Research Colloquium Reinforced Concrete / Exposed Concrete / Concrete Repair

RESEARCH COLLOQUIUM REINFORCED CONCRETE / EXPOSED CONCRETE / CONCRETE REPAIR

Research Colloquium Reinforced Concrete / Exposed Concrete / Concrete Repair

17.02.2022 14:00-17:00

Venue:

TUM / Old Architecture Library (Room 2350) & online.

In the colloquium, reports were given from ongoing research projects on concrete repair. In particular, the focus was on issues related to the preservation of architectural monuments.

The first block dealt with the topic of exposed concrete repair in historic preservation from a historical perspective, early successes and changes in practice since the 1980s, and the monitoring and evaluation of visible traces of earlier repairs today.

The second block focused on the surface qualities of exposed concrete, and how they change in the context of maintenance activities. Two concrete repair methods that are the subject of current research and development were presented and discussed.

In addition to the reports from ongoing research, the open discussion sessions following both blocks of presentations invited participants to broaden their perspectives beyond the boundaries of their fields and to enrich them with practical experience. The lively discussion both in the hall and in the chat of the hybrid broadcast event with about 100 participants showed that the study of exposed concrete buildings in the context of historic preservation currently attracts an interested audience. The desire for further professional exchange and in-depth discussions was expressed several times.

The following summary of the presentations was kindly made available to us by the speakers.

Kaiser Wilhelm Memorial Church Berlin. 40 years of concrete repair Prof. Dr.-Ing. Helmut Weber

The design of the Kaiser Wilhelm Memorial Church in Berlin by Egon Eiermann was completed in 1961. The concrete honeycomb elements of the new buildings around the war-damaged old church tower had to be secured for the first time as early as 1970, and comprehensive repair measures became necessary in 1981/82 and then in 2005. The concrete repairs of the 1980s exemplify a procedure that was later also laid down in the RiLi SIB (DAfStb 1990-92). First, a detailed analysis of the structural condition was carried out, including determination of the carbonation depth, the concrete cover of the reinforcement, the concrete compressive strength, the water absorption and a mapping of the damaged areas. Cracks in the precast elements, which had probably already developed during production, were identified as the cause of the damage, and a repair concept was developed with assignment of the cracks to different hazard classes. Loose parts were removed, the facade was cleaned with water pressure, and the corroded reinforcement was blasted and provided with corrosion protection. After application of a bonding bridge, the defective areas were reprofiled with a polymer-modified cement-based mortar. In order to obtain a surface texture similar to that of the exposed aggregate concrete from the construction period, the aggregate from the construction period was used and exposed by finishing with glass foam blocks. Finally, a carbonation-inhibiting coating with water-repellent effect was applied. The concrete repair of the 2000s was carried out with more advanced products but according to the same procedure; damage had occurred in the meantime only in sections not previously repaired. At the time of repair in the 1980s, the consensus was that “monitoring” should be carried out every 2-3 years according to today’s understanding.

Dealing with historical concrete repairs – DFG research project

Prof. Dr. Andreas Putz ^a, Prof. Dr.-Ing. Christoph Dauberschmidt ^b
Anthea Putz, B. Sc. ^b, Dipl.-Ing. Elisabeth Hinz ^a

^a Technical University of Munich, School of Engineering and Design, Chair of Modern Architectural Heritage, 80333 Munich, Germany
^b Munich University of Applied Sciences, Institute for Materials and Building Research, 80333 Munich, Germany

Increasingly, exposed concrete buildings on which concrete repair measures are to be carried out already show traces of previous repairs. Especially in the context of monument preservation, the question arises as to how to deal with these earlier conditions and temporal layers of the structure. They also reflect a history of repair and construction techniques that has been little researched to date. The aim of the project is to review the history of concrete repair in Germany and to compile an overview of essential repair products and construction methods. In particular, this literature and archive-based research is to be compared with building research and material technology studies on selected case studies. They will serve as a basis for the evaluation of historic preservation and, together with the structural assessment of the repair sites, will form the foundation for the development of strategies for dealing with historic concrete repairs.

The preservation of exposed concrete as a historical practice, Dissertation project TUM

Dipl.-Ing. Elisabeth Hinz
Technical University of Munich, School of Engineering and Design, Chair of Modern Building Conservation, 80333 Munich, Germany

Literature research shows that the powerful narrative of reinforced concrete as a “maintenance-free” building material has been countered since the middle of the 19th century by studies dealing with damage processes, repair and protection of reinforced concrete. As a working hypothesis, it is assumed that repair measures on exposed concrete surfaces can be divided into three basic approaches, local repairs, surface protection and full-surface replacement; these repair practices can thus be traced back to the beginnings of concrete construction and, in this sense, can be read as historical practices.

Since there are new findings on the relationship between carbonation and reinforcement corrosion in the 1960s and subsequently there is a flurry of research, development and standardization activity, the subsequent period up to the early 2000s is particularly relevant for consideration.

The aim of the work is to examine the development history of repair practices for continuity and to clarify possible connections with the respective state of knowledge about damage processes and the available repertoire of construction diagnostics. How have variants of exposed concrete repair evolved? How have the various measures been reported? What insights does a re-examination of the case studies discussed at the time provide from today’s perspective? Literature and archive research will be compared with construction research on case studies. Of particular interest are buildings that were prominently discussed in German professional discourse at the time.

The project aims to supplement the assessment of existing repairs according to purely technical and aesthetic parameters with aspects from the field of the history of science and building technology.

Monitoring of repair measures on exposed concrete structures of post-war mondernism. Investigations on the new burial hall – Main cemetery Saarbrücken
Sarah Steiner ^a, Michael Auras ^b, Christian Heese ^a

^a RhineMain University of Applied Sciences, Architecture and Civil Engineering, Department of Technology of Solid Building Materials and Solid Building Conservation, 65197 Wiesbaden
^b Institute for Stone Conservation, 55116 Mainz, Germany

Cautious repair has gained in importance in recent years, especially for listed exposed concrete structures. Small-scale, locally limited repair measures ensure the greatest possible preservation of the architectural and visual appearance of the structure or its surfaces in the original style. However, cautious repair is often criticized because it partly deviates from the current guidelines (Rili SIB, TR Instandhaltung von Betonbauwerken), which is why its durability is questioned. The investigations presented here on the new burial hall built between 1963 and 1965 at the main cemetery in Saarbrücken (architect: P. P. Seeberger) use a systematic follow-up investigation to show the current condition of the concrete repair measures carried out between 2007 and 2009. In addition to the classic visual inspection of the structure, which forms the basis of the condition assessment and evaluation, colorimetric examinations, infrared thermography and measurements with a portable ultrasonic tomograph (A1020 Mira Lite) were also carried out. Visually, some of the repair measures were elaborately adapted to the historic concrete in order to mimic the board-form structure of the surface. The old concrete, however, shows large variations in brightness, which is why, despite good color matching of the repair mortar, the repaired areas appear to be settling in many places. In addition, isolated incipient delamination of the repair mortar as well as partially superficially slightly damaged structural areas of the still untreated facade were observed. The results of the investigation show that continuous monitoring can help to better assess the future extent of damage, as damaged areas can be detected even before the historic facade actually flakes off.

Timber formwork construction and fair-faced concrete. Dissertation project TUM
Meltem Çavdar, M.Sc., M.A.
Technical University of Munich, School of Engineering and Design, Chair of Modern Building Conservation, 80333 Munich, Germany

This paper is devoted to the role of formwork carpentry for board-formed fair-faced in-situ concrete construction in the mid-20th century. The study takes a look at the involvement of carpenters in the production of wooden formwork, as well as the transfer of their traditional knowledge and skills in relation to exposed concrete buildings. The continuity of craft wood formwork construction in the shadow of industrialization in the mid-20th century is examined based on an analysis of historical contemporary literature and building standards, original building design documents, site photographs, and on-site observations of existing buildings. It concludes with an example of how empirical research on the surviving buildings should be deepened to better understand the construction history of the wood formwork, which has been lost but still left visible imprints on the surface. The work confirms that the exposed concrete construction of the postwar period was not a type of construction that could be easily carried out by inexperienced workers, but rather owed its existence to the existence of a skilled wooden formwork carpentry and carpenters on the construction site.

Betoninstandsetzung mittels textilbewehrter UHPC-Systeme. DFG-Forschungsprojekt
Prof. Dr. Bernhard Middendorf ^a, Prof. Dr.-Ing. Jeanette Orlowsky ^b
Dr. Michael Auras ^c, Dr.-Ing. Franziska Braun ^c, Prof. Dr.-Ing. Christoph Duppel ^d, Melanie Groh, M.Sc ^b, Dipl.-Ing. Nikolaus Koch ^d, Dr.-Ing. Viola Koch ^a

^a University of Kassel, Department of Civil and Environmental Engineering, Institute of Structural Engineering, Department of Materials in Civil Engineering and Construction Chemistry, 34125 Kassel, Germany
^b Dortmund University of Technology, Faculty of Architecture and Civil Engineering, Chair of Construction Materials, 44227 Dortmund, Germany
^c Institute for Stone Conservation, 55116 Mainz, Germany
^d RhineMain University of Applied Sciences, Architecture and Civil Engineering, 65197 Wiesbaden, Germany

Concrete restoration according to the currently valid technical regulations is not possible on most culturally and historically important concrete structures without major loss of substance and alteration of the original appearance. Using the example of the Europe 1 broadcasting center Felsberg-Berus in Saarland, the results of concrete investigations carried out on the broadcasting tower will be presented and the development of microstructurally optimized, dense high-performance fine-grain concretes with textile inlays, which will be used in a section of the broadcasting tower, will be reported. The combination of dense high-performance concretes with integrated textile reinforcement allows visually adapted, very thin and yet durable repairs to be carried out without changing the character and charm of the object to be repaired.

Reinforced concrete bridge over the Mangfall. Findings, condition, retrofitting possibilities – an interim report
Dr.-Ing. Jörg Rehm ^a, Prof. Dr.-Ing. Oliver Fischer ^b

^a Technical University of Munich, School of Engineering and Design, Chair of Design and Construction, 80333 Munich, Germany
^b Technical University of Munich, School of Engineering and Design, Chair of Solid Construction, 80333 Munich, Germany

The so-called Mangfallsteg near Weyarn was built in 1910. The slender bar arch bridge made of reinforced concrete with a span of up to 28.5 m has not been modified since then. The state section for torrent control planned and built the bridge taking into account the guiding principles of the German Concrete Association. After investigations already carried out, it is to be subjected to a maintenance measure.

Research colloquium of the Professorship for Modern Building Conservation, Prof. Dr. Putz (TUM) and the Institute for Building and Materials Research, Prof. Dr.-Ing. Dauberschmidt (HM).

The colloquium took place within the framework of the SPP 2255 Cultural Heritage Construction.