###### Abstract
The correct evaluation of such data is becoming a prerequisite for the correct use of numerical models in practice. Therefore, this research area was covered by the currently solved research project \"Advanced characterization of cracks propagation in composites based on alkali-activated matrix\". An extensive numerical and experimental analysis of the fracture behavior of  
Figure 1: The surface of the alkali-activated slag (AAS) materials with a different activator (waterglass (**a**) and sodium hydroxide (**b**)) cured in relative humidity (RH) \(\geq\) 95% (240\(\times\) magnification). selected composites with an alkali-activated matrix subjected to static (also in the mixed-mode) and cyclic/fatigue loading was performed. For a description of the crack propagation under mixed-mode I/II conditions, various test configurations were designed based on the literature search of test specimens used for testing the fracture parameters of rocks and cement-based composites. For this purpose, semi-circular disc specimens in three-point bending [7; 8; 9; 10; 11], centrally cracked Brazilian discs [12; 13; 10], and prismatic-specimens in asymmetric three- [14; 15] or four-point [14; 16] bending configurations are mostly used. Semi-circular discs were chosen for the present study. The type of specimens was chosen with respect to the practical application to the in situ structures when drilled cores are usually taken for the verification of real mechanical characteristics. Selected semi-circular specimens with an inclined initial notch were loaded in a three-point bending configuration (SCB) for the purpose of experimental verification of numerical simulations of crack propagation under mixed-mode I/II condition; see the selected configuration in Figure 2a. Note that numerical simulation was performed prior to the experimental verification to suggest different geometrical configurations with various mixed-mode I/II conditions (to cover as wide a range of mixed-mode levels as possible) and to design the experiment. The detailed information can be found in a separate article, which is currently under consideration for publication [17]. The numerical modeling of the fracture initiation and propagation in quasi-brittle materials has been developed for several decades. Impressive results have been achieved with continuous models (usually with the help of the finite element method (FEM)) enhanced by non-linear constitutive relations where, after reaching the tensile strength, the stress decreases gradually with the crack opening. If the model does not contain information about material meso-structure directly, spurious sensitivity of the results to mesh discretization appears [18]. Such mesh dependency must be eliminated with help of a localization limiter (crack band model, non-local model, gradient model). The continuous models are typically studied on simple experiments such as a three-point bending test, but they achieved excellent results also in cases of complex mixed-mode configurations [19]. When some of the models described above shall be applied, several important mechanical fracture parameters need to be determined/known. One of the fundamental fracture parameters is the fracture energy representing cracking resistance and fracture toughness. To be able to estimate the FPZ size and shape, the necessary parameters (such as tensile strength, fracture energy, stress\(-\)strain diagram, etc. ), methods, and approaches have to be known. Commonly used standard test specimens (prisms with nominal dimensions of 40 \(\times\) 40 \(\times\) 160 mm\({}^{3}\)) were manufactured and tested under typical configurations to obtain the basic physical, mechanical, fracture, and fatigue characteristics essential for numeri  
Figure 2: Three-point bending fracture test configuration of a selected semi-circular disc specimen with an inclined initial notch (**a**); and a beam specimen with a central edge notch (**b**). cal simulations.