Water requirement for concrete to be compacted fully for given effort or practical effort is a measure of workability; also placing without segregation and efficient finishing are also important in workability of concrete. A workable concrete is desirable in concrete engineering to facilitate placing, compaction and other subsequent operations.
Water required for particular mix design is measured by the weight of cement as a ratio of it. Now we will learn about the influence of aggregate shape over workability of concrete. We concrete engineers are familiar with aggregate shapes of
-round
-Angular
-elongated
-flaky etc.
Now we have to consider which shape has more surface area and posses more voids which are very important in measuring water requirement. Actually, angular, flaky and elongated shaped aggregate produce a concrete of harsh property while round or cubical shaped aggregate results a concrete of smooth, less frictional resistant i.e. can be compacted easily with a less compaction effort.
Later three types of aggregate have more surface area and more voids as well which leads to more placement and compaction difficulties. These types of aggregate require huge water to have only optimum compaction which leads to selection of large water-cement ratio. We have discussed about relation between strength and W/C ratio of concrete.
In case of round shape aggregate, comparatively less volume of water produce concrete of more workability. Dear reader you perhaps read our posts regarding high performance concrete, where one of the main aims is to reduce W/C ratio to minimum value. In many cases only 0.25 W/C is expected. Though this degree of W/C ratio cannot be achieved only by selecting right aggregate shape, but aggregate shape plays a important role over there.
The advantage of round aggregate is observed in case of river sand or gravel. This aggregate provides greater workability in comparison to aggregates that derived from crushing.
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