Updated: Jul 29, 2021
The oceans cover 71% of the world’s surface and contain 97.2% of the Earth’s water. With the increase of human population, effects of pollution on the oceans have also drastically increased, putting ecosystems and fish stock in jeopardy. According to the United Nations, many marine species worldwide are affected by marine debris, and as much as 80% of that litter is plastic. One of the best platforms to educate future generations about the effects of pollution on our planet are public oceanariums. They offer a “true world experience” in a controlled environment, which can be used for creating awareness, learning and inspiring change of habits for a cleaner environment.
Bringing the ocean into a building is not a simple task. A huge amount of technology and husbandry know-how is required to bring an ocean ecosystem into an oceanarium tank. Construction methods to build these specialized concrete tanks require specific needs in order not to destabilize the exhibit’s water parameters while combating any possible structural deterioration from seawater.
Fig. 1a: Oceanarium 3 million litres per hour non-metallic recirculation system
Fig 1b: Oceanarium automated filtration system
Seawater contains about 3.5% soluble salts (chlorides and sulfates) by weight and has a pH of around 7.5 to 8.4. It is a catalyst for corrosion, and like any exposed concrete structure to seawater in nature, direct exposure may deteriorate concrete through the effects of various chemical and physical processes. For example;
• Sulfate attack
• Leaching of Lime (Calcium hydroxide)
• Alkali-aggregate expansion
• Salt crystallization from wetting and drying
• Corrosion of embedded reinforcing
Controlling or stopping the deterioration through these processes is best done by reducing concrete permeability. Low permeability not only prevents tank leakage but, it also helps to keep seawater out of the concrete, thus slowing leaching and protecting the reinforcement steel from corrosion. Newly laid bare concrete, in whatever form, leaches when submersed in seawater. Leaching is very dangerous and lethal for an aquarium inhabitant causing spikes in pH and leaching of chemicals into the exhibit’s water column. The trick to building a successful oceanarium tank is a good waterproofing tank system and most importantly, to get it right the first time, as not to jeopardize the fishes when introduced into the tank.
An oceanarium concrete tank structure can be grouped into 3 exposure zones; submerged, splash and atmospheric. The submerged zone is continuously covered by seawater, the splash zone is subject to wetting and drying and the atmospheric zone is exposed to seawater spray. Concrete in the submerged zone is not as vulnerable to corrosion compared to the 2 other zones. Oxidation works slower when submersed, but the flip side is that the leaching of lime can be fatal to fishes. Moreover, if metallic corrosion does happen underwater, the effects can be detrimental to some species, affecting the nervous and navigation system of most elasmobranchs (sharks and rays).
Damage of concrete due to deterioration is like cancer; it slowly eats into your reinforced structure and spreads from there, increasing porosity and permeability to the concrete. There are multiple ways and systems available in the market that reduces permeability in the concrete but nothing beats a good lining system. Choosing a high strength, low permeability concrete mix with a minimum reinforcement cover of 50mm and a good non-toxic lining systems (eg. pure polyurea etc.) goes a long way towards creating a maintenance free and long service life concrete in a marine environment while keeping the fishes safe from contamination.
Although a good design mix is a good start in ensuring a long concrete life, one must not forget that design and construction practices will affect strength, permeability and durability. We have found that a good lining system and low permeable base concrete base makes the worries go away. The reliability that every inch of concrete is placed properly in good construction practices can be a worrisome task and not practical for large tanks and areas. In addition, probable issues of external groundwater damages in structures below the water table are inherently difficult to identify. Lining systems like pure polyurea have revolutionized the construction and waterproofing of oceanarium tanks because it reduces the risk of permeability problems and the quick cure time allows work for other trades to continue efficiently.
Fig 2a: Poorly placed new reinforced concrete tank that required rectification.
Fig 2b: New reinforced concrete with lesser than 50mm cover
Like with any protection membrane installation, a good base concrete is extremely important, as it (the lining) would be considered as the first line of defense and concrete cover as the second, before seawater reaches the reinforcing. In addition to this, high-risk areas for corrosion in seawater such as construction joints can be mitigated. It is found that with systems like these, localized rebar corrosion from construction joints and cracks is reduced drastically.
Fig. 3a: Typical concrete tank surface preparation
Fig. 3b: Pure polyurea waterproof lining system application
In order to have a composite system to fully work together, the chemical bonding of lining and concrete plays a very important role. Proper moisture mapping, surface preparation and application are key in the laying of a 3mm pure polyurea lining system. Other key procedures such as viewing panel silicone bonding test between polyurea lining and the acrylic prior to installation, helps ensure all these material components are fully integrated and watertight.
Fig 4: Silicone chemical bonding test to acrylic viewing system and waterproofing lining system, where the best primer is selected
Fig. 5: Completed tank with aquascaping and fish (inhabitant) introduction
In conclusion, bringing the ocean and encapsulating it into a tank is truly a unique multi faceted task and its poses a unique set of problems to overcome. When building an oceanarium, it is important that designers are fully educated in the nature of seawater and the importance of the details in specifying marine structure corrosion mitigation systems. Having the right specialist from the start is also the utmost importance, where proper structural mix and lining system are selected with experienced on-site quality control managed, so that inhabitants of the oceanarium is safe and the nature of the oceans can be truly appreciated.
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