Contribution à l'étude des mécanismes des réactions alcalis-granulats
The alkali-aggregate reaction (AAR) is a chemical and physical process of deterioration affecting the concrete. In the theoretical part, the following points are examined: (1) a description of aggregate properties is given; mainly about their degree of reactivity which depends of the type of silica mineral and the silanol distribution at the silica surface; (2) a study of a model of silica dissolution in the concrete pore solution of the colloidal quaternary system Na[subscript 2]O-CaO-SiO[subscript 2]-H[subscript 2]O. In particular, it is examined the possible role of the calcium ion as a catalytic agent; (3) a characterization of the concrete pore solution flow inside the aggregate. It is based on a model of the microstructure of the aggregate and the hydrated cement paste; (4) a kinetic model of the AAR concrete expansion is also proposed. It is based on a sigmoid growth curve (Avrami model) as well as on a model of nucleation by Delmon; (5) a suggestion is made concerning the utilization of a function to model the progressive mechanical damage of the concrete during the AAR; (6) a review of the finite element procedures used to model a concrete structure affected by AAR. The experimental program includes: (1) a mechanical property assessment of the AAR affected concrete of the Beauharnois dam and the identification of the degree of advancement of the reaction; (2) a characterization of the mechanical properties of blocks of concrete taken from the Beauharnois dam. The strength of the bond between the steel and the concrete is also assessed; (3) a laboratory study based on compressive triaxial tests of the progressive mechanical deterioration of concrete made with reactive and non reactive aggregates; (4) a study of the effect of stresses to prevent the expansion of AAR concrete blocks. The study shows two main effects: (1) the steel reinforcement considerably reduces the overall AAR expansion; this is normal, but it also homogenizes the deformations and (2) an external load of 3,3 MPa is not sufficient to stop the AAR expansions; (5) an assessment of in situ deformations of hydraulic concrete structures affected by AAR was made with concrete inclusion stress cells instrumented with vibrating wire extensometers (CIUS of the Université de Sherbrooke); (6) a measure of the potential expansion of a concrete structure is based on laboratory tests performed on core specimens, from three dams, and on large concrete blocks (1 m[superscript 3]) made with the same aggregates than the dams."--Résumé abrégé par UMI.
- Génie – Thèses