Guest Blogger
Head of Arup Advanced Technology and Research (AT+R) in the UK
A Chartered Engineer and Member of the Institution of Mechanical Engineers, Peter has worked on projects from vibration mitigation through to being a Logistician for a 100 bed hospital in Sierra Leone. He is currently involved in a number of projects related to the electrification of transport and high value research facilities.
Recycling bottles and jars is a concept we are all familiar with. The 750,000tonnes that we put in bottle banks each year goes someway to offsetting the 2 million tonnes or so that we use for containers. Half as much glass (at least 1m tonnes) is used to make ‘flat’ glass – mostly for buildings, but some for vehicles. Recycling is possible, but harder for flat glass. Reducing usage and re-using ‘old’ glass can also mitigate the environmental impact of glass in the construction sector. Graham Dodd, glass expert and Arup Fellow, explains.
In times of austerity it is natural to try to be more economical with materials and right now the theme of materials efficiency is aligned with increasing focus on the embodied impacts of building materials.
Glass is one of the fundamental building materials of the modern age and it seems to have been on a trajectory of “more is better” for many years, as the size of glass panes increase with the development of processing machinery and client budgets. It may be that this trend continues but in the last 12 months a new theme seems to be emerging: ’use less and use it again’.
Using less
Last week, at the international glass trade fair, Glasstec in Düsseldorf, Corning Glass was showing its very thin, chemically strengthened glass for architectural applications. Originally developed in the 1960s for aerospace applications, it is strengthened by a chemical process and has been re-born as a scratch resistant screen for smartphones and display equipment. Being thin (0.5 to 2.0mm) and strong it can be bent elastically, opening up possibilities for new architectural applications.
At the same show, Lisec was promoting its air bed machinery to thermally toughen (temper) very thin glass from 0.9 to 6.0mm. This gave Arup the opportunity to design a sculpture that made use of the size, strength and flexibility of glass in this form. Using two layers of 2mm heat treated glass laminated together into a curved shape and fixed with a new transparent structural silicone adhesive from Dow Corning, the piece looks like a flower or a turbine, depending on your point of view. The nine “petals” are 4.5m tall and up to 1.5m wide, and are stabilised by their curvature and interconnections.
Re-use
I have held a couple of assumptions about the use of glass for a number of years – that old glass from buildings could not be re-used because it is uneconomic to re-process, and that it could not be recycled into new float glass because it would be too contaminated.
But when the time came for Lloyd’s of London to adapt its iconic building to meet higher tenant expectations and to remain competitive as real estate alongside its newer neighbours those assumptions were overturned.
At the time we started the project – designing a scheme to add vision area to the cladding whilst still respecting the building’s grade 1 listed status – there were reports of re-using glass within the Empire State Building. Doing something similar here with the Lloyds building looked to be an interesting challenge but when glass processor and original manufacturer Saint-Gobain Glass experimented with old panes of Lloyd’s glass, they found it easier to cut and heat treat than anyone had expected. Doing this for a total of 1182 bays reduced the cost and time of making new rollers to replicate the original unique light diffusing pattern.
And recycle…
After chemical analysis the 50 tonnes of surplus glass removed from the Lloyd’s building were sent for recycling into new flat glass through a scheme that was already established for factory off-cuts.
So this great example makes me think there is more to be done with less glass, and more value in old glass than we had previously realised. In fact, the big obstacle to re-using materials is often a matter of having the right information about dimensions, composition, properties or condition. As we design new buildings with the advantages of building information models (BIM), maybe we can preserve that information about other materials, to increase their value for re-use.
I had no idea flat glass was problematic to recycle – can anyone explain the precise nature of the difficulty? I’m presuming its something more than contamination?
I was part of a team tasked with developing a “zero to landfill” policy for all office waste disposal for the Company at which I worked. 20 HQ buildings and over a thousand branches made this an ‘interesting’ project. As part of this we visitied several large waste processing facilities, where a large part of waste seperation was automatically done with some very smart machinery. However at one end of the Factory unit was a huge pile of what looked like sand but was in fact ground up bottles etc. I was told there was little demand for re-using Glass and/or bottes so it was ground down and sold as building sand.
The Lloyds glass was not re-melted and remade, rather it seems old panes were cut to new sizes, treated, and re-used. Excellent practice but of little major impact in overall recycling terms.
I understood that glass becomes more brittle with age and for that reason it is difficult to reuse old glass.
I would also expect there to be some contamination of the sand and other raw materials used in glass.
It is also surprising that the reuse of bottles is no longer practised. Empties used to have a value – and not just to the home brewers.
after 40 yrs in scientific glass i can advise that glass will happily be remelted repeatedly so long as there is no contamination that will act as nucleation sites within the atomic structure [glass has an amorphous structure that resists crystalisation] which creates crystals thus becoming opaque.
I would have thought that re-use of flat sheets of glass, even if cut to new sizes, would be preferable over having to melt the glass down again, given the amount of energy required to melt it again.
Similarly, why the modern need to re-melt glass for jars and bottles, rather than sterilizing and re-filling them?
It is an urban myth that glass gets more brittle with age. It is about as brittle as a material can be to start with and its fracture toughness does not decrease with age. It does acquire scratches, which make it weaker over the first few years.
The Lloyd’s glass that we could not re-use was indeed recycled into new float glass because it was handled carefully and screened to avoid impurities.
This is an interesting discussion. It is difficult to recycle construction/demolition glass because currently, it is difficult to collect it without unacceptable levels of contamination. People have tried it a few times – labelled skips have been placed on construction sites and the workers asked to only put glass into it. However, invariably, bricks, stones, drinks cans, metal spacers etc are also thrown into the skips. This is a serious problem because if small pieces of metal etc enter a glass furnace, they will not melt, but will drill holes in the walls and floor, causing very serious damage and potentially leaks. There is also a chemical issue with certain metals making glass weak. These problems are so serious that some glass sites ban all metal drinks cans from their site; drinks can only be sold in plastic bottles. It is also difficult for a recycler to clean up the glass to a sufficient quality within technological and economic constraints. Hence, it is vital to minimise contamination at the source. This has been done successfully a few times. We would like to do more and are looking at this area. Please contact me if you are interested in this field or would like to know more. Thanks. -British Glass