Reuse, remanufacturing, recycling: the case of glass for buildings

Glass for Europe

Review of the technical feasibility and sustainability potential of the different end-of-life options for various building glass products

In March 2020, the European Commission (EC) adopted a new Circular Economy Action Plan (CEAP) (COM (2020) 98 final) that promotes greener manufacturing, waste reduction, reuse, remanufacturing, and recycling of construction products. This action plan is part of the EU Green Deal agenda, which aims to support the EU climate neutrality objective and strengthen sustainability practices in Europe.

As expressed in Glass for Europe’s 2050 vision document[1], the European flat glass sector is committed to maximizing its contributions to the EU climate neutrality objective and seeking constant sustainability advances in all its activities.

The adequate end-of-life management of building glass products can be key in advancing these two objectives. For this reason, Glass for Europe issues this paper to shed light on the end-of-life management options for the different types of building glass products. The paper outlines how the different concepts of ‘reuse’ and ‘remanufacturing’ could apply to flat glass products and explains the technical possibilities and challenges of the different options. It also emphasizes the importance of promoting the closed-loop recycling of flat glass, which has the potential to become the most sustainable end-of-life option for much larger quantities of end-of-life flat glass.

1. What is to be understood as reuse and remanufacturing?

Considering that building glass products are covered by the EU Construction Products Regulation[2], the following definitions are used in this paper:

• ‘used product’ means a product that is not waste or has ceased to be waste in accordance with Directive 2008/98/EC, and which has been installed at least once into a construction work, and that:

• has not undergone a process going beyond checking, cleaning or repairing recovery operations, by which the product or components of products are prepared so that they can be used for construction purposes without any other pre-processing; or

• has been subject to a transformative process going beyond checking, cleaning and reparing recovery operations which according to the applicable harmonised technical specification is qualified as non-essential to the product’s performance;[3]

• ‘remanufactured product’ means a product that is not waste or has ceased to be waste in accordance with Directive 2008/98/EC, which has been installed at least once into a construction work, and that has been subject to a transformative process going beyond checking, cleaning and repairing recovery operations which according to the applicable harmonised technical specification are qualified as essential to the product’s performance;[4]

In addition, ‘remanufacturing’ means an industrial process that produces a product from used products where at least one change is made that influences the product’s safety, original performance, purpose or type. The product created by the remanufacturing process may be considered a new product when placed on the market.

Considering the definitions given above, ‘reusing’ a product would mean using it for its original purpose more than once without further processing. Preparing for reuse then means checking, cleaning, or repairing retrieval operations, by which products or components of products are prepared so that they can be reused without any other pre-processing[5].

Glass for Europe recognizes the interest in reusing/remanufacturing flat glass when it is technically achievable and can effectively reduce CO2 emissions during the whole life cycle. There are, however, considerations to apprehend and technical constraints that can limit the potential for reuse and remanufacturing of flat glass products. These are outlined in the following sections.

2. Potential and recommendation for the reuse of flat glass

Glass products for building and construction applications are generally custom-made. The glass product is selected to satisfy legal requirements and the individual preferences of the building owner, considering the building design, usage, climatic zone, etc. The characteristics of the glass (e.g., size, type) are bespoke, except for certain specific applications like glass doors or roof windows where standard glass sizes exist. As a result, a window or a roof glazing suitable for one building is unlikely to be suitable for another building or another location.

The possibilities for reusing are thus limited, and the legal requirements related to the new application need to be carefully checked and compared with the product requirements. From a technical perspective, the elements to be verified when preparing a product for reuse depend on the glass type:

a) Annealed monolithic glass

Monolithic annealed glass can last several centuries, depending on the product’s environmental conditions. However, the glass surface properties may change throughout its life.

Mechanical impacts over a long period of time may result in scratches of randomly distributed length, depth, and orientation that may or may not be visible, depending on the observation conditions. Surface lacerations that may not be disturbing under a certain installation and observation condition may well become obtrusive under other conditions, especially when the glass surfaces are coated.

In case of chemical attacks or deterioration, changes in the surface chemistry will appear. Depending on the type of chemical attack, the surface structure and/or the refractive index at the glass surface may result in colour changes of the reflected light, increased roughness, variations in wettability, haze, or cloudiness.

b) Thermally pre-stressed glass

There are several thermally pre-stressed glass products:

• Thermally toughened safety glass

• Heat soaked thermally toughened safety glass

• Heat strengthened glass

These products have a lifetime that is like the one of monolithic glass.

c) Laminated glass

Laminated glass has a shorter lifetime than monolithic glass as it includes organic interlayers, which, even if not visible, may change the safety and security properties of the products when exposed to UV radiation, moisture or high temperature over a long period.

d) Insulating glass units (IGUs)

The expected lifetime of insulating glass units is 25-30 years. This is because the edges are sealed using organic sealants. Moisture, which permeates through the edge seal, is usually absorbed by desiccants, which are incorporated in the spacer bars, keeping the glass sheets at the desired distance. If the desiccant is saturated, the ingress of additional moisture in the IGU will leach off the inner glass surfaces and possibly attack silver-based coatings. These processes will lead to a deterioration of the product properties and adversely affect the visual appearance of the IGU.

When discussing IGUs, one also needs to ensure that the performance of the product is still adapted for today’s needs. An IGU can be considered “high-performance” and thus adequate for incorporation in buildings from an energy efficiency perspective if it has a U-value of about 1,0 to 1.4 W/m²K in case of double glazing and 0,5 to 0.9 W/m²K in case of triple glazing[6]. Up-to-date insulating glass units usually incorporate coated glass and can be filled with gas, mostly with argon and less frequently with krypton. Both operations improve the U-value and the g-value of the IGUs to allow adequate energy efficiency in the buildings where the IGUs are installed. For gas-filled IGUs, a small percentage of the gas will be lost over time due to permeation through the edge seal. The loss is less than 1% per annum but may deteriorate the U-value of about 0,1 W/m²K after 30 years. Considering these points, even if a used product might have a low U-value (< 1,5 W/m²K), it is most likely unsustainable to reuse it since it will limit the energy performance of buildings.

The market penetration of high-performance glazing is not identical everywhere in the EU and depends on local climates, market availability of products, and national legislation requirements[7]To assess whether the remaining expected lifetime of the product meets the customer’s needs, it is necessary to know at least the year of production and the place of first installation.

The constraints described in this section mean that glass products often cannot be reused, and other end-of-life processes must be considered.