WTA-YPA 2026 in the category "Educational"
The International Association for Science and Technology of Building Maintenance and Monuments Preservation e.V. annually awards the WTA-Prize for outstanding achievements in the fields of research and practice of building preservation and monument conservation.
This year's WTA Young Professionals Award in the cathegory 'Educational' was awarded to
Mrs Hasti Sharifi B.Eng.for her Bache thesis
'Development of a Possible Restoration Approach for the Exposed Concrete Façade with Wooden Formwork Texture at the Listed Lecture Hall Centre East (Hörsaalzentrum Ost) of Ruhr University Bochum'.
In a short presentation, Mrs Sharifi presented the main aspects of her work.
You can find the complete work here.
Zusammenfassung
1. Introduction
The restoration and preservation of existing buildings play an increasingly important role in sustainable and resource-efficient construction. Compared to new construction, refurbishment significantly reduces CO₂ emissions and helps conserve material resources. This is particularly relevant for heritage-listed structures, where original materiality, appearance and architectural identity must be maintained.
This study investigates restoration options for the exterior façade of the Hörsaalzentrum Ost (HZO) at Ruhr University Bochum. Constructed in 1972 and listed as a historic mon-ument in 2015, the building is characterised by exposed concrete surfaces formed with a special wooden board formwork [1]. Figure 1 shows the façade’s distinctive horizontal board-formed texture, which represents a key architectural element that must be preserved during any intervention.
A notable feature of this texture is the alternating recessed and protruding wooden boards, creating a three-dimensional relief across the façade. As illustrated in the figure 2, every second board is shifted slightly forward or backward by a few millimetres. This pattern forms an essential part of the building’s historical identity and must be replicated accurately during restoration.
Previous investigations by the engineering office WISSBAU identified significant damage to several façade panels, including carbonation, insufficient cover, corrosion of reinforcement, spalling and deteriorated joint sealants. Although these studies highlighted safety and durability concerns, the earlier repair proposals did not consider the heritage requirements, such as retaining the original colour tone and the characteristic wooden texture.
The bachelor thesis therefore aims to develop restoration strategies that are both structurally feasible and compliant with conservation guidelines. The main objectives include:
- evaluating the façade’s condition through visual inspection and extraction of concrete cores,
- determining concrete strength and adhesion properties,
- assessing the condition of embedded stainless-steel anchors,
- and testing various reproduction methods for the wooden formwork texture, including timber formwork, standard silicone matrices and custom 3D-printed matrices.
The overall goal is to identify restoration solutions that ensure structural safety while maintaining the architectural authenticity of the listed HZO façade. This introduction provides the foundation for the subsequent analysis of the façade’s condition and the de-velopment of texture reconstruction methods.
2. Condition survey of the façade
The condition assessment of the Hörsaalzentrum Ost (HZO) façade provides the technical basis for evaluating structural safety, durability and restoration needs. As a listed building, both the material condition and the preservation of the original appearance must be considered. The assessment combined visual inspection, destructive and non-destructive testing and laboratory strength measurements.
During the visual inspection, extensive deterioration was observed across many façade panels. As shown in Figure 3, large areas of the north façade exhibit corrosion-induced spalling, exposed reinforcement and loss of concrete cover. These damages are mainly caused by advanced carbonation, which reduces concrete alkalinity and compromises the protection of steel reinforcement. Hollow areas were also detected, indicating subsurface detachment caused by corrosion expansion. Joint defects were identified as well, contributing to moisture ingress and accelerating deterioration.
To better understand the façade construction, original drawings and archival documents were reviewed. The façade consists of precast concrete panels (10 cm thick), followed by a 10 cm insulation layer and a 20 cm in-situ concrete wall. Each panel contains double-layer Q131 reinforcement. The structural integrity depends heavily on the anchorage system: Figure 4 shows that each façade panel is connected to the in-situ concrete through three fully embedded anchors, which penetrate both the panel and the structural concrete. This composite anchorage must be carefully evaluated to determine whether panels can be repaired or require replacement.
Core drilling was performed at selected locations to examine material properties and anchor conditions. Drilling locations were chosen based on construction drawings and reinforcement detection using a Proceq Profometer. Panel A (north side) was selected due to severe visible damage, while Panel B (south rooftop) served as a reference panel without visible deterioration. The extracted cores were prepared in the laboratory; Figure 5 shows the trimming and surface grinding required for proper load application, and Figure 6 illustrates the compressive strength test.
Mechanical testing revealed unexpectedly high concrete strength. Based on direct core testing and rebound hammer measurements, the average compressive strength was calculated at 57.54 N/mm², corresponding to old concrete class A5. This classification exceeds earlier external estimations and confirms the high load-bearing capacity of the material. Adhesion (pull-off) tests yielded an average strength of 2.6 N/mm², also within class A5, indicating that the substrate is suitable for mineral repair mortars.
The anchors were evaluated through core drilling and endoscopic inspection. Despite the visible deterioration of the concrete surface, the anchors — made of corrosion-resistant steel — were found to be in excellent condition with no signs of corrosion, confirming their structural reliability. However, because the anchors are fully embedded, façade panels cannot be removed without destroying the existing anchorage; any replacement panels would therefore require entirely new anchor systems.
A regression analysis, shown in Figure 7, was used to correlate rebound hammer values with core compressive strength, enabling reliable interpretation of measurements in areas where core extraction was restricted by conservation constraints.
In summary, the façade of the HZO suffers from severe surface deterioration, insufficient concrete cover and carbonation-induced corrosion, even though the concrete itself exhibits high mechanical strength. The anchorage system is structurally sound, but surface damage and loss of the original wooden texture confirm the urgent need for restoration. These findings form the technical basis for selecting suitable restoration and texture reproduction methods in the following chapter.
3. Simulation of the Façade Surface
The simulation of the façade surface is a central part of the restoration concept for the Hörsaalzentrum Ost (HZO), as its architectural identity is defined by the unique wooden board-formed concrete texture. Since the building is listed as a historic monument, any restoration must accurately reproduce this characteristic three-dimensional surface. The goal of this chapter is to analyse and compare reproduction methods capable of matching the original formwork texture.
The process began with analysing the remaining intact façade segments. Although decades of weathering, biological growth and previous incompatible repairs have altered parts of the surface, selected areas still preserve sufficiently clear textures for documentation. These areas were cleaned and scanned to capture the alternating recessed and raised board pattern, the relief depth of 2–5 mm and the alignment of the boards. High-resolution 3D surface scanning produced detailed point clouds and height-profile models. Figure 8 illustrates the digital height model, which served as the reference geometry for reproducing the façade texture.
Based on this geometric data, three reproduction methods were evaluated:
1. Timber Formwork
Traditional timber formwork was assessed first. However, despite its historical relevance, it proved unsuitable: moisture-related deformation led to irregular relief depths, inconsistent spacing and an appearance that differed from the original boards. The natural grain of modern timber also does not match the historic texture, making this method inappropriate for heritage restoration.
2. Commercial Silicone Matrices
Standard silicone matrices offer good detail accuracy, but their generic wood grain patterns do not correspond to the specific HZO relief. Their repeating structures and incorrect depth profiles result in an inauthentic appearance that does not satisfy conservation requirements.
3. Custom Matrices Based on 3D-Scanning
The most successful method uses the digital height model to create custom, mould-ready negative forms. These can be produced either through 3D printing or by casting silicone over a printed master. As shown in Figure 9, the resulting matrices from Reckli —created via laser-mode surface scanning and photogrammetric Zephyr modelling — achieve a near-exact reproduction of the original façade texture.
The custom matrices were tested through laboratory casting trials. The resulting concrete samples demonstrated excellent accuracy: the micro-relief, the alternating raised and recessed boards and the irregularities characteristic of the original surface were reproduced within tolerances of less than one millimetre. The visual contrast between textured and recessed areas closely matched the still-intact façade segments.
In addition to precision, practical considerations were evaluated. Custom silicone matrices proved durable, reusable and easy to handle on site. Their modular format allows production of manageable panel sizes, and new matrices can be fabricated at any time — an important requirement for long-term heritage preservation and future repairs.
In conclusion, the simulation results clearly show that digital reproduction combined with custom-fabricated silicone matrices is the only method capable of ensuring a heritage-accurate reconstruction of the HZO façade texture. Timber formwork and commercial matrices cannot replicate the original relief with the necessary precision or consistency. The digitally supported method provides both technical reliability and conservation compatibility, forming the basis for the restoration approach presented in the next chapter.
4. Restoration methods for façade restoration
The restoration of the Hörsaalzentrum Ost façade requires a combination of structural, material and conservation-oriented measures. As a listed monument, the work must address both the technical deterioration of the concrete and the preservation of the characteristic board-formed surface, colour appearance and architectural rhythm of the façade.
Decades of environmental exposure have caused carbonation, loss of passivation, reinforcement corrosion and spalling of the cover concrete. Inadequate concrete cover has intensified corrosion, especially on moisture-exposed panels. Additionally, erosion, biological growth and previous incompatible repairs have resulted in partial loss of the original wooden texture. Restoration measures must therefore balance structural repair with the conservation of the historic material.
The first essential step is the removal of damaged or delaminated concrete. Areas showing spalling, hollow zones or exposed reinforcement must be carefully removed until sound concrete is reached. Clean edges are required to ensure proper bonding and avoid visually irregular repair patches.
After removal, reinforcement must be cleaned and treated. Rust is removed mechanically or by blasting, and corrosion protection may be applied. If crosssection loss is significant, reinforcement must be supplemented or replaced. Given that the building relies on anchors embedded in both the façade and the in-situ concrete, the integrity of reinforcement is particularly important.
The next step involves reprofiling the damaged areas with compatible mineral repair mortars. These mortars must have mechanical properties similar to the existing concrete, be durable under environmental exposure, and ensure adequate carbonation and frost resistance. For heritage reasons, the mortar must also match the original colour and surface characteristics to avoid visible patching.
Reconstruction of the façade’s board-formed texture is a decisive part of the restoration. The texture is not merely aesthetic but a defining architectural element. Various reproduction methods were assessed earlier, including timber formwork, commercial matrices and custom moulds. Only custom-made silicone matrices derived from 3D-scanned geometry can replicate the original depth, relief and alignment of the texture. These matrices allow the repair mortar to harden with a surface nearly indistinguishable from the original, preventing a patchwork-like appearance.
Following structural repairs and texture reproduction, protective treatments must be applied. Suitable options include mineral-based hydrophobic treatments or breathable, colour-neutral coatings. These systems must remain vapour-permeable and visually unobtrusive, avoiding glossy or colour-altering effects that would compromise the historic façade.
The restoration concept must also address the façade joints. Damaged sealants allow moisture ingress and accelerate deterioration. Joints must therefore be repaired with elastic, compatible sealants and shaped with correct backfilling and dimensional proportions.
Finally, long-term maintenance is essential. Regular inspections, gentle cleaning, renewal of hydrophobic protection and early repair of microcracks help ensure durability and prevent the recurrence of damage.
In summary, the restoration of the HZO façade requires a coordinated approach combining structural repair, surface reprofiling, accurate texture reproduction and protective treatment. By integrating modern digital reproduction technologies with conservation principles, the proposed methods ensure both long-term structural performance and faithful preservation of the building’s historic architectural character.
5. Heritage Authority Position
The restoration of the Hörsaalzentrum Ost façade must comply with the requirements of the local heritage authority, as the building is listed as a historic monument. The authority stresses that the architectural authenticity of the façade must remain visually unchanged, particularly the horizontal board-formed concrete texture, the specific relief depth and the characteristic material appearance.
For this reason, the authority strictly rejects any industrial surface coatings such as polymer films or thick mineral layers - that could alter colour, gloss or texture. Restored areas must blend seamlessly with the original surfaces and must not create visible contrasts.
A central requirement is the precise reproduction of the original wooden formwork texture. The alternating recessed and protruding sections, the pattern depth and the historical grain must be replicated as accurately as possible. Standard timber formwork or commercially available silicone matrices are considered unsuitable, as they cannot re-produce the unique, non-repetitive pattern of the HZO façade.
Instead, the authority supports digital documentation methods, including 3D surface scanning and the fabrication of custom matrices, because these ensure accuracy, reversibility and material compatibility. The reproduction must avoid mechanical repetition and maintain the handcrafted character of the original texture.
Regarding damaged façade panels, the authority acknowledges that structural interven-tions may be necessary. However, original material should be preserved whenever possible, and complete panel replacement should only occur when unavoidable. Replacement panels must accurately replicate the appearance and geometry of the originals, and all interventions must be documented.
Surface protection systems are permitted only if they are mineral-based, breathable and visually neutral. Treatments that trap moisture or create glossy or colour-shifting surfaces are not allowed. Throughout all restoration steps, the principle of minimal intervention must be applied.
Finally, the authority emphasises the need for a long-term maintenance plan, including regular inspections, gentle cleaning, renewal of protective treatments and early repair of emerging defects. This ensures that the restored façade retains its architectural and cul-tural value over time.
In summary, the heritage authority endorses a restoration strategy that combines precise digital reproduction of the texture with careful, minimally invasive repair. These guidelines ensure that both the structural integrity and the historic identity of the Hör-saalzentrum Ost are preserved for future generations.
6. Summary
This bachelor thesis develops a restoration approach for the exposed concrete façade with wooden board texture of the listed Lecture Hall Centre East (HZO) at Ruhr University Bochum. The aim was to assess the condition of the façade panels, simulate the characteristic surface texture, and evaluate restoration methods in accordance with heritage requirements.
The condition assessment, supported by the WISSBAU engineering report and additional core drilling, revealed severe deterioration such as carbonation, insufficient concrete cover, corrosion-induced spalling and damaged surfaces. Although the façade shows significant visible damage, the embedded stainless-steel anchors were found to be fully intact and corrosion-free. Compressive strength and adhesion tests classified the concrete as A5, indicating high material quality and good load-bearing capacity.
To reproduce the façade’s wooden board texture, several trial castings were conducted. Timber formwork produced inconsistent results and was therefore unsuitable. Silicone matrices were tested in three variants: standard matrices with sprucefir board patterns, and two custom-made matrices created through photogrammetry and surface scanning. All matrices produced good results, but the standard versions did not match the original board widths. The heritage authority therefore recommended using the custom-made matrices, while allowing standard matrices only if their dimensions were adapted.
Various restoration strategies were discussed with the heritage authority, including complete panel replacement, removal of the outer concrete layer followed by recasting, partial reprofiling with repair mortar, and further innovative methods. Partial reprofiling using mineral repair mortar combined with matrix imprinting was identified as the most appropriate solution. The repair mortar must match the historical aggregate composition and the colour of the existing façade. Although a colourless hydrophobic impregnation was tested, additional surface protection systems were not approved.
The recommended restoration concept includes documenting the façade using photogrammetry, scanning all damaged areas, producing custom silicone matrices for each texture segment, reprofiling damaged areas with compatible mortar, and imprinting the façade texture onto the fresh mortar. This ensures a technically reliable and heritage-compliant restoration that preserves both the structural integrity and the unique architectural character of the HZO façade.