Suivi de l'évolution de la réaction alcalis-silice par méthodes ultrasoniques et par tomographie sonique
The Alkali-Silica Reaction (ASR) causes the swelling of concrete structures and creates microcrackings inside the concrete and macrocracks at the surface cracks mapping. This phenomenom affects the durability of structures and involves technical and economical issues for structure managers. Development of non-destructives methods, aiming at monitoring ASR evolution, would help managing the structures rehabilitation works. The scope of this thesis is to monitor the evolution of damages associated with ASR using non-destructives methods based on ultrasonic wave propagation and resonant frequencies of concrete specimens in order to establish criteria associated to each methods. However, it is not easy to measure ultrasonic properties variations due only to ASR. Indeed, non-destructives methods are sensitive to mixture proportions of concrete and to environmental conditions. In addition, it is difficult to monitor ASR evolution directly on structures because ASR is a very slow reaction (over ten years). In order to achieve this objectives two studies were carried out. The first was conducted in a laboratory. The ASR evolution was monitored with ultrasonic methods (pulse velocity, attenuation and resonant frequencies of concrete specimens) on reactive laboratory concrete specimens (100x200 mm or 75x75x300 mm) kept in accelerated conditions. Temperature and water content of these specimens varied in order to evaluate the effect of these parameters on non-destructives measurements. Mixtures of non-reactive specimens were batched with Limeridge limestone (metamorphic limestone from the Appalachia) and reactive specimens with Spratt limestone or Posdam sandstones. Both reactive aggregates have different reaction rate. Ultrasonic tests that were performed are based on the measure of pick-to-pick amplitudes, ultrasonic wave attenuation in spectral domain, centroid frequencies, rise time and resonant frequencies of concrete specimens. In this thesis we also have studied the ASR evolution was with electrical methods. Results showed that concrete proportion parameters and environmental conditions affect significantly the measurement of electrical resitivity. It is not relevant to use this method to monitor the ASR evolution. Results of electrical measurements are presented in this thesis in order shows the inapplicability of this method. The second study aims at evaluating the in-situ behaviour of some of the non-destructives methods used in the first study. Sonic attenuation topography was performed on a lock. The followings observations and recommendations are drawn: (1) In order to carry out laboratory tests, the study of longitudinal resonant frequencies on cylinders (100x200 mm) is the most relevant method for measuring ASR evolution. Furthermore, this method may assess the damage state of concrete, when water content of hardened concrete varied. (2) In the case of structures subjected to high humidity conditions, it is recommended to conduct attenuation tomography based on the inversion of centroid frequencies calculated from the output signal FFT. (3) Finally, if the structures is in a high temperature variation area (temperature less than 4 [degré] C or more than 40 [degré] C), it is recommended to carry out attenuation tomography based on the reverse of rise time calculated with Blair et Spathis method. It is also recommended to use a light weigh hammer (250g to 450g) to generate the signal. In order to compare ail the methods, a synthesis table is presented at the end of this thesis. The comparison is made with three criteria: sensitivity of methods to ASR, sensitivity of methods to environment conditions and quality of tomographies obtained with reverse of sonic parameters of each method. This synthesis will help for the planning of future tomography survey of ASR affected concrete structures.
- Génie – Thèses