There are numerous materials in this world that are by-products of a process or industry and it only takes a little imagination to get them to be of use.
As a fine residue from coal-fired thermal power plants, flyash is a serious health hazard if released into the atmosphere. These days, it is filtered out before the flue gasses are released and then dumped in "ponds". But what's to be done with all this flyash? For one thing, we can make good use of it!
Flyash is a pozzolan - it has cementatious properties. While it can't be used as an alternative to cement, it can act as a good filler for concrete which turns out stronger - and uses less water - than that made with cement alone.
In India, it is usually used to manufacture bricks that are stronger than the traditional terracotta ones; they use less mortar to lay, absorb less water and don't require to be fired in a kiln, thereby not adding to the pollution in the atmosphere.
At a recent project, we used flyash bricks and adding red iron-oxide to the mix. The resultant colour was a pale terracotta that is quite pleasant. Next time, I'll try getting yellow bricks with yellow oxide. The manufacturer's factory is near Virar, North Bombay (Mumbai), but the quality of the last batch of bricks we received deters me from recommending him.
This is the waste from sugar cane once the sugar is extracted. It can be used to make particle boards or other fibre-boards. Unlike wood-based products, it isn't affected by borers. One company, that I know of, which uses bagasse and other agricultural waste products like cotton stalks is Ecoboard Industries based in Pune.
If anyone knows of another company/product that belongs to the same category, please let me know.
Rubber wood is a by-product of rubber plantations that are found over a large part of Southern India. Left to itself, the wood rapidly deteriorates and discolours but, if treated properly, can be used for a variety of purposes - especially in furniture. It has a pale golden yellow colour when given a natural polish. One drawback that needs to be taken into account is the extent of its response to moisture. Since the wood is kiln dried, the moisture content is low when you receive the material but it can react quite alarmingly during the monsoon.
Rubber wood can be got from any of the producers listed here
This is a product that, I have to admit, I haven't used. Yet! I've seen the samples though and what's so appealing about it - apart from the fact that it's made from waste coconut husk - is the wonderful dark natural colour.
The company that manufacturers it, Natura Fibretech Pvt. Ltd, is in Bangalore, so getting a small quantity to Bombay works out much too expensive.
This is not something that can be used on a regular basis or in large quantities but, when one is doing a plinth backfill, it makes sense to use debris from some other construction. Every little bit helps. The tragedy of places like Bombay is that this debris is being systematically dumped by unscrupulous builders into our vanishing mangroves.