Aggregate most of which pass through 4.75 mm IS sieve is known as fine aggregate. Fine aggregate shall consists of natural sand, crushed stone sand, crushed gravel sand stone dust or arable dust, fly ash and broken brick (burnt clay). It shall be hard, durable, chemically inert, clean and free from adherent coatings, organic matter etc. and shall not contain any appreciable amount of clay balls or pellets and harmful impurities e.g. iron pyrites, alkalies, salts, coal, mica, shale or similar laminated materials in such form or in such quantities as to cause corrosion of metal or affect adversely the strength, the durability or the appearance of mortar, plaster or concrete.
The sum of the percentages of all deleterious material shall not exceed 5%. Fine aggregate must be checked for organic impurities such as decayed vegetation humps, coal dust etc.
Following are the tests for sand:
1. Organic impurities test – this test is conducted at the field, for every 20 cum or part thereof.
2. Silt content test – this is also a field test and to be conducted for every 20 cum.
3. Particle size distribution – this test can be conducted at site or in laboratory for every 40 cum of sand.
4. Bulking of sand – this test is conducted at site for every 20 cum of sand. Based on bulking of sand, suitable water cement ratio is calculated for concrete at site.
1. Silt Content Test of Sand:
The maximum quantity of silt in sand shall not exceed 8%. Fine aggregate containing more than allowable percentage of silt shall be washed so as to bring the silt content within allowable limits.
2. Grading of sand: On the basis of particle size, fine aggregate is graded into four zones. Where the grading falls outside the limits of any particular grading zone of sieves, other than 600 micron IS sieve, by a total amount not exceeding 5 percent, it shall be regarded as falling within that grading zone.
|IS Sieve||Percentage passing for|
|Grading Zone I||Grading Zone II||Grading Zone III||Grading Zone IV|
|4.75mm||90 – 100||90 – 100||90 – 100||90 – 100|
|2.36mm||60 – 95||75 – 100||85 – 100||95 – 100|
|1.18 mm||30 – 70||55 – 90||75 – 100||90 – 100|
|600 micron||15 – 34||35 – 59||60 – 79||80 – 100|
|300 microns||5 – 20||8 – 30||12 – 40||15 – 50|
|150 microns||0 – 10||0 – 10||0 – 10||0 – 15|
3. Deleterious materials in sand: Sand shall not contain any harmful impurities such as iron, pyrites, alaklies, salts, coal or other organic impurities, mica, shale or similar laminated materials, soft fragments, sea shale in such form or in such quantities as to affect adversely the hardening, strength or durability of the mortar. The maximum quantities of clay, fine silt, fine dust and organic impurities in the sand / marble dust shall not exceed the following limits:
(a) Clay, fine silt and fine dust when determined in accordance within not more than 5% by mass in IS 2386 (Part-II), natural sand or crushed gravel sand and crushed stone sand.
(b) Organic impurities when determined in colour of the liquid shall be lighter in lighter in accordance with IS 2386 (Part –II) than that specified in the code.
4. Bulking of sand:
Fine aggregate, when dry or saturated, has almost the same volume but dampness causes increase in volume. In case fine aggregate is damp at the time of proportioning the ingredients for mortar or concrete, its quantity shall be increased suitably to allow for bulkage. Table below gives the relation between moisture content and percentage of bulking for guidance only.
|Moisture content (%)||Bulking percentage (by volume)|