Have you ever wondered if concrete sets well under water? The answer is yes, concrete sets under water and it does so very well because hydration is excellent. However, there are some issues to consider when building underwater structures.
Firstly, it is important to take into account the currents present in the environment when carrying out underwater construction. Until the concrete sets, the finer particles, including the cement, can escape from the mixture, carried away by the currents, and spoil the setting process.
Sea salts, on the other hand, are a major problem for concrete in the construction of structures submerged in the sea. Sea salts deteriorate the concrete and, if they cause cracks in the concrete, they will permeate into the reinforcement inside the concrete. The water contains oxygen, which will cause the steel inside the concrete to rust and corrode.
Fortunately, chemistry has come a long way to avoid this problem in submerged construction at sea. There are products that, when added to the mix, make the concrete less porous and effectively protect the steel bars in the reinforcement. But this is not the only solution. Glass fibre reinforcement is also used, which does not corrode in marine environments and has a tensile capacity approximately 4 times higher than that of steel.
Interestingly, the area most affected by corrosion in a submerged structure is not the area under water, but the area that is exposed to the elements and yet remains wet. This area is attacked by water and is also exposed to the air, which facilitates the penetration of oxygen through any fissures. It also tends to withstand the impact of waves and is an area rich in algae and molluscs.
All this makes the construction of submerged structures in tidal zones the most delicate. Many technicians opt to use prefabricated elements in these areas. In fact, in harbours and breakwaters, natural stone is no longer used in favour of blocks and prefabricated concrete elements.
In any case, both in the construction of submerged structures and in the construction of structures out of water, the chemistry and performance of concrete are similar. However, it is necessary to pay special attention to concrete structures located under seawater, due to the aggressive nature of the marine environment.
By Jorge Laguna, Head of the structures section of Amusement Logic’s architecture department.
