Importance Of Concrete In Concrete

As we know nowadays concrete plays an important in civil engineering field. Use of concrete has also overcome the brick masonry.

Concrete is mixture of cement, aggregate (fine and course), water and chemical admixture is also added when needed. About 75% of total concrete material is acquired by aggregate. So, it is important to choose the right type, quality and quantity of aggregate. The main matrix of concrete is made by aggregate. The aggregate particles are bounded with each other by cement and water. There are two types of aggregate: (1) coarse aggregate and (2) fine aggregate (sand). The course aggregate forms the main matrix and the fine aggregate forms the filter matrix by filling up the space between the course aggregate. With the

If concrete mix is designed properly, the use of admixture is not needed. However, to change the properties of concrete the admixture could be most convenient way.

Compare to other building materials such as metals and polymers, concrete is significantly more brittle and exhibits poor in tensile strength. Based on fracture toughness values, steel is at least 100 times more resistant to crack than concrete. Concrete in service thus cracks easily, and this cracks create easy access routes for deleterious agents resulting in early saturation, freeze thaw damage, scaling, discoloration and steel corrosion, which ultimately results in structure failure.

The concerns with inferior fracture toughness of concrete are alleviated to large extent by reinforcing it with fibers of various materials. The resulting material with a random distribution of short, discontinuous fibers is termed as fiber reinforced concrete (FRC) and slowly becoming a well-accepted mainstream construction

Therefore, a single representative value, known as characteristic strength is used.

Characteristic strength of concrete:

It is defined as the value of the strength below which not more than 5% of the test results are expected to fall (i.e. there I s 95% probability of achieving this value only 5% of not achieving the same)

Tensile strength of concrete:

The estimate of flexural tensile strength or the modulus of rupture or the cracking strength of concrete from cube compressive strength is obtained by the relations.

The tensile strength of concrete in direct tension is obtained experimentally by split cylinder. It varies between 1/8 to 1/12 of cube compressive strength.

Creep in concrete:

Creep is defined as the plastic deformation under sustain load. Creep strain depends primarily on the duration of sustained loading. According to the code, the value of the ultimate creep coefficient is taken as 1.6 at 28 days of loading.

Shrinkage of Concrete:

The property of diminishing in volume during the process of drying and hardening is termed Shrinkage. It depends mainly on the duration of exposure. If this strain is prevented, it produces tensile stress in the concrete and hence concrete develops