CONCRETE MIX DESIGN BUILDING TECHNOLOGY AND MANAGEMENT (b

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CONCRETE MIX DESIGN

• BUILDING TECHNOLOGY AND MANAGEMENT

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INTRODUCTION

• Concrete is obtained by mixing cement, fine
  aggregate, coarse aggregate, water and admixtures
  in required proportions. The mixture when placed
  in forms and allowed to cure becomes hard like
  stone.
• The hardening is caused by chemical action
  between water and the cement due to which
  concrete grows stronger with age.
• It is the most widely-used man-made construction
  material in the world.

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CONCRETE MAKING MATERIALS

• Cement
• Aggregates
• Water
• Admixtures

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CEMENT

• Cement and water forms the active component of
  concrete, while the inactive group comprises the
  fine and coarse aggregates.
• The cement and water form a paste that hardens
  and bonds the aggregates together.
• Types of Cement
• Although around 18 types of cements are
  recognized by BIS, more commonly used ones are
• Ordinary Portland Cement 33, 43, 53 grade OPC,
• Blended Cements (PPC and PSC).
• Sulphate Resisting Cement (SRC),
• Low Heat Portland Cement (LHPC),
• Hydrophobic Portland Cement,
• Colored Cement (White Cement).

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AGGREGATES

• They are cheaper than cement and impart greater
  volume stability and durability to concrete.
• The main purpose is to provide bulk to the
  concrete.
• Some of the aggregates may be chemically active.
• CLASSIFICATION
• Geological origin natural and artificial
• Size fine, coarse and all-in
• Shape rounded, irregular, angular, flaky and
  elongated
• Unit weight normal-weight, heavyweight and
  lightweight

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WATER

• The most important and least expensive ingredient
  of concrete.
• One part of the water is used in the hydration of
  cement to form the binding matrix.
• The remaining water affords lubrication and
  workability to the concrete.
• Water-cement ratio depends on the grade of
  concrete, its workability, durability, nature and
  type of aggregates etc.
• Potable water is ideal for concreting.
• Seawater may be used in PCC.

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ADMIXTURES

• Added to the concrete immediately or during
  mixing to modify its properties in the fresh or
  hardened state.
• Types
• Accelerators - speed up the initial set of
  concrete.
• Retarders delay the setting time of concrete
  mix.
• Plasticizers and Super-plasticizers - water
  reducers.
• Air entraining admixtures
• Water proofers
• Pigments
• Corrosion-inhibiting chemicals
• Antifungal admixtures

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TYPES OF CONCRETE MIXES

• NOMINAL MIX
• Mixes of fixed proportions, IS456-2000 permits
  nominal mixes for concretes of strength M20 or
  lower
• DESIGN MIX
• Designed on the basis of requirements of the
  concrete in fresh and hardened states.

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• TRIAL MIXES
• Prepared to verify whether the Design Mix would
  perform as per the assumptions. If appreciable
  variation exists, the available alternatives are
• directly employ the trial mix proportions at the
  site
• modify the trial mix proportions on the basis of
  intuition and employ the revised proportions at
  the site
• prepare further trial mixes incorporating changes
  in the proportions based on the feedback
  generated from the previous mix.

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CONCRETE MIX DESIGN

• DEFINITION
• Mix Design is the science of determining the
  relative proportions of the ingredients of
  concrete to achieve the desired properties in the
  most economical way.

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PRINCIPLES OF MIX DESIGN

• The environment exposure condition for the
  structure
• The grade of concrete, their characteristic
  strengths and standard deviations
• The type of cement
• The types and sizes of aggregates and their
  sources of supply
• The nominal maximum sizes of aggregates
• Maximum and minimum cement content in kg/m3
• Water cement ratio
• The degree of workability of concrete based on
  placing conditions

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• 9 Air content inclusive of entrained air
• The maximum/minimum density of concrete
• The maximum/minimum temperature of fresh concrete
• Type of water available for mixing and curing
• The source of water and the impurities present in
  it.

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IS 4562000
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IS 4562000
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IS 4562000
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FACTORS DEFINING THE CHOICE OF MIX PROPORTIONS

• Compressive Strength
• Workability
• Durability
• Type, size and grading of aggregates
• Aggregate-cement ratio

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• COMPRESSIVE STRENGTH
• Abrams Law
• log F log A1 x log B1
• where F is the compressive strength
• A1, B1 are constants and
• x is the w/c ratio by weight

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• WORKABILITY
• that property of freshly mixed concrete which
  determines the ease and homogeneity with which it
  can be mixed, placed, consolidated and finished.
• DURABILITY
• the resistance to weathering action due to
  environmental conditions such as changes in
  temperature and humidity, chemical attack,
  abrasion, frost and fire.

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REQUIREMENTS AND TESTS OF MATERIALS REQUIRED FOR
MIX DESIGN

• ASSIGNMENT 1 TO BE SUBMITTED BY 07-02-2011
• Roll s 01-21 Cement
• Roll s 22-42 Aggregates
• Roll s 43-63 Water and Admixtures

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METHODS OF CONCRETE MIX DESIGN

• American Concrete Institute Committee 211 method
• Bureau of Indian Standards Recommended method IS
  10262-82
• Road note No. 4 (Grading Curve) method
• Department Of Environment (DOE - British) method
• Trial and Adjustment Method
• Fineness modulus method
• Maximum density method
• Indian Road Congress, IRC 44 method

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American Concrete Institute Method of Mix Design

• (a) Data to be collected
• (i ) Fineness modulus of selected F.A.
• (ii ) Unit weight of dry rodded coarse
  aggregate.
• (iii ) Sp. gravity of coarse and fine aggregates
  in SSD condition
• (iv ) Absorption characteristics of both coarse
  and fine aggregates.
• (v ) Specific gravity of cement.
• (b) From the minimum strength specified, estimate
  the average design strength by using standard
  deviation.
• (c) Find the water/cement ratio from the strength
  and durability points of view. Adopt the lower
  value.

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• (d) Decide the maximum size of aggregate to be
  used. Generally for RCC work 20 mm and
  pre-stressed concrete 10 mm size are used.
• (e) Decide workability in terms of slump for the
  given job.
• (f ) The total water in kg/m3 of concrete is
  determined, corresponding to the selected slump
  and selected maximum size of aggregate.
• (g ) Cement content is computed by dividing the
  total water content by the water/cement ratio.
• (h) Select the bulk volume of dry rodded coarse
  aggregate per unit volume of concrete, for the
  particular maximum size of coarse aggregate and
  fineness modulus of fine aggregate.

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• ( j ) The weight of C.A. per cubic meter of
  concrete is calculated by multiplying the bulk
  volume with bulk density.
• (k ) The solid volume of coarse aggregate in one
  cubic meter of concrete is calculated by knowing
  the specific gravity of C.A.
• (l ) Similarly the solid volume of cement, water
  and volume of air is calculated in one cubic
  meter of concrete.
• (m) The solid volume of FA is computed by
  subtracting from the total volume of concrete the
  solid volume of cement, CA, water and entrapped
  air.
• (n) Weight of fine aggregate is calculated by
  multiplying the solid volume of fine aggregate by
  specific gravity of F.A.

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ACI METHOD DESIGN EXAMPLE

• 1 Design a concrete mix for the construction of
  an elevated water tank. The specified design
  strength of concrete (characteristic strength) is
  30 MPa at 28 days measured on standard cylinders.
  Standard deviation can be taken as 4 MPa. The
  specific gravity of FA and C.A. are 2.65 and 2.7
  respectively. The dry rodded bulk density of C.A.
  is 1600 kg/m3, and fineness modulus of FA is
  2.80. Ordinary Portland cement (Type I) will be
  used. A slump of 50 mm is necessary. C.A. is
  found to be absorptive to the extent of 1 and
  free surface moisture in sand is found to be 2
  per cent. Assume any other essential data.

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• 1 Mean Cylinder Compressive Strength
• Assuming 5 per cent of results are allowed to
  fall below specified design strength,
• The mean strength,
• fm fmin ks
• 30 1.64 x 4
• 36.5 MPa
• Water/cement ratio
• Strength criteria
• Durability criteria

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Strength Criteria
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Durability Criteria
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3 Mixing Water Content
Slump 50 mm Maximum size of aggregate 20 mm
Concrete is non air-entrained
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The mixing water content is 185 kg/m3 of concrete
The approximate entrapped air content is 2.
The required cement content 185/0.47
394 kg/m3
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4 Bulk Volume of C.A.
Maximum size of C.A 20mm
Fineness Modulus of F.A. 2.80
Find the dry rodded bulk volume of C.A.
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The dry rodded bulk volume of C.A. 0.62 per
unit volume of concrete
The weight of C.A. 0.62 x 1600
992 kg/m3
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5 The first estimate of density of fresh
concrete
2355 kg/m3
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6 Weight of FA
The weight of all the known ingredients of
concrete Weight of water 185 kg/m3 Weight
of cement 394 kg/m3 Weight of C.A.
992 kg/m3 Weight of F.A. 2355 (185
394 992) 784
kg/m3
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Alternatively, the weight of F.A. can be
determined by the more accurate absolute volume
method
Absolute Volume weight/(1000?) m3
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Total absolute volume 697 x 103 cm3
Absolute volume of F.A. (1000 697) x 103
303 x 103 Weight of
FA 303 x 2.65
803 kg/m3
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7 Estimated quantities of materials per cubic
meter of concrete are
Cement 394 kg F.A 803 kg C.A 992 kg Water
185 kg
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8 Proportions C F.A C.A water 394 803
992 185 1 2.04 2.52 0.47 Weight of
materials for one bag mix in kg 50 102 126
23.5
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9 The above quantities is on the basis that
both F.A and C.A are in saturated and surface dry
condition (SSD conditions).
FA has surface moisture of 2 Total free surface
moisture in FA (2/100 x 803)
16.06
kg/m3 Weight of F.A in field condition 803
16.06 819.06 kg/m3
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C.A absorbs 1 water
Quantity of water absorbed by C.A. (1/100 x
992) 9.92 kg/m3 Weight of C.A in field
condition 992 9.92
982 kg/m3
Change in Water Content
Water contributed by F.A 16.06 kg Water
absorbed by C.A. 9.92 kg Extra water
contributed by aggs. 16.06 9.92 6.14 kg
Total water content 185.00 6.14
179 kg/m3
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Quantities of materials to be used in field,
corrected for free surface moisture in F.A and
absorption characteristic of C.A
Cement 394 kg/m3 F.A. 819 kg/m3 C.A.
982 kg/m3 Water 179 kg/m3 Field density of
fresh concrete 2374 kg/m3
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• 2. A mix with a mean 28-day compressive strength
  of 35 MPa and a slump of 50 mm is required, using
  OPC. The maximum size of well shaped, angular
  aggregate is 20mm, its bulk density is 1600 kg/m3
  and its specific gravity is 2.64. The available
  fine aggregate has a fineness modulus of 2.60 and
  a specific gravity of 2.58. No air-entrainment is
  required.

Water/Cement ratio
As durability criteria is not mentioned, consider
strength alone
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Strength Criteria
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• Water/cement ratio 0.48

Slump 50 mm Max size of aggregate 20 mm
Determine water content
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• Composition of concrete (kg/m3)
• Water 185
• Cement 386
• CA 1020
• FA 738
• Density of Concrete 2329 (kg/m3)

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ROAD NOTE No. 4 METHOD OF MIX DESIGN

• Proposed by the Road Research Laboratory, UK
  (1950)
• Procedure
• 1. The average compressive strength of the mix to
  be designed is obtained by applying control
  factors to the minimum compressive strength
• Water/cement ratio is read from compressive
  strength v/s w/c ratio graph
• Proportion of combined aggregates to cement is
  determined from tables, for maximum size 40 mm
  and 20 mm
• If the aggregate available differs from the
  standard gradings, combine FA and CA so as to
  produce one of the standard gradings

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• The proportion of cement, water, FA and CA is
  determined from knowing the water/cement ratio
  and the aggregate/cement ratio.
• Calculate the quantities of ingredients required
  to produce 1 m3 of concrete, by the absolute
  volume method, using the specific gravities of
  cement and aggregates.

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DRAWBACKS OF ROAD NOTE NO. 4 METHOD

• Cannot be used directly for the design of air -
  entrained concrete
• No recommendations for durability or strength,
  regarding the water/cement ratio
• The design tables refer to mixes in which the FA
  and CA are of the same shape
• In selecting aggregate/cement ratio, only 3
  shapes of aggregates and 4 gradings are
  recommended.

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DOE METHOD OF MIX DESIGN

• Can be used for concrete containing fly ash.
• PROCEDURE
• Target mean strength is calculated
• Select water/cement ratio, from the type of
  cement and CA. Compare this with the ratio from
  durability conditions.
• Decide the water content for required workability
• Compare the cement content with the minimum
  cement content value and adopt the higher value
• Find out the total aggregate content
• Determine the proportion of FA using the
  appropriate FA v/s CA size graph, and find the
  weight of CA and FA
• Work out a trial mix.

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BIS RECOMMENDED MIX DESIGN METHOD

• The BIS recommended mix design procedure is
  covered in IS 10262-82.
• In line with IS 456-2000, the first revision IS
  10262-2009 was published, to accommodate some of
  the following changes
• Increase in strength of cement
• Express workability in terms of slump, rather
  than the compacting factor
• Extend the W/C ratio v/s compressive strength
  graph

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Modifications in IS 10262-2009
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MIX DESIGN BASED ON IS RECOMMENDATIONS

• Based on IS 102621982
• Procedure

• Target mean strength for mix design
• fck fck tS
• where fck characteristic compressive strength
  at 28 days
• S standard deviation
• t a statistical value depending on
  the risk factor.

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• 2. Selection of Water/Cement ratio

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• 3. Estimation of Entrapped Air

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• 4. Selection of Water Content and Fine to Total
  Aggregate ratio

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• 5. Calculation of Cement Content
• cement by mass Water content/Water cement ratio
• To be checked against the minimum cement content
  for the requirement of durability and the greater
  of the two values to be adopted.

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• 6. Calculation of aggregate content

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• 7. Actual quantities required for mix
• Adjust the mix for deviations from assumed
  conditions

8. Check the calculated mix proportions
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DESIGN EXAMPLE BIS RECOMMENDED METHOD

• Grade M20
• (a ) Design stipulations
• (i ) Characteristic compressive strength
• required in the field at 28 days - 20 MPa
• (ii ) Maximum size of aggregate - 20 mm (angular)
• (iii ) Degree of workability - 0.90 compacting
  factor
• (iv ) Degree of quality control - Good
• (v ) Type of Exposure - Mild

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• (b) Test data for Materials
• (i ) Specific gravity of cement - 3.15
• (ii ) Compressive strength of cement at 7 days -
  Satisfies the requirement of IS 2691989
• (iii ) 1. Specific gravity of coarse aggregates
  - 2.60
• 2. Specific gravity of fine aggregates - 2.60
• (iv ) Water absorption
• 1. Coarse aggregate - 0.50
• 2. Fine aggregate - 1.0
• (v ) Free (surface) moisture
• 1. Coarse aggregate - Nil
• 2. Fine aggregate - 2.0

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Design Procedure

• Target mean strength of concrete
• fck fck tS

fck 20, t 1.64 , S 4
fck 26.6 MPa
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2. Selection of Water/Cement Ratio
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Durability Criteria Mild Exposure Conditions
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• W/C ratio from strength considerations 0.50
• W/C ratio from durability considerations 0.55
• Adopt the lower value

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3. Selection of water and sand content
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Adjustments in Water and Sand Contents
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4. Determination of cement content

• Water-cement ratio 0.50
• water 191.6 kg/m3

Cement 191.6/0.50 383 kg/m3
Is this satisfactory for mild exposure
condition?
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5. Determination of coarse and fine aggregate
contents

• Specified max. size of aggregate 20 mm
• Corresponding entrapped air 2

fa 546 kg/m3, Ca 1188 kg/m3
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Final Mix Proportions