This study introduces a statistical mechanics framework for modeling fracture and damage processes in concrete materials, leveraging the semi-grand canonical ensemble. By conceptualizing fracture as a monolayer adsorption process and damage as a multi-layer adsorption phenomenon, the approach extends classical fracture mechanics through statistical observables and ensemble-based formulations. Through simulations on notched beams, the framework demonstrates key insights into the energy dissipation mechanisms underpinning fracture. Statistical observables, such as isosteric heats of adsorption, provide a robust method to predict fracture behavior without the need for experimental size-effect studies, while damage isotherms are highlighting the influence of configurational pressure on material degradation. The results emphasize the potential of this framework to enhance the predictive modeling of quasi-brittle materials, paving the way for applications in material design and structural engineering.

A gap test is a new experimental and numerical test proposed by Bažant et al. Its main goal is to show that the effective mode I (opening mode) fracture energy depends on the crack-parallel normal stress. Moreover, the authors of the test believe that the FE crack band model coupled with microplane model M7 and the lattice discrete particle model allow to fit results of the laboratory gap test satisfactorily. A specimen is in form of a concrete beam with a notch. A static scheme of the specimen changes when a gap between specimen and roller supports vanishes. The authors of this paper tried to recreate numerically the gap test using the concrete damaged plasticity (CDP) model. A finite element analysis was performed using Abaqus software. Main results compared with Bažant et al. were: a force-displacement relationship and a crack pattern. The numerical test will answer the question if the CDP model allows to recreate the gap test properly. To simplify computations the specimen was divided into elastic and plastic regions. The plastic region was fine meshed and a coarse mesh was assigned to the elastic regions. The gap modeled in the test was equal to 3 mm, so a pinned and a roller supports became active only when displacements of both ends of the specimen reached 3 mm. Displacement control was chosen in the FEM model in form of a displacement imposed on a top steel pad. Bottom pads were modeled as made of polypropylene. The force-displacement relationship was established using results obtained for the top steel pad and the crack pattern was presented with the equivalent plastic strain of concrete in tension.

With the advancement of computational techniques, numerous nonlinear constitutive laws have become available in finite element analysis software. While these models are well-suited to analyze plain and simple reinforced concrete structures, their applicability to prestressed structures, which constitute a significant portion of concrete constructions, requires validation. This study presents a finite element (FE) model composing a prestressed composite concrete girder, incorporating nonlinear stress-strain laws for the concrete, reinforcement steel and prestressing steel, as well as the concrete-to-concrete interfaces between prefabricated girder and cast-in-situ top-slab. To accurately capture the fracture process of the concrete, the total strain crack model is employed while the potential failure of the interface between the prefabricated girder and cast-insitu top slab is modelled with two-dimensional line interface elements. The numerical model is validated using experimental results from precast continuous concrete inverted T-beams provided by TU Delft. A parametric study is subsequently conducted to assess the sensitivity of the numerical results to key assumptions in the nonlinear FE model. Specifically, the influence of adopting either a rotating or fixed crack model under high axial load is analyzed. Additionally, the effects of the shear retention factor and mesh size on the numerical response are investigated. While the numerically evaluated global load-displacement behavior shows good agreement with experimental results, it exhibits a sensitivity to the chosen mesh size and the specific smeared crack formulation. The findings also highlight the importance of considering the specific material properties and interface behavior in the modeling process to ensure reliable predictions of structural performance.

Recently, X-ray tomography is used to explore the microstructure of different materials non-destructively. Here, we utilized it for the reconstruction of the microstructure of cement-mortar. Cement-mortar was prepared by mixing the cement and sand in a ratio of 1:1. The phase distribution in the cement mortar is quite complex due to the random size and distribution of the sand particles. Also, the contrast between sand and cement is low due to their neighboring densities. Thus, a combined distribution of greyscale values exists in the reconstructed images in these phases of the mortar, which makes the segmentation process difficult. However, the segmentation of the voids at this length scale resolution is possible by defining a suitable greyscale cut-off value. Here, we have used an optimum window and median-based greyscale markers to differentiate these phases for segmentation. Later, the segmented image was meshed into the finite elements, and the fracture process of the mortar is predicted using concrete damage plasticity. The predicted effective stress/strain response of the specimen was similar to one reported in the literature for concrete. It is found that the response is consistent with the previously reported observations. The elastic and softening behavior of the cement mortar is captured.

The paper presents a novel 2.5D model to simulate concrete or reinforced concrete specimens. The main idea of this approach is to define the set of 2D plane models extracted from the 3D model or specimen’s microtomography (μCT) scan along selected direction. The definition of several cut planes allows for defining different material and geometrical configurations (e.g. different mesostructure topology and the inclusion of reinforced bars). These plane cuts can be analysed independently as simple standalone 2D models, but they also can interact with neighbouring plane or planes. Interaction between planes is adhered to by adding a set of horizontal and vertical springs with a prescribed stiffness. Consequently, the proposed approach is still a two-dimensional model but is capable of mimicking the behaviour of three-dimensional specimens. A detailed description of the method is provided, along with some preliminary results, and the difference between pure 2D simulations and the 2.5D approach is outlined.