Aggregates

Aggregates

Aggregates

In Civil Engineering Aggregates plays vital role. Therefore we have to have good knowledge of aggregates. Making it most simple to understand, we will first see why and what for we need Aggregates.

1) Metal  :- It take Strength in the concrete. 

2) Sand :-   Only to fill gaps 

Metal :-

 Cement is only binding agent. So  it binds Metals.  And make a big pavement. which is as per design can take loads. For proper binding and interlocking we need metal a bit angular  and hard. Aggregates which pass through sieve of opening of size 80 mm and are entirely retained on 4.75 mm  sieve, are known as coarse aggregates.
            The size of the Particles to be used for concrete depends on the type of work and Reinforcement. Coarse aggregates consist of aggregates such as stone gravel.

Acceptance :-

•     Should not be porous, as porous material corrodes the reinforcement.
•     Elongates and laminated particles are good in shear.
•     Must be clean and free from clay lumps, vegetable and other organic material. Clay/ dirt in the           aggregates slows down the setting and hardening of cement and reduces the strength.
•     Angular and roughly cubical particles are ideal.
•    25 mm  and 12.5 mm size coarse aggregates are normally used in R.C.C. works.
•     For mass concrete upto 40 mm size coarse aggregates can be used.
•     The maximum size of coarse aggregates should be within the limits specified.

Sand:- 

Sand is use to fill gaps. so it all depends of fineness modulus [F.M.], F.M. may range between 2.6 % to 3.6% for concrete up to 1.6% for plastering , and up to 3% for masonry as per IS 386-1963. sand passes through 4.75 mm I.S. Sieve.
            Sand should consist of sharp angular grains of various sizes. Recent studies show that rounded grains too interlock sufficient, to produce a strong concrete.

Acceptance :-

•     Ensure that the sand is river wet or artificially we  [ to increase the bulk-age.]
•     Check if the fineness [ type ] of the sand supplied is as per the purchase order.
•     Sand should be free from slit, clay, slat, mica and organic material. Sand is generally found     to contain some percentage of slit and clay. maximum 7%  of silt  and clay be allowed in sand at construction sites.

Aggregates test:-

Metal :-
                             
1) Water Absorption test :- For metal to be used in concrete work, water absorption should not be more than 4%.                 
Sand :-

1) Test for bulking of Sand:- This bulking of sand should be known for proper correction to be applied when calculating dry and requirement.
2) Silt content of sand :- Total silt content should not be more than 7% for good quality sand.
3) Organic Impurities :- This should not be more than 1% of the total sand received.