Homogeneous and heterogeneous rheology and flow-induced microstructures of a fresh fiber-reinforced mortar

Abstract

External wall insulation (EWI) usually comprises a porous cement mortar used as protective external render into which short fibers are added to enhance its mechanical properties. The rheology of these porous, fibrous, and granular suspensions was investigated using lubricated compression tests in the fresh state, whereas flow-induced porous microstructures were studied using X-ray microtomography. We show that these suspensions exhibit a homogeneous isovolume flow regime and two heterogeneous flow regimes, i.e., a consolidating regime, and a consolidating and segregating regime. A decrease in the compression strain rate and/or an increase in the number of fiber contacts in the entangled fibrous network induced flow heterogeneity accompanied by heterogeneous modifications of density, porosity, and pore size distribution of render. These undesirable microstructure changes are prone to occur during mortar processing and placement. They drastically affect the properties of renders such as the permeability that was calculated using X-ray microtomography images and pore scale numerical simulation.