Shifting sands of construction

House construction is relying more on manufactured sand as natural sources are diminishing

Why is there a need to replace natural sand?

Sand is typically derived from natural resources such as river beds. But demand has been increasing and natural sources (which take many years to form) are running out. For instance, in Andhra Pradesh, the estimated annual demand for sand was about 200 lakh cubic metres in 2016, while production of river sand was about 100 lakh cubic metres.

In many regions, sand is not readily available and must be transported long distances. Due to the demand-supply mismatch and transportation cost, natural sand is often not available, or is very expensive. Also, illegal mining activities and sand mafias have damaged the environment including change in the natural flow of rivers and higher risk of floods. Hence, we need alternatives to river sand.

What are the alternatives?

Sand can be manufactured artificially from different source materials and through different processes. For example, crushed sand is made by crushing hard stones or gravel. Mixed sand is produced by blending natural sand and crushed-stone/gravel sand in suitable proportions. Manufactured fine aggregates are made from different materials such as metal slag and mine/construction/demolition waste. These are all called manufactured sand or m-sand.

A variant of m-sand is called p-sand or plastering sand, which is just m-sand with finer-grained particles. For instance, m-sand for concreting has a granule thickness of up to 4.75 mm, whereas the one for wall plaster and tiling is finer (thickness of up to 2.36 mm). There is also m-sand for masonry, block laying and brick work.

How does the price of m-sand compare against that of natural sand?

M-sand is typically 40-50 per cent cheaper than natural sand. The current sale price of m-sand (at a plant) is ₹500-600 per tonne. Transportation costs may add ₹300-400 per tonne, depending on the distance, resulting in a total cost of ₹800-1,000 per tonne. In comparison, riverbed sand is priced at ₹1,500-2,000 per tonne (including transportation).

Is m-sand as good as natural sand?

Yes, and in certain parameters, better.

For example, river sand is coarse and may contain high percentage of silt and clay which reduces concrete strength. There may also be higher levels of organic impurities, making it unfit for concrete work. In some cases, it may be adulterated with sea sand which is salty and unsuitable.

In contrast, m-sand made in controlled conditions has the right shape and grade, and optimises cement use. It is also stronger and has lower shrinkage. Washing the sand also provides an added benefit of reducing water absorption in concrete preparation. This makes it easier to work with.

There is also lesser wastage — 10-15 per cent of river sand bought is typically wasted in sieving due to irregular size; m-sand is already sieved to the required size (below 4.7 mm). M-sand has been available in India for over a decade and has been used in areas such as Pune and Bengaluru. The Pune-Mumbai Expressway was completely built using manufactured sand. In fact, the World Bank requires that every project financed by them use m-sand.

Has the government approved its use and given certifications?

As early as in 2002, the State Bureau of Building Materials Industry created a standard (GB/T14648 ‘building sand’) for artificial sand. As per the National Building Code, m-sand used in preparation of concrete and in plastering should confirm to IS-383 Zone-II (sieve size classification), as per Indian Standard Codes. Also, the Indian Standard IS: 383-2016 includes the requirements for natural and manufactured aggregates used in making concrete.

Use of m-sand in construction is accepted in many States and some such as Karnataka and Andhra Pradesh have policies on it. The AP government’s m-sand policy requires that all government engineering departments specify in their contracts that at least half of the total sand is met by m-sand produced from local units (within 50 km radius). Telangana has an online portal to book and transport sand so as to have full monitoring control over the resource.

What should you check when buying/using m-sand?

The key issue is that of quality. Data on Tamil Nadu, where over a third of the daily demand of 35,000 loads of sand is met by m-sand, show that nearly 30 per cent of the m-sand available is of poor quality.

You must check if you are getting true m-sand or replacements such as crusher or quarry dust which looks like m-sand in wet conditions. Look for certified manufacturers in your State. For example, in Tamil Nadu, there were 320 manufacturers who own quarries and crushing units, but only 66 were certified by the State’s Public Works Department for quality, as of September 2018.

Test for dust and silt levels in the m-sand. These can lead to weak compression strength or cracks.

The writer is an independent financial consultant

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