Introduction

Glass Fibre Reinforced Concrete (GFRC) as a material has been developed over the last 50 years into the material it is today, using glass fibres for reinforcement, (1) (2) (3) (4). Since the development of GFRC, it has mostly been used as a cladding material for buildings as thin-wall GFRC panels. However, the history of thin-walled panels (reinforced with asbestos fibres) can be traced back to 1901, where Ludwig Hatschek (5) developed the method known today as the Hatschek Method (6). The product is better known as “Eternit”. However, the production method used asbestos fibres for reinforcement and due to their related health and safety issues (7), alternative fibre materials were sought such as glass fibres used in the yacht-building industry and were a suitable substitute. Thin-walled GFRC was very popular during the early days of its development and landmark buildings, such as the 30 Cannon Street building London, (formally Credit Lyonnais), by Whinney, Son & Austen Hall in 1974-7 (8), and the UOP Fragrance Factory in Tadworth UK, by Rogers and Piano in 1973-4 (9), were clad with this material. Thin-walled GFRC cladding in the 1980s and 1990 was being used predominately as decorative cladding (10), however, for the 2008 Expo in Zaragoza, Zaha Hadid Architects (ZHA) used thin-walled GFRC as cladding on the Expo bridge and for the 2010 world cup in South Africa, HOK architects designed the Soccer City stadium with thin-walled GFRC (11). Both projects utilized flat thin-walled GFRC panels, shown in Figure 1.1 and Figure 1.2

Advancing the manufacture of complex geometry GFRC for today's building envelopes

Thin-walled glass fibre reinforced concrete (GFRC) panels are being used as the primary cladding material on many landmark buildings especially in the last decade. GFRC is an ideal material for building envelopes because it is durable, it can resist fire and the environmental impact is low compared to other materials, because the base materials used in the production of GFRC are widely available throughout the world. Thin-walled GFRC was initially developed as a cladding material in the 1970s and 1980s where the majority of the available research lies. The introduction of 3D CAD software has enabled the design of buildings with complex shapes that, in the past, would have been rationalised to meet budget and time constraints. However, when GFRC has been proposed for buildings with a complex free-form geometry it has been replaced with alternative materials such as glass reinforced plastic (GFRP) due to the high cost and time required to fabricate suitable GFRC panels using conventional manufacturing methods. The literature showed that empirical performance characterization of GFRC had not been researched in detail regarding the limits of functionality or any systematic approach to understanding their use in complex geometry building envelopes.As a first step the key architectural demands, the main barriers and limitations in the manufacture of complex geometry thin-walled GFRC were identified by interviewing and visiting manufacturers, designers and key buildings. This identified the key barrier to be the process of producing the mould for casting the complex geometry GFRC panels. Solutions to resolve them were tested over several stages for each of the main production methods most suited for the manufacture of thin-walled GFRC, namely; the automated premixed method, the premixed method and the sprayed method. The results from the laboratory testing over all the stages, and the prototype structure manufactured with the identified solution from the testing, answered the main research question:How can the manufacture of complex geometry thin-walled GFRC be advanced to meet today’s architectural demands?So, the architectural demands for thin-walled GFRC cladding were identified, together with a clearly defined range of complexity of thin-walled GFRC panels. The key demands were; a smooth surface texture, no visual fibres in the surface, minimal air-bubbles or voids, consistent colour across all thin-walled GRFC elements, no visible cracks, and the need for edge-returns and panel offsets. The suitability of selected production methods were evaluated against these demands. Firstly the automated premixed method was tested on a flexible table, (single reconfigurable mould surface, with computer controlled actuators  capable of forming free-formed geometries). This showed that the flexible table alone would not meet the requirements for an edge-return, with the manufacturing speed required, to produce many unique shaped panels within normal building project time-schedules. Following this test a solution was proposed that used the flexible table to produce free-formed shaped moulds using fast curing foam, enabling moulds to be produced within hours allowing more rapid utilization of the flexible table. This solution was first tested for the premixed method by casting positive and negative mould parts enabling an edge-return to be cast because flexible tables are only able to produce moulds with a continuous surface. The new mould solution for complex geometry shapes also demonstrated that it was difficult to avoid air-bubbles and voids when casting the GFRC panels using the premixed method. So a second mould solution was developed for the sprayed method. This resolved the challenges of forming an edge-barrier on the mould, while allowing an edge-return to be successfully cast on a double curved panel that met the key architectural demands.From the research and the tests it was possible to devise a fully automated process for the manufacture of complex geometry thin-walled GFRC, comprised of:– Stage 1: Initial architectural geometric concept. – Stage 2: Panelization and geometric offsetting. – Stage 3: Identifying the right production method. – Stage 4: Casting process. – Stage 5: Transportation and Installation.Solutions for each of these stages all contributed to advances that will enable current and future free-form thin-walled GFRC architectural designs to be realised.The contribution to knowledge from the tests and the resulting automated process was used to produce the moulds for 9 unique double curved elements to form each row of a 10m tall self-supporting thin-walled shell. This show-cased how the identified solution enabled a faster and more cost effective method to produce free-form thin-walled GFRC panels. One of the main conclusions of the research showed that the sprayed method currently provides most flexibility in the manufacture of complex geometry thin-walled GFRC panels when the identified architectural demands must be met. To advance the manufacture of complex geometry thin-walled panels further a fully automated and digital manufacturing process must be developed. As identified in the research this can be done by upgrading current automated premixed production lines by integrating the new solution for complex geometry shaped moulds into the production line and automatically spaying the GFRC onto the mould.When fully developed this fully automated method would enable free-form shell elements to be produced, that may also incorporate insulation, allowing segments for a self-supporting free-form shell to be constructed. With this research the current architectural knowledge base has been advanced in terms of complex geometry thin-walled GFRC for building envelopes. The identified solutions should allow building with complex geometries to be realised using thin-walled GFRC as the envelope cladding

Introduction to state‑of‑the‑art thin-walled GFRC

Thin-walled fibre reinforced concrete (FRC) elements are being adapted for large scale buildings with complex geometry envelopes. The current production methods, developed in the initial stages of glass fibre reinforced concrete (GFRC) elements in the 1970s, are limited when striving to produce more complex shaped FRC elements. The limitations of the FRC elements in terms of material properties and surface quality are described for these current state of the art production methods. New production methods and casting techniques are proposed that will advance the application of thin-walled FRC for buildings with complex geometry envelopes. Evaluation of the current state of the art production methods concluded that the sprayed GFRC methods are currently the most flexible solution which has the greatest potential for adapting the method to the requirements of complex geometry buildings. Further development of thin-walled GFRC elements would be possible by developing a mould system for complex geometry panels with an edge-return, which can utilise glass fibre reinforced ultra high performance concrete (GF-UHPC) with a vacuum technology, it would be possible to produce complex geometry GFRC elements with an increased material performance and yet still meet the aesthetic requirements of minimal visual defects in the surface of thin-walled elements

Developing a solution for the sprayed concrete method and proposing automated process.

Resolving the challenges of advancing thin-walled glass fibre reinforced concrete (GFRC) requires a novel, more automated digital design and manufacturing process that meets the requirements of present demands for thin-walled GFRC panels. The design, optimisation and manufacture of moulds using existing approaches is subject to many limitations and constraints that result in feedback loops between each stage of the design and manufacturing processes. This precludes the efficient and fully automated digital design and manufacture of complex geometry thin-walled GFRC panels. The proposed mould system overcomes many of these constraints, and when combined with new software plug-ins, will be capable of digitally resolving the limitations or constraints that interrupt each key stage of the design and manufacturing processes. These plug-ins have been characterized to provide a seamless interface between software and hardware with minimal delays caused by design feedback loops to allow a fully automated digital design process to be realised. The impact of the new mould on this novel process is analysed and further research necessary to advance the process is identified

Testing of solutions and proof of concept for the automated process

Developing and testing a novel manufacturing method for thin-walled complex geometry glass fibre reinforced concrete (GFRC) panels is required to advance towards a more digital automated process. The experimental procedure described identified the main bottleneck during the manufacture of complex geometry thin-walled GFRC panels, namely, the time taken to make the mould and cast the GFRC panels. The primary outcome was the development and application of a new mould capable of casting complex geometry thin-walled GFRC panels with good surface quality using a manufacturing method that enables more rapid automated large-scale production. This intermediate mould was tested successfully using the sprayed GFRC method and was the key element during the development of a novel cost effective manufacturing method for complex geometry thin-walled GFRC panels. This method was used to manufacture 9 different double curved intermediate moulds for a 10m high GFRC self-supporting, thin-walled hyperbolic shell, with 12mm thick panels at the base of the structure. The completed structure show-cased the effectiveness of the novel manufacturing method by reducing the production time from an estimated 100 days to 10 days if using a single reconfigurable mould surface, with computer controlled actuators capable of forming free-formed geometries

Developing a solution for the premixed concrete method and proposing a step by step fabrication process.

Complex geometry concrete is being used in building and infrastructure projects however, costly in-situ mouldings are necessary to achieve these geometries. Advancing discretised concrete shell structures requires the development of a new moulding system at lower cost and reduced mould production times. Future thinwalled glass fibre reinforced concrete (GFRC) elements must possess good continuous surface quality, with the required edge-returns and panel offsets, combined with the physical material properties to increase spans and lower the risk of visible surface cracks. Existing moulding systems do not have the capability to meet these contemporary architectural aesthetic and design aspirations. A new mould system to produce free-form thin-walled GFRC elements is presented and can be used to replace CNC milled moulds for the manufacture of thin walled GFRC. Such a system allows the mould for thin-walled GFRC elements to be produced in a fast, cost effective and more efficient manner. A new step-by-step process to achieve such new thin-walled GFRC panels is described, permitting the fabrication of complex geometry thinwalled GFRC elements using more cost effective large-scale production methods. This process bridges the gap between the limited capabilities of current solutions, and the architectural aesthetic demands for good surface quality, with the option of having an edge-return and the same surface quality as the front surface to give a monolithic appearance

Key problems associated with complex geometry GFRC

Glass fibre reinforced concrete (GFRC) elements have become a sought after cladding material since their introduction as rain screen cladding for buildings. To advance GFRC for a range of complex geometry building envelopes this also requires advances in existing moulding techniques for thin-walled GFRC elements. To do so it is necessary to define the current state of thin-walled GFRC elements and the constraints and limits placed on them by existing production techniques. This paper identifies the current architectural and aesthetic requirements of thin-walled GFRC elements and maps their range of complexity, from 1-D to 3-D, to the limits of the most appropriate production method. This will inform guidelines for the future design development of thin-walled GFRC and enable an innovative approach to further advance the moulding techniques for thin-walled GFRC elements for a variety of complex geometry building envelopes. The paper concludes on which further steps need to be taken to advance thin-walled glass fibre reinforced concrete for tomorrow’s architectural buildings envelopes with complex geometries

Conclusion

The literature review for this research work has shown that there is a substantial body of research in the field of GFRC with a focus on its material behaviour. Advances and innovation in GFRC for application in the building industry was missing, so this work has advanced the material research considerably by taking the latest state-of-the-art material research and applying it to fabrication processes in the building industry and aligning it with today’s architectural demands for complex geometry thin-walled GFRC. Initial research identified state-of-the-art production technologies, and advantages and disadvantages were collated to identify the manufacturing method optimally suited to the production of complex geometry thin-walled GFRC panels. The conclusions of this research work should enable designers to realise complex geometry building envelopes at a lower cost using thin-walled GFRC panels with the high degree of complexity demanded, while providing the industry with solutions that advance the processes of manufacturing thin-walled complex geometry GFRC

Advancing the manufacture of complex geometry GFRC for today's building envelopes

Thin-walled glass fibre reinforced concrete (GFRC) panels are being used as the primary cladding material on many landmark buildings especially in the last decade. GFRC is an ideal material for building envelopes because it is durable, it can resist fire and the environmental impact is low compared to other materials, because the base materials used in the production of GFRC are widely available throughout the world. Thin-walled GFRC was initially developed as a cladding material in the 1970s and 1980s where the majority of the available research lies.  The introduction of 3D CAD software has enabled the design of buildings with complex shapes that, in the past, would have been rationalised to meet budget and time constraints. However, when GFRC has been proposed for buildings with a complex free-form geometry it has been replaced with alternative materials such as glass reinforced plastic (GFRP) due to the high cost and time required to fabricate suitable GFRC panels using conventional manufacturing methods. The literature showed that empirical performance characterization of GFRC had not been researched in detail regarding the limits of functionality or any systematic approach to understanding their use in complex geometry building envelopes. As a first step the key architectural demands, the main barriers and limitations in the manufacture of complex geometry thin-walled GFRC were identified by interviewing and visiting manufacturers, designers and key buildings. This identified the key barrier to be the process of producing the mould for casting the complex geometry GFRC panels. Solutions to resolve them were tested over several stages for each of the main production methods most suited for the manufacture of thin-walled GFRC, namely; the automated premixed method, the premixed method and the sprayed method. The results from the laboratory testing over all the stages, and the prototype structure manufactured with the identified solution from the testing, answered the main research question: How can the manufacture of complex geometry thin-walled GFRC be advanced to meet today’s architectural demands? So, the architectural demands for thin-walled GFRC cladding were identified, together with a clearly defined range of complexity of thin-walled GFRC panels. The key demands were; a smooth surface texture, no visual fibres in the surface, minimal air-bubbles or voids, consistent colour across all thin-walled GRFC elements, no visible cracks, and the need for edge-returns and panel offsets. The suitability of selected production methods were evaluated against these demands. Firstly the automated premixed method was tested on a flexible table, (single reconfigurable mould surface, with computer controlled actuators  capable of forming free-formed geometries). This showed that the flexible table alone would not meet the requirements for an edge-return, with the manufacturing speed required, to produce many unique shaped panels within normal building project time-schedules. Following this test a solution was proposed that used the flexible table to produce free-formed shaped moulds using fast curing foam, enabling moulds to be produced within hours allowing more rapid utilization of the flexible table.  This solution was first tested for the premixed method by casting positive and negative mould parts enabling an edge-return to be cast because flexible tables are only able to produce moulds with a continuous surface. The new mould solution for complex geometry shapes also demonstrated that it was difficult to avoid air-bubbles and voids when casting the GFRC panels using the premixed method. So a second mould solution was developed for the sprayed method. This resolved the challenges of forming an edge-barrier on the mould, while allowing an edge-return to be successfully cast on a double curved panel that met the key architectural demands. From the research and the tests it was possible to devise a fully automated process for the manufacture of complex geometry thin-walled GFRC, comprised of: – Stage 1: Initial architectural geometric concept. – Stage 2: Panelization and geometric offsetting. – Stage 3: Identifying the right production method. – Stage 4: Casting process. – Stage 5: Transportation and Installation. Solutions for each of these stages all contributed to advances that will enable current and future free-form thin-walled GFRC architectural designs to be realised. The contribution to knowledge from the tests and the resulting automated process was used to produce the moulds for 9 unique double curved elements to form each row of a 10m tall self-supporting thin-walled shell. This show-cased how the identified solution enabled a faster and more cost effective method to produce free-form thin-walled GFRC panels. One of the main conclusions of the research showed that the sprayed method currently provides most flexibility in the manufacture of complex geometry thin-walled GFRC panels when the identified architectural demands must be met.  To advance the manufacture of complex geometry thin-walled panels further a fully automated and digital manufacturing process must be developed. As identified in the research this can be done by upgrading current automated premixed production lines by integrating the new solution for complex geometry shaped moulds into the production line and automatically spaying the GFRC onto the mould. When fully developed this fully automated method would enable free-form shell elements to be produced, that may also incorporate insulation, allowing segments for a self-supporting free-form shell to be constructed.  With this research the current architectural knowledge base has been advanced in terms of complex geometry thin-walled GFRC for building envelopes. The identified solutions should allow building with complex geometries to be realised using thin-walled GFRC as the envelope cladding