Testing the quality of sand is crucial for concrete construction at a construction site. Fine aggregate, which includes materials that pass through a 4.75 mm IS sieve, such as natural sand, crushed stone sand, crushed gravel sand, stone dust, fly ash, and broken brick (burnt clay), must meet certain requirements. It should be hard, durable, chemically inert, clean, and free from adherent coatings, organic matter, and other impurities like clay balls, pellets, iron pyrites, alkalis, salts, coal, mica, shale, or laminated materials that could cause corrosion of metal or affect the strength, durability, or appearance of mortar, plaster, or concrete. The total percentage of deleterious materials should not exceed 5%. Additionally, fine aggregate must be tested for organic impurities, such as decayed vegetation, humps, coal dust, etc.
Testing of Sand Quality at Construction Site
There are several tests that need to be conducted on sand at a construction site. The first is the organic impurities test, which is done in the field and is required for every 20 cubic meters (or part thereof) of sand. The second is the silt content test, also conducted in the field and required for every 20 cubic meters of sand. Another important test is the particle size distribution, which can be done on-site or in a laboratory, and is required for every 40 cubic meters of sand. Finally, the bulking of sand test is conducted on-site and is required for every 20 cubic meters of sand. This test helps determine the appropriate water cement ratio for concrete at the construction site.
1. Test for Silt Content Test of Sand
The permissible amount of silt in sand should not exceed 8%. If the fine aggregate contains a higher percentage of silt than what is allowed, it must be washed in order to reduce the silt content to meet the allowable limits.
2. Test for Grading of sand
Fine aggregate, based on particle size, is classified into four different zones. If the grading of the fine aggregate does not fall within the specified limits of any particular grading zone, except for the 600 micron IS sieve, by a total amount not exceeding 5 percent, it will be considered as falling within that grading zone. This means that if the grading of the fine aggregate is slightly outside the specified limits of a grading zone, but the deviation is not more than 5 percent, it will still be considered as meeting the requirements of that grading zone.
| IS Sieve | Percentage passing for | |||
| Grading Zone I | Grading Zone II | Grading Zone III | Grading Zone IV | |
| 10mm | 100 | 100 | 100 | 100 |
| 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. Test for Deleterious materials in sand
The sand used in mortar should be free from harmful impurities such as iron, pyrites, alkalis, salts, coal, organic impurities, mica, shale, or similar laminated materials, soft fragments, and sea shale. These impurities should not be present in quantities that can adversely affect the hardening, strength, or durability of the mortar. The maximum allowable quantities of clay, fine silt, fine dust, and organic impurities in the sand/marble dust should not exceed the following limits: (a) Clay, fine silt, and fine dust should not be more than 5% by mass, as determined in accordance with IS 2386 (Part-II), in natural sand, crushed gravel sand, and crushed stone sand. (b) Organic impurities, as determined by the color of the liquid, should be lighter than the specified code in accordance with IS 2386 (Part-II).
4. Test for Bulking of sand
Fig: Bulking of sand test
Fine aggregate exhibits minimal changes in volume when dry or saturated, but when damp, it tends to increase in volume. This increase in volume due to dampness must be considered when proportioning ingredients for mortar or concrete. If fine aggregate is damp during the proportioning process, its quantity should be adjusted accordingly to account for bulking. The table provided offers guidance on the relationship between moisture content and percentage of bulking.
| Moisture content (%) | Bulking percentage (by volume) |
| 2 | 15 |
| 3 | 20 |
| 4 | 25 |
| 5 | 30 |