Concrete is a composite material with changeable properties. The ingredients mixing ratio of concrete is variable and depends on the properties of ingredients and mix design. A popular measuring method of concrete ingredients during mixing is by volume. But the weight measuring method is more accurate. However, concrete is prepared by mixing three basic ingredients.
1. Binding material – cement,
2. Aggregate, and
1. Binding material: Most commonly used binding material for concrete is portland cement. Other binding materials used for this purpose, are lime, fly ash, silica fume etc. The selection of cement for concrete is depend on the “cement properties“.
2. Aggregate: Two types of aggregates are used in concrete. Coarse aggregate and Fine aggregate.
Coarse aggregate: Big sizes aggregates in concrete are coarse aggregates. The size of it varies between 1/2″ to 1.5″ depending on concrete mix design. Generally, crushed stone or brick chips are used as coarse aggregate.
Fine aggregate: The smaller size aggregates in concrete are Fine aggregates. The FM (Fineness Modulas) of fine aggregates can be between 1.2 to 2.5 depending on mix design. We use sand as fine aggregate in concrete.
3. Water: The most important concrete ingredient is water. Water can decrease and increase the concrete strength depending on its using. Water just starts and continues the chemical reaction of cement. High water content in concrete mix increases the workability of concrete but decreases the strength. On the contrary, low water content increase the concrete strength but makes concrete less workable.
Other than cement, water and aggregate we add other substances to concrete mixes for the purpose of altering properties of fresh or hardened concrete that is admixture. For specific conditions or circumstances, admixtures may sometimes be necessary to alter specific properties of the concrete.
Most commonly used admixtures in residential concrete construction are-
- Chemical admixtures,
- Air-entraining agents and
- Coloring pigments