GlassPass Background

Updated: Jun 23, 2020

Why is glass so special?!

Throughout centuries glass material has been altered to serve humankind in various ways. It has the abilities to be remoulded and re-created countless times to serve a different purpose.

Current Issue – Sand Wars [1]

Sand is the main material that modern life and modern cities are made. It is used to make concrete, glass, asphalt, porcelain, silicon chips, etc.

Despite having being used for construction since at least the ancient Egypt, it was the advent of the modern industrialized world that brought with it a colossal scale use of sand, as it became the key material to create mass-manufactured structures and products demanded by a fast growing population.

This widespread use of sand in modern life is making us start running out of it, as though the supply might seem endless, usable sand is a finite resource like any other. (Desert sand generally doesn’t work for construction; shaped by wind rather than water, desert grains are too round to bind together well.). It is estimated that nearly 50 billion tons of sand and gravel is consumed every year, being the 3rd most used natural resource, after air and water.

The ever increasing demand for sand is resulting in riverbeds and beaches around the

world being stripped bare. Farmlands and forests are being torn up. And people are being imprisoned, tortured, and murdered, over sand and sand mining.

In India, sand miners are taking control over communal lands on river floodplains that used to be mostly agricultural and are stripping away the topsoil to dig up the sand built up by centuries of floods. The sand mining affects not only the area where it is extracted but also the surroundings, as the dust kicked up by the operation stunts the growth of surrounding crops.

The fact that sand mining is illegal in some of these locations doesn't stop the miners to take over the lands. Despite pledges to the police, government officials and courts nothing has been done to stop the mining. Local authorities are believed to either being bribed or to be involved in the business themselves.

And the few people that try to stand against the miners end up paying with their lives or ending up injured, and that includes police officers, government officials and whistleblowers.

India's scenario may be the most extreme, but large-scale sand extraction happens in dozens of countries.

One way or another, sand is mined in almost every country on Earth, but the supply of sand that can be mined sustainably is finite.

Depletion of sand is one of the biggest challenges in glass productions. As sand is overused in the construction industry, it becomes crucial that we find new sustainable solutions from our raw materials to the products we make in the glass industry.

Sand quarries [2]

Applications of Glass

  1. Variety of applications of glass and historical use of this material including composition

  2. It is used as stained glass windows, some of most historical uses as vessels, seeing glasses

  3. Today is broadly used in different industries as windows, external walls, insulation, fibre cable, photovoltaic panels, medical and laboratory equipment, windshield screens, etc.

Glass has changed the world like no other substance, and it’s present in our everyday life in things that range from reading glasses, to packaging or fibre optic cables, etc. but people usually overlook it and its potential as a sustainable material due to its possibility to be re-melted endlessly.

Domestic Glass Recycling Facts

  1. The current recycling rate per household is 45% [3] which is currently decreasing.

  2. Glass does not decompose and so it puts a great strain on landfills.

  3. Clear glass bottles contain around 25% recycled glass, whereas green bottles contain as much as 90% recycled glass.

  4. The average person in the UK throws away around 400kg of waste each year only of which 180kg is recycled.

Construction Glass Recycling Facts [4]

  1. 0.6% of construction industry waste is glass waste and equivalent to around 200,000 tonnes million tonnes yearly.

  2. From the glass currently being recycled by flat glass manufacturers, only a maximum of 3% is post-consumer construction glass.

  3. The construction glass waste that is not taken back to glass production is either due to contamination or because of a very onerous and time-consuming disassembling and separation process required

  4. It is estimated that the majority of the construction glass waste in the UK is not recycled back to flat glass. Most of it is downcycled into aggregate, insulation, downgraded to produce glass bottles for packaging or deposited to landfill.

  5. There is currently a disparity the potential of glass as material and it's life span and the short service life of the window and curtain wall systems they're installed onto.

  6. The recycling industry isn’t communicating with local craftsmen and artists in utilising recycled glass cross-country

Current use of recycled glass in the flat glass manufacture

Flat glass manufacturers already use a percentage of cullet in the mix of raw materials to produce glass.

The three primary sources of this cullet are:

  • Pre-consumer internal cullet: rejects or offcuts from the float line

  • Pre-consumer external cullet: from the processing industry including glazing unit manufacturers

  • Post-consumer glass: glass retrieved from refurbishment and demolition

Currently the main source of cullet is pre-consumer internal, followed by pre-consumer external.

From the recycled content used in the manufacture of new glass only a maximum of 3% is post-consumer.

Contamination and sorting to avoid difference in composition (recipe mismatch) are the biggest challenges to overcome in order to increase the amount of post-consumer glass in the flat glass manufacture.

The sorting and dismantling process on site is currently too time consuming and onerous to be seen as viable by demolition contractors and glass manufacturers.

This means that most of the float glass is downcycled into bottles, insulation products, crushed and used for aggregates or sent to landfill.

Current Industry Practice: Grades of culet [4]

Cullet (broken glass returned to the furnace for re-melting) is organised into 3 different grades, according to its quality and purity:

  1. Class A is high quality glass, clear, clean, zero contamination

  2. Class B is from laminated sources, suitable for wool insulation

  3. Class C is used for road pain, crushed sand, ceramic fritted, etc

The below diagram shows the characteristics and common use of each of them:

Grades of cullet. Based on Arup's diagram [4]

How the treatments applied to glass affect its recyclability [4]

The way glass is processed and the different treatments applied impact its recyclability.

From the different processes, laminating and ceramic printing are the ones the currently can't be recycled by flat glass manufacturers.

The laminating process uses interlayers sandwiched between two or more panes of glass, laminated together under heat and pressure. To recycle as the layers need to be separated and the laminate layer removed. This is currently done by a pulverizing and separating machinery, that crushes and grinds the glass into small pieces. These pieces are however too small to be used by flat glass manufacturers.

Screen-printing and digital printing patterns are obtained by fusing ceramic frits into the composition of the glass.

The presence of ceramic frit does not currently allow this glass to be returned and recycled into flat glass.

The different processes and their impact on the recyclability of glass are shown below:

Treatments of glass and their recyclability. Based on Arup's diagram [4]

Environmental impact of glass production

  • High carbon emissions from melting activities and from the raw materials extraction operations

  • Sand depletion

  • High percentage of waste that goes into landfill

Benefits of using glass waste in new flat glass production

  • 1 tonne of cullet saves 1.2 tonnes of raw materials and 0.3tonnes of CO2. [4]

  • Saves natural resources, reduces requirements for mining and quarrying, as well as the associated processing and transportation.

  • For every 10% cullet added to the furnace, 3% less energy is used [3] (Saint-Gobain estimates that their inclusion of 40% cullet has saved 15% energy).

  • Reduction of waste sent to landfill by recycling construction glass in a closed loop cycle.

  • Increases the life of the furnace by up to 30% due to decreased melting temperatures and a less corrosive batch. [5]

Design for recycling and circularity

Recycling, material selection and circular economy principles must be considered from the very beginning of the design process.

Some of the steps that can be taken into more sustainable and circular buildings are:

  • Specify glass with a higher percentage of recycled content.

  • On the specification in demolitions and refurbishment projects, a clause should be included for the glass on site to be sorted, disassembled and stored separately, to then be sent for recycling.

  • Design for disassembly (design having in mind the end of life of the building helps to repurpose its materials).

  • Reuse and repurpose existing glass instead of using new glass (recycling materials should be almost the last resort and using glass with no or low recycled content should be avoided).

  • Design to avoid waste and cut offs.

Moving towards circular economy will involve changes in the way the construction industry works, in which materials are chosen and research and innovation will be needed to find and create materials and construction methods that enable not only recycling but ideally reuse of most of the materials and components of a building. Connections details will need to be revised in order to allow for an easier disassembly without damage of the components in order to enable its reuse, if desired.

The glass and glazing industry must aim for a better sorting of post-consumer glass and its identification in order to retrieve it to plant for re-melting and to ensure that that doesn't affect the quality of the new glass produced. A higher percentage of cullet should also be included in the recipe.

Innovative delaminating techniques must be found in order to allow laminated glass to be recycled and an alternative or a solution to ceramic frit glass recycling must be found.

The glazing industry must aim to make dismantling of windows and curtain wall frame and spacers easier, to make to whole demolition and recycling process of glass more efficient and to address the current disparity between the glass life span and the curtain wall / window system service life.

Case study - Verde SW1 building [6]

Verde SW1 is a major refurbishment project in the heart of central London comprising more than 282,000 sq. ft. of Grade A office space.

The building is the result of a redesign and redevelopment of the former Eland House, by Aukett Swanke, to meet contemporary office requirements.

High environmental targets and the occupant comfort, health and wellbeing were the main drives of the renovation works.

The renovation used 85% recycled glass used for the façade. However, this glass didn't come from the former Eland House building. That glass (less than 40% of the retrieved glass). Most of the glass waste was however crushed with the rest of the construction waste.

As mentioned above, the new façade is made using 85% recycled glass, but that glass was imported from Germany. the same happened with the glass retrieved from the existing building - it was shipped to the EU to be re-melted in bottle manufacture plants as the market for recycled glass in the UK is still too small.

Original building (Eland House), glazing sorting process, and Verde SW1 building. Images from Multiplex.

Verde SW1 in numbers: [6]

  • 9,880 tCO2e reduction in embodied carbon during construction

  • 11,600 tCO2e reduction in embodied carbon achieved by reusing the original concrete structure

  • 55,000 Sq. Ft. of façade glass recycled

  • 340 metric tons of glass recycled

  • 100 tCO2e saved by recycling the façade

  • 85% recycled glass, 100% recycled aluminium & 80% recycled steel were used in the new façade

The diagram [6] below gives an overview of the overall process and also the steps needed on site to ensure a an efficient glass disassembly, sorting and storage, to make it possible to retrieve it to plant.

Glass recycling process for Verde SW1 [6]

Case study - Diana Hernandez

Diana is an artist who uses recycled glass as the material for her works.

Her Waste Labs [7] started as an initiative to create new business models for urban areas to help tackle the problems of business waste, reducing the waste streams to landfills, in response to the Mayor of London Business Waste Policy.

In her Waste Labs project Diana proposes small businesses to contact Glass Lab to book a collection time and date through an app. The Glass lab then sends its electric vehicle to collect the glass. The glass is crushed on site (glass crusher installed on vehicle) and it is reduced to 20% volume, helping collect more glass per run.

The crushed glass is then taken to the Glass lab facilities where it is graded into fine, medium and coarse and added to Diana’s products use bioresin (a biodegradable material used to make surf boards) to manufacture products for public use, such as bollards.

These products are sold to the local authorities to be used in parks and public spaces.

Diana is here targeting small business and commercial application of glass, as currently

42% of businesses don’t recycle glass waste.

Waste Lab process and the bollards made using recycled glass and bioresin [7]

Innovations and research towards a more sustainable glass industry


Rice growing countries are suffering environmental problems due to the large amounts of rice husk (the by-product of rice paddy).

in the process to obtain rice paddy, the rice husk is burnt in boilers.

This process generates annually around 20 million tons of rice husk ash [8], which is disposed of by sending it to landfill. this operation is a great environmental threat, that damages not only the land but also the surroundings of where it is dumped.

Simultaneously the shores are being occupied with quarries, for silica extraction. This operation not only scarres irreversibly the landscape but also releases carbon into the atmosphere.

As rice husk contains 95% silica, this source of is being studied as an alternative to sand to be used in glass production. [8]

The glass resulting from that process has a light grey tone and is ‘heat absorbing’. [8]

Burned rice husk as waste material and rice husk ash [9].


In one way or another, glass blocks/bricks have been used in several buildings.

Research is taking place in TUDelft [5] to develop dry assembly interlocking glass blocks, mad out of recycled glass waste.