Fresh Concrete:

The process of manufacturing concrete passes through various stages, i.e. batching and dry mixing of concrete ingredients, mixing of concrete ingredients with water, transporting and placing of fresh concrete mix, compacting and finishing and finally hardening of concrete. Fresh concrete is also called as green concrete or wet concrete or concrete in plastic stage. It is important to note that most of the handling operations of concrete are performed on fresh concrete, i.e. right from mixing to finishing operation.

Basically, good quality hardened concrete means the concrete with required strength, adequate volume stability and desired durability. In order to produce good quality hardened concrete it is necessary to monitor the various properties of fresh concrete such as, workability, segregation, bleeding, desired compaction, etc. Amongst all these, workability is the most important. The main feature of fresh concrete is the hydration of cement that is responsible for converting the fresh concrete to hardened concrete. A chemical reaction of cement along with water is known as hydration of cement and the products of this reaction are called as hydrated compounds that are in the form of gel. The quality of these hydrated compounds, which is responsible for strength and other properties of hardened concrete majorly, depends upon the quantity and quality of water and cement.

Here, the quality of water and various important properties of fresh concrete including hydration of cement, workability, etc. have been discussed. In addition, the associated parameters such as, Abrams' water cement ratio law, segregation and bleeding and factors affecting the workability, have been discussed. Finally, some of the important tests for determining the workability in laboratory/at site have been explained in brief.

Objectives

After studying this unit, you should be able to

• Describe the importance of workability, factors affecting the workability and also the importance of quality and quantity of water in manufacturing the concrete,
• Create a list the undesirable impurities present in water along with their acceptable limits for manufacturing of concrete,
• Determine the values of these parameters in laboratory or on site as per the procedures recommended by relevant IS codes/lab manuals, and
• Handle the concrete in fine way to produce a good quality concrete with better strength and durability.