On Friday, 12. September 2025 at 10 AM, the doctoral defense of Simon Peters will take. The title of his dissertation is "Computational Multiscale Modeling of Low-Carbon Concretes at Elevated Temperatures".

Abstract:
Despite decades of research, the underlining mechanism of explosive concrete spalling at elevated temperatures remains unknown. This thesis proposes a fully coupled numerical chemo-thermo-hygro-mechanical model, advanced through a micromechanical framework, providing a deeper understanding of the multiphysical nature of explosive spalling.

Key contributions include the development and validation of the micromechanical framework to analyze the binder-specific dehydration behavior, chemically induced material evolution and microstructure. This framework enhances applicability and reduces experimental calibration requirements for the well-established multiphysical macroscale model, particularly for concretes based on CO2-reduced cements.

By means of virtual parametric studies, the main findings of the thesis are: i) The binder-specific dehydration behavior of CO2-reduced cement pastes is not the primary driving mechanism behind fire-induced concrete spalling. ii) Aggregates characterized by high thermal conductivity can lead to a significant increase (even more than 35%) in pore pressure when compared to aggregates with lower thermal conductivity. iii) The dense microstructure is the primary factor driving the susceptibility of concretes containing CO2-reduced cements to fire-induced concrete spalling compared to ordinary concretes. iv) The moisture clog theory is not supported.

On Monday, 11th August 2025, a research group from Wuhan University, China visited us - the Institute for Structural Mechanics, Ruhr University Bochum, Germany - again. Since January 2021 we both have been actively collaborative in the research project "Multiscale Tests, Simulation, Optimization and 3D-Printing of UHPFRC Materials and Structures", a project between Prof. Günther Meschke (Institute for Structural Mechanics, RUB) and Prof. Zhenjung Yang (Wuhan University, China), that has been embedded in a mobility programme. Now, after 4 years of research, it comes to an end.

The joint research focused on the development of innovative solutions in the field of 3D-printed ultra-high-performance fibre-reinforced concrete (UHPFRC). The Wuhan University team performed CT scans and provides high-resolution CT images. We, the team from the Institute for Structural Mechanics, used these CT images to create high-resolution digital 3D models from which directly numerical models are automatically generated. These numerical models allowed us to analyze the failure mechanisms of 3D-printed fibre-reinforced concrete on the meso-scale very precisely.

The completion of this joint research project represents an important milestone in our collaboration. The results achieved provide valuable insights into UHPFRC materials and structures and contribute to the current knowledge in this area.
Moving forward, there are several potential directions for further research. The findings from this project can serve as a foundation for additional studies or applying these results in practical settings or expanding the scope to include new variables.
This project has also paved the way for continued collaboration between our teams, allowing us to address more complex challenges in the future.

The open access paper titled "Computational hydro-thermal design of ground freezing in tunneling: Optimization of pipe layout and real-time prediction" has been witten by Rodolfo Javier Williams Moises, Yaman Zendaki, Ba Trung Cao, and Günther Meschke.
It is now published in "Tunnelling and Underground Space Technology" by Elsevier.

Abstract:
Artificial ground freezing is used in tunneling for temporary ground improvement mainly to control the groundwater flow and to provide excavation support. The principle of ground freezing is based on freeze pipes drilled into the ground where a coolant flows through the freeze pipes. In tunneling, artificial ground freezing is applied to form a closed arch of frozen ground around the tunnel. However, high groundwater seepage can delay the formation of this frozen arch, or even prevent it entirely, which can lead to unsafe temporary frozen ground support. In this work, we propose a computational design strategy to systematically reduce the freezing time by optimizing the layout of freeze pipes. The strategy includes a computational model able to simulate the freezing process for various pipe arrangements, and the generation of a machine learning model of the freezing process trained by means of virtual, simulation-based data to allow real-time predictions. This surrogate model is constructed based on the combination of Proper Orthogonal Decomposition and Radial Basis Functions, while the freezing process itself is simulated with a hydro-thermal finite element model. Using the surrogate model, possible pipe layouts are rapidly evaluated and optimized in real-time by means of the Particle Swarm Optimization approach, identifying the optimal arrangement of freezing pipes for given groundwater flow conditions which lead to the shortest freezing time. The computational design framework for optimization of freeze pipe layout is integrated into an in-house user-friendly software which performs real-time predictions within a parametric design space.

The open access paper is available here: https://doi.org/10.1016/j.tust.2025.106875

The latest article titled “Concretes containing blended-cements with reduced carbon-dioxide emissions: A chemo-thermo-hygro-mechanical model for elevated temperatures” by Simon Peters, Tim Pittrich, Ludwig Stelzner, Frank Weise, and Günther Meschke has been published in the volume 163 of Cement and Concrete Composites by Elsevier.

Abstract:
A comprehensive analysis aimed at understanding and assessing the high-temperature behavior of concretes containing blended cements (CEM III/A, CEM II/B-Q, and CEM IV), characterized by low carbon-dioxide emissions (during clinker’s production) is necessary to reliably model the damage in the concrete, thermal spalling included. To this purpose, a numerical chemo-thermo-hygro-mechanical model is formulated, to investigate – among other phenomena – heat transmission and pore pressure for different aggregate types.

Based on an available hydration model, a dehydration model is established to numerically investigate the evolution of dehydration and porosity at elevated temperatures. Based on the properties of concrete and cement constituents on multiple scales, an analytical homogenization process is proposed to predict the thermal conductivity of the concrete. This process is later validated and implemented into a macroscopic modeling framework.

Chemo-thermo-hygro-mechanical analyses show that the dehydration characteristics of blended low carbon-dioxide release cements may increase pore pressure in the concrete by up to 13% compared to the concrete containing ordinary Portland cement. In addition, aggregates exhibiting high thermal conductivity may contribute to a further increase (even more than 35%) in pore pressure compared to aggregates with low thermal conductivity.

Last but not least, the proposed model provides the basis for the reduction of the number of the parameters commonly required in the chemo-thermo-hygro-mechanical modeling of cementitious materials.

You can read the open access article here:

As part of the Research Academy Ruhr's "Research Explorer Ruhr" program, PhD Tulio Antunes Pinto Coelho from the Federal University of Mato Grosso do Sul, Brazil, visits our institute from 22 June to 5 July 2025.

The program offers prospective and early postdocs the opportunity to learn about the research landscape of the University Alliance Ruhr, as well as its funding opportunities and career paths. At best, the program will lead to further research collaborations and proposals.

We would like to thank Tulio Antunes Pinto Coelho for enriching us – in particular the institute’s research group “Structural Intelligence and Reliability” – with his knowledge from the research areas of fire design of reinforced concrete as well as uncertainty modeling and reliability analyses.

We are looking forward to further deepening this scientific exchange in research.