Fine aggregate/Sand

Aggregate is the granular material used to produce concrete or mortar. Sand is a form of silica (quartz) and may be of argillaceous, siliceous or calcareous according to its composition. Natural sands are formed from weathering of rocks (mainly quartzite) and are of various size or grades depending on the intensity of weathering. The sand grains may be of sharp, angular or rounded. Aggregates passing through 4.75mm sieve and retained on 75micron sieve is termed as fine aggregate.

Fine aggregate sand is important ingredient of mortar and cement concrete. Sand particles consist of small grains of silica. It is formed by decomposition of sand stone due to various effects of weather. River sand is widely used as fine aggregate. Fine aggregates are classified as follows: 

1. Source of Origin 
2. Grain Size 
3. Composition

I) Classification according to Sources of Origin

Sand particles consist of small grains of silica (Si02). It is formed by the decomposition of sand stones due to various effects of weather. The following are the natural sources of sand.

1) Pit Sand

This sand is found as deposits in soil and it is obtained by forming pits to a depth of about 1m to 2m from ground level. Pit sand consists of sharp angular grains, which are free from salts for making mortar. Clean pit sand free from organic matter and clay should be used.

Pit Sand

2) River Sand

This sand is obtained from beds of rivers. River sand consists of fine rounded grains. Colour of river sand is almost white. As the river sand is usually available in clean condition, it is widely used for all purposes.

River Sand

3) Sea Sand

This sand is obtained from sea shores. Sea sand consists of rounded grains in light brown colour. Sea sand consists of salts which attract the moisture from the atmosphere and causes dampness, efflorescence and disintegration of work. Due to all such reasons, sea sand is not recommendable for engineering works. However be used as a local material after being thoroughly washed to remove the salts.

Sea Sand

The natural product which is obtained as river sand & pit sand is called sand.

II) Classification Fine Aggregate According to Grain Size

Fine aggregate	Size variation (mm)
Coarse Sand	0.5 – 2.0
Medium sand	0.25 –  0.5
Fine sand	0.060 – 0.25
Silt	0.0020 – 0.06
Clay	<0.002

III) Classification Fine Aggregate According to Composition 

1) Clean Sand 

These are well-graded sand containing quartz particles in a wide range of grain sizes. 

2) Silty Sand 

These are poorly graded, having a considerable proportion of silt and other non-plastic fines. 

3) Clayey Sand 

There is poorly graded sand that has a prominent clay fraction and also plastic fines.

Requirement of good sand

1. It should be hard
2. It should be chemically inert
3. It should be free from salts
4. It should free from organic matters
5. It should be well graded

Uses of sand

1. It is used in mortar
2. It is used in concrete
3. It is used for the filling the gaps between the building blocks
4. It is used as binding materials in the form of paste
5. It prevents the shrinkage of cementing materials.

Alternatives to river sand

Sand is a vital ingredient in making two most used construction materials viz. cement concrete and mortar. Traditionally River sand, which is formed by natural weathering of rocks over many years, is preferred as fine aggregate. The economic development fuelling the growth of infrastructure and housing generates huge demand for building materials like sand. The indiscriminate mining of sand from riverbeds is posing a serious threat to environment such as erosion of riverbed and banks, triggering landslides, loss of vegetation on the bank of rivers, lowering the ground water table etc. Demand for sand is increasing day by day and at the same time mining threats cannot be ignored. Hence, sand mining from riverbeds is being restricted or banned by the authorities like National Green Tribunal, State Environmental Impact Assessment Authority and Pollution Control Board. Hence it is necessary to find and use the alternative for river sand.

Some of the Alternatives to River sand are:

• Manufactured sand
• Processed quarry dust
• Processed crushed rock fines
• Offshore sand
• Processed glass
• Aluminum saw mill waste
• Granite fines slurry
• Washed soil (filtered sand)
• Fly ash (bottom ash/ pond ash)
• Slag sand
• Copper slag sand
• Construction Demolition waste

Manufactured Sand (M-Sand)

Manufactured sand is an alternative for river sand. Due to fast growing construction industry, the demand for sand has increased tremendously, causing deficiency of suitable river sand in most part of the word. Due to the depletion of good quality river sand for the use of construction, the use of manufactured sand has been increased. Another reason for use of M-Sand is its availability and transportation cost. Since manufactured sand can be crushed from hard granite rocks, it can be readily available at the nearby place, reducing the cost of transportation from far-off river sand bed. Thus, the cost of construction can be controlled by the use of manufactured sand as an alternative material for construction. The other advantage of using M-Sand is, it can be dust free, the sizes of M sand can be controlled easily so that it meets the required grading for the given construction.

M-Sand

Advantages of Manufactured Sand

• It is well graded in the required proportion. It does not contain organic and soluble compound that affects the setting time and properties of cement, thus the required strength of concrete can be maintained. 
• It does not have the presence of impurities such as clay, dust and silt coatings, increase water requirement as in the case of river sand which impair bond between cement paste and aggregate. Thus, increased quality and durability of concrete.