Concrete is one of the basic and most widely used construction material. Concrete is made by mixing cement and aggregates (stone and sand) with water. The paste made by mixing cement and water fills the gap between the coarse and fine aggregate. Once the mixture is made a chemical reaction called hydration starts and the concrete starts hardening and with time it gains strength and become hard like a rock.
During the hardware process the concrete changes from its soft fluid and mouldable form to a hard, strong and durable state. This characteristic of concrete makes it suitable to be used in every structure be it a simple house or a bridge or a skyscraper.
Making Concrete Mixture
All ingredients are put into a concrete mixer. Concrete mixer is basically a drum rotating with the help of a motor or an engine. To make good concrete all the ingredients are mixed properly. The proportion of all the ingredients should be such that neither it is too fluid nor dry. The water-cement paste has to fill all the gaps between the stone and sand. If the cement-water paste is too fluid or less in quantity the concrete will have a bad work-ability and will be difficult. Also once placed in the form-work the paste and the aggregate will not form the bond. If the paste is too thick than also the concrete will have bad work-ability and will not be placed easily. So we need to make the mixture with proportionate quantities of cement, aggregate and water. Once mixed we need to fill the concrete in the form-work of the desired shape and size.
Once the concrete is poured into the form-work the hydration process starts. During hydration process water-cement paste transforms into calcium silicate hydrate compounds. These compounds are the ones that make the concrete as we know strong, hard and durable.
We need to maintain the moisture of the concrete so that the hydration process is continued. As long as the moisture and the hydrated cement exists in the concrete the strength, density and roughness keep increasing. As a result the concrete keeps getting denser and denser. As the porosity of the concrete decreases the it looses moisture in evaporation. Evaporation also happen due to the heat generated during the hydration process. if the concrete dries out,the hydration process stops and concrete stops gaining strength. To maintain the level of moisture inside the concrete we need to cover and cure the concrete after placing.