Prepared By : Mahavirsinh Parmar (120224106002) Vidhan Patel (120220106006) Sanjay Thakor

1. Fresh Concrete Workability Prepared By : Mahavirsinh Parmar (120224106002) Vidhan Patel (120220106006) Sanjay Thakor (120220106038) Guide By: Prof. D. J.Variya, Department of Applied Mechanics, GEC, Patan.

2. Main topics : Definition Workability Factors affecting workability 2 3 1

3. Fresh concrete “ Fresh Concrete is a freshly mixed material which can be moulded into any desired shape.”

4. Workability : • The diverse requirements of partial properties of concrete like mix ability, stability, transportability, place ability, mobility, compact ability and finish ability are collectively referred to as ‘workability’. It thus, a composite property. • IS : 6461 (Part-VII) – 1973 defines workability as that property of freshly mixed concrete or mortar which determines the ease and homogeneity with which it can be mixed, placed, compacted and finished. • As per Road Research Laboratory, U.K. workability isdefined as ‘the property of concrete which determines the amount of useful internal work necessary to produce full compaction.

6. Water Content : • Water Content is one of the important factor affecting workability. • Water plays a role of lubricant in the fresh concrete. • The addition of water to concrete increases the fluidity of • concrete. • Use of higher water content will result in more serious problems of • shrinkage and creep of hardened cement. • Therefore, an increase in water content must be accompanied by an • increse in cement content in order to maintain the water / cement • ratio constant so that the strength of concrete does ot decreases.

7. Mix Proportions : • Aggregate / cement ratio is an important factor affecting workability. • The higher the aggregate / cement ratio, the leaner is the concrete. • In the lean concrete, less amount of paste is available for lubrication of aggregate particles, per unit surface area of aggregate and hence the mobility of aggregate is restrained. • i.e. Workability is reduced.

8. Size of Aggregates : • The bigger size of aggregate, the lesser is the surface area. • Hence, less amount of paste is required to lubricate the surface of aggregates. • Hence, for a given quantity of water and paste, bigger size of aggregates will give higher workability.

9. Shape of aggregates : • The shape of aggregates have great influence on the workability of concrete. • The rounded and cubical shaped aggregates requires comparatively less quantity of paste for lubrication and gives better workability. ROUND AGGREGATES

10. Shape of aggregates : • On the other hand, angular and rough aggregates, having more surface area, requires more quantity of paste for lubrication and reduces workability. • Similarly, increased flakiness and elongation of aggregates also reduces workability. ANGULAR FLAKY

11. FLAT ELONGATED ROUND ANGULAR

12. Surface texture of aggregates : • For the same value of aggregates, the total surface area of rough textured aggregate is more than the surface area of smooth textured rounded aggregate. • Hence, smooth textured aggregate will show better workability while rough textured aggregate will give poor workability. • Further, smooth, textured aggregate offer less inter particle frictional resistance and contributes to higher workability. ROUGH SMOOTH

13. Grading of aggregates : • The grading of aggregate has a considerable effect on workability of concrete. • A well graded aggregate is one which has the least amount of voids in a given volume. • When the total voids are less, excess paste is available to give better lubricating effect. • The better the grading, the less is the void content and higher the workability.

14. Use of admixtures : • Use of plasticizers and super plasticizers greatly improve the • workability . • The use of air-entraining agents produce a large number of minute • air bubbles in the mass of concrete. • These bubbles act as ball bearings the particles to side paste • each other and give easy mobility to the particles, and increases • marketability of concrete. • The fine glassy particles of pozzolanic materials, inspite of increasing • the surface area, provide better lubricating effects and improve • workability.

15. Time : • The fresh concrete loses workability with time mainly because of the loss of moisture due to evaporation. • A part of mixing water absorbed by the aggregate or lost by evaporation and part of it is consumed in hydration of cement. • On an average a 125 mm slump of concrete may lose about a 50 mm slump in the first hour. • The workability in terms of compacting factor decreases by about o.10 during the period of one hour from the time of mixing.

16. Temperature : Temperature Workability fresh concrete aggregates paste

17. References: • Concrete Technology “ Theory and Practice” : M.S. Shetty, S. Chand and Company • Concrete Technology: A.R. Santha Kumar, Oxford University Press • Concrete Technology : K.T. Krishnaswamy & etal, Dhanpat Rai & Sons • Properties of Concrete : A.M.Naville, 4th Edition , Pearson Education

18. Questions?????