, an epoxy coating can be an appropriate encapsulation system if proper surface preparation is applied. Metal sheet barriers can be used for high-temperature applications.