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Concrete Mix Design Manual

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  • (Fourth Revised Edition)

    CONCRETE MIX

    DESIGN

    N.Pokharel

    1

  • INTRODUCTION 1

    AMERICAN CONCRETE INSTITUTE (ACI) METHOD 4

    GENERAL 5

    LIMITATION ACI METHOD 5

    REQUIRED PARAMETERS OF INGREDIENTS 5

    EQUIPMENT AND APPARATUS 6

    DESIGN GUIDE LINE 7

    SUMMARY OF DESIGN PROCEDURE 12

    MIX DESIGN DATA SHEET 13

    DESIGN STEPS 14

    COMPRESSIVE STRENGTH TEST OF SAMPLE 17

    GRAPHICAL DETERMINATION OF REQUIRED

    W/C RATIO 18

    HIGH STRENGTH MIX METHOD 19

    GENERAL 20

    FEATURE OF DESIGN 20

    LIMITATION OF HIGH STRENGTH DESIGN 21

    REQUIRED PARAMETERS OF INGREDIENTS 22

    DESIGN PROCEDURE 23

    EQUIPMENT AND APPARATUS 24

    MIX DESIGN DATA SHEET 27

    DESIGN STEPS 28

    Contents

    2

  • INTRODUCTION

    1. American Concrete Institute (ACI)

    2. High Strength Mix

    Cement concrete is an artificial rock which can be made of required

    size, shape, and strength for the structure in construction work. It is the

    most widely used construction material and is very hard to find its

    substitution . Technologists may select this construction material as their

    requirement such as strength, permanance, durability, impermeability, fire-

    resistance, abrasion resintance etc. Regarding these required properties of

    concrete, it is very important to determine the proportion as well as quality

    of its constituents. Determining process of selecting suitable ingredients,

    its proportion, producing minimum strength and durability as economically

    as possible is called mix design.

    In Nepal, still we adopt the arbitrary proportional ratio method in

    many organizations of HMG departments, municipalities, private buildings

    and other small scaled projects. But most of the large scaled foreign aid

    projects can not ignore the necessity of mix design of the concrete for

    precise supervision. The arbitrary proportinal method may always not

    govern the true proportion of ingredients and cause segregation, bleeding,

    uneconomic and weaker or over strength. People are not conscious to hire

    Basic concept of mix design prevails on the relationship between

    two essential ingredients i.e. aggregates and paste. Paste is not termed as

    solution of cement in water, but the suspension of cement particles. Hence

    the degree of dilution of paste may affect workability and strength of the

    concrete. The more dilute the paste, the greater the spacing between

    cement particles and thus the weaker will be ultimate paste structure. It is

    therefore helpful to consider more closely the structure of the paste. It is

    important that as little paste as possible should be used and here lies the

    importance of grading of aggregates. Excess of paste cause high cost,

    greater shrinkage, greater susceptibility to percolation of water and

    therefore attack by aggressive waters and weathering action. This is

    achieved by minimising the voids by well gradation.

    There are several methods of mix design to adopt, but here we

    describe only two of them in detail which are more effective and viable in

    the contest of Nepal. Most of the renowned projects and agencies of Nepal

    have been adopting these two mix-design methods widely as per their

    requisites of the concrete materials. These methods are -

    3

  • 1. Cement:

    a) Portland cement, of possibly 53 grade

    b) Specific gravity 3.15

    2. Fine Aggregate

    a) Required size and well-graded and washed.

    b) Saturated surface dry condition (SSD)

    c) Very less weathering, alluvial (glacier) blueish grey:

    Specific gravity 2.65 to 2.67 Absorption 1.0%

    d) Less weathering, alluvial deposit (perennial river), yellowish grey:

    Specific gravity 2.62 to 2.64 Absorption 1.5%

    e) Less weathering, alluvial deposit (stream), pale yellow:

    Specific gravity 2.59 to 2.61 Absorption 2.0%

    f) Washed crushed rock:

    Specific gravity 2.62 to 2.65 Absorption 1.5%

    g) Fineness modulus (FM)

    coarser 3.1, moderate 2.9, fine 2.6, very fine 2.3

    3. coarse Aggregate

    a) Required size and well-graded and washed.

    b) Saturated surface dry condition (SSD)

    c) Alluvial / glacier (fresh deposit):

    Specific gravity 2.67 to 2.72 Absorption 0.3%

    d) Alluvial / common perennial river (fresh deposit):

    Specific gravity 2.62 to 2.66 Absorption 0.5%

    e) Alluvial (loose conglomerate):

    Specific gravity 2.62 to 2.65 Absorption 0.7%

    f) Washed crushed rock (stream),

    Specific gravity 2.62 to 2.65 Absorption 0.7%

    a technician to conduct the supervision and rely on a head mason who will

    be contractor of their private construction. In Terai region of Nepal, most of

    these masons have tendency of using more sand with large size coarse

    aggregate and less sand with small size aggregate which is absolutely

    wrong approach . Due this reason, people find their construction defective

    after all.

    Regarding these common problems all over the country, it is highly

    necessary to follow the technical way of construction wheather it's small or

    huge construction. Possibly, it is needed to conduct the test of concrete

    materials to obtain true design parameters. Otherwise adopt in design

    these parameters for concrete materials, if conducting the test is not

    possible. These parameters are here tabulated below according to practice

    and records.

    4

  • g) Compacted density (Kg/m3):

    Aggregate

    Sp.gr. 2.62 - 2.65 2.66 - 2.69

    50 mm

    16001600

    17001750 1800

    1650 1400

    Crushed rock:

    1650 1650

    1550

    From the above statement, a technical person can easily decide the

    nearest true properties of concrete material according to its possession

    regarding location, appearance etc. After conforming these data

    tentatively, here we can proceed the mix design calculation as per our

    requirements. It may give more accurate proportion and workability than

    the arbitrary ratio gives. If little bit difference in volume or workability is

    found, it may be adjusted very easily.

    1850 1750

    2.62 - 2.65 2.66 - 2.69 2.70 - 2.72

    1450 1500

    1700 1550

    38 mm 1750

    10 mm

    20 mm

    1450

    1800 1600

    Screened gravel

    5

  • American Concrete Institute (ACI)

    METHOD

    6

  • GENERAL

    F

    F

    F

    LIMITATION ACI METHOD

    F It is better to design a concrete mix only up to 35 MPa of plastic state.

    F

    F

    REQUIRED PARAMETERS OF INGREDIENTS

    A. CEMENT

    1. Grade and type as ACI - classification

    2. Specific Gravity

    B. FINE AGGREGATE

    1. Gradation (Sieve Analysis)

    2. Fineness Modulus (FM i.e. 2.4 to 3.1preferable)

    3. Specific Gravity (SSD Bulk)

    4. Absorption

    Type-I, non air-entraining (OPC) as per ASTM/C-150, Specific Gravity

    of 3.15

    Coarse aggregate:- Gradation as per ASTM/C-33, Specific Gravity of

    2.68, Absorption of 0.5%.

    Fine Aggregate :- Gradation as per ASTM/C-33, Specific Gravity of

    2.64, Absorption of 0.7%, FM of 2.8

    The American Concrete Institute (ACI) has recommended an efficient

    procedure of concrete mix design considering more economical use of

    locally avilable materials to produce desirable workability, durability and

    strength. The ACI method is able to produce concretes from very stiff to

    fluid state workability as it is required in different conditions.The design

    tables incorporating the basic relationships between the parameters, are

    useful in selecting optimum combinations of the ingredients of non air-

    entrained or air-entrained concrete mixes. The following design criteria are

    assumed in formulating the design tables:

    Though the specific gravity of coarse aggregate is taken 2.68 in this

    ACI manual but if it is different see footnote of table-4.

    It is important to note that the mix design tables serve as a guide in

    selecting proportions and suitable minor adjustments should be

    effected in the field for any departures in quality of aggregates and

    type of cement used.

    Before starting to design a concrete mix, it is very much important to have

    all informations about concrete ingredients i.e physical test reports. These

    physical parameters may be obtained by own laboratory test or by the

    manufacturer. Basicaly for the design mix, the following parameters should

    be available in the time.

    7

  • C. COARSE AGGREGATE

    1. Gradation (Sieve Analysis)

    2. Dry Rodded Unit Weight

    3. Specific Gravity (SSD Bulk)

    4. Absorption

    D. WATER

    1. Chemical content(free of salt and alkalies)

    2. Turbidity (potable or clear)

    EQUIPMENT AND APPARATUS

    A. SLUMP TEST 2. Mixer or mixing pan

    1. Slump cone 3. Triple beam balance (1 g.)

    2. Base plate 4. Scoop

    3. Tamping rod 5. Straight edge

    4. Graduated scale 6. Tamping rod or

    5. Straight edge 7. Vibrator plate

    6. Mixer (1 cft.) or 8. Rubber mallet

    7. Mixing pan with shovel 9. Weighing containers

    8. Scoop 10. Thermometer

    9. Triple beam balance (1 g.) C. STRENGTH TEST

    10. Weighing containers 1. Compressive St. machine

    B. SAMPLE PREPARATION 2. Triple beam balance (1 g.)

    1. 6 nos. cylinder or cube mould 3. Rubber sheet

    To perform a mix design, the following equipment or apparatuses must be

    available in advance:

    10

    15

    20

    25

    30

    35

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