Although PCC is not nearly as strong in tension as it is in compression, PCC tensile strength is important in pavement applications. Tensile strength is typically used as a PCC performance measure for pavements because it best simulates tensile stresses at the bottom of the PCC surface course as it is subjected to loading. These stresses are typically the controlling structural design stresses.
Tensile strength is difficult to directly measure because of secondary stresses induced by gripping a specimen so that it may be pulled apart. Although still specified by ASTM, the direct tension test does not provide any useful insight into the concrete-making properties of cements. It persists as a specified test because in the early years of cement manufacture, it used to be the most common test since it was difficult to find machines that could compress a cement sample to failure. Today, tensile stresses are typically measured indirectly by one of two means: a splitting tension test or a flexural strength test.
Splitting Tension Test
A splitting tension test uses a standard 150 mm diameter, 300 mm long (6-inch diameter, 12″ long) test cylinder laid on its side. A diametral compressive load is then applied along the length of the cylinder until it fails (see Figure 1). Because PCC is much weaker in tension than compression, the cylinder will typically fail due to horizontal tension and not vertical compression.
The standard split tension test is:
- AASHTO T 198 and ASTM C 496: Splitting Tensile Strength of Cylindrical Concrete Specimens