Definition and Significance
Workability of concrete is defined in ASTM C 125 as the property determining the effort required to manipulate a freshly mixed quantity of concrete with minimum loss of homogeneity. The term manipulate includes the early-age operations of placing, compacting, and finishing. The effort required to place a concrete mixture is determined largely largely by the overall work needed to initiate and maintain flow, which depends on the rheological property of the lubricant( the cement paste) and the internal friction between the aggregate particles on the one hand, and the external friction between the concrete and the surface of the formwork on the other. As for concrete planetary mixer manufacturers, making high quality concrete mixer to mix concrete is their responsibility.
Consistency, measured by the slump-cone test or Vebe apparatus(described below), is used as a simple index for mobility or flowability of fresh concrete. The effort required to compact concrete is governed by the flow characteristics and the ease with which void reduction can be achieved without destroying the stability under pressure.
Stability is an index for both the water-holding capacity(the opposite of bleeding) and the coarse-aggregate-holding capacity(the opposite of segregation) of a plastic concrete mixture. A qualitative measure of these two characteristics is generally covered by the term cohesiveness. There are many different models of concrete pan mixers for sale on the market. You should be cautious.
It should be apparent by now that workability is a composite property, with at least two main components:
Consistency (describes the ease of flow)
Cohesiveness (describes the stability or lack of bleeding and segregation characteristics)
Like durability, workability is not a fundamental property of concrete; to be meaningful it must be related to the type of construction and the method of placement, compaction, and finishing. A concrete that can readily be placed in massive foundation without segregation, may be entirely unworkable to form a thin structural member. Concrete judged to be workable when high- frequency vibrators are available for consolidation, would be unworkable if hand tamping is used. The self loading concrete mixer truck has advantages in making and conveying concrete.
The significance of workability in concrete technology is obvious. It is one of the key properties that affect constructibility. Regardless of the sophistication of the mix design procedure used and other considerations, such as cost, a concrete mixture that cannot be placed easily or compacted fully is not likely to yield the expected strength and durability characteristics.