Prestressing Sheathing Ducts: Metallic vs HDPE

When it comes to using prestressing sheathing ducts in the process of constructing prestressed concrete, which type of sheathing to use has been a hotly debated topic in the construction industry for many years. Many people believe that using high-density polyethylene (or HDPE) sheathing is the answer while most traditional contractors remain fast with the opinion that metallic sheathing is the better option.

What Are Prestressing Sheathing Ducts and What Do They Do?

Prestressing sheathing ducts are corrugated lengths of pipe that are used in the process of constructing prestressed concrete. This process involves applying extreme pressure to the concrete in order to give it tensile strength. The finished process makes the concrete extremely strong, and it may be used for various types of construction, like bridges, high-rise buildings or roofs and floors.

A vital part of the prestressing process is that prestressing sheathing ducts are used to create tunnels for steel tendons to be pushed through. Once the tendons have been correctly positioned under tension, a mortar slurry is forced through the pipe in order to secure the steel tendons to the inside walls of the sheathing, forming a strong bond. It also ensures the subsequent bond between the outside of the corrugated pipe and its surrounding concrete. At the correct point of curing, the tendons are released and the process is complete.

What Do the Ducts Need to Endure?

Before a fair opinion can be offered in this debate, it is important to understand the various stresses, pressures and punishment the pipes need to endure, prior to, during and after construction. For example:

They need to be transported to the construction site and then manhandled from the transport to storage. There they may have to endure weeks, if not months, of exposure to the elements and heavy machinery as they are moved from one area to another.
They often need to be craned up to where they will be positioned or rolled out over long distances, connected with one another and firmly secured in place to await the tendons. They need to be malleable enough to allow movement, yet rigid enough to remain in place and not sag.
They need to have the ability to withstand the transfer of tensioning and endure the external pressures of the concrete casting, leaving no intrusions for the concrete into the prestressing duct.
Inversely, the pipe needs to endure the passing through of the tendons without damage and the high-pressure mortar slurry which is forced into the pipe. The pressure must be sufficient to force out any air bubbles ensuring a secure bond between the tendons and the inner wall.
There can be neither leakage into nor spillage out of the pipe under these intense pressures.

HDPE Sheathing vs Metallic Sheathing

The galvanized version of metallic sheathing does not rust. Its durability and dexterity ensure that it can withstand rough handling while remaining malleable yet rigid and steel can withstand substantial temperature changes, while UV rays, rain, extreme temperatures and manhandling may cause its counterpart to become brittle and snap or crack.

While HDPE sheathing is a tough competitor and its ability to withstand extreme pressures through these vigorous processes, along with its high tolerance of post-construction, may be adequate, if not admirable, the essential difference is in the tensile strength as its mild steel counterpart has a higher tensile strength and melting point.

Quality Metallic Prestressing Sheathing Ducts

Armco Superlite’s corrugated steel sheathing resists leakage and remains indentation and buckle-free, withstanding the harshest site conditions, before, during and post-construction. We are listed by the BSI ISO 9001:2015 quality scheme which ensures the quality of all our products and services and our corrugated steel sheathing products are fully compliant with the rules and regulations relating to the African construction industry. If you are looking for quality steel prestressing sheathing ducts, arm yourself with Armco.