USE OF CRUSHED SAND IN CONSTRUCTION AS A SUBSTITUTE OF NATURAL SAND.

Introduction




Natural or River sand are weathered and worn out particles of rocks and are of various grades or sizes depending upon the amount of wearing. Now-a-days good sand is not readily available, it is transported from a long distance. Those resources are also exhausting very rapidly. So it is a need of the time to find some substitute to natural river sand.

The artificial sand produced by proper machines can be a better substitute to river sand. The sand must be of proper gradation (it should have particles from 150 microns to 4.75 mm in proper proportion).

When fine particles are in proper proportion, the sand will have fewer voids. The cement quantity required will be less. Such sand will be more economical. Demand for manufactured fine aggregates for making concrete is increasing day by day as river sand cannot meet the rising demand of construction sector. Natural river sand takes millions of years to form and is not repleneshible.

Because of its limited supply, the cost of Natural River sand has sky rocketed and its consistent supply cannot be guaranteed. Under this circu‎mstances use of manufactured sand becomes inevitable.

River sand in many parts of the country is not graded properly and has excessive silt and organic impurities and these can be detrimental to durability of steel in concrete whereas manufactured sand has no silt or organic impurities



Advantage of Crush Sand


  • Crush sand is easily available in villages and cities and its cost is low due to availability the transportation.
  • Crush sand has a property same as that of Natural River sand i.e. it can be useful for construction as its size, shape is as required. 
  • Crush sand is cheaper than that of natural river sand. The cost of 1brass of crush sand is nearly about Rs 2200. And cost of river sand is Rs 5000. 
  • The concrete with crushed sand performed better than concrete with natural sand as the property of crush sand is better than that of natural sand. 
  • The workability of concrete manufactured with crush sand was lesser than that manufactured with natural sand. 
  • Compressive strength of concrete is increase when we use crush sand because it can not contain any impurity. 
  • Crush sand is free from chemical impurities such as sulphates and chlorides which improves the properties of concrete like strength and durability. 
  • Crush sand contains no organic impurities hence it gives increased strength of Concrete with same cement content. 
  • No wastage in crush sand since Sand is already sieved in the required size (below 4.75 mm). 
  • Crush sand does not harm to the environment in any way as natural sand provide harm causing bank slides, loss of vegetation on the bank of rivers etc.


Comparison between natural sand and crushed sand


Crushed Sand vs. Natural Sand: Make the Right Choice!


A. Shape
  • The shape of Crushed sand is cubical and angular and has a rough texture and hence better for concrete.
  • The shape of natural sand is rounded and has a smooth surface.

B. Moisture content

  • Crushed Sand (Manufactured Sand) has no moisture content.
  • Natural Sand has moisture content. Moisture is generally present in between the particles. Hence, effects the assumptions of concrete mix design and quality of concrete.

C. Concrete Strength

  • Crushed Sand (Manufactured Sand) has higher compressive strength compare to natural sand and it also has more flexural strength.


  • Natural Sand has lower compressive strngth as well as lower flexural strength in compare to crushed sand.


D. Silt Content and organic impurities

  • Crushed Sand (Manufactured Sand) does not contain silt content as well as organic impurities. However screening is not done properly, it may show some stone dust.
  • Natural Sand contains silt and organic impurities as river water contains it due to erosion of soil in its catchment area. Hence it needs washing on site.

E. Over Sized Materials

  • Crushed Sand (Manufactured Sand) is artificially manufactured so there are no oversized materials.
  • Natural Sand has some Oversized materials. Hence needs screening on site.
F. Specific gravity 
  • Crushed sand has specific gravity of 2.7 to 2.9.
  • Natural sand has specific gravity of 2.3 to 2.5.
G. Grading Zone
  • Crushed sand has zone II sand with FM 2.6 - 3.0
  • Natural sand has zone II and III with FM 2.2 - 2.8.



Typical Compressive Strength of Concrete: The following results show the behavior of manufactured sand and riverbed sand when used in concrete:

  • With using River Sand: (All proportions are by weight)
    • Cement -50 Kg
    • River Sand -75 Kg
    • Agg. 20 mm- 75 Kg
    • Agg. 12 mm -37.5 Kg
    • Water -19 ltrs
    Compressive strength achieved after 7 - days curing …….44.1MPa
  • With using Crushed Sand : (All proportion are by weight)
    • Cement -50 Kg
    • Artificial Sand - 70 Kg
    • Agg. 20 mm - 80 Kg
    • Agg. 12 mm - 35 Kg
    • Water - 19 ltrs
    Compressive strength achieved after 7 -days curing …….46.8MPa

Cost comparison of Manufactured sand and River sand:

1. Market rate     900/ Ton       600/ Ton       33% Cheaper
2. In Concrete -  670/cu.m      500/Cu.m   Saves 170/Cu.m
3. In Mortar(1:4)  1580/Cu.m   1050/cu.m    Saves 530/Cu.m


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