Anatomy of cast glass: The effect of casting parameters on the meso-level structure and macro-level structural performance of cast glass components

Cast glass has great application potential in the architectural realm, yet, despite its possibilities and attractiveness, designers, engineers and developers are, from an early design stage, hesitant to employ it; the limited available and craft-based manufacturing facilities, the questionable quality of the product, the missing engineering data and quality control processes and the uncertainties linked with the structural application of cast glass, lead to discouraging high cost/ high risk solutions. Within the listed challenges and uncertainties, perhaps the most striking is our inability to answer the most obvious question: what is the strength of cast glass? A simple answer to this question does not exist, as the mechanical properties of cast glass vary from product to product, and are directly influenced by the employed chemical composition, thermal history, and casting process. Adding to this complexity, further questions over the mechanical properties and quality arise, once waste (contaminated) glass cullet and lower processing temperatures are used, in the efforts of reducing the environmental impact of cast glass components. Focusing on this knowledge gap, the aim of this work is to develop an understanding of the effect of the casting parameters on the meso-level structure of cast glass, and thereupon of the relationship between this meso-level structure and the strength, stiffness and fracture resistance of cast glass components. Towards this aim, the dissertation adopts an experimental approach based on physical prototyping by kiln-casting, and destructive and non-destructive testing. The experimental work shows that by kiln-casting, a larger variety of chemical compositions can be cast, even at relatively low processing temperatures. As a consequence, a broad range of mechanical properties arises, especially when waste cullet is employed. Based on the casting parameters, combinations of different defects, grouped in meso-level structures, are commonly found in cast glass, yet these can often be tolerable when situated in the glass bulk. The dissertation highlights the potential of recycling-by-casting of currently challenging to recycle glass waste into reliable and aesthetically unique structural components, and the advantages of engineering composite cast glasses. It also underlines the need for manufacturing guidelines, test data, product certifications and quality control protocols, for the successful implementation of cast glass in the built environment.Materials- Mechanics- Management & DesignStructural Design & Mechanic

Composite Structural Module out of srPP Facings and a PET-Bottle Core

Subject of this thesis is the development of a lightweight, low-cost and eco-friendly composite structural module, out of a self reinforced Polypropylene (srPP) skin and a core of Polyethylene Terephthalate (PET) bottles. The module can be easily mass-produced, transported, assembled and disassembled, and able to be fully recycled after the end of its functional life. In addition, the module can be produced in different sizes and types (ex. wall, slab components) that form an integral building system, ideal for emergency shelters in cases of natural disasters.Computation and PerformanceBuilding TechnologyArchitectur

Adhesive solutions for cast glass assemblies: Ground rules emerging from built case studies on adhesive selection and experimental validation

Cast glass is a promising, three-dimensional expression of the material for architectural and structural applications, particularly for the creation of all-transparent, self-supporting structures and envelopes. Typically applied in the form of solid blocks, cast glass components can be used as repetitive units to comprise fully-transparent, cast glass masonry walls. To maximize transparency and ensure an even load distribution, the glass blocks are bonded together by a colourless adhesive. Currently, there is a lack of standardized structural specifications, strength data and building guidelines for such adhesively-bonded cast glass-block systems. As a result, any new application is accompanied by experimental testing to select the adhesive and certify the adhesively bonded system. Since the choice of adhesive is highly dependent on the prerequisites set for each case-study -such as the structural and visual performance, available budget, the structure’s geometry and climate conditions- the preselection of the most prominent adhesive family at an early project stage can prevent an excessive budget and construction complications. This paper, therefore, aims to shed light on the selection process of adhesives for cast glass assemblies by first providing an overview of the most suitable bonding media families for such systems; these include stiff adhesives, flexible adhesives and cement-based mortars. Following, the paper reviews the research & development process of the adhesively-bonded glass-block systems in three distinct built projects, in which the TU Delft team has been involved: The Crystal Houses façade (NL), the LightVault, a robotically assembled glass vault (UK) and the Qaammat pavilion in the arctic circle (GL). The adhesive requirements for each of the three case studies are discussed in terms of structural and visual performance and ease-of-assembly (constructability). These criteria are decisive in pointing out the most promising bonding media family per case-study. The final shortlist of adhesive candidates within that bonding media family is subject to the full list of performance criteria, but also to market availability. The shortlist of adhesive candidates are typically experimentally evaluated, first via application testing and then via strength tests in order to choose the most suitable candidate. Based on the above, the review concludes in proposing guidelines for the effective selection, design and experimental verification of adhesively-bonded cast glass assemblies.Structural Design & Mechanic

Cast Glass Architecture in Extreme Conditions

Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Structural Design & Mechanic

Reinforced glass: Structural potential of cast glass beams with embedded metal reinforcement

The shaping freedom of cast glass in combination with the robustness of the resulting voluminous components opens up new, exciting directions in the field of structural glass. Yet, cast glass components remain brittle, limiting their structural applications in hyper-static compressive structures designed with conservative safety factors. Stretching these limits, this work investigates the reinforcement of cast glass by incorporating metal bars during the casting process, in a similar principle to reinforced concrete. Aim is to increase the ductility of the composite glass component, provide a warning mechanism prior to ultimate fracture and secure a postfailure load-bearing capacity. The development of hybrid glass components involves kiln-casting experiments using different metal-glass combinations, of similar thermal expansion coefficients. The method of introducing the metal bar in the glass during casting, and the effect of the selected forming temperature are investigated. The resulting metal-glass interfaces are examined for micro-cracks using a digital microscope, and for internal stresses using cross-polarized light. Two material combinations are found successful; soda lime silica with titanium and alkali borosilicate with Kovar. A hybrid borosilicate-Kovar 30*30*240mm beam is further tested in 4-point bending until failure, while its displacement is measured by Digital Image Correlation. The flexural response of the composite component is compared to the performance of unreinforced cast glass beams of similar composition. Although reinforced and unreinforced specimens show a comparable flexural strength, the reinforced specimen exhibits a warning mechanism well before failure, a gradual fracture and a post-failure load-bearing capacity. These attributes encourage the further exploration of cast glass reinforcement.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Structural Design & MechanicsApplied Mechanic

Glass up-casting: a review on the current challenges in glass recycling and a novel approach for recycling “as-is” glass waste into volumetric glass components

This paper presents the casting of volumetric glass components from glass waste as an alternative glass-recycling approach. The approach is characterized by its flexibility to accommodate a variety of compositions and ability to yield volumetric (solid or thick-walled) glass products that can tolerate higher contamination rates without a significant compromise to their properties. The novelty of the proposed glass-to-glass recycling method lies in the “as-received” recycling of glass waste, using relatively low forming temperatures (750–1200 °C). This reduces both the need for expensive, labour-intensive and logistically complex purifying, segregation and treatment (e.g. removal of coatings) techniques, and the required energy and CO2 emissions for product forming. Aim of this paper is to provide an overview of the potential but also of the technical and supply-chain challenges and limitations that still need to be tackled, in order to introduce this recycling approach to the market. Addressing the supply-chain barriers of glass recycling, the principal challenges linked to the collection and separation of glass waste and the established quality standards for the prevailing glass production technologies are identified, in order to argue upon the potential of this new recycling approach. In continuation, addressing the technical challenges that are mainly linked to contamination, an overview is provided of the main experimental findings on the influence of cullet contaminants and casting parameters on the generation of defects, and how these affect the mechanical properties. The experiments study a broad variety of glass compositions, including soda-lime, borosilicate, aluminosilicate and lead/barium glasses, and different levels of cullet contamination, of embedded (e.g. frit, wire) or external (e.g. stones, glass ceramics) character. Based on the cullet characteristics and imposed firing schedules, different glass quality grades arise and critical defects are highlighted. Thereafter, the most promising glass waste sources that can be recycled via this novel recycling approach are distinguished and directions for future research are highlighted.Structural Design & Mechanic

A case study of apparently spontaneous fracture

Spontaneous failures in thermally toughened glass are frequently reported, although the actual percentage is quite small, suppliers in the Netherlands reporting one or two cases a year while thousands of tempered panels are supplied. These cases are rarely investigated in the Netherlands because the broken thermally toughened glass is usually not in one piece and can thus not be sent for analysis. In 2015 several sliding thermally toughened glass single curved vehicle roof windows failed within several months. A butterfly pattern was seen and NiS failure was suspected by the window manufacturer. As a coloured adhesive foil had been applied during manufacturing the glass shards were kept together. The broken glass was shipped back to the supplier and was together with several non-broken roof windows sent to Delft University of Technology for analysis. The compressive surface pre-stress in the intact roof panels was measured with a SCALP 5 device. It was found that the compressive surface pre-stress varied, as bands of low compressive surface pre-stress alternating with bands of high compressive surface pre-stress appeared in the specimens. Destructive testing of the intact windows showed that the windows failed in the bands of low compressive surface pre-stress. The actual bending strength was far below the strength thermally toughened glass should have. Microscopic analysis of the butterfly fragment of the “spontaneously” failed roof windows showed that the failure was not caused by any inclusion in the glass, but started at the surface of the glass and was probably due to overloading. It is concluded that the failures were not spontaneous but the result of overloading due to uneven tempering of the glass.Structural Design & MechanicsSteel & Composite Structure

Transparent Restoration

This paper investigates the application of structural glass in restoration and conservation practices in order to highlight and safeguard our built heritage. Cast glass masonry is introduced in order to consolidate a half-ruined historic tower in Greece, by replacing the original parts of the façade that are missing. Dry connections between the elements contribute to a completely reversible system that complies with the conservation guidelines suggested by the Venice Charter, while the interlocking nature of the glass units ensures the overall stability and the desired structural consolidation of the monument.Applied MechanicsStructural Design & Mechanic

On the flexural strength and stiffness of cast glass

Cast glass has great potential for diverse load-bearing, architectural applications; through casting, volumetric glass components can be made that take full advantage of glass’s stated compressive strength. However, the lack of engineering, production and quality control standards for cast glass and the intertwined ambiguities over its mechanical properties-particularly due to the variety in chemical compositions and the lack of understanding of the influence of flaws occurring in the glass bulk-act as an impediment to its wide-spread application. Addressing the above uncertainties, this work studies a total of 64 silicate-based glass specimens, prepared in 20 * 30 * 350 mm beam size, either by kiln-casting at relatively low forming temperatures (970–1120 ∘C), or by modification of industrially produced glass. For the kiln-casting of the specimens, pure and contaminated recycled cullet are used, either individually or in combination (composite glasses). The defects introduced in the glass specimens during the casting process are identified with digital microscopy and qualitative stress analysis using cross polarized light, and are categorized as stress-inducing, strength-reducing or harmless. The Impulse Excitation Technique is employed to measure the Young’s modulus and internal friction of the different glasses. Differential Scanning Calorimetry is used on a selection of glasses, to investigate changes in the glass transition range and fictive temperature of the kiln-cast glasses due to the slower cooling and prolonged annealing. The four-point bending experiments are shedding light upon the flexural strength and stiffness of the different glasses, while the fractographic analysis pinpoints the most critical defects per glass category. The experiments show the flexural strength of cast glass ranging between 30–73 MPa, according to the level of contamination and the chemical composition. The measured E moduli by both methods are in close agreement, ranging between 60–79 GPa. The comparison of the flexural strength with prior testing of cast glass involving shorter span fixtures showed a decreasing strength with increasing size for the contaminated specimens, but similar strengths for pure compositions. The results highlight the versatile role of defects in determining the glass strength and the complexity that arises in creating statistical prediction models and performing quality control.Applied MechanicsStructural Design & Mechanic

Adaptive Fluid Lens and Sunlight Redirection System

The paper describes a novel system to alter and redirect sunlight under large span roofs with the help of a fluid lens system. Focus lies on the computational design, testing, measurement and evaluation of the performance of a physical prototype