Predicting the strength due to cracking in quasi-brittle materials such as rocks, concrete or civil engineering materials is of formidable interest. Crack propagation modeling in brittle materials or quasi-brittle materials has long been restricted to simple academic cases and to the macroscopic scale. With recent advances in both numerical simulation methods and experimental characterisation tests, new studies are now possible, allowing the development of fracture models at the microscale, and from realistic microstructure morphologies of complex materials. However, developing predictive models of crack initiation and propagation in three-dimensional (3D) complex and heterogeneous microstructures is highly challenging in regards to modeling, numerical simulation methods and experimental characterization.