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What is Sand?

Sand, also called fine aggregate, is an essential constituent in construction as it acts as filler that occupies bulk volume in mortar 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.

Desirable attributes of Sand

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The sand used in construction should be clean, free from silt, clay and organic matter

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Fine sand is not suitable for concrete as fine sand particles will have more surface area (refer to the illustration below) 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

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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 is known as bulkage of sand.

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While using moist sand, its volume (while proportioning concrete by volume) should be accordingly increased and the water content proportionately reduced to adjust for apparent increase in volume due to bulkage.

Ill effects of using bad quality sand

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If sand contains silt/clay, the water demand of concrete/mortar, increases. As a result, the mortar/concrete becomes weak and has a greater tendency to crack.

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Presence of silt/clay in sand results in delayed setting of mortar / concrete.

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Sand for construction should be free from deleterious chemicals containing sulphates and chlorides, which can harm concrete and embedded steel reinforcement.

Method for Sand Washing

Silt and clay, if present in the sand for construction, can be removed by washing it. The method for sand washing involves following steps:

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For washing sand, a tank measuring 3’X3’X3’ can be made of 9” brick wall with a hole at the bottom for passage of dirty water.

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On top of the tank fine wire mesh should be placed through which only fine particles of silt and clay particles can escape.

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At a time, up to 5-6 ghamelas (pans) of sand can be washed by this method.

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