This section provides information on selected materials which are used in products on the website. The process of assessing environmental impact is complex and can potentially include a very wide range of individual impacts. Those considered here include:
| Bricks and Ceramic Tiles | |
Bricks and terracotta tiles are one of the oldest known building materials, dating back at least 6,000 years. The basic material is clay, a widespread and naturally occurring material to which water, and sometimes sand or slag, is added to make it workable. The formed clay is then fired in kilns at temperatures of up to 1000 degrees Celsius. Energy use for brick manufacture is considerable and increases steeply as firing temperatures increase. As fired clay is a durable material, recycling of bricks and tiles is both possible and desirable, especially where bricks are re-used for facing purposes, which requires higher firing temperatures. However, recycling is only really economic if lime mortars have been used.
Vitrified ceramic tiles are fired from dry pressed clay, often with ground white clay (kaolin) added. The product is fired until vitrified and can be glazed. Both firing and glazing are energy-intensive processes. Recycling of ceramic tiles is impractical. However, certain products contain a high percentage of process waste, which helps to reduce the energy content of manufacture.
| Concrete | |
Concrete consists of approximately 53% gravel, 26% sand, 14% cement and 7% water. Quarrying of gravel and, to a lesser extent sand, have ecological implications because of their impact on landscapes, often in areas of natural beauty, and the impact of transport and waste disposal operations. Portland cement manufacture, from lime with added sand and clay, is energy-intensive since firing temperatures of up to 2000 degrees Celsius are required. This process also releases carbon dioxide (CO2) and is therefore a contributor to global warming.
Use of recycled aggregate made from crushed brick and concrete is possible in casting of concrete slabs for house foundations. In parking spaces, crushed Portland cement concrete can replace up to 20% of the gravel.
Lightweight pre-cast concrete blocks made from cement, sand and lime are a widely used structural material and can contain a large propor tion of PFA (Pulverised Fuel Ash / Fly-Ash). This is a waste material from power-stations burning fossil fuels.
| Plastics | |
Plastics (synthetic materials) are very widely used in construction because of their low weight and great durability; all are currently derived from petroleum, and many require substantial energy input in conversion to raw synthetics.
| Thermoplastics | |
Common thermoplastic materials are polyethylene (PE) and polypropylene (PP), which are obtained by a polymerisation process from the semi-manufactured products ethylene and propylene. The additional pollution caused by this process is minimal, and few, relatively harmless additives are required. Thermoplastics are also easily recyclable.
| PVC | |
Polyvinyl chloride (PVC) is a synthetic material in common use for drainage, window and flooring applications. It is manufactured from ethylene and from chlorine, resulting in ethylene dichloride, whose production process creates large amounts of toxic waste containing dioxins and organochlorines. Many other chemicals are added to PVC as stabilisers, plasticisers, fillers etc; these include the phthalate DEHP, and the heavy metal cadmium, which is usually added to PVC for outdoor use as a stabiliser.
Recycling of PVC is mainly limited to production waste, there being few if any collection systems in place for post-consumer waste. However there are a number of recycled PVC products listed on this website
The environmental pressure group Greenpeace (1) have called on those making decisions about building materials to specify products made from alternative materials because of the dangers of environmental contamination. It should be noted that the British Plastics Federation (2) considers that the environmental impacts referred to above are outweighed by the material’s performance as a product in use, and because its low weight means that less energy is consumed in transportation.
Specifiers thinking of making use of PVC are advised to consider whether or not alternative materials with lower environmental impact will meet their needs. If not, this website provides information on recycled PVC products for external cladding, sheet piling, window cavity closers and floor tiling. Alternatives to these products include timber cladding, steel piling, steel and thermoplastic cavity closers and linoleum and rubber floor tiles (the last product is listed on this website).
| Steel | |
Essential materials for the production of steel are coke (made from coal) and iron ore, whose extraction has ecological impacts due to the strip-mining process. Steel production also results in the emission of greenhouse and acid rain-contributing gases. However steel is easily recycled; while steel produced in the UK only contains around 16% recycled content, the recycling rate is a more important factor in Life Cycle Assessment. Because steel-making in Europe and elsewhere can make use of 100% recycled steel, in turn the UK recycling rate is high. The use of recycled steel means a reduction of about 30% in energy use for primary production.
| Aluminium | |
Aluminum’s principal constituent is bauxite, which is strip-mined, and can cause habitat degradation. The use of large amounts of electricity are indispensable to its manufacture, and this results in very high levels of embodied energy, and CO2 emissions per tonne of product approximately twice that of steel. However much aluminium is recycled in the UK, and making use of recycled aluminium in the production process results in an energy saving of 80-95%.
| Cellulose Insulation | |
Cellulose fibre insulation is made from processed waste paper, usually treated with borax for fire and insect protection. Because of the low intensity production process it has a much lower embodied energy content than most other insulation products. No research has been carried out on toxicity, and potential respiratory impact, but these risks are thought to be low. The product is inherently recyclable.
Glassfibre InsulationSand, limestone and other ingredients are heated to 1350 degrees to make glass fibre. Embodied energy content is about half that of plastic insulation products such as polystyrene and polyurethane, but in turn is over three times higher than mineral wool, and about five times higher than cellulose. A concern is the creation of potentially carcinogenic small fibres which can lodge in the body, although risks to workers can be minimised with appropriate controls.
| Wood and Wood Products | |
Wood is one of the most flexible and adaptable construction materials. It is very widely used in solid form for purposes such as carcassing, trimming, flooring and fittings. It is also increasingly used in wood panel form for many functions such as wall and roof construction, flooring and fittings such as cupboards. Wood panels include such widely known materials as MDF (Medium Density Fibreboard) and chipboard, and are made from wood chips and / or sawdust, which are bound together with resin under high pressure.
Wood is also inexpensive compared with other materials and widely available. The increasing volumes used (approximately 50 millions cubic metres were used in the UK in 1990) have led to wide concern about the destruction of forest habitat and its impacts on plant, animal and human lives in all climate zones of the world. As a result, a number of schemes which certify wood and wood products as being of sustainable origin have been set up, of which the best known is that operated by the FSC (Forest Stewardship Council) (3).
Clearly re-use of wood products such as doors, windows and structural timber, instead of products made from new wood, is beneficial in terms of its saving in energy and resources. A range of such products will be found on the Salvo website.
| References | |