Department of Mechanics: Seminar: Abstract Giorla

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Alain Giorla, Swiss Federal Institute of Technology at Lausanne (EPFL), Switzerland

Role of creep in the degradation caused by alkali-silica reaction

Alkali-silica reaction is a durability issue which affects massive concrete structures such as dams or bridges. The transformation of amorphous silica contained in the aggregates into an expansive silica gel causes damage at the microstructure level and a macroscopic expansion of the material. Since this occurs over very long time scale, the role of creep in the damage propagation at the material scale is investigated. Concrete is simulated at the mesoscale with an explicit representation of the aggregate particle size distribution. The silica gel pockets are modeled with extended finite elements. The cement paste is considered as a visco-elastic-and-damage material. To do so specific numerical methods are required. First, a space-time finite element approach is used to simulate the simultaneous stress relaxation in the paste and the microstructural changes caused by the chemical processes. Second, a novel damage algorithm is implemented, which characterizes where and when damage increases in the microstructure. This leads to a natural coupling between damage and creep in the material. Simulations of affected concrete show that the expansion is function of the total advancement of the chemical reaction but not its rate, but the damage rate in the microstructure is reduced for slower kinetics. This result offers new insights on the comparison between ASR in field and accelerated conditions.