Why Manufactured Sand (also known as M Sand or Crushed Sand) is Required?
Nowadays huge construction projects are very common due to globalization, urbanization and industrialization. The technological advances have made it too easy to achieve this. Concrete has become a major construction material and is in huge demand. This has led to an increase in demand for sand which is one of the most important constituents of concrete.
On one hand, its demand is increasing, while on the other hand, the supply of natural sand is limited. On top of that, the mining of river sand has led to many environmental disasters. Hence an alternative is a must.
- Due to mining of sand from the river bed, groundwater level of water has gone down thereby reducing the water head. As a result percolation of rainwater in the ground is less.
- Due to excess sand being taken from the river, the areas near the river such as river banks face a lot of soil erosion.
- As the supply of natural sand is limited, it increases the material cost, and even then, its constant supply cannot be ascertained.
- In many parts of the world, river sand is not graded correctly and due to this there are excessive amounts of silt and organic impurities in it. This harm the durability of concrete.
Normally, cement and other aggregates are factory made building materials and therefore, their quality and standards can be easily calibrated. But sand is obtained from the river beds or river banks. 35% volume of concrete is comprised of sand. In the process of trying to fulfill the increasing demand of sand, natural sand is getting depleted at an alarming rate and this creates an adverse impact on the environment in many ways as well.
Under such circumstances, there is an urgent need to find an alternative for river sand which can act as a long-term replacement for it. The manufactured sand (M Sand /artificial sand /crushed sand) is an alternative, which has been tried globally and has proved to be successful.
What is Manufactured Sand (M Sand/ Artificial Sand /Crushed Sand)?
The manufactured sand is produced by various crushing equipment like cone crusher, impact crusher, roll crusher etc. and is a better substitute to river sand for concrete construction. It is produced from suitable stones such as hard granite stone and it is produced by crushing them. The artificial sand is of cubical shape with grounded edges. But it must have proper gradation.
M sand should have particles size varying from 150 microns to 4.75 mm in proper proportions. This is because until fine particles are in proper proportion, sand will have more voids, and the requirement of cement would be more.
Different Names of M sand?
M sand is popularly known by different names such as Manufactured Sand, Crushed sand, Artificial Sand, Pozzolan sand, Crushed Stone Sand etc.
Indian Code Recommendations for Various Uses of M Sand / Crushed Sand:
- Concrete M-sand/Sand IS Code: IS 383 1970
- Blockwork M-sand/Sand IS Code: IS 2116 1980
- Plastering M-sand/Sand IS Code: IS 1542 1992
Advantages of M Sand (Manufactured Sand):
01. Cost Effective:
Crushed sand can be manufactured in areas near the construction sites such as nearby quarries. This can bring down the cost of transportation and will provide an assurance for constant supply of sand at reasonable prices.
02. Lesser Impurities:
M sand is free from impurities such as silt content, clay particles, organic compounds or other soluble compounds which affect its strength and the durability.
03. Good Mechanical Properties:
Manufactured sand gives,
- Better crushing strength
- Higher flexural strength
- Good abrasion resistance
- Better bond with the cement as compared to the round particles of natural sand, this is because artificial sand has sharp edged particles.
- Crushed sand has denser particle packing than natural sand, so the unit weight of crushed sand is higher natural sand and it also has lower permeability as compared to natural sand.
04. Compliant with the Standard Guidelines:
Crushed stone sand can be used as fine aggregates in screed and concrete mixes, in accordance with the standard guidelines, i.e. as per Indian standard – IS 383:1970, European standard – EN 13139. Crushed sand can be used as a partial replacement or as a blended mixture with natural sand.
Usage of M sand reduces or prevents dredging of river beds. Dredging leads to environmental disasters as discussed earlier, i.e. groundwater depletion, erosion of soil on land, etc. Thus, manufactured sand or crushed sand is much eco-friendlier than river sand.
Disadvantages of M Sand – Manufactured Sand:
01. Issues of Workability:
Natural sand is smooth and round due to natural gradation, while the same is not the case with M sand. Hence, more water and cement are required to achieve the desired workability of concrete which leads to an increase in cost.
02. Specialized Knowledge and Technology Requirement:
Production of manufactured sand involves processes such as fine crushing and separation which requires specialist knowledge and technology. To ensure that the M sand is appropriate for a purpose or use, it should be ensured that it passes a series of quality tests such as:
(I) Sieve analysis test.
(II) Optical microscopic study to check the particle shape.
(III) Workability test such as Slump test, Compaction Factor test
(V) Adulteration Test
General Requirements of Crushed Sand:
According to ‘Dr. Aswath M U’, Professor & Head of Department Bangalore Institute of Technology,
- The texture of the surface of crushed particles should be smooth, so as to achieve better workability.
- The edges of M sand particles should be grounded.
- The artificial sand should be free from any organic or soluble impurities.
- Silt content in the manufactured sand should not be more than 2 %.
- Only 30 % of the sand should have a ratio of fines below 600 microns.
- The permissible limit of fines is below 75 microns in the M sand and should not be more than 15% overall.
- All M sand particles should have higher crushing strength.
In summary, manufactured sand is the “need of the time”. It is an eco-friendly substitute to natural sand, which can reduce the environmental effects and it also increases compressive strength, flexural strength and durability of concrete. But it is essential to ensure that the M sand is procured from a reliable source and that it has been adequately processed and tested to meet the standard guidelines or required quality specifications.
Image Courtesy: Image 2