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Friday, 2 February 2018

Properties of Green Concrete

1. Workability: This is defined as the ease with which concrete can be compacted fully without
seggregating and bleeding. It can also be defined as the amount of internal work required to fully
compact the concrete to optimum density. The workability depends upon the quantity of water, grading,
shape and the percentage of the aggregates present in the concrete.
Workability is measured by

(a) The slump observed when the frustum of the standard cone filled with concrete is lifted and
removed.
(b) The compaction factor determined after allowing the concrete to fall through the compaction
testing machine.
(c) The time taken in seconds for the shape of the concrete to change from cone to cylinder when
tested in Vee-Bee consistometer.
The suggested values of workability for different works are as shown in Table 3.2.

2. Segregation: Separation of coarse particles from the green concrete is called segregation.
This may happen due to lack of sufficient quantity of finer particles in concrete or due to throwing of theconcrete from greater heights at the time of placing the concrete. Because of the segregation, the
cohesiveness of the concrete is lost and honey combing results. Ultimately it results in the loss of
strength of hardened concrete. Hence utmost care is to be taken to avoid segregation.

3. Bleeding: This refers to the appearance of the water along with cement particles on the
surface of the freshly laid concrete. This happens when there is excessive quantity of water in the mix or
due to excessive compaction. Bleeding causes the formation of pores and renders the concrete weak.
Bleeding can be avoided by suitably controlling the quantity of water in the concrete and by using finer grading of aggregates.

4. Harshness: Harshness is the resistance offered by concrete to its surface finish. Harshness is
due to presence of lesser quantity of fine aggregates, lesser cement mortar and due to use of poorely
graded aggregates. It may result due to insufficient quantity of water also. With harsh concrete it is
difficult to get a smooth surface finish and concrete becomes porous.

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