Compressible cementitious composite materials: Multiscale modeling and experimental investigation

Tunnel linings installed in difficult geological conditions characterized by a high expansion potential, such as Opalinus Clay and rocks containing anhydrite, may exhibit a loss of integrity due to excessive ground deformations in case water penetrates the rocks. One of the potential remedies against lining deterioration and failure of the tunnel structure is the incorporation of a compressible cementitious layer around the tunnel. This compressible layer serves as a cushion that protects the tunnel structure by tolerating a certain amount of deformations prior to collapse. The deformation capacity of the compressible layer can be enhanced by introduction of various soft inclusions or air bubbles in the cementitious mix. However, such soft inclusions reduce the overall elasticity modulus and strength of the composite. Hence, it is crucial to determine the optimal mix that provides the required compaction potential without compromising on stiffness and strength. For this design purpose computational modeling can be adopted. The model should be able to account for the material properties of the individual components and their volume fraction, which strongly influence the overall behavior of the cementitious composite, and to capture the main features characterizing compressible composites, such as a yielding plateau after a certain threshold loading has been reached. The compaction process of such a composite is described by a voxel model with a discrete distribution of material properties, where the voxels are compacted by applying an Eigenforce when the local stress state reaches a threshold value. This threshold is determined within the framework of continuum micromechanics on the scale of individual inclusions. The model predictions are compared with data from experimental investigations on the compression behavior of different cementitious mixes.