September 29, 2009

Visual Inspection: The Start of the Project

by Bob Murphy

Concrete as a building material has been widely used in the construction of water and wastewater facilities. Concrete is easy to place and form, and its lower cost and higher durability have made concrete a construction material of choice. Protecting concrete from the constant acidic attack of the waste stream has become a challenge for facility owners.

There are many factors to consider in maintaining today’s water and wastewater treatment facilities. More stringent environmental regulations have led to a variety of corrosion issues both with steel and, more importantly, concrete.

There are five steps needed in the development of a protective coating program for wastewater treatment facilities:

  • Evaluation
  • Specification
  • Surface Preparation
  • Application
  • Inspection

Prior to the evaluation step, a checklist should be established. This checklist will enable the person conducting the survey to document the entire layout and obtain all relevant information.

  • Visually survey the entire layout
  • Draw a diagram of the area or zones to be coated
  • Document the surface/matrix conditions – coating, cracks, delamination, MVER, soundness, etc.
  • Document depth of contamination (core if possible)
  • Document environmental conditions
  • Document total surface area to be coated

During the evaluation stage an overall visual inspection of the facility should be completed to document any corrosion issues such as degraded concrete, exposed rebar, cracks, leaks, delaminations and unsound concrete.

During this evaluation step, non-destructive testing can be accomplished. This testing could include such procedures as pH testing, and Qualitative Moisture Testing per ASTM4263, Standard Test Method for Indicating Moisture in Concrete by the Plastic Sheet Method.  This qualitative method will indicate the presence of moisture movement, but it will not quantify it, and is only useful in determining that additional testing is required. Presence of moisture within the substrate should be noted.  If moisture is noted after conducting the Plastic Sheet test, where practical use ASTM F1869. ASTM has published a standard for the use of calcium chloride to measure moisture vapor emission from concrete; ASTM F1869-04 is the most current edition of the protocol. The results are accepted by most flooring, adhesive and resinous coating manufacturers in establishing the benchmark of acceptability for the installation of their products over a concrete substrate.

Often on large projects, where the concrete surface is in poor shape, core samples will be taken in various areas to determine the depth of the degradation and underlying condition of the concrete. These core samples may be subjected to a number of tests that would include pH, chloride levels, compressive strength and depth of carbonation. Once these tests are completed the engineers can develop concrete repair systems to bring the concrete substrate back to “plane.” This testing will also enable the engineer to determine if the steel rebar has been damaged and needs repair as well.

Through visual inspection and various substrate testing methods a clear picture of the concrete structure comes into focus and the correct procedures can be specified to help aid in the preparation of a proper specification. This is just  the start of a good coating project.

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