Ultrasonic Monitoring of Shrinkage Development of HPC Under Isothermal Conditions

The development of the autogenous shrinkage of a high performance concrete HPC has been investigated in detail as there is a cracking risk at early age due to restrained shrinkage existing in a steel-HPC bridge deck with U-shaped precast in Belgium. The autogenous shrinkage determination was carried out on a test rig designed to start the measurements just after casting. The test rig is immersed inside a temperature controlled bath. The displacements of the upper head of the specimen are measured by an external transducer. The concrete is placed in a corrugated PVC mold to avoid any friction during the test. The initialization time of the deformations is fixed after the observation of two different methods of ultrasonic monitoring of setting (BTPULS, LCPC’s prototype and FreshCon, University of Stuttgart). It corresponds to the time when the ultrasonic velocity starts to increase which corresponds to a point in the penetration resistance graphs determined by traditional methods.