Note that a complete scientific paper describing the Hamburg Simulation Chamber study can be obtain in the Technical Paper section
Even if "pure acid" tests are quite easy to perform in the laboratory, experience shown that they are unable to correctly predict the durability of sewer repair materials exposed to actual biogenic corrosion. For instance, inert coatings do resist these "pure acid" tests but inert liner failures are countless in real sewers. At the opposite end of the spectrum, while SewperCoat® cannot resist the pure acid test, it exhibits an exceptional durability to biogenic corrosion in real life applications.
This is why Kerneos Research has worked with leading Universities around the world to better understand the key factors for the durability of concrete in the wastewater infrastructure environment. Biogenic corrosion is created by the development of a complex living ecosystem and multi-disciplinary teams are required to link material and microbiology sciences.
At the beginning of the 90's, a research team from Hamburg University, in Germany, developed a laboratory simulator able to reproduce the biogenic corrosion ecosystem found in sewers. The goal of this team, lead by Dr. Bock, was to provide the industry with material durability data more representative of actual field conditions than pure acid tests. The main outcome was the development of the "Hamburg Simulation Chamber", allowing to expose specimens to a realistic biogenic corrosion process at an accelerated rate. This section summarizes the actual Hamburg Simulation Chamber program and presents what was learned about the durability of SewperCoat®.
Still today, there is not yet a standardized biogenic corrosion test because creating a complete ecosystem in a laboratory is not easy. The Hamburg Simulation Chamber is really the model and tool the industry needs to guide the choice of proper materials for sewer building and rehabilitation.
The essential objective of the Hamburg Simulation Chamber was to compare the behaviour of various cementitious materials in a well simulated sewer environment, under carefully controlled laboratory conditions. The Hamburg Simulation Chamber maintained the ideal ecosystem conditions to permit the colonization and growth of Thiobacillus bacteria in order to expose real building materials to the very severe conditions of biogenic corrosion.
One key feature of this simulator is its capacity to accelerate the biogenic corrosion process, allowing a faster durability assessment. By comparing the corrosion rates recorded in a real corroding "reference sewer" Vs. the rate observed in the Chamber, the acceleration factor was found to be 24. In other words, the damages observed after one year in the Hamburg Simulation Chamber would take 24 years to happen in the reference sewer.
Various materials commonly used in the industry were included in the Hamburg Simulation Chamber over the several years it was operated, including various Portland cements, calcium aluminate cements, and SewperCoat®.
The Hamburg Simulation Chamber principle is quite simple to explain: in a close volume, you create the ideal conditions for the growth of the various bacteria strains responsible of biogenic corrosion. By providing the right temperature, moisture, food, source of energy (Hsub>2
As shown in the diagram, the chamber is made of a closed volume with stands to expose the specimens (mortar cubes). The chamber is equipped with sprinklers to bring moisture and nutrients essential for bacteria growth. A heating system maintains the temperature at 30°C, the optimal temperature to maximize bacteria activity. H2S gas in injected in the chamber to maintain 10 ppm level. Finally, a powerful ventilation system ensures that uniform conditions exist in every location of the chamber.
Because it takes time for the bacteria to "colonize" the surface of new cementitious specimens, the exposure duration in the Hamburg Simulation Chamber was one year. To evaluate material resistance to biogenic corrosion, cube specimens were monitored for visual appearance, bacteria count, surface pH, weight loss, depth of attack and the trend of attack.
The test is essentially comparative, with Portland cement specimens being the reference. The effectiveness of the chamber is confirmed by the rapid deterioration of Portland cement concrete specimens.
This picture shows the actual Hamburg Simulation Chamber open, with various cementitious specimens inside. The large volume of the chamber allows exposure of a large number of specimens at the same time.
(For a detailed explanation of the surface preparation requirements please see ACI RAP-3 "Spall Repair by Low Pressure Spraying" page 2. ACI 546R "Concrete Repair Guide", chapter 2 also provides a good reference for important considerations for repairing concrete surfaces using mortar.)
This graph shows the evolution of weight loss over one year for different cementitious specimens exposed in the Hamburg Chamber.
After one year in the Hamburg Simulation Chamber, the 2 types of OPC cement specimens were completely destroyed by bacterial activity, i.e. the weight loss was 100%. The trend of attack actually accelerated due to the disruptive ettringite formation within the OPC cement paste. The Blast Furnace Slag cement showed some little improved results, but the trend of deterioration was still upward and the weight loss at 1 year was still 100%.
Exposed to the very same conditions, the SewperCoat® mortar specimens exhibited only a limited weight loss after one full year of exposure (around 20%). Moreover, the trend for further attack did not increase over time. This illustrates the effectiveness of the "protective barrier" provided by the 100% calcium aluminate nature of SewperCoat®. Electronic microscopic observation confirmed the presence of the AH3 barrier.
It is to note that the CAC concrete, made with natural occurring aggregates, did performed better than the OPC specimens (around 40% weight loss at one year) but far from the performance obtained with SewperCoat® made at 100% of calcium aluminate (both cement and aggregates are calcium aluminate).
This graph shows the evolution of the surface pH over one year for different cementitious specimens exposed in the Hamburg Chamber.
It shows that the surface pH of OPC specimens rapidly decreases to around 1, allowing rapid acidic corrosion. Adjacent to these specimens, exposed to the same environment, the surface pH of SewperCoat® specimens stabilized around 3, indicating a significant reduction of the bacterial activity. The fact that the pH does not decrease below 3, which correspond to the threshold of alumina gel dissolution, confirmed the importance of the aluminate composition of SewperCoat®.
The Hamburg Simulation Chamber was run for several years in the 90's, allowing the study (under very controlled conditions) the biogenic corrosion ecosystem found in sewers and its impact on building materials. For the calcium aluminates based materials, the bacteriostatic effect induced uniquely by CAC was conformed without doubt. The unequalled durability of 100% calcium aluminate specimens was also confirmed. These quantitative observations fit the qualitative observations made in thousands of SewperCoat® repaired sewers around the world.
One question often raised is the expected service life of SewperCoat®. Each sanitary sewer application presents a completely unique and dynamic environment and there is not yet a modeling system able to predict how every specific environment will evolve. However, the Hamburg Simulation Chamber demonstrated that in an extremely severe corrosion environment - one year in Hamburg Chamber worth 24 years in a corroding sewer - SewperCoat® lost only 20% of its weight. Such a carefully monitored quantitative study permits to assess that SewperCoat® has the potential to provide "Protection for Generations".