This thesis is concerned with the development of a constitutive model for cementitious bimaterial interfaces and investigations for the quantification of their fracture properties. The constitutive model is implemented into a FE analysis program system and validated by numerical simulations. The interface in question is located between cold-jointed cementitious solids. Since no further connection means are used, the fracture properties of the interface only depend on the surface adhesion and the properties of the adjacent interface transition zone. The interfacial fracture properties are determined by three point bending tests, modified torsion tests and splitting tests and they are compared to fracture properties of monolithic specimens determined in the same way.Hence tensile and shear strengths, mode I and mode II specific fracture energies are measured and the softening functions are determined by inverse analyses.For the properties the influence of different surface treatments are taken into account by three test series: high pressure water jetting, steel brushing and smooth cleaning of the interface surfaces. The different interface surfaces are characterised by several surface parameters. To provide accurate macroscale failure analyses of these interfaces, the mesoscale cohesive zone model of Caballero and Carol is modified. The elasto-plastic interface model is implemented as a traction separation law for zero thickness interface elements in Abaqus. Additional requirements regarding robustness, accuracy and efficiency are evaluated by ISO-error plots for the implemented algorithm. Improvements of the latter features are achieved by an adaptive sub-stepping method and by an alternative starting point of the Newtoniteration. The numerical simulations are employed for validation of the implemented interface model. Excellent agreement between numerical and experimental load-crack-opening diagrams can be stated.