Understanding Metallic Sheathing Ducts: A Comprehensive Exploration of Workability, Load Tests, and Water Retention

Metallic sheathing ducts play a vital role in the pre and post-tensioning of concrete structures. They create a space within the concrete, allowing cables or tendons to stretch freely during the stressing process. This article delves into the evaluation of metallic sheathing ducts through various tests, including workability, transverse load rating, tensile load, and water loss.

Types of Sheathing Ducts: Metallic vs. HDPE

Before we delve into the tests, let’s briefly explore the two main types of sheathing ducts: metallic and HDPE.

Metallic Sheathing Ducts

Metallic sheathing ducts are crafted by rolling CRCA steel strips, featuring spiral corrugation along their length. These corrugations enhance bonding with the concrete externally and the cement grout internally.

Workability Test: Assessing Duct Bending Performance

The workability test aims to evaluate how well the sheathing duct withstands bending. Here’s a step-by-step breakdown:

Procedure:

1. Secure a 1100mm sheathing duct to a base plate using soft soldering.
2. Fasten the duct with a cable and pull it through a pulley fixed 1m apart on both sides.
3. Perform bending up to a radius of 1800mm on both sides alternately, repeating the process three times.
4. Visually inspect sealing joints for any signs of failure or opening.
5. If an opening is detected, the sample is considered unsuccessful.

Transverse Load Rating Test: Determining Deformation Limits

This test assesses the duct’s ability to withstand transverse loads without significant deformation. Follow these steps:

Procedure:

1. Measure the outer diameter (D1) of a 500mm sheathing duct.
2. Place the sample on a stand and add loads on a centrally located loading plate, as per Table No-1.
3. Measure the outer diameter after loading (D2).
4. The sample is deemed acceptable if the permanent deformation is less than 5% of the sheathing diameter.

Transverse Load Rating Test

Tension Load Test: Evaluating Strength under Tensile Forces

The tension load test focuses on subjecting a test specimen to increasing tensile loads. Here’s how it unfolds:

Procedure:

1. Fill the bellows core with a wooden circular piece.
2. Screw on a coupler and load the sample incrementally, following the load specifications in Table No 2.
3. If no joint deformation or coupler slippage is observed, the test is considered satisfactory.

Tensile Load Test

Water Loss Test: Ensuring Watertight Integrity

The water loss test evaluates the duct’s ability to retain water under pressure. Here’s a step-by-step guide:

1. Seal one end of the sample and fill it with water.
2. Connect the other end to a system capable of applying 0.05 MPa pressure.
3. Maintain a constant 0.05 MPa pressure for 5 minutes using a hand pump with a pressure gauge.
4. Collect and measure the water coming out of the duct.
5. The sample passes if the water loss does not exceed 1.5% of the initial water volume.