Understanding cementitious resurfacers in water and wastewater environments

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Courtesy of Tnemec Company, Inc.

An adhesion study of cementitious repair mortars used to address the surface defects and irregularities found in new or rehabilitative concrete construction is generating interest within the municipal water and wastewater construction industry, according to the author of a technical paper and several articles on the subject.

Vaughn O’Dea, Director of Sales – Water and Wastewater Treatment for Tnemec Company, has written extensively on the rehabilitation and protection of concrete wastewater collection and treatment structures from the destructive effects of biogenic sulfide corrosion. His latest series of articles were fueled by a paper he presented to the International Concrete Repair Institute (ICRI) in which he addresses proper curing and surface preparation of commercially available thin-patch cementitious mortars prior to topcoating with high-performance lining systems.

“Resurfacing improves the film quality of a protective coating by eliminating possible pinholes and bughole-induced outgassing, and ensures long-term barrier protection of concrete,” according to O’Dea. “Too often, however, competent commercially available resurfacers are improperly cured and topcoated with high-performance linings outside of industry recommendations.”

In his concrete repair study, O’Dea tested 12 commercially available cementitious resurfacing materials for their bond strength properties. Testing was performed in accordance with ASTM D7234, which describes a procedure for evaluating the direct tensile strength of a coating on concrete. “Enhanced repair material properties, such as tensile strength, become more important as cementitious repair materials become thinner,” O’Dea noted. “The study underscored the importance of proper curing and preparation in providing cementitious resurfacing materials with the physical properties required to support topcoating in these severe environments.”

Reaction has been favorable to the study, which is described in-depth in O’Dea’s ICRI technical paper and published articles in Public Works, Concrete Repair Bulletin, Concrete Surfaces and Journal of Protective Coatings and Linings. “We’ve had positive feedback, reinforcing the fact that our findings were right on track with what people are seeing in the field, particularly related to cases involving failures,” O’Dea acknowledged. “The study helps explain why they’ve seen sub-par performance out of various cementitious resurfacing materials that have been topcoated.”

O’Dea is currently finishing up a new technical report that focuses on the finishing/preparation of resurfacers prior to topcoating, specifically comparing a broom-finished surface verses a mechanically profiled surface. “The preparation of resurfacers prior to topcoating is often ignored,” he explained. “If cementitious repair mortars develop a laitance layer – similar to that which forms on concrete – the preparation requirements of these repair products should mirror that of concrete before topcoating.”

Protective coatings manufacturers and those who use their products face an ongoing challenge as new cementitious resurfacing materials and methods continue to be introduced at an increasing rate. “Tnemec is playing a primary role in researching and educating the industry on proper curing and preparation of cementitious resurfacers to produce maximum topcoat adhesion,” O’Dea added. “We feel it’s important to educate the industry about this challenge.”

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