Technical Papers / Publications

BIOGENIC AND CHEMICAL SULFURIC ACID CORROSION OF MORTARS

This academic paper from Pr. Bock's team at Hamburg University (Germany) was the first to put in evidence on a quantitative basis the dramatic improvement of durability to biogenic corrosion of 100% calcium aluminate mortar, i.e. SewperCoat^®. The approach of Pr. Bock was to recreate in a laboratory simulator - the Hamburg Chamber - the ecosystem found in sewers and responsible for biogenic corrosion. By optimizing the environmental conditions for bacterial growth, the Hamburg Chamber permitted acceleration of the corrosion process by a factor 24, i.e. that one year in the Chamber is equal to 24 years of exposure in the Hamburg reference corroding sewer. In such aggressive conditions, the Ordinary Portland Cement mortar specimens were completely corroded in one year (100% weight loss) while the 100% calcium aluminate samples exposed to the very same conditions lost only 16% of their original weight. In parallel to biogenic corrosion tests, the paper explains why "pure acid test" is not representative of the material behavior when exposed to biogenic corrosion. Because Pr. Bock was a microbiologist, a lot of attention was paid to explain why the sulfuric acid producing bacteria - thiobacillus thiooxidans - were barely able to corrode 100% calcium aluminate specimens. The paper explains how 100% calcium aluminate mortar is able to create a biostatic effect which blocks the sulfuric acid production, hence almost stopping the corrosion process.

PROTECTION OF CONCRETE IN COOLING TOWERS FROM MICROBIOLOGICALLY INFLUENCED CORROSION

Summary: Microbiologically induced corrosion (MIC) is not limited to municipal sewers; it is also observed in cooling towers used in geothermal power plants where the warm temperature is favourable to bacteria growth. This paper presents a comparative study conducted at Brookhaven National Laboratory on different repair material options to repair the corroded concrete of cooling towers, both cementitious and polymer products. Tests were done both in laboratory and in-situ. In laboratory, specimens were exposed to Thiobacillus ferrooxidans in an Atlas cell arrangement as described in ASTM C 868. Other specimens were exposed inside a real cooling tower. While the other cementitious specimens demonstrate various degree of corrosion, this study documents that SewperCoat^® was resistant to biogenic corrosion just as well as the epoxies used in the test.

INNOVATIVE APPLICATIONS FOR CALCIUM ALUMINATE REPAIR MATERIALS

Summary: Biogenic corrosion is not limited to municipal sewers. This paper describes the situation around a cooling lake at a power facility in the southeast United States. Around the large manmade cooling lake for process water, 33 lift stations pump the water to avoid the earthen berm becoming saturated. The soil in this area is naturally rich in sulfates, leading to highly sulfate rich groundwater. These sulfates are the source of food needed for establishing the same biogenic acid producing ecosystem found in sewers, and all the pumping stations were suffering from severe biogenic corrosion. The paper presents more pictures and more details about this use of SewperCoat^® outside the classical municipal septic sewers.

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FIELD INVESTIGATIONS OF HIGH PERFORMANCE CALCIUM ALUMINATE MORTAR FOR WASTEWATER APPLICATIONS

This paper presented at the Centenary conference of Calcium Aluminates Cements in Avignon, France, in 2008 starts from the documented field track records of severely exposed SewperCoat^® rehabilitations over as much as 11 years. Then it summarizes the key academic findings about the "bio-static effect" explaining why calcium aluminate mortar is able to withstand the most severe biogenic corrosion conditions when other cementitious materials got deteriorated.? The paper provides qualitative and quantitative data to explain the unique behavior of SewperCoat^®.

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EVALUATION OF ALUMINIUM SENSITIVITY ON A BIODEGRADING BACTERIA ACIDITHIOBACILLUS THIOOXIDANS: DEFINITION OF A SPECIFIC GROWTH MEDIUM

The key mechanisms explaining SewperCoat^® resistance to biogenic corrosion is its very unique "biostatic effect" on acid-producing bacteria. However, one argument heard from time to time was that not all bacteria are sensitive to the presence of aluminum ions, implying that it was not proven that Acidithiobacillus thiooxidans growth was reduced on SewperCoat^®. The study presented in this paper has been realized by a team of microbiologists to verify the actual growth behavior of Acidithiobacillus thiooxidans in the presence of aluminum ions. After overcoming experimental arteficts, and using two different approaches to confirm the results, the paper shows that Acidithiobacillus thiooxidans growth is effectively stopped when the aluminum ions level inside the thin bacteria biofilm exceed the 350-600 ppm range.

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KERNEOS INC. CONTINUES TO GROW IN MANHOLE MARKET

Summary: After a review of Kerneos Inc. history in USA, the paper focused on SewperCoat^® development since 1990. In USA, there are a plethora of manhole products and methods, and competition is fierce as customers can choose from cementitious liners, epoxies, polyureas, polyurethanes, fiber-glass lining systems, thermoplastic sheet liners, etc. Today, SewperCoat^® have a more than 20 year history, and like any product, the best way to prove that it really works is to have a valid history in the field. The interview underlines the strength for Kerneos in the market is its commitment to education, both in academic research and within the industry. "We are very education based, particularly when we give presentations," says Joe Talley. "We educate on corrosion and the wastewater environment itself. We also sponsor Ph.D. research and candidates at different universities around the world who are doing cement and concrete specific research and we often partner with external laboratories and do a lot of field evaluations and product trials."

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