SSC JE Civil Engineering 2014 Set 2 Solved Paper

Following factors affecting the workability of concrete are
1. Water content : Workability of concrete increases with increase in water content. Higher the water content per cubic meter of concrete, the higher will be the fluidity of concrete.
2. Aggregate/Cement ratio : The higher the aggregate/cement ratio, the leaner is the concrete. In lean concrete, less quantity of paste is available for providing lubrication, hence mobility of aggregate is reduced, resulting poor workability.
3. Size of aggregate : For a given water content, the bigger size aggregate will give higher workability.
4. Shape of aggregate : Rounded aggregate shows a high workability as compared to angular, flaky or elongated aggregates. Rounded aggregate has less surface and less void, so excess paste is available to give better lubricating effect for a given volume or weight. It also has less friction resistance.
5. Grading : Grading of aggregate have the maximum influence on workability. The better the grading, the less is the amount of void in it. When total void are less, excess paste is available to give better lubricating effect.
6. Surface texture of aggregate : Porous and non-saturated aggregate will require more water than a non-absorbent aggregate. For same degree of workability latter will require less water.
7. Time of transit : Fresh concrete stiffens with time and loss workability.
8. Temperature : High temperature reduces workability and increases slump loss. Slump loss is less influenced by temperature in stiff mixes because this type of mix is less affected by a change in water content.
9. Admixtures : Plasticizer and super plasticizers, air entraining agents and Pozzolanic materials greatly improve the workability.
Air entraining agents used to increase the workability. It creates a large number of very minute air bubbles. These bubbles get distributed throughout the mass of concrete and acts as rollers and increases workability.