Recycled Soda-lime Glass Research Articles

Enhanced Photoluminescence of Plasma-Treated Recycled Glass Particles.

Recycled soda-lime glass powder is a sustainable material that is also often considered a filler in cement-based composites. The changes in the surface properties of the glass particles due to the treatments were analyzed by X-ray photoelectron spectroscopy (XPS) and optical spectroscopy. We have found that there is a relatively high level of carbon contamination on the surface of the glass particles (around 30 at.%), so plasma technology and thermal annealing were tested for surface cleaning. Room temperature plasma treatment was not sufficient to remove the carbon contamination from the surface of the recycled glass particles. Instead, the room temperature plasma treatment of recycled soda-lime glass particles leads to a significant enhancement in their room temperature photoluminescence (PL) by increasing the intensity and accelerating the decay of the photoluminescence. The enhanced blue PL after room-temperature plasma treatment was attributed to the presence of carbon contamination on the glass surface and associated charge surface and interfacial defects and interfacial states. Therefore, we propose blue photoluminescence under UV LED as a fast and inexpensive method to indicate carbon contamination on the surface of glass particles.

Developing Techniques for Closed-Loop-Recycling Soda-Lime Glass Fines through Robotic Deposition

Glass is made from sand—a finite resource. Hence, there is a need to maintain glass in the industrial cycle as described in the Ellen MacArthur Foundation’s circular-economy diagram. This research project examines the reallocation of material resources in the form of waste glass fines from the industrial recycling process for soda-lime glass. According to the plant manager of Reiling Glasrecycling Danmark ApS, the fines are currently sold to be used for insulation. Although this process prolongs the lifespan of the fines before they become landfill waste, a closed-loop circular option would be preferable. In order to establish a closed-loop circular model for waste glass fines, this research investigates their material and aesthetic qualities and proposes a strategy for maintaining the fines in the closed loop cycle together with the soda-lime glass. The fines are manipulated through robotic deposition and formed into 3D geometries. To expand the aesthetic applications for the material, an investigation is conducted by combining 3D geometries with the traditional glassmaking techniques of glassblowing and casting. The research contributes knowledge of the materials’ technical qualities including printability, durability and workability of the 3D prints combined with cast or blown recycled container glass as well as with blown waste glass fines. Technical obstacles are revealed and alternative routes for further explorations are suggested. Finally, the performative and aesthetic qualities of the results are discussed, while artistic applications for recycled soda-lime glass fines remain to be explored in future research.

The Glass Produced from Recycled Soda-Lime Glass Cullet by Slip Casting

Slip casting is a ceramic processing technique which can be used to produce complex-shape ceramic object. In the present work, slip casting was applied to produce the 70 mm × 10 mm × 15 mm green samples from recycled soda-lime glass. The slip with 60% solid loading was prepared from 100 g of recycled cullet, 1 g of sodium silicate as a binder, 50 ml of DI water, and 16.7 ml of deflocculant. The deflocculant for slip casting was 0.1 wt% sodium tripolyphosphate solution. After slip casting, the samples were dried at room temperature for 3 days. Then the samples were sintered at 680, 700, and 720 °C with the soaking time of 1 and 2 hrs with 5 °C/min heating rate. The results from statistical analysis showed that there was a high variation on flexural strength which should be from the high closed porosity and high pore-size variation of the samples. Therefore, our glass produced from slip casting is not suitable for load bearing applications. However, this technique still can be used to produce other art products such as Buddha amulets.

CREATION OF A POZZOLANIC MATERIAL FROM WASTE CALCIUM HYDROXIDE AND RECYCLED GLASS POWDER

The use of consumer and industrial waste as supplementary cementitious materials is one solution to the development of sustainable Portland cement. This research studied the partial replacement of cement with a pozzolanic mixture of recycled soda-lime glass powder (GP) and waste calcium hydroxide (CH). The optimal weight ratio of CH and GP was selected from five ratios between 30/70 to 70/30 (CH/GP), using thermal gravimetric analysis and X-ray diffraction. It was found that CH deficient ratios contained residual glass powder, while CH rich ratios contained residual calcium hydroxide and had undesirable carbonation of the CH. The 60/40 pozzolan was selected due to the large amount of calcium silicate hydrate (C-S-H) gel that was formed, the absence of residual GP and a minimum of excess CH. Portland cement (PC) specimens with 20 to 40 wt.% replacement by the 60/40 pozzolan were characterized for porosity and compressive strength at aging times from 3 to 28 days. The PC with 20 to 40 wt.% pozzolan had slightly increased porosity due to an increased amount of unreacted water from the batch. The porosity decreased with increased aging time. The PC with 30 wt.% pozzolan had a compressive strength equal to the reference PC, but only after 7 days or longer of aging. This was likely due to the slower reaction rate of the pozzolan. The 60/40 CH/GP pozzolan appears to be a viable partial replacement for PC when used at 30 wt.%.

Additive manufacturing of cellular structures from recycled soda-lime glass printing inks by robocasting

The robocasting technique has shown great potential due to its versatility, allowing the fabrication of custom-shaped, dense or porous structures, through layer-by-layer deposition. The technical feasibility of robocasting depends on rigorous control of the rheological properties of printing inks, which needs to have fluidity for pumping and plasticity for extrusion/printing, while being able to withstand the weight of overlapping layers. The aim of this work is to produce cellular glass structures by direct printing (robocasting) using bentonite to overcome the lack of plasticity of glass powders. Ceramic inks containing recycled glass powders (d50 < 4 μm) and bentonite (6.5–9.5 wt%) were blended and printed using a 1.60 mm printing nozzle at a printing speed of 10 mm/s. The three-dimensional structures were dried at room temperature for 24 h and then fired at 700 °C for 1 h at a heating rate of 10 °C/min. The components obtained from recycled glass showed porosities of up to 53%, pore sizes between 1090 and 1870 μm and compressive strength of ∼18 MPa.

Thermophysical Properties of Cement Mortar Containing Waste Glass Powder

This study aims to provide a thermophysical characterization of a new economical and green mortar. This material is characterized by partially replacing the cement with recycled soda lime glass. The cement was partially substituted (10, 20, 30, 40, 50 and 60% in weight) by glass powder with a water/cement ratio of 0.4. The glass powder and four of the seven samples were analyzed using a scanning electron microscope (SEM). The thermophysical properties, such as thermal conductivity and volumetric specific heat, were experimentally measured in both dry and wet (water saturated) states. These properties were determined as a function of the glass powder percentage by using a CT-Meter at different temperatures (20 °C, 30 °C, 40 °C and 50 °C) in a temperature-controlled box. The results show that the thermophysical parameters decreased linearly when 60% glass powder was added to cement mortar: 37% for thermal conductivity, 18% for volumetric specific heat and 22% for thermal diffusivity. The density of the mortar also decreased by about 11% in dry state and 5% in wet state. The use of waste glass powder as a cement replacement affects the thermophysical properties of cement mortar due to its porosity as compared with the control mortar. The results indicate that thermal conductivity and volumetric specific heat increases with temperature increase and/or the substitution rate decrease. Therefore, the addition of waste glass powder can significantly affect the thermophysical properties of ordinary cement mortar.

Synthesis and additive manufacturing of calcium silicate hydrate scaffolds

A Calcium silicate hydrate (CSH) powder containing above 60 wt% xonotlite (remaining being tobermorite, scawtite and calcite) were produced from lime and ordinary recycled soda-lime glass via simple hydrothermal synthesis route. The thermogravimetric analysis demonstrated only ~20%weight loss up to 800 °C (at about the transformation temperature of CSHs to wollastonite), reaching a plateau in the 800–1200 °C temperature range. The synthesized CSH powder was employed for the fabrication of both green and heat-treated scaffolds by additive manufacturing (AM), possessing a high porosity (>80 vol%) and limited strength (~0.9 MPa).

Cold sintering of soda-lime glass

Ordinary recycled soda lime glass powder was densified via cold sintering process with the aid of concentrated NaOH solution. Increase in processing time, temperature and concentration of the NaOH solution resulted in the formation of monolithic glass artifacts with higher relative densities. The sample densified the most (95.2%) was obtained when the sintering was performed at 250˚C with a 20 min dwell time using 15 M NaOH solution.

Waste-derived glass-ceramics fired in nitrogen: Stabilization and functionalization

In a circular economy perspective, waste-derived materials are attractive once the adopted manufacturing technology combines low costs, absolute stabilization of pollutants and interesting functionalities of the product. This paper deals with the enhancement of chemical stability and functionalities of highly porous glass-ceramic foams, from vitreous residues the plasma processing of municipal solid waste (‘Plasmastone’), by firing in nitrogen, at 800–1000 °C. Before firing, the processing relied on alkali activation of glass suspensions, followed by intensive mechanical stirring. Previous experiments had demonstrated that the stabilization of pollutants could be achieved only by mixing Plasmastone with 30 wt% recycled boro-alumino-silicate glass, in samples fired in air. The change in the atmosphere had a significant impact on the Fe2+/Fe3+ balance, leading to a different phase assemblage, in turn causing the stabilization of pollutants even operating with more common recycled soda-lime glass. The new phase assemblage also promoted functionalities such as electrical conductivity, relative permittivity and electromagnetic shielding effectiveness.

Performance of recycled soda–lime glass powder in mitigating alkali–silica reaction

Recycled soda–lime glass powder (SLGP) is a valuable supplementary cementitious material. However, it has a high alkali content, and its effectiveness in mitigating the alkali–silica reaction (ASR) is uncertain. In this study, the ASR performance of SLGP was evaluated using the accelerated mortar bar test (ASTM C 1567) and the concrete prism test (ASTM C 1293). It was determined that a sufficient dosage of SLGP can mitigate ASR according to ASTM C 1567, and that finer SLGP is more effective. Meanwhile, the 2-year concrete prism test showed that the same type, fineness and dosage of glass powder as tested by C 1567 does reduce ASR, but not sufficiently and below the ASTM failure threshold. Pore fluid composition monitoring revealed that SLGP, over time, serves as a net contributor to the pore solution alkalinity, but these alkalis are released slowly. Overall, SLGP can reduce ASR, albeit insufficiently and temporarily. This ASR reduction is likely through a combination of reduced pore solution pH at early ages (due to cement dilution) and reduced portlandite content and transport properties at later ages (due to pozzolanic reaction). Long-term ASR testing is necessary to determine if and at what dosage a glass pozzolan may be able to control ASR sufficiently.

STRONG POROUS GLASS-CERAMICS FROM ALKALI ACTIVATION AND SINTER-CRYSTALLIZATION OF VITRIFIED MSWI BOTTOM ASH

Vitrification of municipal solid waste incineration (MSWI) bottom ash is an effective method to produce a chemically stable glass, with metal recovery. In order to justify the high costs of this process, the vitrified residue can then be upcycled into potential marketable products. In this study, vitrified bottom ash was successfully converted into strong and chemically stable porous glass-ceramics by the combination of alkali activation and sintering. After the activation of the glass in a NaOH solution of low molarity, foams were easily produced by intensive mechanical stirring, with the aid of a surfactant, and stabilized by gelation. The obtained open-celled material was further consolidated by a sintering treatment, at 800-900°C. The addition of recycled soda-lime glass allowed activation at low molarity and sintering at lower temperature, but it reduced the mechanical properties and the stabilization of heavy metals. On the other hand, the increase in molarity of the alkaline solution increased the porosity and also the strength of foams from vitrified bottom ash.

Functional glass-ceramic foams from ‘inorganic gel casting’ and sintering of glass/slag mixtures

Abstract The here described investigation was essentially aimed at exploring the chemical stabilization and reutilization of iron-rich slag from copper metallurgy, by the manufacturing of glass-ceramic foams. The foams were developed according to a new method, recently reported for pure recycled soda-lime glass. Mixtures of soda-lime glass/slag powders (with slag content ranging from 10 to 30 wt%), suspended in alkaline aqueous solution, underwent progressive low temperature (80 °C) hardening, owing to the formation of hydrated calcium silicate compounds (C S H). Before complete setting, an extensive foaming could be achieved by vigorous mechanical stirring, with the help of a surfactant. After foaming, glass/slag mixtures could be sintered at 800–1000 °C; the mutual interaction caused an extensive crystallization, with precipitation of Ca Fe silicates and iron oxides (hematite and magnetite), promoting the mechanical properties (up to 4.4 MPa, with a porosity of about 80%). Leaching test confirmed the stabilization of pollutants, from the slag, in the final ceramics. Owing to the separation of iron oxides, particularly magnetite, the newly obtained foams exhibited a ferrimagnetic behavior, that could be exploited in electromagnetic shielding applications.

Development of a glass-ceramic glaze formulated from industrial residues to improve the mechanical properties of the porcelain stoneware tiles

In this research a mixture of 90%wt of industrial residues (recycled soda-lime glass and ashes from a coal power thermal plant) have been vitrified for their use as “secondary raw material”. Then, a glaze suspension was prepared to be applied on the porcelain stoneware tile. The tested pieces have been fired by a conventional porcelain cycle at 1180 °C of maximum temperature. The XRD, XRF, SEM/EDS and the dilatometric analysis have been the instrumental techniques used to characterize the material. Finally, an ecological glass-ceramic glaze perfectly fitting on porcelain ceramic tile has been produced, exhibiting a unique phase, anorthite, which ensures a high flexural strength (around 96 MPa) and a significant Vickers microhardness of 250 GPa, improving the mechanical properties of a conventional the porcelain ceramic tile.

Optimising the bioreceptivity of porous glass tiles based on colonization by the alga Chlorella vulgaris

Green façades on buildings can mitigate greenhouse gas emissions. An option to obtain green facades is through the natural colonisation of construction materials. This can be achieved by engineering bioreceptive materials. Bioreceptivity is the susceptibility of a material to be colonised by living organisms. The aim of this research was to develop tiles made by sintering granular waste glass that were optimised for bioreceptivity of organisms capable of photosynthesis. Tiles were produced by pressing recycled soda-lime glass with a controlled particle size distribution and sintering compacted samples at temperatures between 680 and 740°C. The primary bioreceptivity of the tiles was evaluated by quantifying colonisation by the algae Chlorella vulgaris (C. vulgaris), which was selected as a model photosynthetic micro-organism. Concentrations of C. vulgaris were measured using chlorophyll-a extraction. Relationships between bioreceptivity and the properties of the porous glass tile, including porosity, sorptivity, translucency and pH are reported. Capillary porosity and water sorptivity were the key factors influencing the bioreceptivity of porous glass. Maximum C. vulgaris growth and colonisation was obtained for tiles sintered at 700°C, with chlorophyll-a concentrations reaching up to 11.1±0.4μg/cm2 of tile. Bioreceptivity was positively correlated with sorptivity and porosity and negatively correlated with light transmittance. The research demonstrates that the microstructure of porous glass, determined by the processing conditions, significantly influences bioreceptivity. Porous glass tiles with high bioreceptivity that are colonised by photosynthetic algae have the potential to form carbon-negative façades for buildings and green infrastructure.

Double-layer waste-derived glass-ceramics prepared by low temperature sintering/sinter-crystallisation

Lightweight glass-ceramics with a dense surface layer were produced by a novel sintering approach. The surface porosity of a glass-ceramic body from the direct sintering of an engineered mixture of fly ash from thermal power plants, recycled soda-lime glass and boron waste (residues of the mining and purification of valuable boron containing minerals) was sealed by a glaze, deriving from the sinter-crystallisation of glass powders produced from the same mixture. The use of boron waste, providing B2O3, allowed a substantial viscous flow, for the substrate, even at the relatively low temperature (850–950°C) adopted for a single firing treatment (simultaneous sintering of substrate and sinter-crystallisation of glaze). The dense sinter-crystallised layer, besides imparting improvements in the mechanical properties, was found to feature an enhanced chemical stability.

Fast sinter-crystallization of a glass from waste materials

A glass belonging to the CaO–Al 2O 3–SiO 2 system and corresponding to the melting of a mixture of industrial inorganic waste (feldspar mining residues, lime from fume abatement systems of the glass industry and recycled soda–lime glass) has been successfully transformed into dense and strong sintered glass–ceramics, even for very short holding times (30 min at 960 °C) and a very rapid heating, consisting of direct insertion of pressed fine glass powders in furnace (‘fast sinter-crystallization’). The addition of kaolin clay, conceived as binder for pressed glass powders, proved to positively influence the phase balance, the homogeneity and the degree of crystallization of fast sintered glass–ceramics, thus justifying the achievement of remarkable mechanical properties (bending strength exceeding 100 MPa, micro-hardness exceeding 7 GPa).

Reutilization and stabilization of wastes by the production of glass foams

Glass foams are known to represent highly valuable products for thermal and acoustic insulation, often produced by employing wastes. Although the usage of recycled glass is widely reported for developing the glass matrix, little research has been due to the usage of wastes for the foaming reaction. In this work the cellular structure is achieved after oxidation of SiC-based wastes coming from the polishing of glass articles. The foamed recycled soda-lime glass incorporated the residues from oxidation and provided a reasonably good chemical stability. The addition of MnO 2 to the starting mixtures of wastes led to a certain improvement of the oxidation of SiC, and a complex effect on the correlation between density and mechanical strength. For selected additions, a more homogeneous foaming was found to provide a stronger cellular structure.

Strong porous ceramic made from soda lime glass by an energy efficient process

We report the development of a novel ceramic, made from recycled soda lime glass, which has an unusual microstructure and an interesting combination of properties. It is made by a process which is simple and robust; the glass is powdered, blended with a minor proportion of Ca(OH)2, compacted in a die and cured in saturated steam at ∼100 ◦C. Sophisticated equipment is not needed, and energy requirements are low. We discuss potential applications, and propose the name casamic for this novel calcium, silica ceramic. Green glass bottles were crushed, dry-milled and dry-screened at 150 μm. The particle size distribution (psd) of the product was measured using a Malvern Mastersizer to be 94 mass% <100 μm, 33% <10 μm, 1% <1 μm. The surface area was 0.73 m2 g−1 (BET nitrogen). In a typical synthesis, 100 parts by mass of glass powder was thoroughly mixed with 7–10 parts of commercial grade Ca(OH)2, using a mortar and pastle. Ten parts of water were mixed in at high shear, and the damp powder sifted at 1.4 mm. Portions were placed in cylindrical dies and pressed uniaxially over the range 0.1–200 MPa. The disc of compacted powder was removed from the die and cured in saturated steam within the temperature range 80◦–135 ◦C. After curing, the ceramic (casamic) was allowed to equilibrate in the atmosphere for at least 2 days, before testing. A similar curing procedure has been used [1] to investigate mixtures of Ca(OH)2 and natural pozzolanas. Bending strengths were measured by the “ball-on-ring” method, using a model CK 10 instrument from Engineering Systems, UK. A ceramic disc, 32 mm diameter and 3–10 mm thick, was supported on a ball race, 26 mm diameter, and a 5 mm diameter steel ball was pressed with increasing force into the center of the disc until it fractured. Bending strengths were calculated from the force of fracture using the formula of de With [2], and assuming a value of 0.3 for the Poisson ratio. Figs 1 and 2 show that bending strength increases with compaction pressure, curing temperature and curing time. Other experiments, not reported here, showed that bending strength is relatively insensitive to the type of soda lime glass, the psd of the glass powder, or the relative proportions of glass, Ca(OH)2 and water. It was convenient to adopt a standard procedure of compacting at 50 or 200 MPa and curing at 115 ◦C for 3 h. This resulted in bending strengths of 15–19 MPa and 23–30 MPa for the two compaction pressures respectively. It is instructive to compare these values with the bending strengths of related construction materials (Table I), which were measured using discs of similar TABLE I Bending strengths of casamic and related materials. Earthenware discs were cut from commercial wall tiles. Samples of porcelain were prepared in the laboratory from commercial formulations

Fabrication of cellular structure composite material from recycled soda-lime glass and phlogopite mica powders

A homogeneous composite material with different physical structures has been fabricated from recycled colourless soda-lime glass powders and phlogopite-type mica powders by mixing the two powder components and sintering the mixture at a temperature above 850° C for a period of 30 min or longer. The physical structure of the composite material can be fabricated into either a cellular structure consisting of both closed and open cells or a highly densified ceramic body. The cellular structure composite material is found to have a compressive strength of about 0.877 MN m−2 and thermal conductivity values in the range of 0.290 to 0.306 W m−1 °C−1 when measured at temperatures in the range of 25 to 100° C. The highly densified composite material, on the other hand, is found to have a compressive strength of about 53.0 MN m−2 and thermal conductivity values in the range of 0.198 to 0.250 W m−1 °C−1. The composite material, when compared with other common building materials, is found to be potential material for construction applications because of its superior mechanical and thermal properties.