Testing the Strength of Roofing Tiles: A Practical Approach

Roofing tiles play a crucial role in any construction project, and ensuring their durability is key to the success of the entire structure. One of the essential tests conducted on roofing tiles is the transverse strength test, a method widely acknowledged by standards such as ASTM C 1167-11 and IS 13801. In this article, we’ll delve into the significance of this test and the step-by-step procedure involved.

Understanding Roofing Tile Transverse Strength

Roofing tiles, whether flat or bent, are crafted from various materials like terracotta, slate, concrete, plastic, or waterproof glaze. These tiles are designed not only to resist moisture penetration but also to contribute to the overall stability of a roof structure.

The Objective

The primary aim of the transverse strength test is to estimate the breaking load a roofing tile can endure. This measure ensures that the tile meets the necessary standards and, by extension, doesn’t compromise the integrity of the entire construction project.

Setting Up the Test

Before diving into the specifics of the test, it’s crucial to outline the apparatus and preparation required.

Apparatus

The testing machine, depicted in Fig. 1, is a fundamental component of the transverse strength test. It comprises two support members and a loading member, all of which should have faces made of metal or hardwood.

Specimen Preparation

1. Tile Condition: Five tiles are typically tested either wet or dry, based on mutual agreement between the specifier and supplier.
2. Span Consideration: The span for the test is set at 30.5 cm ± 5% or 2/3 of the tile length, whichever is greater. Special considerations apply for tile lengths less than 30.5 cm, as specified by IS 13801.
3. Schematic Setup: Fig. 2 illustrates the recommended setup for the transverse strength test, providing a clear visual guide.

Testing Machine Specifications

The test is conducted in a three-point bending mode, as illustrated in Fig. 2. Key specifications include the material of support and loading members, the addition of rubber shim strips, and the prohibition of any rotations during the test.

Conducting the Transverse Strength Test

With the apparatus and specimen ready, the actual test can proceed.

1. Machine Setup: Position the roofing tile on the testing machine.
2. Load Application: Apply a uniform and continuous load on the tile without shock at a maximum rate, as specified by the standards.
3. Record and Report: Record the load at the fracture for each of the five tiles, reporting both the average and minimum individual results.

Analysis and Reporting

Once the test is complete, the results need to be interpreted based on the relevant standards.

ASTM C1167-11

Table 1 provides classification criteria for roofing tiles based on the transverse strength test, differentiating between wet and dry conditions. If the span of the testing specimen varies from 30.5 cm, specific adjustments need to be made.

IS 13801

For IS 13801, the wet transverse strength can be calculated using Equation 1, taking into account the breaking load, span between supports, tile width, and fracture thickness.

Equation 1: f = (3pl)/2bt^2

In conclusion, the transverse strength test on roofing tiles is a crucial step in ensuring the longevity and reliability of roofing materials. Following the specified standards and procedures outlined in this article can contribute to the success of any construction project.