Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement that hardens over time. Concrete is the second-most-used substance in the world after water, and is the most widely used building material.
The concrete is composed of different materials. The ingredient of concrete is given below:
- Binding material
- Fine aggregate
- Coarse aggregate
Binding material may be cement or lime. It is used to bind the materials such as fine aggregate and coarse aggregate. Mostly cement (ordinary Portland cement) is used to bind the materials for normal construction. Lime is also used to bind the materials and strong enough for ordinary construction but it is costly.
Fine aggregate is used in concrete for the purpose of fil the pores and spaces between coarse aggregate. Sand is mostly used as a fine aggregate in concrete. The maximum size of sand should not be more than 4.7 mm and the grain size of fine aggregate is around 2 mm there are three types of sand which is given below:
- Fine Sand
- Medium Sand
- Coarse Sand
Coarse aggregate is blend with fine aggregate (sand) to fill the gaps between them and interlock to each other. Coarse aggregate is used to get the desired strength because with the absence of coarse aggregate you can’t achieved demanded strength. The size of coarse aggregate should not be less than 4.7 mm. in concrete the most common size of coarse aggregate is 40 mm and 20 mm is the most common size of coarse aggregate use in construction.
Water is very essential material for concrete because it plays very important role in making bond of cement with aggregate without water cement is not able to mix with aggregate. Water should not be added more or less it must be added as per design of concrete. The water is added with ratio of cement in concrete is called water cement ratio.it is denoted by “W/C” generally water cement ratio is 0.40 to 0.60. when water cement ratio is below 0.40 the concrete will be hard. Its workability will be less and strength will be more. If water cement ratio is more than 0.60 its strength will be less but workability will be more high water cement ratio is directly proportional to the workability and inversely proportional to their strength.
Admixture affects the setting time of cement, and they are used mostly for specific purposes.
Concrete can be divided into three types according to its density:
High-density Concrete: It refers to concrete with density greater than 2600 Kg/m³. It is usually made of high density aggregate (such as barytes , iron ore, steel chips, etc.) or heavy cement (such as barium cement, strontium cement, etc.). Because it is mainly used as radiation shielding structural material in atomic power plants, also known as radiation-proof concrete.
Ordinary Concrete: It refers to concrete with density of 2000-2600 Kg/m³. It is usually made of cement as cementitious material and natural sand and stone as aggregate. It is the most commonly used cement concrete in civil engineering at present.
Lightweight Concrete: It refers to concrete with a density of less than 1950 Kg/m³, usually using porous lightweight aggregate such as ceramsite or concrete without porous aggregate and foam agent. According to its performance and purpose, it can be divided into structural lightweight concrete, thermal insulation lightweight concrete and structural thermal insulation lightweight concrete.