ABSTRACT
The properties of fresh concrete are important since they affect the properties of hardened concrete. For a concrete to be of a desired quality in hardened state for a specific set of job conditions, it must fulfil the following requirements in fresh state (Mindess and Young, 1981):
1. Easily mixed and transported 2. Be uniform both within batch and between batches 3. Have flow properties that makes it fill the forms properly 4. Be compacted sufficiently without excessive effort 5. Not be segregated during placing and compaction 6. Be finished properly
It is obvious that all these requirements are subjective and qualitative. Therefore, the term workability which embodies all the properties mentioned earlier is preferred. Workability of concrete is defined as that property determining the effort required to place, compact and finish a freshly mixed quantity of concrete with a minimum loss of homogeneity (ASTM C 125, 2000). Workability consists basically of consistency and cohesiveness of the fresh concrete. In other words, fresh concrete must be mobile and yet sufficiently stable. Mobility of fresh concrete which is determined by measuring its consistency depends largely on its ‘wetness’ whereas its stability has two aspects: water-holding and coarse aggregateholding abilities. The former shows the resistance to bleeding and the latter shows the resistance to segregation. Both phenomena result in the separation of concrete components in fresh state during placing and compaction. Segregation is the separation of coarse aggregate particles from the concrete body and/or settlement of heavy particles whereas bleeding is the appearance of some of the water in fresh concrete on the surface after compaction and finishing.
