Retrofitting of reinforced concrete columns with composites:: static compressive tests and modelling-creep

The aim of this study is to enable the repair and strengthening of reinforced concrete columns on bridges and buildings and to begin a French national research project on the use of composites in civil engineering. The first step of the study was to realise some static and cyclic flexural tests and develop some numerical methods which were reliable to the design methods. Initially we present the interesting study and the behaviour of concrete 16x32 cylinders retrofitted by composites. We insist that the use of a 2500 kN load capacity test machine be used in the experimental procedure. We measured both longitudinal and transversal strains, using transducers. By comparison with concrete reference tests, the augmentation of loading capacity and the nonproportional loading of concrete are shown. We then developed an incremental behaviour model: with some existing models, we obtained only an estimation of the peak value load. The behaviour model used enables us to obtain longitudinal and transversal strain evolution. This model can easily be implemented in a finite element code. The end of this paper is related to some ideas on the use of this model to calculate the behaviour of actual reinforced columns, with the retrofitting of concrete, the buckling of the column and the strengthening longitudinal flexural effect of composites. The final part of this study is related to the creep compressive behaviour of 16x100 concrete cylinders, which are - or not - retrofitted by composites. We present here some experimental results, with specimens loaded to 30% of the capacity of concrete alone. The main result is that we do not obtain a significant effect of composites on the creep behaviour of concrete : the stresses in the composites are small, and the retrofitting effect does not exist. Different reasons and conclusions related to the columns calculation are discussed.