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Choosing the right sand for conustructing your dream house
Sand, also termed as fine aggregate, is an essential constituent in construction as it acts as filler that occupies bulk volume in mortars and fills up voids between coarse aggregate particles in concrete. Based on its fineness sand is classified as fine, medium and coarse sand. Coarse sand is suitable for concrete, medium sand suits well for brickwork mortar and fine sand is fit for plastering
Below are the recommended usages based on the texture and particle size of sand :
Plastering Works: Fine sand should be used with silt contents not more than 4%.
Brick Works: Medium sand should be used with silt contents not more than 4%.
Concreting Works: Coarse sand should be used with silt contents not more than 4%.
Desirable attributes of Sand:
The sand used in construction should be clean, free from silt, clay and harmful impurities like alkalis, salts, coal, and organic matter. The silt contents should not in any case exceed 4%.
Fine sand is not suitable for concrete as fine sand particles will have more surface area which increases the cement paste demand of the concrete. In case quantity of paste is increased by just adding water, concrete becomes porous, weak and of poor durability and if the volume of paste is increased by increasing cement quantity then the concrete becomes uneconomical.
Also the smaller and rounded particles has binding force lesser than that of angular and particles of different sizes Checking the Quality of Sand
Few handy tests which can be even done at home to check the quality of sand
1. Take handful of sand, rub between your palms and release, fine sand should not stick to your palms.
2. Put some quantity of sand in a glass of water. Shake it vigorously and allow it to settle. If the clay is present in sand, its distinct layer is formed at the top of sand.
3. To detect organic impurities in sand a solution of sodium hydroxide or caustic soda is added to sand and stirred in a glass of water. If the colour of solution changes to brown, it shows presence of impurities
1. Washed sand should be used at site for getting more strength in construction work.
2. Moist sands exhibit volume increase as compared to dry sands. If sand has 5-7% of moisture its volume can increase by up to 35% of its dry volume. This phenomenon is known as bulking of sand. While using moist sand, its volume should be accordingly increased and the water content proportionately reduced to adjust for apparent
Method for Washing Sand
1. Make a tank measuring 3*3*3 of 9inch brick wall with a hole at the bottom for passage of dirty water.
2. On top of the tank place fine wire mesh through which only fine particles of silt and clay particles can escape.
3. At a time place not more than 5-6 pans of sand .
4. Wash it using water.
Effects of using bad quality sand
1. If sand contains silt/clay the water demand of concrete / mortar, increases. As a result the mortar/concrete becomes weak and has greater tendency to crack.
2. Presence of silt/clay in sand results in delayed setting of mortar / concrete.
3. Sulphates and chlorides can harm concrete and embedded steel reinforcement.
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