Environmental performance of glass foam as insulation ...

Environmental Performance of Glass Foam as Insulation ...

Glass foam presents a fascinating solution for utilizing portions of glass cullet that would otherwise end up in landfills. While conventional processes for producing glass foam as building insulation have limitations regarding the purity of the feedstock, implementing an alkali activation process can mitigate these drawbacks. This research employs life cycle assessment (LCA) methodology to evaluate the potential environmental impacts of glass foam created from waste glass via alkali activation in a laboratory-scale facility, adopting a 'cradle to grave' perspective. The system boundaries encompass various phases including the transportation of glass waste, prevention of landfill disposal, the production of glass foam, and the eventual downstream transportation for potential use and end-of-life stages. Data for the life cycle environmental profile of glass foam is compiled using primary data integrated with the Ecoinvent database alongside the ReCiPe impact assessment method, facilitated by SimaPro software.

The findings reveal that the primary contributors to the environmental impacts are linked to the energy consumption during drying and firing, along with the use of surfactants for foaming. Sensitivity analyses indicate that substantial improvements in overall environmental impacts can be achieved by reducing transportation distances both from glass waste to the production site and from glass foam production to its end-use location. Conversely, variations in energy mixes and lower chemical processing temperatures have an insignificant impact on the environmental profile. This research provides valuable insights regarding the upcycling of glass foam production before scaling to industrial levels, highlighting the need for future studies to explore the use of biodegradable surfactants sourced from renewable materials.

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1. Introduction

The alarming rise in resource consumption coupled with increased waste production poses a substantial risk of ecological collapse. Circular economy principles may offer a pathway to tackle this crisis by optimizing resource usage to retain maximum value, thereby reducing both resource inputs (materials and energy) and outputs (products, byproducts, and waste). However, recycling alone may not be sustainable, particularly when downcycling occurs: recycled materials are truly valuable only when they replace virgin raw materials in their second life. As such, recycled materials must demonstrate superior chemical and physical performance. Upcycling poses a significant technological challenge within the circular economy framework, necessitating profitable eco-design solutions.

Recycling, in a strict sense, refers to a closed-loop process that reuses materials in equivalent articles without degradation. Unfortunately, this assumption is often flawed, as recycling typically involves an inherent loss of value, commonly referred to as downcycling—illustrated clearly by examples such as cellulose, which transitions from high-quality office paper to cardboard or PET polymer moving from containers to textile fibers.

Unlike PET, glass does not experience molecular degradation when melted, allowing it to be recycled indefinitely without loss of quality. However, the term '100% recyclable' does not guarantee '100% recycled' status; remelting cullet is contingent upon an expensive preliminary sorting phase that separates glass from other materials. In standard soda-lime glass recycling, the process generally begins with the crushing of containers, followed by segregation of glass fragments intended for remelting from fragments belonging to other materials. This crushing step generates significant quantities of fine particles, enriched in heterogeneities, which remain relegated to landfills. Furthermore, technical challenges, such as fluorine volatilization from fluorine-containing opal glass, can inhibit remelting efforts. The underutilization of discarded glass cullet, often considered industrial waste, underscores a pressing need for innovation. Waste fractions ultimately hold 'negative' value, incurring costs associated with transport and disposal in landfills but can serve as promising feedstock for products that generate sufficient revenue to offset the recovery efforts. Thus, highly porous cellular glasses, or glass foams, present a compelling opportunity for glass waste upcycling.

To quantitatively assess the extensive environmental impacts associated with various products, scientists recommend utilizing multi-criteria assessment methods and life cycle approaches to minimize the risk of shifting burdens across dimensions. Life Cycle Assessment (LCA) is recognized as the most rigorous methodology for evaluating the environmental performance of products, processes, and technologies due to its cradle-to-grave perspective and multi-dimensional impact quantification. Standardized by the International Organization for Standardization (ISO), LCA plays a crucial role in guiding sustainable consumption and production patterns and fostering eco-innovations within the circular economy framework. Over the last two decades, numerous studies have employed LCA to grasp the environmental ramifications of novel products and processes, while also illuminating the origins of various hazards. Furthermore, LCA provides decision-makers with essential information to enhance waste management practices' environmental performance. Within the context of circular economy projects, even though life cycle indicators and circularity measures may diverge, LCA remains applicable for identifying potent circular economy strategies and options. A plethora of literature supports the utility of LCA in R&D and eco-design for assessing the environmental preferability of new materials, optimizing processes or technologies, and spotting supply chain hotspots contributing to overall environmental impacts. LCA is especially beneficial during the early stages of process development, as identifying potential improvements while the process is still in laboratory phase can significantly bolster environmental performance.

The innovative integration of solid waste into building insulation materials resonates deeply with the urgent global challenges of energy scarcity and environmental degradation. LCA provides insights into the environmental implications and performance of construction processes. The integration of insulation materials enhances building energy performance by minimizing heat loss. To enhance environmental benefits further, employing new insulation products derived from recycled materials is highly recommended.

In recent years, numerous studies have surfaced evaluating the environmental preferability of novel insulation materials via the LCA methodology, including investigations of renewable materials or secondary raw materials originating from waste recycling. Despite this progress, only a limited number of studies have explored the environmental impacts associated with glass foams produced from waste glass. Notably, Cozzarini et al. have established that the most significant contributions to environmental impacts stem from chemical consumption and energy demands, surpassing those of more ubiquitous yet less durable polymer-based insulating materials. Additionally, Blengini et al. underscored that sustainability improvements could be achieved by replacing silicon carbide (SiC) as a foaming agent.

As such, this research aims to analyze the LCA impacts arising from glass foams manufactured according to a pioneering method employed at the University of Padova. The focus of this analysis lies in identifying the processing steps that contribute most significantly to the cumulative impact, thereby elucidating the technology's strengths and weaknesses from a life cycle perspective.

1.1. Glass Foam Manufacturing

Glass foams represent a remarkable realization of viscous flow sintering of glass, accomplished at considerably lower temperatures (850–900 °C) in comparison to traditional glass melting (> 1000 °C). The resulting cellular structure arises from gas evolution within a pyroplastic mass formed during glass sintering in the presence of selected additives (foaming agents), leading to decomposition or oxidation reactions. Typical foaming agents include carbonates and sulfates, while oxidation reactions correspond to carbon additives (such as carbon black or graphite). The low-temperature sintering approach permits the incorporation of varying glass powder grades mixed with foaming agents in powder form.

A uniform foaming profile is crucial for cellular glasses. To achieve this uniformity, carbon foaming agents are often supplemented with additives (e.g., sulfates) to provide ample oxygen. Nevertheless, a balance between viscous flow and gas evolution must be established, wherein the firing temperature should sufficiently activate foaming agents without compromising viscosity to prevent gas bubble collapse. If the feedstock consists of uniformly composed glass powders, achieving this balance is relatively straightforward. However, utilizing a mixture of different glass types can create inconsistency in viscosity at the processing temperature, resulting in uneven foam, as depicted in research illustrations.

Fig. 1.

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Scheme of conventional foaming, termed foaming during sintering.

An alternative method has emerged to address these challenges. Through the alkali activation of inorganic gel casting, glass powders transform into pseudoplastic slurries, achieving gelation when immersed in an alkaline aqueous solution. For prevalent soda-lime glass, a moderate alkaline treatment (2.5–3 M NaOH or KOH) prompts the formation of calcium silicate hydrated (C-S-H) gels on the surface of glass particles. Through interactions among surface gels, suspensions transition from lower apparent viscosity (via vigorous mechanical stirring) to higher apparent viscosity (upon cessation of stirring), thus maintaining the integrity of trapped air bubbles. Furthermore, surfactants assist in stabilizing these air bubbles. A robust cellular structure can be established immediately post-drying. Subsequently, thermal treatment at only 700 °C reinforces the bonding of glass particles while releasing additional gas formed from gel decomposition.

Fig. 2.

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Example of glass foam from inorganic gel casting, based on cullet of F-containing opal glass. Left image: after alkali activation, room temperature foaming, and drying. Right image: after firing.

1.2. LCA of Glass Foam

The LCA methodology consists of four phases: goal and scope definition, inventory analysis, impact assessment, and interpretation. Two international standards—ISO principles for LCA application and guidelines for conducting each step—support practitioners in executing comprehensive LCA studies. LCA is frequently employed to quantify the environmental profile of construction material production while assessing buildings' energy performance. In such instances, EN standards must be adhered to for the construction sector.

In pursuit of a circular economy, there has been a focus on recycling waste, such as post-consumer PET bottles, to manufacture new construction materials. In construction, it is common practice to allocate emissions from recyclable products derived from recycled inputs using the cut-off or input-oriented method, prioritizing benefits associated with recycled material use. This approach arises from the extended life expectancy of buildings, which renders future recycling predictions unreliable. Given glass foam's insulation function, various studies on insulation materials have been analyzed. LCA studies of building materials can encompass the entire life cycle of a building or focus solely on the materials used, permitting both cradle-to-gate and cradle-to-grave assessments.

According to international scientific literature, the production of glass foams via waste glass upcycling has been previously examined, with various LCA studies assessing the environmental impacts of different glass foam production methods vis-à-vis other insulation materials. Although the same functional unit to quantify product system performance is requisite for comparative assessments, disparate functional units are often employed to delineate environmental profiles. Some studies attribute area or weight for specific thermal insulation as a functional unit, while others prioritize product dimensions or characteristics. Additionally, leveraging 1 kg of glass foams from waste glass has also been noted as a functional unit in comparative contexts.

A literature review highlights that the production phase consistently remains the focal point in LCA studies, given its differentiation from conventional insulation materials. The energy consumption associated with machinery represents the primary impact throughout a glass foam's lifespan; utilizing renewable energy sources as opposed to fossil-fuel-derived sources can enhance environmental outcomes. Conversely, other life cycle phases of glass foam are often underrepresented in LCA studies. The downstream phase involving the transportation of glass waste from production sites to glass foam production processes is frequently overlooked, yet its impacts can be considerable enough to eclipse the advantages of utilizing recycled glass materials. Furthermore, upstream phases encompassing the distribution and installation of materials in buildings, as well as their end-of-life, are often neglected in life cycle analyses. The use phase is also commonly disregarded, although the environmental advantages of energy savings from glass foam insulation mirror those experienced with other insulation materials.

Consequently, the literature review raises important research questions concerning the LCA of glass foam from waste glass upcycling, advocating for inclusion of both downstream and upstream phases while placing greater emphasis on transport and disposal implications. The contribution of energy consumption warrants further investigation.

Foam Glass: Disadvantages and Advantages of Modern ...

Hello dear readers! How are you feeling? Are you ready for the cold? Have you insulated yourself?

Today, I came across an article that puzzled me. It stated that this winter would be particularly intense, meaning frosty and snowy. On the bright side, this allows for engaging activities like sledding, skating, skiing, and snowball fights. However, the downside is that heating your home will become costly. To avoid being shocked by your heating bill, insulating your home is strongly recommended, and fortunately, there are numerous materials available for this purpose.

I decided to explore what manufacturers offer today. My attention was drawn to the "old new" material—foam glass. Why "old new"? Because it has an impressive 86-year history but has since undergone improvements. Let's delve into the material's characteristics, including its disadvantages, advantages, production processes, costs, and more. Ready? Let's begin!

Cellular Glass: Product Features

A Bit of History

Foam glass was invented by the distinguished scientific worker Isaak Ilyich Kitaygorodsky, who specialized in glass production technology, considering it the material of the future. The invention saw enhancements by US specialists during the 1940s. Initially utilized as a buoyant material, foam glass soon demonstrated remarkable heat and sound insulation properties, being easily glued and processed, leading to its adoption in construction. Canada was home to an early building featuring concrete slabs with a layer of foam glass, reaching a successful outcome. Despite the inventor's commendable effort, foam glass struggled for acceptance in Soviet regions due to high costs and underdeveloped production technology. While foam glass was produced, the quality was inadequate, resulting in factory closures. Fortunately, modern production methods have embraced foam glass manufacture fully.

Concept

Foam glass serves as a heat-insulating material composed of silicate glass and additives that aid gas formation. Insulation is often referred to as foamed or honeycomb glass due to its unique structure.

Production

This heat-insulating raw material is created through powder technology, a relatively straightforward yet time-consuming process comprising several steps:

• Crushing broken silicate glass.
• Thoroughly mixing the glass shards with gas-forming substances.
• Placing the homogeneous mixture on conveyor belts or in molds for oven treatment.
• Softening the glass, transforming it into a liquid yet viscous mixture.
• The mixture undergoes foaming through gas evolution.
• The mixture is allowed to cool slowly.
• The final product is formed into blocks, sheets, or granules.
• The product is further processed according to standards.
• Finally, foam glass products, including blocks, sheets, or granules, are packaged.

In essence, foam glass and standard glass share identical compositions, differing primarily in the presence of gas-filled pores within the foamed product.

Only premium quality materials and innovative equipment are utilized in producing blocks, granules, or sheets, ensuring compliance with European quality standards.

Features of Production

This heat-insulating material is crafted from budget-friendly raw materials, such as fragments and sintered rocks. The production process is both labor-intensive and costly, as granules require heating in specialized forms at 800-900 degrees Celsius.

To manufacture foam glass, the inherent capabilities of silicate glasses to withstand bending, stretching, and compression are harnessed, alongside considerations for sound insulation.

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Foam glass insulation is manufactured using the following steps:

1. Crushing raw materials into a powdered state.
2. Heating and softening the glass powder.
3. Foaming the mass using a blowing agent.
4. Slow cooling of the composition.

Interesting to note! The soundproofing quality of a wall constructed from 12 cm thick brick is practically equivalent to that of a wall made from 1 cm thick glass.

Views

Currently, two primary types of foam glass exist: granular and block. In addition, three types of granular insulation are identified:

• Foam glass gravel.
• Foam glass crushed stone.
• Foam glass sand.

Block insulation also comes in three forms:

• Sheets (standard foam glass).
• Blocks.
• Shells (shaped foam glass).

When comparing thermal properties, it's evident that granular materials are inferior to blocks, sheets, and shells. Nevertheless, granular insulation remains popular due to its relatively low cost.

Varieties of Foam Glass

In the context of individual and urban construction, two types of foam glass insulation are employed:

• Block foam glass—features slab form and cellular structure, targeted for insulating basements, facades, blind areas, inter-floor overlaps, foundations, pipelines, and ceilings. Its non-shrinking nature qualifies it for basic structural applications.
• Granular foam glass—consists of small spherical granules resembling gravel or sand, with sizes ranging from 1 to 20 mm. Utilized for thermal insulation of internal walls, ceilings, and floors.

Despite their operational differences, both forms of foam glass deliver superior insulation and maintain equivalent technical properties.

Scope of Application

Due to its exceptional properties, foam glass finds applications in:

• Private residences.
• Outbuildings.
• Sports complexes.
• Underground structures.
• Industrial buildings.
• Medical institutions.
• Educational facilities.
• Office environments.
• Recreational venues (such as spas and water parks).

The versatility of foam glass as thermal insulation material cannot be overstated:

• For ceiling insulation, a cement-sand mixture is poured onto the attic floor, followed by laying the foam glass boards, which form the base for a reinforcing screed.
• In wall insulation, surfaces are made ready, special adhesive is applied, the product affixed tightly, followed by plastering.
• In flooring applications, a sand layer (3-5 cm) is poured, thermal insulation boards laid, joints sealed, and a screed is then prepared, followed by the installation of floor coverings.

Clearly, foam glass's popularity stems from its commendable technical characteristics.

Properties

Cellular glass is renowned for the following properties:

• Noise absorption—56 dB.
• Water absorption—0.5%.
• Vapor permeability—0.0–0.005 mg/m * h * PA.
• Thermal conductivity—0.04–0.08 W/(m * K).
• Humidity (sorption)—0.2–0.5%.
• Bending strength—0.4–0.6 MPa.
• Compressive strength—0.7–4 MPa.
• Effective operating temperature—-260 to +400 °C.
• Real operating temperature—-260 to +230 °C.
• Deformation temperature—+450 °C.

Based on these data, we can identify notable advantages and drawbacks.

Dignity

This material excels with numerous benefits, including:

1. Safety—free from harmful substances.
2. Environmental friendliness—process utilizes only eco-friendly raw materials.
3. Hygiene—exhibits antiseptic properties.
4. Durability—boasts a service life of over 100 years.
5. Versatility—suitable for insulating any type of building.
6. High adhesion—compatible with various building materials.
7. Biological passivity—resilient against rodents, insects, and microorganisms.
8. Resistance to climatic factors—CDoes not succumb to temperature fluctuations, precipitation, or UV exposure.
9. Robust mechanical properties—maintains structure and properties under impact and high load.
10. Chemical stability—non-reactive with acids.
11. Fire resistance—completely non-combustible.
12. Ease of processing—can be easily cut with standard tools.

Though foam glass carries undeniable advantages, several disadvantages must also be considered.

Foam Glass Insulation Technology

To guarantee the material achieves high thermal insulation quality, strict adherence during installation is requisite:

1. Special glue should be used for affixing the boards, applied uniformly to the board's back and side walls.
2. For uneven surfaces, adhesive may need to be applied in spots to create a level base.
3. When installing on wooden bases, mechanical fastening with dowels is recommended, considering wood's expansion under moisture and heat conditions.
4. When installing slabs on vertical surfaces, use a building level to place the lower plank; a metal profile or rail serves well as supporting strips.
5. Initial board placement should focus on a profile that serves as support; this may be removed after the glue has set; however, it's best to defer removal until all installation is complete.
6. For vertical or inclined surfaces, start from the bottom; for horizontal installations, commence from distant corners.
7. Plates should be laid side by side in alternating rows; once the adhesive cures entirely, it is advisable to fasten the boards further with suitable dowels.
8. Around windows and door frames, install insulation in solid shapes; avoid connecting individual pieces along corner lines.

Foam glass has truly emerged as a high-quality, modern, and lightweight thermal insulation material applicable across various surfaces. Adhering to installation best practices not only optimizes thermal insulation efficiency but also extends the material's lifespan.

Disadvantages

Every material, including foam glass, has its drawbacks. Before committing to purchasing, it's crucial to understand these negative aspects thoroughly:

1. High price point—innovative, high-tech equipment is essential for production, contributing to elevated costs, compounded by substantial energy expenditures.
2. Fragility—despite its strength, foam glass is brittle and susceptible to cracking if installation guidelines are not meticulously followed.
3. Lack of steam permeability—this material is impervious to biological factors, but this can induce moisture issues beneath it.
4. Vulnerability to alkalis and hydrofluoric acid—these substances can destroy foam glass upon contact.
5. Weight—relative heaviness can impact structural integrity in certain contexts.
6. Durability while beneficial—exceeding 100 years, it poses challenges as building materials may not last as long, necessitating insulation replacement.
7. Low mechanical impact resistance—light blows can cause significant damage to foam glass; hence, care must be taken during transport, unloading, and installation.
8. Inability to restore—damaged glass must be discarded, as there is no feasible method for repair.

Ultimately, these properties reflect mixed implications for foam glass, transforming many advantages into challenges.

Main Advantages

Utilizing foam glass as insulation comes with key advantages, such as:

1. Exceptional thermal insulation—attributed to the material's unique structure featuring small closed cells with thin walls.
2. Versatility—can insulate facades, roofs, foundations, communications, walls, and floors, even in high-risk fire environments.
3. Prolonged service life—exceeds 100 years, maintaining performance across temperature fluctuations.
4. Effective sound insulation—10 cm layers can attenuate even loud engine noises, making it suitable for soundproofing as well.
5. Ease of installation—the broad lightweight form allows simple cutting with standard tools, and granules can be laid out easily.
6. Safety—emits no hazardous compounds, thus suitable for residential and public spaces alike.
7. Fireproof—does not ignite, merely melting at elevated temperatures without releasing toxins or smoke.

These advantages underscore foam glass's potential as a premier construction insulation choice.

Price

Foam glass prices can be daunting, typically ranging from $120 to $400 per cubic meter for blocks. Sheets and shells might cost $110 to $350, whereas granular forms can be secured for $35 to $100 per cubic meter.

The question arises—does foam glass insulation represent a sound investment, given its substantial costs and array of disadvantages? Alternatively, it might be worth considering its classification as a material of the future. The choice remains with you, dear readers.

Wishing warmth and comfort to your home; see you on other pages of the blog!

Quote of Wisdom: Reading is the best teacher (A.S. Pushkin).

In spite of the thermal conductivity advantages over foam glass insulation, polyurethane foam encounters its share of criticisms. It typically comes in two forms—rigid slabs and spray-applied on-site. Rigid panels often serve as sandwich constructions, where the primary variation is in the exterior coating material, frequently particle board (OSB) in CIS countries, thereby diminishing fire resistance profile. Conversely, spray polyurethane foam comprises two components mixed right before application, creating difficulties in achieving uniform thickness and surface finish. Plastering directly onto such surfaces are unfeasible without a supporting framework, illustrating its unsuitability for use in facades or on surfaces requiring plastering.

However, the most pressing concern regarding polyurethane foam remains the base compounds, particularly MDI (polyisocyanate), acknowledged as potential carcinogens within European regulations, leading to significant restrictions on industry usage. The slow, incomplete reaction during dual-component production frequently leaves harmful residues, slowly releasing them into the environment and impacting human health adversely.

Additionally, installation challenges abound with PPU, which can complicate facade applications and leave an inherent vulnerability, particularly for materials in direct soil contact.

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