Some vital features of concrete technology

Concrete technology mainly takes care of the behaviour of concrete in different circumstances.

Concrete is fundamentally the blend of cement, wate, fine and coarse aggregate and in certain cases plasticisers are also utilized in concrete.

Given below, some useful properties of concrete :-

WORKABILITY OF CONCRETE: Workability of concrete refers to the volume of concrete to specify it as 'workable'. A workable concrete shows very little internal friction among particle and particle OR which resists the frictional resistance produced by the form work surface or reinforcement comprised in the concrete with just the amount of compacting efforts approaching.

The following factors impact the concrete workability:

Water content, Mix ratios, Size of aggregate, Shape of aggregate, Surface texture of aggregate, Grading of aggregate, Utilization of admixtures.

The following tests are conducted to check the concrete workability:

Slump test, Compacting factor test, Flow table test, Vee-bee test, Key ball test etc.

CREEP AND SHRINKAGE OF CONCRETE:

Creep of concrete: Creep is defined as time dependent part of the strain caused by stress. The stress-strain relationship of concrete is not a straight line rather a curved one.

The ongoing growth in strain devoid of growth in stress with time is because of creep. So creep is also described as raise in strain against sustained stress.

Shrinkage of concrete: Shrinkage leads to the cracks in floor and pavements. The term shrinkage is generally applied to describe the different characteristics of volume changes in concrete owing to the loss of moisture at several phases for various reasons.

Shrinkage is categorized as follow :-

Plastic shrinkage, Drying shrinkage, Autogeneous shrinkage, Carbonation shrinkage.

SEGREGATION AND BLEEDING OF CONCRETE:

Segregation of concrete: Segregation means the partition of the constituent materials of concrete. In standard concrete, all the components are perfectly allotted so that a consistent mixture is produced. Due to segregation, the strength of concrete is reduced significantly. Besides, some adverse properties are also produced in the hardened concrete.

The following three types of segregation are found in concrete :-

1. Coarse aggregate detaching from the rest of the matrix
2. Water detaching away from the coarse aggregate,
3. Water detaching from the rest of the material being as a material of a lowest specific gravity.

Bleeding of concrete: Bleeding stands for water gain in concrete. It refers to a specific form of segregation in which some of the water from the concrete emerges out to the surface of the concrete, being of the lowest specific gravity between all the components of concrete.

Due to bleeding The water goes up and mounts up at the surface. Sometimes, together with this water, specific quantity of cement also moves to the surface.

As the top surface preserves a greater content of water and is also lacking aggregate matter, it produces higher shrinkage cracks. It can be resolved by eliminating the laitance completely prior to pouring of next lift.

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