QUALITY ASSURANCE IN Civil WORKS BY S.N.PANDEY, CIVIL WORKS MANAGER, BIHAR EDUCATION PROJECT COUNCIL, PATNA

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QUALITY ASSURANCE IN
Civil WORKS BY S.N.PANDEY, CIVIL WORKS
MANAGER, BIHAR EDUCATION PROJECT COUNCIL, PATNA

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QUALITY CONSTRUCTION

• Quality construction increases the lifespan,
  stability and serviceability of the structure.
  It also combines all the resources into
  economical output and reduces unnecessary repairs
  and maintenance. To cap all it disseminates the
  reputation of the agency.
• Quality of Civil Work depends on the use of
  correct structural design, specifications and
  proper material and workmanship.
• Rational design is an effective tool for cost
  effective and quality construction. As such the
  design should be based on the latest relevant
  Indian Standards

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SPECIFICATION AND PROPER MATERIALS

• The quality building material, like Cement,
  Brick, Aggregate (Course fine) should be
  procured at competative rate. The community
  should be trained about quality of each building
  material and how to procure them. The aim is to
  procure best possible quality material at
  competative rate.

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CEMENT CONCRETE

• Followings are constituents of concrete -
• Aggregate
• Sand
• Cement
• Plasticizers for workability.

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CEMENT

• Followings are the grades of cement being
  manufactured-
• 33,43 53 MPa.
• ISI / ISO marked cement of ACC, Ultra
  tech/Ambuja Birla Gold/Lafarge, Concreto etc to
  be procured.

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CEMENT

• Price increases with increase in grades
• For good construction 33 43 grades are ideal.
• Initial setting time is 30 minutes final
  setting time is 600 minutes
• With the passage of time cement loses strength
  due to hydration as follows-
• Period - loss in strength of cement
• Three months 20
• Six 30
• Twelve months 40
• As such fresh cement is to be used

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AGGREGATES

• Coarse aggregate- 20mm down, well graded is
  required for all the R.C.C. works in buildings.
• Sand- Sand of I.S. Zone II and F.M. not less than
  2.25
• Grading of coarse and fine aggregates shall
  follow the curve of Road Note 4 which is
  attached. On the basis of large nos. of cube
  tests carried out combination of the aggregates
  is recommended for higher strength and quality
  concrete in concluding Para of this note. The
  method of test for aggregates for concrete is
  given in IS 5779.
• The nominal maximum size of coarse aggregate
  should be as large as possible within the limits
  specified but in no case greater than one-fourth
  of the minimum thickness of the member, provided
  that the concrete can be placed without
  difficulty so as to surround all reinforcement
  thoroughly and fill the corners of the form.
• For heavily reinforced concrete members as in the
  case of ribs of main beams, the nominal maximum
  size of the aggregate should usually be
  restricted to 5 mm less than the minimum clear
  distance between the main bars or 5 mm less than
  the minimum cover to the reinforcement whichever
  is smaller.

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BRICKS

• Bricks as per I.S. 1077 of class 125 preferably.
  The water absorption by the brick should be
  maximum up to 20.

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WATER CEMENT RATIO BULKAGE IN SAND

• I.S. 456 clauses 9.3 and 9.3.1 deals with
  quantity of water of maximum amount to be added
  to per 50 Kg. of cement.
• Water present in sand should be determined. The
  simplest method of determining the bulking of
  sand in the field is to fill a graduated jar with
  the sand being used in the work upto a mark. Add
  sufficient water. Sand will settle down to lower
  mark. Difference in the levels of sand gives the
  rough idea of bulking which has to be compensated
  by increase in the amount of sand. The moisture
  content and bulking of medium size sand is given
  below.
• Moisture content Bulkage
• 0.4 2
• 0.75 4
• 1.45 8
• 3.1 16
• 4 20

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WATER CENMENT RATIO BULKAGE IN SAND

• Moisture content Bulkage
• 5 22
• 8 28
• 10 26
• 12 18
• 15 14
• 20
• There is no bulkage in sand if fully saturated or
  completely dry.
• It is needless to say that very effort be made to
  make silt, clay, dust in the aggregates almost
  nil. The maximum percentage of fines in aggregate
  is limited to 3 of coarse and uncrushed fine
  aggregate according to I.S. 383

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WORK FORCE

• The work force consists of skilled unskilled
  workers as under
• SKILLED Masons, carpenter, plumber,
  electrician, blacksmith, bar benders, etc. if
  these are very well trained, this can make lot of
  dent in quality construction.
• UNSKILLED Labour force, which assist the
  skilled workers, should also be trained in order
  to achieve quality. (examples)

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QUALITY CONTROL MEASURES

• Visual inspection.
• Quantitative Quality measures.
• Testing of building material like
• Sand
• Bricks
• Concrete Mix
• Cement Water ratio
• Cement mortar

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QUALITY CONTROL OF CEMENT CONCRETE

• 1. Concrete Mix Design
• Concrete must be satisfactory in two stages,
  namely in the plastic stage and the hardened
  stage. If the condition of the plastic concrete
  is not satisfactory it can not be properly
  compacted and its structural value is reduced.
  Thus, if there are 5 of air voids due to
  incomplete compaction, the strength will be
  reduced by 30 and 10 of air voids will cause a
  loss of strength of about 60. The satisfactory
  compaction can be obtained only if the concrete
  is satisfactorily and sufficiently workable. The
  property of workability, therefore become of
  vital importance from structural point of view.
• 2. Workability of Concrete
• A Concrete is said to be workable, if it can be
  easily mixed, placed, compacted and finishes at
  the surface.
• A workable concrete should not show any
  segregation or bleeding.
• Segregation occurs when coarse aggregate try to
  separate out from the paste and get accumulated
  at one side. This results in large voids, less
  strength and less durability.

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QUALITY CONTROL OF CEMENT CONCRETE

• 3. Tests for workability
• Slump Test I.S. 1199 para 5 deals with this
  test. The slump test apparatus is very simple and
  cheap and the test can be conducted during the
  progress of work in the filed. I.S. 456 para 7.1
  prescribes the values of workability.

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QUALITY CONTROL OF CEMENT CONCRETE

• 4. Durability
• The durability of concrete depends on adequate
  cement content and low water cement ratio. Cement
  and water is needed to bind together the
  aggregates firmly. Thus, the suitable combination
  of the aggregates is key to quality concrete. The
  proper grading of the aggregates make the
  concrete dense. This also governs the quantity of
  water required for workability

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FACTOR GOVERNING QUALITY OF CONCRETE

• Cement Aggregate ratio
• Grading of the aggregates
• Volume/ weight batching
• Mixing
• Compaction
• Curing
• Water / Cement Ratio
• Quality of Sand
• Quality of Water

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FACTOR GOVERNING QUALITY OF CONCRETE

• Machine Mixing Sequence
• First pour 25 of the total quantity of water in
  the drum.
• Dry coarse and fine aggregates are to be
  discharged into drum
• Full quantity of cement is to be deposited in the
  drum
• Finally balance quantity of water to be poured.
  25 to 30 revolutions are needed for mixing with
  drum rotating _at_ 15-20 revolutions per minute

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(I.S. 456 Clauses 6.1.2, 8.2.4.1 9.1.2)Minimum
Cement Content, Maximum Water-Cement Ratio and
Minimum Grade of Concrete for Different Exposures
with Normal Weight Aggregates of 20 mm Nominal
Maximum Size

• Reinforced Concrete

Minimum Cement Content Kg/m3 Maximum Free Water- Cement Ratio Minimum Grade of Concrete
300 0.55 M 20
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(I.S. 456 Clauses 9.3 9.3.1) PROPORTIONS FOR
NOMINAL MIX CONCRETE
Grade of Concrete Total Quantity of dry Aggregates by Mass per 50 kg of Cement, to be Taken as the Sum of the Individual Masses of Fine and Coarse Aggregates, Kg, Max Proportion of Fine Aggregates to Coarse Aggregates (by Mass) Quantity of Water per 50 kg of Cement, Max
M20 250 kg i.e. coarse aggregate - 166.66 Kg Fine aggregate- 83.33 kg Generally 12 but subject to an upper limit of 11½ and a lower limit of 12½ 30
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Volume batching per bag of cement i.e. 35 liters

• 50 kg cement 250 aggregate (maximum)
• volume 0.0347 m3 Volume - 0.1389 m3
• i.e. cement aggregate ratio ¼ by volume.
• M20 (1 1.5 3)
• i.e. Cement Aggregate ratio 14.5
• By volume (per bag cement) 11.53 3552.5 105
  (all in litres)
• Hence batching is to be done by mass of the
  aggregate.

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REINFORCEMENT

• The standard trade/ I.S. marks is to be taken
  into account. In case standard bars are not
  available the weight of piece bar is to be
  determined by weighing in the shop which should
  be compared with the following table to know
  whether the bar is standard one.
• Diameter of the rod Weight in Kg/metre
• 6mm 0.222
• 8mm 0.395
• 10mm 0.617
• 12mm 0.888
• 16mm 1.578

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TIMING OF CONCRETING IN SUMMER SEASON

• In freshly laid slabs, sometimes cracks occur
  before concrete has set due to plastic shrinkage.
  This happens if concrete surface loses water
  faster than bleeding action brings it to top.
  Quick drying of concrete results in shrinkage and
  as concrete is plastic stage can not resist any
  tension, short cracks develop in the material.
  These cracks maybe 5 to 10 cm. in depth and the
  is width could be as much as 3 mm.
• Rate of evaporation from the surface of the
  concrete depends on temperature of concrete, gain
  of heat from suns radiation, relative humidity
  of ambient air and velocity of wind playing over
  concrete surface. As such in winter days, there
  is no problem of timing of concreting. In summer
  concreting should be done during early hours of
  day when aggregates and mixing water is
  comparatively cool and sun rays are slanting.
  After concreting, top surface of concrete should
  be covered with plastic sheets/gunny bags, straw
  or any other available materials. This will
  minimise surface shrinkage cracking in the
  concrete.

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FORMWORKS

• The shape, and surface finish of concrete depends
  upon the Form Work.
• Suitable chamber in the form works shall be
  provided in horizontal members of the structures,
  specially in long span to counteract the effects
  of deflection. As a rough guide, it may be 1 to
  250 for beams and 1 in 50 for cantilevers.
• The inside surfaces of formwork shall be coasted
  with soap solutions, raw linseed oil or any other
  material, approved by the Engineer in-charge so
  as to prevent adhesion of concrete to formwork.
  Release agents shall be applied strictly in
  accordance with the instructions and shall not be
  allowed to come into contact with any
  reinforcement. Immediately before concreting, all
  formwork shall be thoroughly cleaned.
• Propping and centering- Props used for centering
  shall be of steel or timber post, ballies or any
  other material, approved by the
  Engineer-in-charge.

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FORMWORKS

• The shape, and surface finish of concrete depends
  upon the Form Work.
• It should be strong to support wet concrete and
  have smooth surface to prevent loss of slurry
  from the concrete.
• Thin, deteriorated or non-vertical ballies will
  not be permitted at site.
• Timber ballies shall always be vertical and never
  be in inclined position.
• Any scaffolding shall only be on hard ground and
  not soft soil.

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STRIPPING TIME OF FORM (Ref
IS-456, Para 11.3.1)
Sl. No. Type of Formwork Minimum period before striking forms
1. Vertical formwork to columns, walls, beams 16-24 h
2. Slabs spanning up to 4.5 m Slabs spanning over 4.5 m 7 days 14 days
3. Beams and Arches spanning up to 6.0 m/ over 6.0 m 14 days/21 days
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CONCLUSION MIX DESIGN

• Following mix design of 124 (Cement Sand
  Aggregate) gives strength required for M20
• Cement Aggregate ratio - 16 (i.e. 124)
• Sand - 24
• Nominal size 10mm - 16
• Nominal size 20mm - 60
• This combination gives a minimum of 100 excess
  strength over nominal mix of 124. i.e. M15

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WATER ABSORPTION OF BRICKS

• Field Test The Test specimen shall consist of
  five whole dry bricks and shall be selected at
  random from the stack. The apparatus shall
  consist of a balance sensitive of within 0.2 to
  0.3 percent of the weight of the specimen.
• The test specimen shall be weighed and shall then
  be completely immersed in clean water at room
  temperature and allowed to remain in this State
  for a period of 24 hours. The specimen shall then
  be taken out wiped with a damp cloth and then
  weighed immediately.

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Percentage of water absorption

• Weight of bricks after 24 hours immersion
• ________________________________ x
  100
• Weight of dry bricks

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WATER ABSORPTION OF BRICKS

• Laboratory Test The Test specimen shall
  consist of five whole selected at random from the
  lot of bricks obtained. The apparatus shall
  consist of a balance sensitive to within 0.1
  percent of the weight of the specimen.
• The test specimen shall be dried to constant
  weight in ventilated oven at 1100 to 1150 . The
  specimen, shall then be cooled approximately to
  room temperature and weighed.

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• The dry specimens shall be completely immersed
  without preliminary partial immersion, in clean
  water at 15.50 to 300 C for 24 hours. Each
  specimen shall then be removed, the surface water
  wiped off with a damp cloth 2nd the specimen
  weighed. Weighing any one specimen shall be
  completed within three minutes after removing the
  specimen from the water.

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DETERMINATION OF COMPRESSIVE STRENGTH
OF BRICKS

• Five bricks shall be immersed in water at 250
  to 290 C for 24 hours. They shall then be removed
  and allowed to drains at room temperature for
  about five minutes and wiped free from surplus
  moisture. Their frogs shall be filled with mortar
  composed of one part portland cement and one and
  a half parts clean coarse sand graded to 3 mm and
  down. The bricks shall then be stored under damp
  sack for 24 hours. After the expiry of this
  period, they shall be immersed in water for seven
  days.

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• At the end of seven days, the samples of
  bricks shall be taken out, wiped dry and placed
  with the flat surfaces horizontal and the mortar
  filled face up wards between two-three plywood
  sheets each approximately 3 mm thick and
  carefully centered between the plates of the
  compression to testing machine. The load shall
  be applied axially at the uniform rate until
  failure occurs.
• Arithmetic mean of the Maximum load at failure
• Compressive Strength Area of bricks

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Thank you