Ethio Construction Engineering

👉What do we mean by workability of concrete?

🚧What factors do affect it?

🚧How do we know if a concrete is too workable?

🚧Is there any scientific way of knowing degree of workability of a concrete?

📜Workability of concrete is defined as the ease and homogeneity with which a freshly mixed concrete or mortar can be mixed, placed, compacted and finished. Strictly, it is the
amount of useful internal work necessary to produce 100% compaction.

Another similar term used to describe a freshly prepared concrete is ‘consistency’ which is the ease with which it will flow. It is the wetness of the concrete and the measure of fluidity or mobility.

Wet concretes are more workable than dry concrete, but concretes of the same consistency may vary in workability.

A concrete which has high consistency and which is more mobile, need not be of right workability for a
particular job.

Type of work, thickness of section, reinforcements and mode of compaction are the aspects to be considered while specifying the workability for any particular job.

Workable concrete shows very less internal friction between particles and overcomes the frictional resistance with just the amount of compacting efforts provided.

Workability of the concrete depends on a number of interrelating factors.

Water content, aggregate properties, use of admixtures, fineness of cement are the factors affecting workability.

1. Water content: The increase in watercontent increases the fluidity of the concrete thus providing greater lubrication.

2. Size of aggregates: The surface area of bigger aggregates is less and hence less amount of water is required for lubricating the surface to reduce the friction. Thus the concrete having large sized aggregate is more workable (of course, within certain limits) And other properties of aggregate will affect the workability of concrete.

3. Mix proportions: Aggregate/cement ratio is the measure of how lean or rich the concrete is.

If aggregate/ cement ratio is
higher, the concrete becomes leaner.

In lean concrete less paste is available for the lubrication of the aggregate, while in rich
concrete with low a/c ratio, more paste is available which makes the mix more
cohesive and hence provides better workability.

4. Use of admixtures: Use of admixtures in concrete is the major factor that affects the workability.

The use of plasticizers and super-plasticizers amply increase the workability of the concrete.

Air entraining
agents produce air bubbles which act as rollers between particles and provide better mobility thus improving the workability.

5. Time and temperature: Fresh concrete gets stiffened as the time flows.

This is because some of the water used to mix the concrete gets evaporated and some gets absorbed by the aggregates.

Thus the workability of concrete reduces with time.

This loss of workability with time is known as slump
loss.

The effect of temperature on workability of concrete is noteworthy.

As the temperature increases, the workability of the mix reduces.

💫Measurements of Workability/ workability Tests:

-Slump Test
-Compacting Factor Test
-Vee-Bee Test
-Flow Test
-Kelly Ball Test

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