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In ancient period, the houses were constructed by using the mixture of lime, sand and wood. At present, the people are widely use the cement for construction of houses, dams and bridges. The cement is manufactured by crushing of naturally occurring minerals such as lime, clay and gypsum through milling process.
Cement becomes hardened when it is mixed with water. Gypsum plays a very important role in controlling the rate of hardening of the cement. During the cement manufacturing process, a small amount of gypsum is added at the final grinding process. Gypsum is added to control the “setting of cement”.
In 1824, Joseph Aspdin invented Portland cement by burning finely ground chalk and clay in a kiln. It was named “Portland” cement because it resembled the high-quality building stones found in Portland, England.
Uses of cement
Cement is used as mortar, concrete and reinforced cement concrete.
Mortar is a paste of cement and sand mixed with water. In houses, mortar is used to bind building blocks for constructing walls, to apply coating over them and to lay floor.
Concrete is a mixture of cement, sand and gravel. It is used in the construction of buildings, bridges and dams.
Reinforced Cement Concrete
Reinforced cement concrete is a composite material by mixing iron mesh with cement. This is very strong and firm. It is used in the construction of dams, bridges, centering works in houses and construction of pillars. Huge water tanks, water pipes and drainages are built with this.
Activity 5: Take three empty tumblers of same size and name them as A, B and C. Add two tea spoonful of cement in each of the container. Then pour one tea spoonful of water in container A and two spoonful of water in B and three spoonful of water in C.
After an hour, observe which container of the cement set fast? Touch the containers and see if they are warm or cool. From this experiment, we understand that water and cement should be mixed in a certain ratio for fast setting.
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