Early age deformations of concrete are involved in cracking which can lead to service life reduction. In particular, the development of the concrete shrinkage under restrained conditions often leads to durability problems in concrete structures. This study (part 1& 2) presents an experimental methodology using two different test rigs enabling a monitoring of the stiffness, the creep or the relaxation of a concrete sample at early age. Tension tests realized on the Temperature Stress Testing Machine [1] (TSTM used at ULB) are presented in a second part while compressive tests, realized on another test rig called BTJASPE [2] (designed at IFSTTAR), are presented in the first one. In each part, models are used for the description of the experimental set of data. Results in compression and in tension are compared in the second part. Creep and shrinkage are important parameters to take into account for more realistic descriptions of early age cracking of concrete. The purpose of this study is to answer to the question of the equivalence between the early age creep and relaxation behaviour of concrete in tension and in compression for a typical reference ordinary concrete in sealed conditions. BTJASPE is a test rig which enable early age compressive test on cylinders. Samples are cast inside a stainless steel mould (sealed conditions) around which a flow of water allows the control of the sample temperature. The Young's modulus, the creep or the relaxation of the sample can be monitored at early age. Cyclic loadings are applied at regular intervals. In each cycle, a loading, controlled in displacement is applied, then the stress or the strain are kept constant during a short period and the sample is unloaded to a zero stress until the next cycle. Rheological functions are used to model the observations performed in compression. Results are expressed, after the setting time, in function of the maturity. This time is determined both with ultrasonic measurements and the monitoring of the stiffness with the cyclic loading protocol. Parameters of the creep model are used as input for the relaxation model whose response is compared to experimental results.
