Proceedings of the International rilem conference Materials, Systems and Structures in Civil Engineering 2016
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- 3. Conclusions
- EXPERIMENTAL STUDY OF CORROSION-INDUCED DEGRADATION OF REINFORCED CONCRETE ELEMENTS Olaf Loukil (1)
- Chaussadent (3) , Frédéric Ragueneau (4) , Xavier Bourbon (5) , Laurent Trenty
92 International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service Life of Cement-Based Materials and Structures 22-24 August 2016, Technical University of Denmark, Lyngby, Denmark
The experimental results show that approximately half of the global air leakage is in the gusset. This result confirms that all the containment wall history, especially at early age, matters in the air leakage study. Indeed, this result seems to show that early age gusset cracks reopen during the pressurization test. Global air leakage has been overestimated by all teams except by Team 49 which underestimated it. Team 21 and Team 23 results are very high compared to experimental and other Teams results. Only Team 21 has identified the gusset as the major contributor to the global air leakage. Other teams predicted that its contribution would be very low. All teams, except Team 50, identified the cylindrical part as a major contributor to the global air leakage and overestimated its contribution. Dome contribution to air leakage has been globally well estimated, except Teams 49 and 37 which overestimated its contribution. The hatch area contribution to air leakage has been significantly overestimated by Teams 50 and 23. Other teams didn’t identify hatch area as a contributor of the global air leakage. The repartition given in the following graph [Figure 12] is in percentage of the global air leakage. Figure 12: Air leakage repartition (percentage)
Following the presentation of the results one can retain, from the first international benchmark on the VeRCoRs mock-up, the good quality of the work done by the participants. Regarding the theme “gusset at early age” (theme 1), the results provided show that the temperature curves are close to experimental results despite some approximations in the
93 International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service Life of Cement-Based Materials and Structures 22-24 August 2016, Technical University of Denmark, Lyngby, Denmark
starting data. This allows us to affirm that the tools and their uses are mastered to reproduce the thermal aspect of concrete hydration reactions. For strains, the results are more scattered. Strains provided by participants are always below the measured deformations. Participants generally found the setting in tension of the gusset, even if the results are relatively scattered. One team manages to predict fairly precisely when cracking occurs at early age. Predictions about the cracking at early age in the gusset are good, but only few participants were able to deliver results on this point. This shows that modeling the concrete behavior at early age is still unconventional for civil engineers. About modeling the containment behavior since its concreting to its first mechanical loading (theme 2), the results provided are more numerous. These calculations are indeed more common in the profession. Some participants have undertaken comprehensive and complex calculations incorporating all the construction phases of the containment. Some have obtained results very similar to experimental measurements, showing a good understanding of the behavior of the structure. Nevertheless there are sometimes significant differences both between the participants and compared with experimental measurements. The gusset area in particular is complex to model and its behavior remains poorly mastered. To a lesser extent, the dome can also result in more scattered results. However, interpretation of these results is difficult in some cases because the compared values include several phenomena with sometimes opposing effects (effects due to time / mechanical loadings effects). So, it was not always possible to distinguish the source of a significant deviation with other participants or in comparison to the experience. For future benchmarks, it will be important to ask results in a very precise way to compare and interpret more thoroughly the results transmitted. One can also note that the results for cracks are distant from experimental results. In particular one can notice: - That, ignore the effects associated to early age is a gap in forecasting the state of active cracking during pressurization, particularly in the gusset; - That, built the determination of cracking on a postprocessing of the stress state based on a linear calculation, can lead to overestimation of active cracking. Efforts seem necessary to move forward on modeling strategies integrating nonlinearities throughout the whole history of the building Finally, the prediction of the leakage flow remains a difficult exercise. The results show a factor of 1 to 200 between the lowest flow and the highest. However, this factor is much better than that which was obtained in previous benchmarks on the subject of the leak through a concrete wall. This shows that this type of calculation becomes more controlled. However it appears clearly that the determination of the cracking state is a major element to forecast leakage. VeRCoRs should be a real way to further improve the air leakage prediction tools.
95 International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service Life of Cement-Based Materials and Structures 22-24 August 2016, Technical University of Denmark, Lyngby, Denmark
(1) Université Paris-Est, MAST, SDOA, IFSTTAR, France. (2) Université Paris-Est, MAST, EMMS, IFSTTAR, France. (3) Université Paris-Est, MAST, CPDM, IFSTTAR, France. (4) LMT/ENS Cachan/CNRS/Univ. Paris 6/PRES UniverSud, France (5) ANDRA, Chatenay-Malabry, France
Abstract Corrosion of steel reinforcement is the main cause of damage for reinforced concrete structures. Iron oxides produced during the corrosion process can induce concrete cracking, loss of adhesion at the steel-concrete interface, loss of reinforcing bar cross-section and even spalling of the concrete cover. In the presented research, the durability problems related to the corrosion of the reinforcement are investigated by combining experimental and numerical studies. However, this paper particularly focuses on the experimental methodology used for the time evolution of damages (steel corrosion products formation and crack patterns) induced by the accelerated corrosion test. The accelerated corrosion tests were carried out by applying a constant current between reinforcement used as an anode and a counter electrode. To control the corrosion process, electrochemical parameters (such as free corrosion potential, polarization resistance, electrical concrete resistance) were measured. The purpose of this paper is to determine the width and length of the cracks and their orientation according to the current density and time.
Introduction
Corrosion of steel reinforcement is one of the main causes of deterioration of existing reinforced concrete (RC) structures. The consequences of this phenomenon are degradation of the steel/concrete bond, reduction of the steel rebar cross-section and concrete cover cracking [1]. This last phenomenon results from the production of oxides which occupy a volume two to seven times higher than the parent steel. Actually, when this production is greater than diffusion of iron oxide in the concrete, pressure increases at the interface between the surrounding concrete and the rebar [2] [3] and exerts tensile stresses in the concrete all along the corroding reinforcements. If these stresses exceed concrete tensile strength, the cracking initiates and propagates towards the outer surface leading to the delamination of the concrete Yüklə 8,6 Mb. Dostları ilə paylaş:
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