Prepared By :

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
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
  is defined as the property of concrete which
  determines the amount of useful internal work
  necessary to produce full compaction.

5
(No Transcript)
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?????