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The Case for Manufactured Sand

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manufactured Sand
Shyam Chander K
Specialist, Market Systems and Entrepreneurship, Terwilliger Center for Innovation in Shelter, Habitat for Humanity International
Deepak Visvanathan
Senior Technical Advisor, Terwilliger Center for Innovation in Shelter, Habitat for Humanity International

Sand in the Indian construction industry

Sand is an important mineral for society; in aquatic ecosystems (rivers and lakes), it supports organisms that are vital to the food chain, protects shorelines and riparian systems; It is used in industry to make concrete, being a vital material for civil infrastructure and housing construction.

In the past few decades, the demand for construction grade sand has been increasing exponentially, due to rapid economic development and growth of construction activities. However, mining and removal of large amounts of natural sand from river banks can have adverse consequences to the environment, as it destroys the habitat of organisms residing in the eco-system, destabilizes river banks and beds, and affects the natural flow of rivers and streams, increasing the risks of floods, destroying bridges and causing crop damage.

In 2017, the annual sand demand in India was of approximately 700 million tonnes and predictions are that this figure will increase in years ahead. Whereas certain regions in India are self-sufficient in the supply of sand, others have a severe deficit of the resource. The construction industry has come to the realization that river sand mining alone cannot meet the needs of the sector in the near future.

The demand and supply gap has also led to illegal mining and selling practices through dubious channels.

Sand ‘mafia’ groups use indiscriminate practices such as mining of sand more than allotted quota, excavation of sand from non-allocated river beds and so on which accelerate environmental damage and create local law and order problems. To address these challenges, sector organizations are looking towards viable and sustainable alternatives to river sand in regions where there is a material deficit and reduced output seasons.

The Terwilliger Center for Innovation in Shelter, a unit from global non-profit organization Habitat for Humanity, partners with relevant stakeholders in the M-Sand value chain to catalyze supply and demand and facilitate market driven solutions to address various constraints and market failures that prevent widespread adoption and usage of M-Sand in all construction activities, including those at the low income group segments and economically weaker sections whose housing construction needs are expected to contribute to more than 95% housing demand by 2022.

Advantages of M- Sand over River or Natural Sand

Sustainable supply of material

Due to a variety of suitable sources and better availability of raw material, M-Sand manufactured from crushed rock is the most desirable fine material for use in construction. River sand, in contrast, is marred with low quality composition in some locations, and existing supply gaps leads to illegal mining and high costs from environmental impact.

High quality

Due to controlled conditions of manufacturing, manufactured sand achieves optimum shape and grade. This is particularly helpful in optimizing cement use. In addition, both compressive strength and flexural strength (bend strength or stress strength of the material) is improved by using cubical aggregates produced. M-sand offers markedly improved workability and reduced bleeding and shrinkage.

Minimum void content

Since the particles of M-Sand are evenly shaped and sized, and fine in nature, the amount of void in the concrete is reduced, making it even more durable.

Purity

Natural sand often contains undesirable minerals and clays, and these can affect the quality of concrete produced. The use of manufactured sand, however, reduces the risk of impurities.

General terminology of types of sand in use

River or Natural Sand:

Sand obtained from river beds and banks is called river, uncrushed or natural sand. These are fine aggregates resulting from the natural disintegration/erosion of rock and deposited by river systems. River sand is viable for all construction activities, such as concrete production, masonry and plastering, as it is naturally graded. As per Indian standard codes set for manufactured sand / M-Sand in National Building Code, sand used in preparation of concrete & in plastering should confirm to IS-383 Zone-II. (Sieve size classification)

Manufactured Sand (M-Sand):

Manufactured sand is produced via crushing of aggregates into finer materials of specific particle size (generally using Vertical Shaft Impactor technology). Since quality control is maintained in the preparation process, the sand conforms to the Zone-II grading standards better. It does not have any organic or silt inclusions.

M-Sand can be further classified as follows:

  1. Crushed Sand

Crushed Stone Sand: Fine aggregates produced by the crushing of hard stones.

Crushed Gravel Sand: Fine aggregates produced by the crushing of natural gravel.

  1. Mixed Sand:

Fine aggregates produced by blending natural sand and crushed stone sand or crushed gravel sand in suitable proportions.

  1. Manufactured Fine Aggregate:

Fine aggregate manufactured from other than natural sources, by processing materials using thermal or other methods such as separation, washing, crushing and scrubbing. Examples are: Iron/steel/copper slag aggregate, Mine OB (Over Burden), Construction and Demolition (C&D) waste etc.

Manufacture of M-Sand

Primary Crusher:

Feed size generally varies from -400 mm to -550 mm.

Secondary Crusher:

The output of Jaw crusher is fed to Secondary crusher i.e. a Cone Crusher. The feed size -150 mm rock is crushed to -40 mm size. Cone crusher consists of two truncated cones with different diameters. These two truncated cones are called Concave and Mantle, which are made of Manganese alloy. Rocks are crushed in between the chamber of Concave and Mantle.

Tertiary Crusher:

This is the final crushing stage, where the output of Cone Crusher is fed to Vertical Shaft Impactor (VSI) through screens. M-sand is produced from the output of VSI as an end product. The VSI crusher, by means of its unique design and action, produces well-shaped fine aggregate particles. The cubicle structure of particles is imparted in the sizing chamber of VSI, making the product most amenable for construction. Usually, -40mm-sized rocks can be reduced to varied sizes, ranging from -20mm to -2mm.

When the stones are processed through the Vertical Shaft Impact Crusher, not only fine aggregates, but also coarse aggregates, another end product, acquire improved particle shape and reduced surface roughness. Manufactured Sand plants ensure better grading of fine aggregates for better particle size distribution. Few plants are equipped with air filter systems and/or washing facilities, which maintains micro fine sand particles (the ones passing 75 micron) 3% by weight.

Washing provides an added benefit of keeping Manufactured Sand wet or in partially wet conditions. This helps reduce the water absorption rate of Manufactured Sand concrete preparation which in turn contribute to the better workability and workability retention.

 

 

Technical specifications for M-Sand

The composition of sand is highly variable, depending on the local rock sources. The most common constituent of sand is silica (silicon dioxide, or SiO2), usually in the form of quartz. VYTGG

An improved and well-functioning M-Sand value chain, adoption of IS standards among all M-Sand manufacturers leading to better quality and consistency, improved accessibility and adoption among end consumers, better skills among construction labour to use M-Sand appropriately and finally better policy environment are vital to meet the growing demand for new constructions and to prevent the natural disasters such as flooding, ecological imbalances created by indiscriminate river sand mining. The size of the housing deficit in India to the tune of 90 million units by 2022and the huge demand for sand required in construction make a compelling case for a market systems approach to help housing and construction markets be more responsive and ecologically sensitive

To advance such initiatives, the Terwilliger Center for Innovation in Shelter is looking to support the M-Sand sector stakeholders with technical knowledge to make the M-Sand value chain more inclusive and sustainable. Manufacturers, distributors and aggregators, professional associations and academics can apply to join the program by sending an expression of interest for a chance to receive financial and technical support, benefiting from Habitat’s expertise and latest findings from on-going research and global best practices.

Fineness Modulus (FM): The aggregate sieve analysis results are denoted in Fineness Modulus.

The latest Indian Standard IS: 383- 2016 “Coarse and Fine Aggregates for Concrete- Specification (Third Revision)” covers the requirements for aggregates, crushed or uncrushed, derived from natural sources, such as river terraces and river beds, glacial deposits, rocks, boulders and gravels, and manufactured aggregates produced from other than natural sources, for use in the production of concrete for normal structural purposes including mass concrete works.

M-Sand for concreting- Its granule thickness/sieve size is 150 Microns-4.75 mm and adheres to IS Code 383:1970

M-Sand for plastering-This is used for Wall plaster and tiling purposes. Its granule thickness/sieve size is 150 Microns-2.36 mm and this adheres to IS Code 1542:1992

M-sand for Brick work-This is used for Masonry, block laying and brick work. Its granule thickness is 150 microns-3.55mm and it adheres to IS Code 2116:1980

M- Sand Quality

Aggregates can strongly influence concrete’s properties, mixture proportions and economy. Therefore, the selection of aggregates is an important process in concrete production. Although some variation in aggregate’s properties are expected, considered characteristics include:

  • Grading
  • Durability
  • Particle shape and surface texture
  • Abrasion and skid resistance ·
  • Unit weights and voids
  • Absorption and surface moisture

Aggregate crushing value (the aggregate crushing value, when determined in accordance with IS: 2386 (Part IV)-1963, shall not exceed 30 percent for concrete for wearing surfaces, such as runways, roads and pavements. 30 percent for aggregate used for concrete other than for wearing surfaces).

  • Aggregate impact value
  • Aggregate abrasion value
  • Soundness of aggregate
  • Testing M-Sand

Crushed sand should adhere to the highest standards, and must undergo the following quality tests:

  • Test for silt and clay
  • Sieve analysis
  • Optical microscopic study to check the particle shape
  • Workability (slump test by slump cone method)
  • Cube test for compressive strength

References

  • https://mines.gov.in/writereaddata/Content/sandminingframework260318.
  • M-Sand for Eco Friendly Development Prof K Srihari HOD Mining, GIET Rajamundry

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