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|Title:||High solids and zinc-rich epoxy coatings for Corps of Engineers civil works structures|
|Authors:||Repair, Evaluation, Maintenance, and Rehabilitation Research Program (U.S.)|
|Publisher:||Construction Engineering Research Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: For many years, the Army Corps of Engineers has relied heavily on the use of vinyl paints for coating hydraulic structures. The systems have performed well in many environments, however their high solvent content has made their use illegal under some local air pollution control legislation. As a result, alternative systems that are environmentally safer were sought. An early study by the Corps of Engineers (Baker and Beitelman 1992) investigated a number of proprietary coatings meeting the more restrictive air pollution regulations. This study coupled with field evaluations concluded that high solids epoxies held the best hope as replacement coatings systems. Coatings currently available in specifications E-303d and MIL-P-24441 provided a level of protection equal or superior to any of the proprietary coatings evaluated. These coating systems are listed in the Civil Works Guide Specification (CWGS) 09940, Painting: Hydraulic Structures and Appurtenant Works, as System No. 21 AZ and System No. 21 BZ. Experience has shown that high performance coatings of this type are often applied to excessive thicknesses, in weather that is either too hot or too cold, over improperly prepared substrates or in adverse weather conditions. It was a concern that these improper application procedures could result in poor adhesion of the coating and would ultimately lead to failures, thus resulting in damage to the underlying structure. Evaluating these epoxy coatings was necessary to respond to field inquiries relating to specific application irregularities and anticipated problems. The objective of this investigation was to evaluate the application parameters of the currently used E-303d (and the proposed MIL-P-24441/19 [Formula 159]) zinc-rich primers, and of MIL-P-24441 Type IV Formula 150 primer/Formula 151 topcoat epoxy polyamide coatings. Laboratory test methods were developed to simulate the poor application and poor application environment often encountered on hydraulic structures. Heavy emphasis was placed on the coatings' physical properties, including the spraying and drying characteristics. Application variables included the following: high and low temperature application, excessively low and high thickness variation, poor surface preparation, improper thinning, improper spray gun-to-substrate distance, ultraviolet (UV) exposure on primer, and extended cure time between coats. The adhesion was evaluated and all of the coatings were exposed to laboratory environments that simulated actual conditions found on hydraulic structures.
|Appears in Collections:||Technical Report|