Note: There are methods available today that will remove chlorides from existing in-place concrete. These methods should be evaluated and considered by building owners and engineers. Such methods may be appropriate depending on the extent of the damage and of the desired repair.
- Clean rebar with an appropriate method to remove all corrosion, and repair appropriately to ensure the integrity of the completed repair.
- Coat the exposed rebar with a high-performance anti-corrosion and bonding agent. To improve bonding of the repair mortar to existing concrete, coat all areas of the repair with the same bonding agent.
- Select an appropriate repair mortar with the required performance and application characteristics.
- While this completes the defined ACI repair method, MAPEI recommends going one critical step further to solidify the repair's longevity by an exponential factor — ultimately decreasing lifecycle costs to the owner. For this fifth step, coat the entire structure — both the original concrete as well as the repaired area — with a cementitious, flexible waterproofing and protective coating.
5th step proves successful
The benefit of cementitious coating for repairs was validated by Chris Atkins, senior materials engineer within the Materials and Corrosion Engineering Section of Mott MacDonald Consulting Engineers, in Altrincham, UK. In a recently published interview in the Journal of Protective Coatings and Linings, Atkins concluded that the application of a polymer-modified cementitious coating at thicknesses over 2 mm (80 mils) is the best method to protect concrete structures in wastewater treatment systems.
An independent study of MAPEI's Mapelastic™, designed to provide a crack-bridging barrier that impedes carbonation and chloride penetration of the concrete, showed effectiveness in halting chloride penetration. The test evaluated two specimens — uncoated concrete, and concrete coated with Mapelastic. In the test environment, both specimens were immersed in a 10 percent solution of sodium chloride (NaCl) for 60 days. According to National Italian UNI 7928 standard test method, analysis of the specimens showed that the uncoated sample exhibited chloride penetration of 35 mm, while the Mapelastic-coated sample had chloride penetration depth of 1 mm.
Todd Miller is the Product Line Manager for MAPEI's Concrete Restoration Systems division. Experienced in product line management, marketing, systems development and customer service, Todd is committed to innovative products and positive customer solutions.
For information on MAPEI products and systems, visit www.mapei.com.