How is Concrete Made?
Concrete is a blend of aggregates or rocks and paste, and the paste is made from Portland cement with water, used to coat the surface of the aggregates. Hydration takes place and hardens the paste that becomes a strong rock-like mass which is called “concrete.” Concrete is plastic and malleable when freshly mixed, and transforms into strong and durable form after hardening. Thanks to these qualities, this material called concrete is so versatile and can build skyscrapers, bridges, sidewalks and even superhighways and dams that easily withstand the test of time.
Step 1 –Proportions
The right proportions and mixing of the different ingredients is the key to achieving the desirable strength and durability and a higher grade of concrete. A mixture which has a higher proportion of the paste will be easy to work with and produce a smooth surface, but it will develop cracks easily. Cement mixed with water will form a paste to give a coating to cover every particle of stone and sand also known as aggregate. This then undergoes hydration and hardens. The quality of the paste is the deciding factor as to how the concrete will behave, while its strength depends on the cement-water proportion.
Pure, portable grade water is used as mixing water for concrete because excessive impurities affect setting time and strength, also causing efflorescence, corrosion of reinforcement, staining and reduced durability. Aggregates cover 60 to 75 percent of the total volume of concrete and the aggregate used depends on many factors such as thickness and use of the final concrete product.
After mixing the aggregates, water, and cement, the mixture will harden. Portland cement is hydraulic in nature and will set through a chemical reaction call hydration. After mixing, the concrete becomes workable and should be molded or placed as desired or it can become too stiff and unworkable. When making slabs, concrete is left to stand till the surface moisture dries up then the concrete is smoothened with a float. Floating gives an even but slightly rough, texture that is slip resistant.
Curing is then done after the exposed surfaces of the concrete have hardened, curing is done by sprinkling with it water fog, or by using moisture-retaining fabrics, using seals of plastic or certain sprays. For higher strength, the concrete must be kept wet for a longer duration.