Creep testing of concrete since setting time by means of permanent and repeated minute long loadings
Monitoring the evolution of early age properties of concrete is necessary to provide input data to the models of prediction of the behavior of concrete structures since setting time. The experimental challenge lies in the fact that this monitoring must be fully automatic since the earliest age because the hardening process of the concrete takes place continuously over a period counted in hours and even in days after the casting time. This research paper presents a new methodology developed at ULB and IFSTTAR to monitor the creep and relaxation of an ordinary concrete chosen as reference concrete since setting time. Compressive creep rigs and two test devices were used: at ULB, a Temperature Stress Testing Machine (TSTM) specifically designed for testing concrete since setting time under free and restraint conditions and at IFSTTAR, a test set up called BTJASPE developed to monitor, in compression, the modulus of elasticity, the creep and the relaxation of a concrete since very early age. For the sake of the study, the same concrete has been used in the two laboratories. In addition, this study is performed at a constant temperature to exclude this parameter, at this step of the study. The methodology is based on experimental measurements with two kinds of test. A classical creep test with permanent loading during one week and a repeated minute long loading test for which every 30 min, a loading is applied and kept constant during 5 min and finally totally removed. The classical test is used to characterize the non aging creep function and the repeated minute long loading test is used to quantify the aging creep functions.