The demand for sand has crossed sustainable threshold limits, and mindless extraction to keep the supply going cannot continue. Growing environmental degradation caused by mining has buttressed the case for regulating supply. More important, the present crisis imposes a responsibility on the Indian construction industry, which has an annual turnover of about Rs. 384,000 crore, quickly to find substitutes and consider modes of recycling.
Sand is an ubiquitous raw material in construction. It is a cheap and an essential ingredient to create workable mortar and strong concrete. A sturdy floor requires a well laid-out and an even sand bed. Yet, sand is not difficult to replace in this sector; alternatives are available.
The widely accepted replacement for natural sand is M-sand, or manufactured sand. This is produced by grinding stone gravel and also obtained as a by-product. Fine particles are left behind when rocks are cut and broken to make gravel. Instead of dumping them in landfill sites, sensible material manufacturers store, sieve, clean and use it like sand. However, not all rock dust could serve as such a replacement. Flaky dust could affect the workability of mortar, and the presence of chemicals could affect the strength of concrete. Only those particles that meet the specifications of chemical properties, shape and size will qualify.
In cities such as Hong Kong, which produce a considerable amount of glass waste, builders use powdered glass as a substitute for sand. Glass panes and bottles are broken, ground to a suitable size and processed. Singapore, which is perpetually short of sand and depends on South-East Asian countries for it, is looking at copper slag, a by-product of copper production. The Building and Construction Authority of Singapore, a government agency that promotes best practices in built environment, prescribes controlled replacement of sand in concrete with treated copper slag. In the U.S., furnace slag and moulding sand used in foundries are recycled and used as alternatives.
Ravindra Gettu, Professor of Civil Engineering at IIT Madras, finds M-sand the most promising alternative. Substitutes such as crushed glass or recycled copper slag are right now in an experimental stage, he says. “M-sand is reliable, but the quality of supply needs to be monitored and regulated.”
One way to reduce the need for sand is to recycle construction and demolition waste. About 10 to 12 million tonnes of construction waste is generated annually, and only a portion of it is reused. The Municipal Solid Waste (Management and Handling) Rules, 2000, require construction debris to be separated, but it is often mixed with other waste and discarded. Bricks and concrete could be crushed for aggregates. In countries including Australia, concrete and brickwork are reused to lay roads. Discarded gypsum is recycled into gypsum board.
Realising the importance of recycling, the European Union, through its revised Waste Framework Directive, has asked member-states to recover a minimum of 70 per cent of all construction and demolition waste by 2020. Countries such as Denmark salvage about 94 per cent of demolition debris. There are no such benchmarks in India. And there are not enough deterrents for dumping construction waste.
“There is a third way to reduce demand on construction material,” says Professor Gettu. “Most of the structures are designed for strength and not durability. As a result, structures are not used for a long period. By building more durable structures that have extended life, consumption of materials could be reduced.”
Though substitutes for sand abound and recycling methods are available, the industry has not felt the need to adopt them. For sand is still relatively cheap. There are not enough deterrents to check unbridled consumption. On the contrary, even small countries such as Sri Lanka have evolved a national sand policy, seeking to regulate methods of extraction and consumption. There are no such national or State-level targets in India.
Even judicial orders on sand mining are followed more in the breach. If the construction industry does not go for self-regulation and course-correction, the state has to enforce sustainable practices. Green construction is no more an option, but an imperative.