Aggregates affect concrete/mortar properties such as water requirement, cohesiveness and workability of concrete in the plastic stage, while they affect strength, density, durability, permeability, surface finish and color in the hardened state.

1. Surface moisture content and absorption

The surface moisture in the aggregate affects the water-cement ratio, strength and durability of the mixture. To determine the surface moisture content of moist or wet aggregate, the method is as follows-

frying pan method

The following equipment is required:

  • a frying pan or metal tray,
  • gas stove or electric hair dryer,
  • a metal or glass stirring rod and
  • Scales for measurement.

The following procedure is followed during the test

  1. For coarse aggregate 2 kg sample is sufficient and for fine aggregate 0.5 kg sample is sufficient.
  2. Then the wet/damp sample is weighed wet weight (w)
  3. On a frying pan or metal plate heated very slowly and stirred with a glass or metal rod to maintain an even distribution of heat, until the gloss disappears from the surface. The fine aggregate surface becomes dry when it starts showing free flow characteristics.
  4. The aggregate is then cooled and weighed again. surface dry total weight (AndSD) has come into view. The surface moisture is calculated as-

surface moisture = [(W – Wsd) / Wsd] x 100%

  1. Overheating should be avoided, as it will not give proper moisture to the surface,
  2. If on fry pan or in oven continue to heat until total bone dry The total weight (Wbd) after continuous heating is noted. The absorption (absorbed water content) is calculated as follows-

Absorption = [(Wsd – Wbd) / Wbd] x 100%

Similarly, if dry aggregates are obtained on site and the absorption capacity is to be determined, the aggregate is first soaked in water and then the above methods are deployed to determine the absorption capacity of the aggregate.

2. silt content test for sand

silt content test
silt content test

The permissible silt content (fine aggregate) in sand should not exceed the values ​​specified in the standards. However, this method can only be used for natural sand, it should not be used for crushed rock sand.

The only equipment needed for this test is a 250ml glass measuring cylinder.

The amount of silt on the basis of volume is determined in the following manner:

  1. The glass cylinder is filled with a salt-water solution up to the 50 ml mark (the concentration of the solution will be a teaspoon full of common salt for every 570 ml).
  2. Add sand until the sand level reaches the 100 ml mark.
  3. Then add the salt-water solution until the 150 ml mark is reached.
  4. Place your palm at the mouth of the glass cylinder and shake vigorously.
  5. Place the cylinder on a hard flat surface and pat it around so that the sand is level.
  6. Wait three hours for the silt to settle on top of the sand.
  7. Measure the thickness of the silt layer and the height of the sand. The silt content can be calculated as follows:

Silt (%) by volume = [(Thickness of silt layer/ Height of sand + Silt) x 100 %]

If the amount of silt is more than 3% by weight, then sand washing is necessary. After doing some tests, a correlation can be developed for the thickness of the silt layer at different intervals of time. The silt content at 10 min can be fixed as the inspection criterion.

3. sand. bulk of

When the sand is moist, the water coating on the surface of each sand particle causes the surface tension to separate the particles from each other. This creates a pile of sand. Bulked sand occupies a greater volume and therefore if volumetric measurements are made while measuring it proportionately, bulk correction is necessary.

The bulking test is performed as follows:

  1. Sand is filled in loose condition into a box of measured height (h cm).
  2. The box is then filled with water and roding is done to solidify and strengthen the sand. Care should be taken that the sand does not overflow during flooding and compaction.
  3. The sand is then leveled into the box and the drop in height (h cm) is measured.
  4. The bulk is calculated as follows: Bulk % = H/H x 100%

Dry sand occupies the same amount as fully saturated sand. Bulking will vary from load to load and from day to day depending on the fineness of the sand and the moisture content of its surface. Therefore, it is very necessary to carry out bulk correction by examining the actual bulking of the sand proposed to be used by volumetric batching for mortar or concrete.

Moisture content % by age wt. Bulk % by Quantity
2 15
3 20
4 25
5 30

4. sieve analysis

Sieve analysis is done to check the gradation of aggregate. The test is done as follows.

  1. Take the required amount of total sample (approximately 2.5 kg for coarse aggregate and 0.5 kg for fine aggregate)
  2. Arrange the required number of sieves in a descending manner as per the requirement of the contract or job. (ie keep the largest sized sieve open at the top and the smallest sized at the bottom)
  3. Shake the sieve set vigorously for at least 2 minutes.
  4. Then measure the total load on each sieve and express it as a percentage of passing.

Now compare these values ​​with the recommended values ​​to know whether it falls within the range or not. If you do not get the desired promotion, then take necessary action.

The grading range of coarse aggregate and fine aggregate is given below for reference.

Grading limit of coarse aggregate
Grading limit of coarse aggregate
Grading Limit of Fine Aggregate
Grading Limit of Fine Aggregate

This test is performed initially for concrete mix design and is conducted periodically for subsequent mix ratio adjustments if it is suspected that the grading of the aggregate has changed significantly.

5. fineness modulus

The fineness modulus is commonly used to estimate how thick or fine an aggregate is. A higher fineness modulus value indicates that the aggregate is thicker and a smaller fineness modulus value indicates that the aggregate is finer.

  1. Filter the aggregate using appropriate sieves (80 mm, 40 mm, 20 mm, 10 mm, 4.75 mm, 2.36 mm, 1.18 mm, 600 µm, 300 µm and 150 µm).
  2. Record the total weight placed on each strainer.
  3. Calculate the cumulative load of the aggregate placed on each sieve.
  4. Calculate the cumulative percentage of the total retained.
  5. Add up the cumulative weighting of the total retained and divide the sum by 100. This value is called the modulus of fineness.

Compare the test value with the values ​​in the table below and you can get an idea of ​​how rough or fine the sand is.

Only sand between FM 2.6 to 2.9 is considered suitable for the nominal mixing ratio.

sand type fineness modulus value
very fine sand below 2.2
fine sand 2.2 to 2.6
medium sand 2.6 to 2.9
coarse sand 2.9 to 3.2
very coarse sand 3.2. at over

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.