Contribution à l'étude de l'expansion résiduelle des bétons atteints de réactivité alcalis-silice
Date de publication2002
The aim of this thesis is to bring about some new elements that may contribute to the development of a method to predict the future expansion of structures affected by alkali-silica reaction (ASR). The main contribution of this work is to report experimental results on the variations of the alkali concentration in the pore solution of various concrete specimens affected or not by ASR. Five mixtures (four reactive and one non reactive) were tested Three Canadian aggregates were used: the Spratt limestone, the Potsdam sandstone (both reactive), and the Limeridge limestone (non reactive). Several concrete prisms were made from these alkali-enriched mixtures and were stored at 38 [Celcius degrees] in humid air (>90% H.R.) in order to accelerate the reaction (Canadian standard CSA A23.2-14A). Some cores drilled from a large hydroelectric dam suffering from ASR were also kept in these conditions. Expansion and mass measurements were taken at regular interval on these specimens. Several investigations have been performed on the tested specimens: quantitative petrographic examination, analysis of the extracted pore solution, dissolution of the reactive silica in NaOH solution, characterization of the reaction rim. The main conclusions are: (1) A relation is shown between the expansion of reactive prisms and their water gain. (2) The pore solution alkalinity of concrete submitted to the accelerated test CSA A23.2-14A decreases with time. (3) According to an alkali mass balance performed in this thesis, no more than 30% of the total alkalis would be in solution after 12 weeks. (4) It seems more realistic to consider the alkali critical limit stopping ASR in terms of concentration rather than in terms of alkali content. (5) The results obtained from this thesis confirmed that a certain part of the alkali ions in concrete pore solution that had become fixed by drying are not subsequently extracted after re-wetting: the alkali concentration [Na+K] was reduced from 34% to 61% by the drying and re-wetting treatments. (6) A direct correlation is shown between the dissolution rate of silica and the temperature when reactive sandstone aggregates are kept in concentrated NaOH solution. (7) The reaction rim surrounding reactive sandstone particles is mainly composed of precipitated silica."--Résumé abrégé par UMI.
- Génie – Thèses