Aggregate is an aggregation of non-metallic minerals obtained in particulate form and can be processed and used for civil and highway engineering construction.
The aggregates passing 4.75 mm tyler sieve and retained on .075 mm sieve are classified as Fine Aggregate.
Types of Fine Aggregate
Usually, sand, crushed stone, and crushed bricks are used as fine aggregate in concrete or pavement construction.
Sand is an important engineering material. In concrete works, sand is used as a fine aggregate. Sand is a form of silica (quartz) and may be of argillaceous, siliceous or calcareous according to its composition. Natural sands are formed from weathering of rocks (mainly quartzite) and are of various size or grades depending on the intensity of weathering. The sand grains may be of sharp, angular or rounded.
Classification according to Source
- Coral Sand
- Glass Sand
- Immature Sand
- Gypsum Sand
- Ooid Sand
- Silica Sand
- Pit Sand
- River Sand
- Sea Sand
- Green Sand
- Desert Sand
- Lithic Sand
- Mixed Carbonate-silicate Sand
- Biogenic Sand
- Garnet Sand
- Olivine Sand
- Volcanic Sand
- Heavy Mineral Sand
- Sands with Hematitic Pigment
- Continental Sand
- Quartz Sand
Grading of Sand
All sand particles should pass No. 4 to No. 16 sieves. But at the same time, sand should not contain very fine particles. In between these two extreme sizes (3/16 to 1/16 inch), sand should contain particles of uniformly varying sizes or it should be well graded in order to get dense mortars The grading of these various sizes of sand particles is determined using ‘Sieve Analysis’. A known quantity of dry sand (generally 100 to 200 gm) is taken and sieved through a consecutive order of standard sieves. The cumulative percentages of the respective retained quantities are added and divided the sum by 100 to obtain a figure termed as ‘Fineness Modulus’ of the sample. It is generally denoted by ‘F’. The fineness modulus sand should be between 2 and 3. A smaller value of fineness modulus indicates the presence of finer particles and vice versa.
If good sand is not available in the nearby of the site, the substitutes may be used as fine aggregate.
Stone screenings are fine particles obtained by screening crushed stones. The grains are sharp and strong, and hence impart better strength to the concrete.
Surki is made by grinding freshly burnt and well-burnt bricks. It should be perfectly clean, free from foreign matter and sufficiently fine to pass through No. 8 sieve (US).
Surki is largely used in making lime mortar, lime plaster, and lime concrete.