A modified effective stress principle for chemical active multiphase materials with internal mass exchange

A modified effective stress principle based on the Theory of Porous Media (TPM) subjected to internal mass exchange is presented. The material under consideration can be viewed as three overlapping and interacting continua consisting of a solid, a fluid and a superabsorbent polymer phase (SAP). The latter one has the ability to absorb and bind large amounts of the aqueous fluid phase. To this end, the polymer phase swells to a hydrogel and its mechanical properties differentiate tremendous from both the free pore fluid and the dry polymer. A strict exploitation of the entropy inequality in the sense of Liu-Müller leads to admissible, thermodynamic-consistent forms for the partial stress tensors of the involved phases. Subsequently, an effective stress principle is derived by expressing the total stress tensor of the mixture in terms of the partial stress tensors of the phases. In contrast to well-established effective stress concepts, the proposed modified effective stress principle presented in this contribution shows a transient behavior for materials subjected to internal mass exchange, which is controlled by micro-structural processes. Furthermore, a promising technical application of the model to two-component grouting mortars is discussed.