Comparison of simulated and measured mass loss up to 700 °C for CEM I, CEM III/A and CEM II/B-Q at a heating rate of 10 K/min.
Source: BAM
To reduce the CO₂ footprint of the concrete industry, clinker-efficient cements are increasingly being used in practice. However, with their growing use, the risk also increases that a structure made with such cements may be exposed to fire. Experimental investigations show that concretes with clinker-efficient cements show increased spalling susceptibility. The occurrence of spalling leads to a reduction in the cross-section, ultimately decreasing the load-bearing capacity of the affected structural element. Thermo-hydraulic mechanisms play a crucial role in this spalling process, as it is assumed that crack formation due to rising pore pressures leads to the sudden vaporization of superheated water, causing concrete fragments to explosively break away from the component.
To reliably model the high-temperature behavior of these CO₂-reduced concretes, dehydration processes in the cement paste were numerically described based on a hydration model and validated with experimentally determined data to capture water release and porosity development. Based on the properties of concrete and cement components at various scales, an analytical homogenization method was then used to predict the thermal conductivity of concrete. After successful validation, this method was integrated into a macroscopic modeling framework for simulations at the component level.
The chemo-thermo-hygro-mechanical analyses show that pore pressure in CO₂-reduced concretes can reach up to 13% higher values compared to concrete made with conventional Portland cement due to altered dehydration behavior. Furthermore, the use of aggregates with high thermal conductivity leads to an additional increase in pore pressure in fire-exposed concrete by up to 35%.
The proposed multi-scale approach provides a foundation for significantly reducing the number of material parameters required for chemo-thermo-hygro-mechanical modeling of cementitious materials, thereby minimizing the need for costly experimental investigations.
This contribution was developed as part of an ongoing DFG collaborative project between Ruhr University Bochum and the Federal Institute for Materials Research and Testing, in which the relevant thermo-hydraulic processes are represented using numerical models, with validation carried out through experimental analyses.
Concretes containing blended-cements with reduced carbon-dioxide emissions: A chemo-thermo-hygro-mechanical model for elevated temperatures
Simon Peters, Tim Pittrich, Ludwig Stelzner, Frank Weise, Günther Meschke
Cement and Concrete Composites, 2025