The ability of the indirect tensile strength test to predict the tensile strength of a bituminous mixture is of significance as it helps to evaluate the relative quality and strength of the materials as well as in pavement design, evaluation, and analysis. Bitumen has higher strength in compression as compared to tension. The higher the tensile strength, the higher the cracking resistance of the pavement.

Indirect Tensile Strength Test Procedure

A cylindrical asphalt specimen is statically loaded on its edge in much the same manner as in the Marshall test head, with a constant deformation speed until failure. At the constant load, the sample’s deformation is monitored for 1,000 seconds, and then the sample is loaded to failure. The maximum load is recorded and used to calculate the indirect tensile strength.

Required equipment for the indirect tensile strength test

• Marshall Compaction Test Apparatus
• An indirect tensile stress loading frame
• Water bath accurate to 1.0 oC
• An extruder
• 6 specimen molds

Test Procedure

• Test samples are prepared. The test specimens used in this test can either be core samples taken from road pavements or made in the laboratory. The sample is quartered and riffled to obtain 6 samples of 1200g.
• When drilling the cores from the surface or base layer made from cold-mixed materials, there should be minimal use of water to avoid unnecessary moistening of the specimens.
• Put in the oven to have a uniform temperature.
• Remove the samples from the oven and fill the mold, then compact by 75 blows on each side using the Marshall Compaction apparatus.
• After all six are compacted, they are extruded from the molds; the three cores are tested in dry conditions and the other three in wet conditions.

Dry conditions

• The samples are air-dried at room temperature (25 oC) for 72 hours.
• The samples are Put in a water bath at 25 oC for 1 hour and then crush.
• The sample is loaded on its edge with a constant deformation speed until failure. At the constant load, the sample’s deformation is monitored for 1,000 seconds, and then the sample is loaded to failure. The maximum load is recorded.