Concrete is used since ages in construction and the basic ingredients of concrete is same till date. Depending upon the necessity one can change the proportion of the ingredients. And depending upon the situations or uses one can add the admixtures for different kinds of the purposes.
Basic Ingredients of concrete:
Concrete consists of hard inorganic materials called aggregates such as gravel, sand, crushed sand, slag etc. cemented together with Portland cement and water. When the above materials are mixed together to form a workable mixture. The ingredients of concrete will be as per follows,
Cement is the main ingredients of concrete used in concrete to bind the material together. Cement acts as the glue in concrete and keep everything together. It hardening property also allows cement to get hard when mixed with water and it gets placed after mixing. There are different types of cement is available in market. Generally Portland cement is used for the construction. The percentage of cement in concrete will vary from 15% to 30%. Cement, being hygroscopic, attracts moisture quickly and sets, So storage of cement should be carefully attended to and no set or even partially set cement should be used.
2. Fine aggregate (sand) & Coarse aggregate:
Aggregates in concrete give strength to concrete. The percentage of aggregates (combinedly sand & coarse aggregate) is up to 70%. This high percentage makes the mixture more economical–as gravel and sand are both stronger and more cost-effective than the cement. The well combination of sand and coarse aggregate should be used for concrete.
Strength of concrete shall depend to a great extent on the voids in it. As such to have lesser voids so as to get stronger concrete the aggregates should be well graded i.e., they should have particles of various sizes so that the voids of bigger particles are filled up by the particles of smaller sizes.Graded aggregates give solid and dense concrete (free from holes or voids) which is stronger, more durable and water tight.
Poorly graded aggregate & excessive water content is the major cause of segregation. A badly proportioned mix, where sufficient matrix is not there to bond and contain the aggregate cause aggregates to settle down. To avoid that, the proportions of all the ingredients of concrete should be designed properly.
Water is need to for combination, to make the cement active and to form a workable mixture of all ingredients. Water is very important aspect in concrete. Water has very much impact on workability of concrete. To maintain the workability of concrete, the quantity of water is decided by the ration of water and cement. Usually the water cement ratio is considered from design codes. It is considered between 0.4 to 0.6. The higher the water cement ratio, weak the concrete (or less strength of concrete). It means more the water in concrete, less the strength to hardened concrete. Shrinkage, cracking, bleeding, segregation also the result of wrong water content.
The water used for the concrete should be free from silt, clay ect.
The slump test is good way to test the workability of concrete. This will help to determine whether the water is less or more in concrete.
Admixtures are optional in concrete. This is used for the special purposes like to increase or decrease the initial or final setting time of the concrete. Admixtures are used in special cases only.
The proportion of all the ingredients of concrete is considered as per grade of the concrete or as per mix design of concrete. mix design or proportion of concrete is very much important to avoid the defects in concrete.