Page 65 - Highway Engineering Handbook Building and Rehabilitating the Infrastructure

48 CHAPTER ONE

Sodium Bicarbonate Blast Cleaning. Either jetted water or compressed air can be used
to propel water-soluble sodium bicarbonate against the bridge surface. This method does
not remove mill scale or rust effectively. Dust is significantly reduced when jetted with
water, thereby reducing the potential for lead inhalation, but lead ingestion remains a
hazard. Containment of the water is difficult. It may be demonstrated on a case-by-case
basis that the sodium bicarbonate serves to stabilize lead in the paint so that it does not
leach into the water in concentrations great enough to render the blasting water a hazardous
waste. There is no grit waste. This method requires inhibitors to prevent flash rust from
forming when the paint is removed.
Carbon Dioxide Blast Cleaning. Small pellets of dry ice can be propelled using com-
pressed air against the bridge surface. This method does not remove mill scale or heavy
rust, and production is slow. This method reduces the volume of waste to only the actual
paint being removed. It also greatly reduces sparking risk, and dust is reduced. Worker
exposure is reduced, though it must still be controlled. The equipment and materials for this
method are relatively expensive.
Combinations of Removal Methods. Combining methods, if done effectively, may reduce
the volume of waste or increase productivity or the quality of surface preparation. The objec-
tive is to select methods that are complementary. An example would be first using a chemi-
cal stripper, which yields low dust and minimizes the need for containment. The chemicals
will remove the leaded paint but not the mill scale. Once the hazardous substances are
removed, another method, such as wet blasting, can remove the mill scale and rust without
necessitating further hazardous waste disposal.
Abrasive Blasting with Proprietary Additive for Lead Stabilization. The equipment and
procedures used are identical to open abrasive blasting, except that the abrasive is pre-
blended with a proprietary material that stabilizes the lead, typically creating a nonhazardous
waste for disposal.
Thermal Spray Vitrification. This method involves the application of molten glass to the
surface that binds with the coating. Upon cooling, the glass/paint composite cracks, and
spontaneously disbonds from the surface.

Laser Paint Removal. This method involves the use of lasers to instantaneously vapor-
ize the paint, turning it into an ash that is vacuumed for disposal.

1.5.6 Containment Considerations

Design of proper containment requires the participation of specialists in structural engi-
neering, coatings, ventilation, and exhaust. The following considerations should be
addressed in the development of a containment system:
• The environmental media (air, water, soil) that are vulnerable and the containment
methods that will provide the best protection
• Durability
• Compatibility with the selected removal method, and potential for interference with the
productive removal of the paint, mill scale, and rust and the application of a new coat
of paint
• Ease of construction, disassembly, and moving from one area of the structure to another
• Local climate conditions
• Continued usability of the structure and proximity of nearby structures and people