Whilst the optical and structural properties of the glasses containing tantalum oxide have been considerably investigated, research into their mechanical properties is not substantially established. This work reports on the mechanical characterization of transparent germanate glass samples, obtained via the melt-quenching technique, with a molar content of Ta2O5 ranging from 0% to 20%. The introduction of Ta2O5 in the samples is related to significant improvements in the mechanical properties. The transition from glass to transparent glass-ceramic via the controlled crystallization of Ta2O5 proved to be a tool to increase both the elastic modulus and the hardness while keeping the transparency of the material. The average elastic modulus of the studied compositions ranged from 69.2 GPa to 99.1 GPa, while the average hardness of the same samples varied from 5.10 GPa to 7.34 GPa. ... Read more

Among the environmental factors affecting glass weathering are humidity, exposure time, temperature, and the presence of pollutants in the atmosphere. Notwithstanding that the weathering produced depends on numerous factors, the important weathering effect of high humidity may be specifically mitigated by using a good chemical composition for the glass. To evaluate this relationship, flat glass samples from three suppliers were studied. The chemical composition of the samples was determined and the variability in compositions was evaluated to verify to what extent these small differences can affect their chemical durability. The chemical durability of the samples was evaluated by determining the hydrolytic resistance of crushed glass powder and using a visual appearance evaluation of bulk samples. The results demonstrate that when the samples are frequently washed, the compositional differences found between the suppliers can cause a significant difference in durability. The samples possessing the highest molar concentrations of Al2O3, and alkaline earth oxides (MgO + CaO) exhibited the highest hydrolytic resistance and the least visual deterioration. Differences encountered for the weathering products of glasses of comparable bulk compositions highlight that the process parameters play a major role in the alteration of the surface compositions of the glasses. For the unwashed samples, no consistent correlation was found between hydrolytic resistance and visual deterioration. ... Read more

The investigation of new compositions is crucial for the expansion of possible applications of glass, from the typical applications for building engineering, in the form of cast blocks or float glass, to more advanced technologies, such as 3D-printed glass or glass-to-metal connections. Since high melting temperatures and brittleness are two important drawbacks of glass, this work aims to improve both properties. Characterisation techniques, such as thermal analysis, nano-indentation, and UV/VIS spectroscopy, are used to evaluate the properties of the samples. The modification of the properties is achieved via changes in the composition of the glass, using compounds such as phosphorus pentoxide, aluminium oxide and boron oxide. Then, the choice of different glass formers and modifiers contributes to the development of compositions with lower melting and glass transition temperatures. The reduction of the melting temperature allows a saving of energy during the manufacturing. The structures of the glasses differ from the standard soda–lime–silica and borosilicate glasses, leading to a different mechanical behaviour. Furthermore, these new compositions incorporate up to 35% of fly ash in their formulas. The valorisation of these by-products reduces costs and gas emission. ... Read more

The investigation of new glass compositions is crucial to expand the possible applications of glass, from the typical applications for building engineering, in the form of cast blocks or floated glass, to more advanced technologies, such as 3D-printed glass or glass to metal connections. Despite the intense research activity and new glass compositions being investigated every day, there has been little innovation or evolution in the composition of architectural glass. This is partially explained by the fact that a substantial part of glass research is not relevant to practical large-scale applications. This thesis is more concerned about the development of compositions with optimized properties than the studies of the short- and intermediate-range structure of a theoretical glass that would hardly find a practical application. Thus, these compositions are inexpensive and appropriate to mass production, utilizing conventional melting techniques. Since the high melting temperatures and the brittleness are two important drawbacks of glass, this work aims to improve both properties. The modification of the properties is achieved via changes in the composition of the glass, using compounds such as phosphorus pentoxide, aluminium oxide and boron oxide. Then, the choice of different glass formers and modifiers contributes to the development of compositions with lower melting and glass transition temperatures. The reduction of the melting temperature allows a saving of energy during the manufacturing and recycling processes. The structures of the glasses differ from the standard soda-lime and borosilicate glasses, leading to a different mechanical behaviour. For instance, an anisotropic structure, which could exhibit a better mechanical performance than standard glasses. Furthermore, these new compositions incorporate up to 35% of slag and fly ash in their formulas. The valorization of these by-products that would otherwise have been previously discarded reduces costs and gas emission. The developed compositions have high water resistance, amorphous structure proved by x-ray diffraction and indentation toughness comparable to a standard soda-lime glass. The coloration of the samples varies depending on the composition and, for the samples containing slag, depending on the melting temperature. In this case, melting at higher temperatures allows the production of colorless glass. The color of the glasses is mainly influenced by the presence of sulfur and iron oxide. In conclusion, this thesis describes the development of new glass compositions containing fly ash and slag. The focus of the work is on the improvement of the properties and a comparison of performance of these new compositions with the glasses currently used in building engineering. The promising results point to the possibility of expansion of the current applications of glass. ... Read more

The classical image of glass is that of a rigid, transparent brittle material characterized by a non-crystalline microstructure. This 19th and 20th century image however is mostly based on the contrast between soda lime glass and metals. It does not really make sense in the 21th century where more modern testing methods have increased our understanding of the physiochemistry of glass. Based on recent results and the development of computational molecular dynamic software modelling a new approach to the physiochemistry of glass is outlined. The consequences this view has on glass properties and processing are explained. ... Read more

Although in theory glass can be endlessly re-melted without loss in quality, in practice only a small percentage gets recycled, mainly by the packaging industry. Most of the discarded glass fails to pass the high quality standards of the prevailing glass industry – due to coatings, adhesives, other contaminants or incompatibility of the recipe – and ends up in landfill. However, using discarded glass in cast components for building applications can be a good way to reintroduce this waste to the supply chain. Such components can tolerate a higher percentage of inclusions, without necessarily compromising their mechanical or aesthetical properties. This paper explores the potential but also the limitations of recycling glass in order to obtain load-bearing components. First, an overview is provided regarding which types of glass reach the recycling plants and which not, arguing on the reasons behind this selection. Afterwards, a series of experiments is presented, exploring the possibilities of recycling everyday glass waste, from beer bottles and Pyrex trays to mobile phone screens. Each type of glass waste is cast at different temperatures and firing/cooling rates to define its flow capability and risk of crystallization. The above information is linked to the X-ray fluorescence (XRF) analyses of the samples prior to recycling. The results point out the types of glass with potential in structural applications, and the overall feasibility of the concept. This paper is an extension of previously reported work by Bristogianni et al. 2018. ... Read more

Despite a large number of products developed from waste materials, most of them consist of non-transparent applications, partly because it is a challenge to get transparent materials at reasonable temperatures from these waste products. In this work, we produced transparent glass samples incorporating slag and fly ash into a phosphate glass matrix. The compositions were adjusted in order to circumvent typical drawbacks of phosphate glasses: a high thermal expansion coefficient and low chemical durability. The use of phosphate as a glass former, instead of silicate, is a remarkable innovation, and according to the knowledge of the authors, no other work reports its utilization for building engineering purposes. These novel glasses incorporate amounts up to 35% (in weight) of blast furnace slag or fly ash. Thermal, structural and mechanical characterization were performed. The glasses possess a low melting temperature in relation to the standard soda-lime and borosilicate glasses, melting in temperatures between 1100ºC and 1350ºC. This drastic reduction of the melting temperature allows to save energy during the manufacturing process. Furthermore, the valorization of materials that would otherwise have been previously discarded reduces costs and gas emission. It contributes to fill a current appeal for a more sustainable glass manufacturing process. ... Read more

The growth of the industrial production generates a high volume of waste materials. These products have a significant impact on the environment. Therefore, the valorization of industrial wastes, especially those produced in huge quantities, is an important social and ecological issue. Waste reuse and recycling could help to develop new products and aggregate value to materials that would have been previously discarded. Furthermore, it could reduce the consumption of natural resources and pollution. Blast furnace slag and fly ash are waste materials largely used in concrete production, mainly as an aggregate, and road construction, as porous asphalt and in other contexts. These wastes contain many elements that are also present in typical glass formulas, such as CaO, SiO2, Al2O3, and Fe2O3. However, these elements are highly refractory, and their presence in complex compositions leads to a high tendency to crystallize and to high working temperatures. For this reason, it is a challenge to get transparent materials at reasonable temperatures from these waste products. Glass is a material that allows large amounts of various elements in solution, and is suitable for assimilating the complex materials in its compositions. In this work, we produced transparent glass samples incorporating amounts up to 35% (in weight) of blast furnace slag or fly ash. The compositions were adjusted in order to allow for chemically durable glasses in relatively low melting temperature: the samples were successfully submitted to water durability tests and were obtained in melting temperatures between 1100°C and 1350°C, depending on the composition. The melting conditions were optimized in order to achieve a higher transparency. The optical, mechanical and thermal properties of the samples were measured and compared to the standard borosilicate and soda-lime glasses. ... Read more

Although in theory glass can be endlessly remelted without loss in quality, in practice only a small percentage gets recycled, mainly by the packaging industry. Most of the discarded glass fails to pass the high quality standards of the prevailing glass industry -due to coatings, adhesives, other contaminants or incompatibility of the recipe- and ends up in the landfill. However, employing discarded glass in cast components for building applications can be a way to reintroduce this waste to the supply chain. Such components can tolerate a higher percentage of inclusions, without necessarily compromising their mechanical or aesthetical properties. This paper explores the potential but also the limitations of recycling glass in order to obtain load-bearing components. First, an overview is provided regarding which types of glass reach the recycling plants and the which not, arguing on the reasons behind this selection. Afterwards, a series of experiments is presented, exploring the possibilities of recycling everyday glass waste, from beer bottles and Pyrex® trays to mobile phone screens. Each type of glass waste is initially cast separately to define its flow capability and risk of crystallization. The above information is linked to the X-ray fluorescence (XRF) analyses of the samples prior to recycling. Then, the possibility to mix different glass recipes without fracturing is evaluated. The results point out the types of glass with potential in structural applications, and the overall feasibility of the concept. ... Read more