Brick is one of the most commonly used building materials worldwide.
Typically made of a clay mixture and then kiln fired, brick is usually made from local resources and requires straightforward building techniques which have, in most cases, gone unchanged for generations. Kiln firing of bricks greatly strengthens them, but uses vast quantities of wood, coal, natural gas, and other fuels. Brick-making also pumps an average of 1.4 pounds of carbon into the atmosphere per brick, and creates air pollution in developing countries such as India and China.
Alternative options for materials can address these issues, however, while also making use of waste materials.
Cellulose is the component in green plants that gives the cell walls their strength. It’s an abundant and recyclable resource found in hemp, cotton, and wood, and many companies have created bricks from recycled paper, wood, and textiles.
Timbercrete, based in Australia, started in 1994 when potter Peter Collier devised his own formula for bricks. The patented mixture contains cellulose, cement, sand, and binders. The cellulose, from sawdust, makes up about 50 per cent of the mix, and the mixture does not need kiln firing, saving huge amounts of energy and avoiding pollution.
Timbercrete bricks come in a few sizes for use in walls and as pavers, and offer a few significant advantages over standard clay and concrete bricks, including:
- Lighter weight—about half the weight of clay or concrete.
- Higher insulation value at R2.5 for the 250 millimetre brick.
- Carbon sequestration, as the cement in the mix locks up the carbon in the wood.
- Easier to work with, with techniques including nailing, screwing, and using standard woodworking tools.
- Fire rating of FRL240/240/240 at 190 millimetre thick.
Though the bricks are weather resistant, they are not truly waterproof, so the company recommends an exterior sealer, as well as a sealer for the mortar. The company says the overall the price is comparable to standard bricks, but the difference comes down to the design details. For example, neither an interior nor exterior finish coat is needed, which could save substantial amounts of money.
In Hong Kong, more than 3,000 tonnes of construction waste get dumped into landfills daily, along with thousands of glass bottles. Some of those materials, however, are now diverted for use in bricks.
In 2002, Professor Poon Chi-sun of the Department of Civil and Structural Engineering at Hong Kong Polytechnic University began developing a brick paver, Eco-Block, that substitutes waste materials for some of the aggregate, cement, and sand.
The process recycles waste concrete into useable aggregate, replaces 20 per cent of the cement with fly ash, and replaces about half of the sand with recycled and pulverized glass bottles. The mixture is then formed into bricks without kiln firing, saving huge amounts of energy, and decreasing CO2 production by 80 per cent compared to standard bricks.
In addition, the bricks receive a coating of titanium dioxide that reacts with nitrogen oxides emitted by motor vehicles, power plants, and other combustion sources. The titanium dioxide, in the presence of ultraviolet radiation (sunlight), converts the polluting nitrogen oxides into nitrates that are then washed away by the rain.
Eco Blocks are now produced by Laputa Eco-Construction Material Company Limited and sold as Tiostone.
Researchers from Spain and Scotland have developed clay bricks that are 37 per cent stronger than standard clay bricks and do not require kiln firing. By adding wool fibres and a seaweed polymer to normally available clay, the researchers from the University of Seville and University of Strathclyde, Carmen Galán and Carlos Rivera, have created bricks that both perform better and create less pollution than standard clay bricks.
"These fibres improve the strength of compressed bricks, reduce the formation of fissures and deformities as a result of contraction, reduce drying time and increase the bricks' resistance to flexion," the researchers noted.
As the bricks don’t require kiln firing, they avoid one of the most pollution-causing steps in the brick manufacturing process.
Though not yet commercially produced, the researchers continue to work on the project and have published their paper, The Mechanical Properties and Molecular Bonding Characteristics of Clay-Based Natural Composites Reinforced with Animal Fibres, in the Journal of Biobased Materials and Bioenergy.