Conference Agenda

In multiscale modeling of heterogeneous softening materials, the choice of boundary conditions (BCs) applied to the fine-scale (micro/meso scale) model significantly influences both the strain localization patterns and the macroscopic response. Commonly used Periodic BCs tend to produce artificially ductile behavior, characterized by excessive energy dissipation, when the localization band inclination does not match the periodicity directions. To address this limitation, recently proposed Tessellation and Percolation-path-aligned BCs adapt the periodicity frame to align with the evolving localization zones and enable the formation of arbitrary localization bands. In this work, we perform a numerical study to assess the applicability of these BCs to a discrete lattice particle model of concrete at the mesoscale. A two-dimensional square fine-scale model is subjected to uniaxial tension under varying loading directions. The resulting macroscopic responses and localization patterns are compared against those obtained using conventional periodic BCs. The results indicate that Percolation-path-aligned BCs exhibit major shortcomings: they can lead to multiple localization bands due to uneven straining of their two boundary sections, with the weakly constrained section prone to spurious localization. In contrast, Tessellation BCs consistently produce a single, well-defined localization band. The band length is determined solely by the square geometry of the model, making it straightforward to account for during post-processing. Consequently, the observed dependency of the dissipated energy on the loading direction can be clearly attributed to the geometry of the model rather than artifacts of the boundary conditions.

The transition towards a greener and more resilient construction sector often deals with mix design optimization to fulfil target performance. Customised mixes generally differ in terms of aggregate and binder types, aggregate size distribution, and additives. Optimizing concrete mixes requires understanding how different components interact and affect the concrete’s overall performance. This contribution presents a 2-phase discrete meso-scale model able to simulate how chemical reactions and transport phenomena of heat and moisture are affected by aggregate and binder properties. Benchmark numerical simulations of 1D moisture and heat diffusion in concrete are performed to showcase the enhanced capability of the proposed model to capture the spatial variability in moisture and temperature gradients.

A new DEM-based 3D model for fracture propagation was developed to simulate pore-scale ther-mal-hydro-mechanical processes, including heat transfer and phase changes (evaporation and condensation) in low-porosity, non-saturated frictional-cohesive materials (like concrete). Numerical simulations used a bonded granular specimen, combining DEM with CFD (based on a fluid flow network) and heat transfer to integrate discrete mechanics with fluid and heat transfer at the meso-scale. Both the fluid (through diffusion and advection) and bonded particles (via conduction) participated in heat transfer. The coupled thermal-hydraulic-mechanical (THM) model’s results were validated through a thermal contraction test with a bonded particle assembly during cooling, which led to the formation of a macro-crack. The study examined the im-pact of the macro-crack on the distribution of fluid pressure, density, velocity, and temperature.

Carbonation in concrete has been of wide interest lately due to its potential applications in selfhealing, carbon capture/storage and carbon curing. Mineralization of CO2 in concrete is a chemo mechanical process, initiated by the dissolution of Ca2+ into the solution from portlandite (CH). It is further controlled by factors such as saturation index, mechanical stress and crystallization pressure. In a recent study by the authors (Alex et. al., 2023), the nanoscale modeling of concrete carbonation was carried out, focusing on nano-crystalline structure formation, dissolution/precipitation rates, and the development of mechanical properties, thereby establishing a benchmark for future research. In this work we make a further improvement to the simulator: coarse grain the nano-scale particles to microscale (1 particle=1 micron). The extended simulator is also designed to accommodate biologically mediated pathways such as microbially induced carbonate precipitation (MICP). Because MICP relies on the same coupled dissolution–precipitation chemistry as abiotic carbonation, the present coarse-grained formulation offers a natural bridge between these processes. In this paper we present the coarse graining part of the work. The coarse-grained system samples larger time and length scales and is validated against transition state theory (TST) rates of CH dissolution and precipitation.