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Comprehensive Guide on Fresh Concrete Workability

Learn about the definition of workability, factors affecting it like water content, mix proportions, aggregate size, shape, texture, grading, and the use of admixtures for optimal results. Understand how temperature and time impact workability.

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Comprehensive Guide on Fresh Concrete Workability

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  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.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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

  10. FLAT ELONGATED ROUND ANGULAR

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. Temperature : Temperature Workability fresh concrete aggregates paste

  16. 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

  17. Questions?????

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