G Sreenivasa, General Manager (Business Development), UltraTech Cement Limited Bangalore

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

Manufactured Sand
Manufactured sand River sand

However, many people in India have doubts about quality of concrete / mortars when manufactured or artificial sand are used. Manufactured sand have been regularly used to make quality concrete for decades in India and abroad.

Pune - Mumbai expressway was completely built using artificial/manufactured sand.

Issues with Manufactured Sand
  1. The Civil engineers, Architects, Builders, and Contractors agree that the river sand, which is available today, is deficient in many respect. It does content very high silt fine particles (as in case of Filter sand).
  2. Presence of other impurities such as coal, bones, shells, mica and silt etc makes it inferior for the use in cement concrete. The decay of these materials, due to weathering effect, shortens the life of the concrete.
  3. Now-a-days, the Government have put ban on lifting sand from River bed.
  4. Transportation of sand damages the roads.
  5. Removing sand from river bed impact the environment, as water table goes deeper & ultimately dry.
General Requirements of Manufactured Sand
  1. All the sand particles should have higher crushing strength.
  2. The surface texture of the particles should be smooth.
  3. The edges of the particles should be grounded.
  4. The ratio of fines below 600 microns in sand should not be less than 30%.
  5. There should not be any organic impurities
  6. Silt in sand should not be more than 2%, for crushed sand.
  7. In manufactured sand the permissible limit of fines below 75 microns shall not exceed 15%.
Crushing, Screening, and Washing

Manufactured Sand Manufactured Sand
Rotopactor( Sand Making machine) Vertical Shaft Impactor

Manufacturing of Sand process involves three stages, crushing of stones in to aggregates by VSI, then fed to Rotopactor to crush aggregates into sand to required grain sizes (as fines). Screening is done to eliminate dust particles and Washing of sand eliminates very fine particles present within. The end product will satisfy all the requirements of IS:383 and can be used in Concrete & construction. The VSI Plants are available capacity up-to 400Ton Per Hour(TPH).

Manufactured Sand (M Sand)

Manufactured Sand
VSI Crushed Sand -Cubical Jaw crushed sand -Flaky

Only, sand manufactured by VSI crusher/Rotopactor is cubical and angular in shape. Sand made by other types of machines is flaky, which is troublesome in working. The Jaw crushers, are generally used for crushing stones in to metal/aggregates. Manufactured sand from jaw crusher, cone crusher, roll crusher often contain higher percentage of dust and have flaky particle.

IS Code Provisions

BIS Guidelines IS: 383-1970 for selection and testing of Coarse and Fine aggregates available. Generally, Sand is classified as Zone I, Zone II, Zone III and Zone IV (i.e. Coarser to Finer). There is sieve designation for each zone. Gradation is made in accord with the usage of the sand. There are testing sieves, consists of 4.75mm, 2.36mm, 1.183mm, 600microns, 300 microns, 150 microns and a pan

Typical Sieve analysis: Comparison of River & Manufactured Sand
IS Sieve % of passing(River Sand) % of passing (Manufactured Sand ) Zone II (As per IS:383)
4.75mm 100 100 90-100
2.36mm 99.7 90.7 75-100
1.18mm 89 66.2 55-90
600micron 60.9 39.8 35-59
300micron 17.7 25.5 8-30
150micron 3.1 9.9 0-20
75micron Max 3 Max 15 Max 15
Zone II Zone II
Zone IIZone IINote: The gradation of manufactured sand can be controlled at crushing plant

Technical specification – comparison between Manufactured and River sand
Sl No Property River sand Manufactured sand Remarks
1 Shape Spherical particle Cubical particle Good
2 Gradation Cannot be controlled Can be controlled
3 Particle passing 75micron Presence of silt shall be less than 3%(IS:383-1970)reaffirmed 2007 Presence of dust particle shall be less than 15% Limit 3% for uncrushed & limit 15% for crushed sand
4 Silt and Organic impurities Present (Retard the setting & Compressive Strength) Absent Limit of 5% for Uncrushed & 2% for Crushed sand
5 Specific gravity 2.3 – 2.7 2.5 – 2.9 May vary
6 Water absorption 1.5 - 3% 2 – 4% Limit 2%
7 Ability to hold surface moisture Up-to 7% Up-to 10%
8 Grading zone(FM) Zone II and III
FM 2.2 -2.8
Zone II
FM 2.6 – 3.0
Recommends Zone II for Mass Concrete
9 Soundness(Sodium sulphate-ss & Magnesium sulphate -ms) (5 cycles) Relatively less sound (Ex. >5) Relatively sound
(Ex. <5)
Limit 10% ss and 15% ms
10 Alkali Silica Reactivity 0.002 -0.01 0.001- 0.008 Limit 0.1%expansio

Behaviour of Manufactured & River Sand when used in Concrete:
Sl No Property River sand Manufactured sand Remedies
1 Workability & its retention Good & Good retention Less & Less retention Control of fines & apply water absorption correction, use of plasticisers
2 Setting Normal Comparatively faster Apply water absorption correction, use retarders
3 Compressive strength Normal Marginally higher As shown above
4 Permeability Poor Very poor
5 Cracks Nil Tend to surface crack Early curing & protection of fresh concrete

Cost comparison of Manufactured and River sand:
Sl no Location- Bangalore City River sand Artificial sand Remarks
1 Market rate Rs 1100 per MT Rs 600 per MT 50% Cheaper
2 In Concrete - Rs per Cu‎m Rs 770 – 880 Rs 420 – 480 Saving of Rs 350-400 per cu‎m
3 In Mortar(1:5) for 100kgs Rs 198 Rs 156 20% less

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

  • With using Riverbed 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 Artificial 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

Vastu Aspects of River sand

Now-a-days, Vastu Shastra is more popular, consults Vastu by many people while constructing a house. As per Vastu Shastra, the building material must be free from traces of human or animal body. The river sand contains bones of human beings and animals. The shells are also a kind of bone. It is not easy to take out all such things present in the river sand. Hence, the best solution for this is to use artificial/crushed sand of good quality for human well being.

Environmental Impact

The River sand lifting from river bed, impact the environment in many ways:
  • Due to digging of the sand from river bed reduces the water head, so less percolation of rain water in ground, which result in lower ground water level.
  • The roots of the tree may not be able to get water.
  • The rainwater flowing in the river contents more impurities.
  • Erosion of nearby land due to excess sand lifting
  • Disturbance due to digging for sand & lifting, Destroys the flora & fauna in surrounding areas
  • The connecting village roads will get badly damaged due to over- loading of trucks, hence, roads become problem to road users and also become accidents prone
  • Diminishing of Natural Rivers or river beds, not available for future generations.
Conclusion
  • Considering, the acute shortage of river sand, huge short coming on quality of river sand, high cost, greater impact on road damages and environmental effects, The Construction Industry shall start using the manufactured sand to full extent as alternative, reduce the impacts on environment by not using the river sand.
  • The Local Authorities/PWD/ Govt, shall encourage the use of Manufactured sand in Public Construction Works, if possible, shall make mandatory to use Manufactured sand wherever available with immediate effect.
  • The Govt. Shall come out with, Policy on Sand – encourage the industry people to set up more no of Sand crushing Units across the all Districts, States to meet the sand requirements of the Construction Industry.
References

www.vsicrushers.com

www.robosilicon.com

ICOMAT Report

NBMCW April 2012