Building Underwater Bridges: The Role of Hydraulic Lime and Cofferdams

The Importance of Hydraulic Lime in Underwater Construction

Hydraulic lime plays a crucial role in the construction of underwater bridges due to its unique ability to set underwater. Unlike non-hydraulic lime, which sets through carbonation and requires exposure to carbon dioxide in the air, hydraulic lime sets by hydration. This means that it can bond and harden even in the presence of water, making it ideal for underwater construction projects (1).

One type of hydraulic lime used in underwater construction is natural hydraulic lime (NHL) mortars. These mortars are obtained from limestone naturally containing a sufficient percentage of silica and/or alumina. The presence of these substances enables the lime to set underwater, providing the necessary strength and durability for bridge construction (3).

In addition to natural hydraulic lime, artificial hydraulic lime is also utilized in underwater construction. Artificial hydraulic lime is produced by introducing specific types and quant***** of additives to the lime source during the burning process or by adding a pozzolan to non-hydraulic lime. These additives enhance the lime's hydraulic properties, allowing it to set underwater (4).

The Science Behind Concrete Curing and Construction Methods

Concrete, the primary material used in underwater bridge construction, undergoes a curing process rather than drying. During this process, chemicals in the concrete mix react with and bond to water, resulting in its hardening over time (6). Surprisingly, water on the outside of the concrete actually aids in the curing process by keeping the concrete moist and preventing dehydration, which could lead to weak spots or cracks (7).

To ensure the proper placement of concrete in underwater construction, forms are used. These forms prevent the concrete from thinning and spreading once it displaces the water, maintaining the desired shape and structure (8). It is important to note that wet concrete is corrosive and should be washed off the skin promptly to prevent skin reactions and corrosion (11).

Construction Methods: Pre-made Pillars and Cofferdams

When it comes to building underwater bridges, there are various methods employed. One approach involves transporting pre-made concrete pillars to the bridge location and driving them into the ground. This method provides instant bridge support without the need to wait for the concrete to cure (12).

Another commonly used method is the construction of cofferdams. A cofferdam is an enclosure or wall around the work area that can be pumped of water, allowing construction to take place in relatively dry conditions (13). By diverting water away from the construction site, either through pumping or redirecting the flow of a river or stream, a dry working environment is created (14).

Working within a cofferdam offers several advantages. It eliminates the challenges posed by working underwater, making construction easier and more efficient (17). Once the construction is complete, the water is allowed to flow back into the area, and the cofferdam can be removed (18). Cofferdams provide a temporary solution for creating a dry working environment in underwater construction projects (19).

The Benefits of Cofferdams in Underwater Bridge Construction

The use of cofferdams in underwater bridge construction allows for more efficient and effective construction processes (20). By creating a dry working environment, construction teams can work with greater precision and accuracy. The elimination of underwater challenges simplifies the construction process and reduces the risks associated with working in water.

Hydraulic lime and cofferdams play vital roles in the construction of underwater bridges. Hydraulic lime, whether natural or artificial, enables the concrete to set underwater, providing the necessary strength and durability. Meanwhile, cofferdams create a dry working environment, simplifying construction and improving efficiency. These innovative techniques contribute to the successful completion of underwater bridge projects, ensuring safe and reliable infrastructure for years to come.