Equipment for tensile testing of fresh concrete

The development of equipment suitable for measuring tensile stress-strain curves on fresh concrete is described. With such weak materials, it is essential to eliminate friction effects and this is achieved by the use of air-bearing plates. The objective of the new equipment is to enable data to be obtained to define the rapidly changing tensile stress-strain performance in the first 6 h after water is added at the mixer. This information is important for understanding plastic shrinkage cracking. The equipment is also being used to investigate early-age internal cracking problems which have been observed with high-strength concrete and which are related to the internal tensile failure strain of the cement paste. Some typical tensile stress-strain curves obtained using the equipment are shown for two types of concrete.