Introduction
Any construction activity that takes place under the surface of the water is known as underwater construction. This can be as varied as rigs and oil platforms across the seas or the simple bridge on the river passing through town. But there is a big difference in construction on the seas and on the river. That is the salinity of the seawater which would mean some kinds of construction material cannot be used at all.
It can be broadly said that there are three types of construction material suitable for underwater construction. Concrete, steel and acrylic materials. Each is discussed in brief with their main points below.
Concrete
The concrete that is used in underwater construction by the Southern Divers Commercial Diver tends to be rather different from what is used on dry land. It must have certain properties that make is not just suited but can thrive in the saline conditions prevalent in such construction sites.
Flow ability
This defines how easily the concrete flows to the various sections of the pour after it has been poured. Unlike the surface concreting, it would not be possible to use needle vibrators and such tools to help settle in the concrete. It has been noticed that concrete that has a good flow able nature tends to bring on a correct setting as well.
Setting Time
Take any concrete into consideration and it would soon be evident that there is a certain setting time which causes the poured concrete to settle down to a solidified piece. When constructing underwater, it would not be possible for the concrete to be kept still as there could be currents that flow with the water. Hence a concrete mixture that has a faster setting time than normal must be chosen.
Dispersion
By dispersion, it is the ability of the concrete to disperse in the surrounding water as it stays to set. It has a direct relation to the setting time as a faster setting concrete does not have the freedom to disperse. In addition, most construction work would involve some sort of anti-dispersal agent in the mixture all the time.
Steel
Steel has many uses in the construction industry and with underwater construction as well. What has to be noted is that it is structural steel that is usually used to form structures underwater. Most of the time, the steel is used alongside the concrete encasing but it is possible to come across completely steeled in structures too. The properties of construction steel are as discussed below.
Strength
The term strength used in steel is meant to denote the load-bearing capacity or the limit in loading that causes the steel to fail. Basically the strength of steel that is used above the water on the ground is no different from those used underwater. Most of the time, it is the treatment that is carried out to the steel to make it suited to the marine applications that sets them apart.
Stiffness
Stiffness is measured on the ability of the steel to retain its shape during the construction. Often when bars and steel rolls are used, they are provided with grooves on the sides to increase the stiffness of the steel during the construction. Steel that is not stiff enough tends to lose shape during the concrete pouring stages.
It is the ability of the steel to retain shape while it is loaded that determines the toughness of the steel. Steel that is not hard enough or tough enough tends to pick up pits when used in underwater construction.
Acrylic
Acrylic is nothing but a type of plastic which is used broadly in underwater construction. In many ways, acrylic is not a construction material but an architecture material. Like the typical construction material, acrylic too does have its operational properties.
Optical Clarity
This is the visibility factor to the material on either side of the sheet of acrylic to the other. The most visually pleasing acrylic often tends to be as clear as glass. Often designers use the acrylic to provide a visual experience to those areas under the water.
Resistance to Sunlight
Despite the fact that water does not freely let in sunlight to great depths, it is never the less one of the defining aspects of using acrylic in underwater construction. All acrylic are affected by sunlight. They tend to lose their clarity and strength as well. Proper treatment of the acrylic material can ensure that the material can be accepted as a building material underwater.
Rigidity
This is nothing but the impact strength of the acrylic material. Often during the construction phase, the material is put to severe stress and strain. It is a rigid material that can withstand the rough and tumble of the construction to turn out as a finished product.
Conclusion
It would be evident that the three main underwater construction materials have differing appearances and properties. The designers tend to pick out the materials depending on the actual conditions at site. It would take a professional judgment to get the construction right the very first time around.
