What are the Properties of Sand

SAND • Sand is an important building material used in the preparation of mortar, concrete, etc. • Sources of Sand: Sand particles consist of small grains of silica (Si02). It is formed by the decomposition of sand stones due to various effects of weather. The following are the natural sources of sand • 1. Pit Sand 2. River Sand 3. Sea Sand Aggregate Fine Aggregate Sand Coarse Aggregate Crushed Stone Pit Sand Gravel River Sand Broken pieces of brick Sea Sand PIT SAND Pit sand is classified under coarse sand which is also called badarpur in common language. This type of coarse sand is procured from deep pits of abundant supply about 1 to 2 m below the top soil. • Rough, sharp or angular (enhances binding) • free from organic matter and clay • considered to be the best fine aggregate for use in mortar and concrete The sand grains are free from salts hence does not show deliquescence .i.e. does not absorb moisture content from air and damage the structure Pit sand is generally red-orange in color, due to a coating of iron oxide It is widely used for construction and building of permanent structures due to its superior binding qualities. RIVER SAND • This sand is obtained from beds of rivers. River sand consists of fine rounded grains. Color of river sand is almost white. As the river sand is usually available in clean condition, it is widely used for all purposes. SEA SAND This sand is obtained from sea shores. Sea sand consists of rounded grains in light brown color. Sea sand consists of salts which attract the moisture from the atmosphere and causes dampness, efflorescence and disintegration of work. Due to all such reasons, sea sand is not recommendable for engineering works. However be used as a local material after being thoroughly washed to remove the salts. CHARACTERISTICS OF GOOD SAND • It should be chemically inert. • It should be clean and coarse. It should be free from organic matter. • It should contain sharp, angular and durable grains. • It should not contain salts which attract the moisture from atmosphere. • It should be well graded, i.e. should contain particles of various sizes in suitable proportions. BULKING OF SAND • The presence of moisture in sand increases the volume of sand. This is due to fact that moisture causes film of water around the sand particles which result in the increase of volume of sand. • For a moisture content of 5 to 8 percent, the increase in volume may be about 5 to 8 percent, depending upon the grading of sand. The finer the material, the more will be the increase in volume for a given moisture content. This phenomenon is known as Bulking of Sand • a. A container is taken and it is filled two third with the sample of sand to be tested. b. The height is measured, say 20cm. c. Sand is taken out of container. d. The container is filled with water. e. Sand is then slowly dropped in the container and it is thoroughly stirred by means of a rod. f. The height of sand is measured say 16cm, then bulking of sand = 25% • Depending upon the size of their particles aggregates are classified as: (1) Fine aggregates (2) Coarse aggregates • (1) Fine Aggregates: • Aggregates whose particles pass through 4.75 mm IS sieve are termed as fine aggregates. Most commonly used fine aggregates are sand (pit or quarry sand, river sand and sea sand) and crushed stone in powdered form, how ever some times surkhi and ash or cinder are also used. • (b) Crushed stone: It is obtained by crushing the waste stones of quarries to the particular size of sand. Sand obtained from by crushing a good quality stone is excellent fine aggregate. Mortar made with this sand is usually used in ashlar work (good quality of work). • Coarse aggregate • Aggregates whose particles do not pass through 4.75 mm IS are termed as coarse aggregates. Most commonly used coarse aggregates are crushed stone, gravel; broken pieces of burnt bricks,etc. • Crushed Stone • It is an excellent coarse aggregate and is obtained by crushing granite, sand stone or grained lime stone and all types of stones. Crushed stones are used for the construction of roads and railway tracks, etc. • (b) Gravel: It is an other very good coarse aggregate. It is obtained from river beds, quarries and sea shores. The gravel obtained from sea shores should be well washed with fresh water before use in order to remove the impurities which may be clay, salts ,silt,etc. It is commonly used in the preparation of concrete. • (c) Broken pieces of bricks: It is also a good artificial source of coarse aggregates. It is obtained by breaking well burnt bricks. It is generally used in lime concrete at places where aggregates from natural sources are either not available or are expensive. It can be used at places where low strength is required. It should be watered well before using it in the preparation of concrete. It is commonly used for mass concrete in foundations and under floors. GOOD QUALITIES OF AN IDEAL AGGREGATE An ideal aggregate used for the manufacturing of concrete and mortar, should meet the following requirements. (1)It should consist of natural stones, gravels and sand or in various combinations of these materials. (2)It should be hard, strong and durable. (3) It should be dense, clear and free from any coating. (4) It should be free from injurious vegetable matters. (5) It should not contain flaky (angular) and elongated pieces. (6) It should not contain any material liable to attack steel reinforcement in case of reinforced concrete. CHARACTERISTICS OF AGGREGATES • Important characteristics of aggregates which influence the properties of resulting concrete mix are discussed as under • 1.Composition: • Aggregate containing the constituents which generally react with alkalies in cement cause excessive expansion, cracking of concrete mix, should never be used. Suitability of aggregates should be judged either by studying its service history or by laboratory tests. 2. Size and shape: • The size and shape of the aggregate particles mainly influence the quantity of cement required in a concrete mix and ultimately economy of the concrete. For the preparation of economical concrete, one should use largest coarse aggregates feasible for the structure. • Type of structure Max. size of aggregate 1. Mass concrete work 40 mm i.e. dams, retaining walls, piers and abutments, etc. 2. R.C.C work 20 mm i.e. beams, columns, etc 3. Flooring 10 mm It may be clearly noted that the size and shape of the aggregate particles influence the properties of freshly mixed concrete more as compared to those of hardened concrete.