Fine Aggregates | Specific Gravity of Sand / Fine Aggregate
Fine Aggregates for Concrete
Aggregates consist of sand, gravel, and stones, either crushed or and crushed or a suitable combination of them. Aggregate should be strong, hard, dense, durable, and free from injurious amounts of alkali. They should comply with the local Standard Code. Aggregates containing harmful material should be avoided as it causes corrosion to reinforcement and damages concrete stability.
Types of Aggregates
Aggregates can be categories into two types.
- Fine Aggregate/Sand
- Coarse aggregate
Fine aggregates are sand or crushed stones, which are less than 4.75 millimeters. Usually, they’re 35 to 45% by mass or volume in concrete. Coarse aggregates are gravel and crushed stone. they are of size greater than 4.75 millimeters, up to 90 millimeters and are usually 60 to 65% by mass or volume of concrete
What is Sieve analysis?
Sieve analysis is a procedure for the determination of particle size distribution of aggregates by sieving or screening.
Other categories of aggregates are;
- Boulders are sized larger than six inches.
- Cobbles (3 to 6 inches)
Fine Aggregates Properties
Fine aggregate is either natural sand harvested from riverbeds, crushed stone produced by crushing hard stone, or crushed gravel sand by crushing natural gravels. Fine aggregate sizes range from 4.75 millimeters to 200 microns.
The aggregate used percentage is generally 40% of fine aggregate and 60 % of coarse aggregates are used in the concrete mix.
Sand is mainly used as a fine aggregate, and before using the sand, it is crucial to check silt and clay content. Content smaller than 200 microns are classified as clay. The clay decree bond with cement, and a maximum permissible limit is 7%.
Sand undergoes buckling in which the volume of sand increases due to an increase in water presence. It is important to ensure the avoidance of buckling and the proper content of sand in the concrete mix.
Based on particle size and is divided into four zones. Zone one sand is very coarse, and zone four sand is very fine. Zone category is established based on sieve analysis. The percentage passing 600-micron sieve is determined, and accordingly, the zone of fine aggregates is established.
The grading tolerances of fine aggregates based upon the four zones. It is divided into;
It is an index number, which represents the mean size of the particles in sand. It is calculated by performing a sieve analysis. It provides an idea about how costs are fine the sand.
Fine Aggregate Size
Fine aggregates are of sizes ranging from 4.75 millimeters to 150 microns. The quality of fine aggregates greatly affects the quality of concrete.
Assessing the Quality of the Fine Aggregates.
Natural sand, manufactured sand, and crushed gravel are different varieties of fine aggregates. Sand should be hard, clean, and free from an adherent coating, organic matter, etc.
Fine aggregates should not contain more than 5% of silt, clay lumps, and chemical impurities. The silt content should not be more than 3% for river sand and 15% for manufactured sand.
These materials adversely affect the hardening, strength, and durability of concrete by initialising corrosion of reinforcement. Any organic impurities like leaves, grassroots, decayed vegetation will interfere with concrete setting and binding properties.
The void content between aggregate particles affects the amount of cement paste required for the concrete mix. Angular aggregates increase the void content. Larger sizes of well-graded aggregate and improved grading decrease the void content.
Types of Sand
Sea sand should not be used as it causes efflorescence, corrosion of reinforcement, and retards setting hardening of concrete, damp sand exhibits more volume; this is called bulking. When the damp sand is measured by volume, up to 15% extra sand is to be added to compensate for bulking.
Sand should be so stacked that dust and other foreign matter are prevented from getting mixed with it due to adverse impact on the environment by rampant mining of natural sand.
The government is encouraging the use of manufactured sand, which is satisfactory for making concrete. Manufactured sand is scientifically produced in specially designed crushers to ensure compliance with national standards.
Crusher Dust and Manufactured sand
Users should not be confused between manufactured sand and crusher dust. Crusher dust is the waste product from the manufacturing of coarse aggregates, which have very high silt content and fine particles.
Fine Aggregate Specific Gravity / Specific Gravity of Sand.
Fine aggregate Specific gravity or Specific gravity of sand is the ratio of the weight of a given volume of fine aggregate (sand) to the weight of an equal volume of water. The Fine aggregate Specific gravity is often considered to be 2.65.
For road construction, fine aggregate has a wide range from about 2.5 -3.0 but on average 2.68.