What is clay?
Clay is one of the oldest building materials known to man. It is a naturally occurring aluminium silicate mostly made up of fine-grained minerals. Depending on soil content, clay can vary in colour from dull grey to rich vibrant red colours. When water is added clay exhibits elasticity, allowing it to be shaped and moulded.
Clay can be moulded into bricks which become firm as they dry. If it is fired in a kiln, permanent chemical changes occur causing the clay to become ceramic. This method is used to produce ceramic pottery and modern kiln-fired bricks. Model showing how rammed-earth walls are constructed.
How is clay used?
Throughout history clay has been used for a wide variety of applications. Clay has been used to create pottery and writing tablets since the earliest known human civilizations. It is still commonly used in pottery today, especially in the developing world. Historically clay has been used for various medical applications, including wound treatment and controlling diarrhoea.
As a building material, clay has an especially important place in human history. Some of the earliest known mega-structures in the world, the Sumerian Ziggurats, were built using clay ‘mudbricks’. These bricks are hand shaped and left to dry in the sun. In south Asia mud brick houses have been in use since 7000BCE. Other ways of using clay as a building material began to emerge soon after.
Rammed earth has been used as far back as 5000BCE along the Yellow River in China. Building rammed earth walls involves compressing a damp mixture of sand, gravel and clay into an externally supported mould to create either a solid wall or individual building blocks. Walls built in this fashion are sturdy, incombustible, highly insulative and can last for hundreds or even thousands of years.
Construction methods using unfired clay have become less popular in the 20th century as costs for modern materials such as steel, concrete and kiln fired bricks have decreased. Modern kiln fired bricks have much different qualities to traditional sun-dried bricks, but still use clay as a primary material.
Who uses clay?
Ancient civilizations on every inhabited continent used clay as a primary building material. Today fired clay bricks are still a primary construction material across the globe, especially for homes. This is the case in both advanced and developing nations, including Australia. Usage statistics for clay are not readily available, but it is widely accepted that China is currently the world’s biggest consumer. Most of this consumption is used in the production of kiln-fired bricks for domestic construction.
Some remote communities in developing nations still build homes using non-fired clay bricks or rammed earth techniques, which have been popular through-out history.
Where does clay come from?
Clay is found in abundance all over the globe and most countries use clay to produce bricks for domestic construction purposes. On a global scale the largest use of clay is in fired brick production, which is highly concentrated. About 75% of global fired brick production occurs in just four countries:
- China produces 700-800 billion bricks a year, roughly 54% of global production
- India produces 140 billion bricks a year, roughly 11% of global production
- Pakistan produces 100 billion bricks a year, roughly 8% of global production
- Bangladesh produces 50 billion bricks a year, roughly 4% of global production
Interesting facts about clay:
- Clay tablets were the first known writing medium, inscribed with a stylus made from reed.
- The first forms of ceramic were sintered clays.
- Artefacts found in Yuchanyan Cave in China provide evidence that humans were using clay as far back as 15,000BCE.
For more information, visit our Mining and Metals
Image courtesy of Wikipedia.