School of Architecture and Civil Engineering

Research activities

The focus of our Chair is teaching and research of building materials.

Building materials
Properties of special concretes and mortars, durability of building materials, manufacturing technology, high temperature behaviour of building materials, numerical simulations of material behaviour.

Structural engineering
Steel composite special components, load-bearing, deformation and long-term behaviour of steel composite structures, fire behaviour of structural components (wood, steel, reinforced concrete, steel composite), numerical simulation of load-bearing and deformation behaviour of structural components and overall structures at normal temperature and under fire load.

Fire protection
High-temperature behaviour of building materials, fire behaviour of building components and structures, dynamic simulations for fire development and smoke extraction from buildings, contaminant transport, safety concepts.

Technology transfer
Chemical and mechanical building material investigations, building material developments, component investigations in situ and in the laboratory, structural analyses, development of remediation concepts, risk assessments, development of fire safety concepts and overall solutions for structural, operational and organisational fire protection, damage assessments.

Current Research Activities

Systematic investigations of the deterioration of high- (HPC) and ultra high-performance concrete (UHPC) subjected to fatigue loading are currently not available. This holds especially true for steel-fiber modified HPC and UHPC subjected to multi-level and sequence loadings. Furthermore, numerical approaches and models are often calibrated using experimental data from literature, which does not allow a comprehensive calibration due to lacking coordination between experiments and numerical models. Therefore, this project aims at testing, describing and modelling the ongoing deterioration including damage accumulation of steel-fiber modified HPC and UHPC subjected to fatigue loading, using multiscale approaches and phase-field theory. In addition to single-stage fatigue loads and the fatigue loads include multi-stage collectives. Two high-performance concretes (reference concretes of the SPP2020) are used for the investigations. A high-strength concrete with hooked-end steel fibres with fibre contents of 23 kg/m3 to 115 kg/m3 and an ultra-high-strength concrete with smooth, high-strength short steel fibres and fibre contents of 57 kg/m3 and 115 kg/m3 are used. For the experimental and numerical analysis of the damage evolution, extensive static fibre pull-out tests as well as static and cyclic bending tensile tests and cyclic compression tests were carried out in the first funding period and the degradation was described based on damage indicators. These indicators include crack opening development, residual stiffness development and energy dissipated into damage. The close collaboration between experiment and numerical simulation enabled calibration and validation of the models and material descriptions. In the second funding period, the experiments will be supplemented by high cyclic multi-stage loading sequences, taking into account sequence effects under flexural and compressive fatigue loading. For the in silico tests, the already existing simulation models are further developed with regard to efficiency, especially in the area of high cyclic loads. For this purpose, cycle jump approaches are developed, calibrated and validated on the basis of specific tests to model and predict degradation at high cycle loadings. Based on the procedure in the planned work program, the interaction of experiments and modelling is evaluated and optimized in the sense of an experimental virtual lab. With the help of this lab, it will be possible in future to numerically evaluate the fatigue behaviour of high-performance concretes based on few tests.

In the clinker burning process, approx. 2/3 of the CO2 emissions are unavoidable due to the deacidification of geogenic limestone, as an essential component of the raw material. The remaining 1/3 of the CO2 emissions result from the fuels. If it was possible to reuse already deacidified lime, e.g. from processed demolition waste from concrete structures, it would not only be possible to save a significant percentage of CO2 emissions, but also to protect resources by substituting geogenic limestone. This goal can only be achieved if the cement paste and aggregate are separated in the best possible way and lime enrichment in the fine constituents is achieved. As a positive side effect, a high-quality recycled aggregate is achieved.

Previously, various techniques were proposed to achieve optimized separation of hardened cement paste and aggregate. Examples are conventional mechanical crushing processes; newer processes such as electrodynamic fragmentation or separation by means of water pressure require high investments and are currently only available on a pilot plant scale. In other approaches, demolition waste from concrete structures was processed at high temperatures up to 700°C before reuse.

Preliminary work has shown that cyclic high-temperature exposure can cause severe damage to the hardened cement paste even at relatively low temperatures. Effective temperatures below 500°C can be made available as process heat in industry, e.g. in cement plants, and do not have to be generated by energy input. The aim of cyclic thermal pre-damaging is to significantly improve the separability of aggregate and cement paste in a "friction grinding" process. For this purpose, conventional grinding techniques can be used with modified process parameters.

In this research project, two conventional concretes are used as basis to investigate whether a combination of cyclic-thermal pre-damaging of the demolition waste combined with a friction grinding process can ensure the necessary enrichment of lime constituents in the grinded material, which can be fed back into the clinker burning process as virtually "CO2-free secondary raw material". At the same time, geogenic limestone is substituted and a high-grade recycled aggregate is achieved.

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