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Two micromechanical models are developed to simulate the expansion of
cementitious composites exposed to external sulphate attack. The
difference between the two models lies in the form of chemical reaction
of the ettringite formation (through-solution vs. topochemical). In both
models the Fick's second law with reaction term is assumed to govern the
transport of the sulphate ions. The Eshelby solution and the equivalent
inclusion method are used to determine the eigenstrain of the expanding
ettringite crystals in microcracked hardened cement paste. The
degradation of transport properties is studied in the effective medium
and the percolation regime. An initial-boundary value problem (2D) of
expansion of a mortar specimen immersed in a sodium sulphate solution is
solved and compared with available test data. The obtained results
indicate that the topochemical mechanism is the one capable of producing
the experimentally observed amount of expansion. |
