Homeland Security Research

Research Highlights

Removing Radiological Contamination From Concrete Using Strippable Coatings

EPA evaluates homeland security related technologies that will help protect human health and the environment from the adverse impacts of terrorist acts. Radiological attacks may require massive evacuation to protect human health and greatly interfere with economic and business activities. As a result, there is much interest in technologies that can be used to mitigate these effects and help with the cleanup following terrorist acts.

As part of this effort, EPA has evaluated two strippable coating technologies for their ability to remove cesium-137 (Cs-137) from concrete surfaces:

• Stripcoat TLC Free™ (Bartlett Services Inc.)
• Orion^TM Strippable Coating (Orion™ SC) (Isotron Corp.)

Figure 1. Applying the Coating with a Sprayer

The coatings were applied to concrete coupons contaminated with Cs-137. Both products can be applied like paint, using commercially available, airless paint sprayers, brushes, or rollers. Figure 1 shows application with a paint sprayer, the method used in this evaluation. The treated surfaces were allowed to cure overnight into a solid coating and were then removed from the concrete surface. Orion™ SC apparently binds radiological material through chemical and physical interactions when it is cured. Stripcoat TLC Free™ apparently binds radiological material only through physical interaction between the radiological material and the cured coating. Each technology was evaluated for:

• Decontamination efficacy (percent removal) from vertical and horizontal surfaces, 7 days and 30 days after contamination of the coupons
• Application and removal times
• Ease of use on irregular surfaces
• Labor requirements
• Utility requirements
• Portability
• Secondary waste
• Surface damage
• Preparation and cleanup
• Cost

Note that the 7-day and 30-day tests were performed to determine if a more rapid response would provide a better decontamination efficacy with these products. Another important objective of the evaluation was to determine if the wet strippable coatings would adhere adequately to a vertical surface.

Test Design

To evaluate the decontamination technologies on vertical surfaces (simulating walls) as well as horizontal surfaces (simulating sidewalks and driveways), a test stand was fabricated that held four rows of six concrete coupons to create surfaces that were approximately 90 centimeters (cm) wide x 60 cm deep (horizontal) or tall (vertical). Concrete coupons were made of standard building concrete that met the specifications for both Type I and II Portland cements. Each coupon was 15 cm square and 4 cm thick. Six of the 24 coupons used to construct each surface were contaminated with Cs-137 (approximately 53 microcuries [µCi]).

Figure 2 shows several concrete coupons and a test stand loaded with the coupons.

Figure 2. Concrete Coupons (left) and Test Stand With Contaminated Coupons (right) - H and V indicate horizontal and vertical orientation, respectively, and A–F indicate the surface positions

After the coupons were contaminated with Cs-137, some were allowed to age for 7 days and some for 30 days prior to their placement in the test stand for application and removal of the coatings.

Following application, the coatings were allowed to dry overnight, and then removed by first scoring an edge with a paint scraper and then pulling the coating off the surface by hand or scraping lightly. Following the manufacturers’ recommendations, this application and removal process was repeated three times. Figure 3 shows the removal processes for each coating. After the final removal of the coatings, the residual radioactivity on the coupons was measured. The decontamination efficacy was determined from the difference in activity before and after application of the decontamination technologies.

Figure 3. Removal of Stripcoat TLC Free™ (left) and Removal of Orion™ SC (right)