(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