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The transverse strength test of roofing tile is commonly carried out based on the specifications of applicable standards such as ASTM 1167-11 and IS 13801. It involves wet or dry method test and conducted in the lab to estimate breaking transverse load for the roofing tile.

The roofing tile transverse strength is one of the requirements that the tile need to meet otherwise it jeopardize objective of the project.  Roof tile is rectangular flat or bent unit that is produced from terracotta, slate, concrete, plastic, or waterproof glaze. It is designed to resist moisture penetration and usually hung from framework of a roof.

 Aim

Estimate the transverse breaking strength of roofing tiles

Apparatus

The tile testing machine

Testing Machine
Fig. 1: Testing Machine

Specimen Preparation

  • Five tiles (6 tiles in accordance with IS) shall be tested wet after a 24-h submersion in water at a temperature range of 24 to 30°C.
  • Alternatively, five tiles shall be tested dry after heating in a ventilated oven for 24 h at a temperature of 110 to 115°C.
  • The choice of method, wet or dry, shall be mutually agreed upon between specifier and supplier.
  • The span for the test shall be 30.5 cm Plus/Minus 5 % or 2/3 of the tile length, whichever is greater.
  • If tile length is less than 30.5cm, then shorter span can be used but it should not be less than two-thirds of the tile length.
  • In accordance with IS 13801, chosen span for the test is 15cm, 20cm, and 25cm for tile size 20x20cm, 25x25cm, and 30x30cm, respectively.
Schematic Representation of Tile Set Up for Transverse Strength Test
Fig. 2: Schematic Representation of Tile Set Up for Transverse Strength Test

Testing Machine Specifications

  • The tile shall be tested in a three-point bending mode as schematically illustrated in Fig. 2.
  • The two support members and the loading member shall be of metal or hardwood with 25 mm wide faces.
  • Hardwood (if used instead of metal) shall be backed up with steel bearing plates at least 13 mm thick.
  • A rubber shim strip (4.8 mm thick and 25 mm wide) shall be placed between the faces of the support and loading members and the surface of the tile, as shown in Fig. 2. IS 13801 recommended plywood with 3mm thick and 20mm wide.  
  • The length of the support and loading members need to be greater than the tile width.
  • Longitudinal and transvers rotation of the support members and the loading with respect to the test specimen is prohibited.
  • Supporting and loading members need to be adjusted to avoid transvers and longitudinal rotations (According to IS 13801, one support member should be self-adjusting).

Test Procedure

  1. Set up the testing machine on which the roofing is place to be tested.
  2. Apply uniform and continuous load on the tile without shock at maximum rate of 4550N/min (2000N/min based on IS13801) until fracture.
  3. Record the load in kilograms at fracture of each of the five tiles (IS13801: six tiles)
  4. Report the average of the five tests and the minimum individual result.

Calculation and Results

ASTM C1167-11 provides table 1 for the classification of the tested tile based on the transverse strength test.

Table 1 Transverse Breaking Strength Requirements

Type (All Grades) Wet Transverse Strength, min, N Wet Transverse Strength, min, N Dry Transverse Strength, min, N Dry Transverse Strength, min, N
Average of five tiles Individual tile Average of five tiles individual tile
Type I-High profile 1334 1157 1779 1556
Type II-Low profile 1001 890 1334 1112
Type III-others 1001 890 1334 1112

If the span of the testing specimen is smaller than 30.5 cm, then the values in table 1 are multiplied by (12/span used (in.)).

If the span of testing specimen is greater than 35.6 cm, the values provided in table 1 should be multiplied by (width in (in.)/14)

Based on the IS 13801, the following equation can be used to calculate wet transverse strength.

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

Where:

p: breaking load

l: span between supports

b: tile width

t: fracture thickness of the tiles measured from the fracture line            

About Madeh Izat HamakareemVerified

Madeh is a Structural Engineer who works as Assistant Lecturer in Koya University. He is the author, editor and partner at theconstructor.org.