Types of Joints in concrete

Concrete shrinks irreversibly as it cures and dries out. After this initial shrinkage has occurred, concrete expands and contracts reversibly with changes in temperature and moisture content. This movement can cause concrete to crack uncontrollably unless it is reinforced with steel. Although, reinforcement increases the strength of concrete and absorbs the stress of expansion and contraction, it can not prevent cracking altogether – it can only distribute the stresses so that there will be many irregular cracks instead of a few big ones. Irregular cracks are unsightly and difficult to maintain. So, concrete is build with special joints that are designed to control cracking location. Actually, joints are pre-planned cracks.

Following are the some kinds of joints we generally use in concrete:

  • Control/Contraction/shrinkage joint
  • Construction joint
  • Isolation/expansion joint

Properties of aggregate and their behaviour in concrete

Aggregate is one of the building materials used to produce concrete and mortar. When cement is mixed only with fine aggregates it is called cement mortar. Masonry mortar is different from a simple cement mortar because it contains other ingredients as well.

Concrete contains both fine and coarse aggregate. Aggregates add strength to concrete and reduce its potential for shrinkage. In other word, aggregates act as bone of concrete.

Aggregates actually make up 60% to 80% of the volume of hardened concrete. So their properties and characteristics are very important.

Most commonly used aggregates in concrete are sand, gravel, crushed stone, crushed slag and pumice. The discussion about both fine and coarse aggregates are given below-

Admixtures and purposes of their using in concrete

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

 

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