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ISSN 0974-5904, Volume 05, No. 04 (02)
August 2012, P.P. 1030-1033
A Realistic Approach to Concrete Mix Design based on Cement
Strength Criteria
SUBHASH C. YARAGAL
Department of Civil Engineering, National Institute of Technology Karnataka, Surathkal, Mangalore 575 025, India
Email: subhashyaragal@yahoo.com
Abstract: Concrete mix design is a step by step procedure to workout the various proportions of the ingredients for
the most economical mix that meets the minimum criteria of strength, workability, durability, aggregate
characteristics and economy. Mix design procedures require 28 day strength of cement to decide the curve
designation A, B, C, D, E and F, which then is used to fix up w/c ratio corresponding to 28 day targeted concrete
strength. Several types of cements available in market today with various brand names necessitates one to study
them in detail for their exact pattern of strength gain. To speed up mix design procedures, strength of nearly thirty
five branded cements have been tested for 3d, 7d and 28d strengths with at least five samples for each type of
cement for ready reference to be used by the concrete mix designer.
Keywords: Cement, Concrete, Mix Design, Strength Ratios.
Introduction:
Concrete is a most widely used construction material in
the world. The popularity of this material as a
construction material is due to the fact that it is made
from commonly available ingredients and can be
tailored to meet the functional requirements in any
situation. The art of arriving at a proper mix through a
suitable combination of cement, aggregates, water and
admixtures, if required, lies in proportioning concrete
mixes, The main objective of the concrete mix design is
to select the optimum proportions of the various
ingredients of concrete which will yield fresh concrete
of desired workability and the hardened concrete
possessing the specified characteristic compressive
strength and durability. The mix proportions should
also satisfy the additional requirement of the use of
minimum possible cement content so that maximum
economy is achieved. The most commonly used
method of mix design is based on IS:10262-1982. The
usual procedure of concrete mix design is to interpolate
the value of w/c ratio for compressive strength of
concrete from the standard curves presented in
IS:10262-1982.
In India the cement industry underwent a number of
changes and reforms mainly to suit the Government
policies and the economics of the manufacture. The
strict Government control for several years and rising
costs of production resulted in production of poor
quality of cement thereby resulting in poor quality of
concrete structures. The partial relaxation of
Governmental control from 1982 and a total relaxation
of control after March 1989 revived the cement industry
and resulted in its phenomenal growth. This resulted in
a competitive market and cement manufactures had to
improve their quality of cement as it was now a battle
for survival of the best. In the late eighties the dry
process cement manufacturing took precedence over the
more power oriented wet process.
The cement
manufacturers modernized their old plants which were
in various stages of obsolescence. The wet process
plants were converted to more economical and efficient
dry process or semi-dry process plants. This led to the
production of high quality cement. Several leading
organizations diversified into cement manufacture and
thereby created the much desired consumer oriented
market with range of brands available at competitive
prices. The 33 grade ordinary Portland cement (IS:2691989) has virtually disappeared and is displaced by
higher strength ordinary Portland cements of 43 grade
(IS: 8112-1989) and 53 grade (IS:12269-1987).
A high strength cement although preferable to a lower
strength cement may not give a consumer the complete
benefit unless and until it is giving consistently high
strength with minimum variation. A high strength
concrete if specified for any structure will also be more
desirable from the durability point of view. It is often
observed that low strength concrete is more vulnerable
to environmental forces than high strength concrete but
at the same time high strength concrete too needs to be
extremely carefully batched, mixed, transported, placed,
compacted and cured. The durability requirements of
the structure are as important, if not more, as the
strength of the structure. A strong concrete may not
result in high performance concrete if the durability
#02050454 Copyright ©2012 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.
SUBHASH C. YARAGAL
requirements are not complied with. Selection of high
quality cement can only mean a good beginning but it
does not assure the consumer of a final product which is
the strong and durable concrete structure. However,
selection of poor quality cement or cement of
inconsistent quality is like taking a wrong step right at
the beginning and will certainly lead to poor quality
concrete structure if not a disaster.
Cement Strength Classification:
IS:10262-1982, which gives the recommended
guidelines for concrete mix design, has generally
classified the cement grade wise from A to F, depending
upon the 28 days strength in ( kg/cm2 ) as follows, A
(325 – 375), B (375 – 425), C (425 – 475), D (475 –
525), E (525 – 575), and F (575 – 625). However, it
may be noted that some brands sold as 53 grade cements
generally give 28 days strength of around 625 to 675
kg/cm2. However, most of the 53 grade cements
available in the market generally fall in the category F
or above and the 43 grade cements available in the
market are generally in the category D. It must be
ascertained either from the manufacturer or through
laboratory tests the actual strength of the cement before
it’s use in the concrete mix design to get the maximum
benefit of the additional strength and superior quality.
The relation between free water-cement ratio (w/c) and
concrete strength for different cement strengths (grades
A to F), as given in IS: 10262-1982, is used to
determine the w/c of the concrete mix for specified
target concrete strength if the cement grade is known.
Cement Strength vs Concrete Durability:
Cement consumption works out to be lesser and lesser
as the grade of cement used is higher and higher.
Durability requirements as specified in IS-456 must be
satisfied depending on the various exposure conditions.
Studies have shown that concrete manufactured using a
higher grade of cement even after considering that lower
grade cement may be marginally cheaper than the
higher grade cement.
For high performance concrete generally it is very
important to go for higher grade of concrete (above
M25 grade). If this concrete is made with high strength
cement then it will fetch both technical as well as
financial advantage. Table 1 shows the extent to which
different grades of cements can be used for different
environmental conditions and various grades of
concrete. It is generally observed that even today the
structural engineers and architects specify M15 and
M20 grade of concrete in coastal area. This has already
led to serious durability problems and low performance
of concrete structures. M15 grade of concrete can be
achieved with w/c much greater than 0.55 if 43 and 53
grades of cements are used and since 33 grade cement
1031
has now virtually disappeared from the market. All
M15 grade concrete structures in coastal areas are
therefore bound to be a happy hunting ground for
concrete rehabilitation agencies as is being observed at
present. The durability problem is most likely to
multiply several times if at the specification stage itself,
proper precautions are not taken.
Lower grades of concretes with generally poor type of
quality control prevalent are observed to be of very poor
durability, needing extensive repairs within a few years.
As good quality cements are now available it is strongly
recommended to go in for higher grades of concrete i.e
above M25 grade. This will improve the performance
of the structures, prove more economical in most cases
and in the process of achieving higher strengths it will
automatically comply with the durability requirements.
Advantages of High Strength Consistent Quality
Cement:
Besides saving of concrete quantity and cement cost per
cubic meter of concrete, there are several other
advantages and savings due the use of high strength
cement. It is observed that the best advantage of
specifying high strength cement is derived if at the
planning and design stage itself, high grades of
concretes are specified. The higher grade concretes
may have smaller cross sectional are under other
identical conditions and thereby quantity of concrete
reduces considerably. The saving in concrete quantity
can easily lie between 1% to 25% depending on the type
of structural member, its layout and its function.
However, in addition to this saving, higher grades of
concrete will be less permeable and more durable than
lower grades. Besides, specifying higher strength
would also result in (i) Saving of reinforcement steel (ii)
Saving of formwork quantity (iii) Reduction in quantum
of finishing works such as plaster, painting etc. (iv)
Overall saving of manpower and construction time and
(v) Increase in the carpet area of the building.
Discussion and Results:
In order to strengthen the confidence of concrete mix
designer, it was felt necessary to document in detail the
strength grain of several of the most popular branded
cements in use. It is clear that from this study, one need
not wait for the 28 day strength test of cement to
commence the concrete mix design.
Series of
experiments were conducted in the department of Civil
Engineering, National Institute of Technology
Karnataka, Surathkal for this purpose. For ease of
presentation they have been grouped as 53 grade tested
as per IS:12269 (3d:7d:28d strengths need to be atleast
27 MPa, 37 MPa and 53 MPa), 43 grade tested as per
IS: 8112 (3d:7d:28d strengths need to be atleast 23
MPa, 33 MPa and 43 MPa), Flyash based (IS:1489) or
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04 (02), August 2012, pp. 1030-1033
A Realistic Approach to Concrete Mix Design based on Cement Strength Criteria
1032
Slag (IS:455) (3d:7d:28d strengths need to be atleast 16
MPa, 22 MPa and 33 MPa) and Sulphate resisting
cement tested as per IS:12330 (3d:7d:28d strengths need
to be atleast 10 MPa, 16 MPa and 33 MPa). Since 33
grade cements have not been in production, these have
not been presented. The values in Table 2, are the
average values of atleast five or more sets of
experiments on each brand of cement.
It is observed from the above table that on an average
both for 43 and 53 grades of cements the 3 day strength
is about 63% of the 28 day strength and 7 day strength
is about 79% of the 28 day strength. One can compare
the tested 3d and 7d strength for a particular brand of
cement and then make his own judgement of the 28 d
strength that could be anticipated. However either for
flyash based or slag cement 3d/28d is 51% and 7d/28d
is 62%. On the other hand for Sulphate Resisting
cement these are 60% and 74% respectively. The
variations are large for flyash based or slag and for
Sulphate resisting cement, therefore it opined that the
individual brand strength gain be made use of, rather
than the group average.
Conclusions:
The experimental results presented are of immense help
to the concrete mix designer for proceeding with trial
mixes without waiting for the 28d strength of cement to
be tested. The strength gain of 35 brands of most
popular cements in market have been tested and results
presented for use. However it is recommended that
based on the actual cement strength of 3d and 7d, the
present results be used for right assessment of the
probable 28d strength. The group average for 43 and 53
grade of cements seems alright, but for the other two,
namely either flyash based or slag cements and for
Sulphate Resisting cement, variations are significant.
Therefore for these two assessment be based on
individual brand strength gain, rather than the group
average.
References:
[1] Gambhir, M. L. (1986), Concrete Technology, Tata
McGraw Hill Publishing Company Ltd., New Delhi
[2] Nevelle, A. M. (1981), Properties of Concrete, 3rd
edition, Pitman Publishing Company, London.
Table 1: Suitability of Various Grades of Cements in Different Exposure Conditions
Characteristic
concrete grade
(N/mm2)
15
Quality control
Fair/Good/Very
good
Very good
Good
Fair
20
Very good
Good
Fair
Very good
Good
Fair
Very good
Good
Fair
25
30
Cement grade suitable for different exposure conditions
Mild
Moderate
Severe
2
A,C,E
A,C,E
A,C,E
3
A,C,E
A,C,E
A,C,E
4 A,C,E
A,C,E
C,E
5 C,E
C,E
C,E
Note:
I. Grade A, C, and E cements can be theoretically
equated to commercially available 33, 43 and 53
grade cements
II. (Cement grade): suggested to be used for different
exposure conditions, will not be economical and the
A,(C),(E)
A,(C),(E)
A,(C),(E)
(A),(C),(E)
(A),(C),(E)
(A),(C),(E)
A,C,(E)
A,C,E
A,C,E
A,C,E
A,C,E
C,E
C,E
C,E
C,E
A,(C),(E)
A,(C),(E)
A,(C),(E)
A,C,(E)
A,C,(E)
C,(E)
C,E
C,E
C,E
concrete mix design will be governed by durability
parameters and not strength parameter.
III. Grade A cement cannot be used beyond M25 grade
concrete with good control.
IV. No cement is economically suitable if M15 grade
concrete is specified for severe exposure
conditions.
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04 (02), August 2012, pp. 1030-1033
1033
SUBHASH C. YARAGAL
Table 2: Cement Strengths for 3d, 7d and 28d for Various Types and Brands of Cements
Type and brand
Average strength in Mpa
Strength gain
3day
7day
28day
(3d/28dx100)
53 Grade (IS:12269)
(1) Ambuja
47.4
56.9
63.8
74
(2) L and T
38.5
46.4
56.8
68
(3) Birla super
40.0
47.2
62.0
65
(4) Coromandal king
34.2
43.5
55.0
62
(5) CCI Param shakti
31.2
43.0
54.4
57
(6) Zuari
34.0
42.7
53.7
63
(7)Penna power
34.3
42.3
57.4
60
(8) Birla Vasavadatta
35.0
45.4
61.3
57
63
Group average
43 Grade (IS:8112)
(9) Vasavadatta
35.9
45.0
53.9
67
(10) Coromondal
29.8
34.7
51.9
57
(11) A C C
35.5
44.3
50.7
70
(12) Rajashree
34.0
40.6
53.7
63
(13) Super Panyam
29.5
40.1
43.8
67
(14) Raasi
25.5
36.9
53.2
48
(15) Ratna
33.9
38.9
45.8
74
(16) Penna
36.0
45.7
54.2
66
(17) Shankar
36.0
46.0
62.7
57
(18) Ramco
33.9
44.9
50.5
67
(19) Chettinad
28.3
35.7
47.3
60
63
Group average
Flyash based (IS:1489) or Slag based (IS:455)
(20) ACC Suraksha
31.9
38.5
51.5
62
(21) Ultra-Tech
29.4
38.7
53.8
55
(22) Birla star
33.0
37.7
54.7
60
(23) Mysore diamond
20.0
29.3
47.3
42
(24) Bagalkot shakti
22.7
31.3
50.0
45
(25) Diamond super
22.0
36.4
47.1
47
(26) Birla shakti
38.0
45.0
56.0
68
(27) Chettinad super
14.0
19.0
37.0
38
(28) ACC
20.0
27.0
43.0
47
(29) Penna suraksha
19.0
27.0
50.0
38
(30) Ramco super
25.0
32.0
44.0
57
(31)Coromandalsuper
27.0
35.0
49.0
55
(32) Ramco 53 plus
21.5
28.0
55.0
39
(33) Zuari super fine
25.0
31.0
45.0
56
51
Group average
Sulphate resisting cement (IS: 12330)
(34) Birla coastal
40.4
47.7
58.7
69
(35) Chettinadu
23.0
30.0
45.0
51
60
Group average
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04 (02), August 2012, pp. 1030-1033
Strength gain
(3d/28d x 100)
89
82
76
79
79
80
74
74
79
83
67
87
76
92
69
85
84
73
89
75
80
75
72
69
62
63
77
80
51
63
54
73
71
51
69
62
81
67
74