IS:10262 is the code specified by Bureau of Indian Standards for Concrete Mix Design. The code came to existence in the year 1982. Keeping pace with the advancing technology the code has been revised in December 2009. Significant changes have been made in the revised version and a brief discussion is presented in this paper comparing the two versions of IS:10262. The basic points where the guidelines have been modified are discussed. Besides one numerical example has been solved using guidelines of both the versions to understand the differences. Though the 2009 version encourages mixing of mineral admixtures to meet greater challenges of modern concreting, a simple example is considered with use of no additives.
Introduction
Mix Design of Concrete is the process of deciding the proportions of the ingredients of concrete so as to be produced most economically, that would satisfy the desired properties of fresh and hardened concrete as well. In simpler words, the concrete should be well workable when fresh and the designed compressive strength as well as durability should be achieved at hardening.
The wide use of concrete as the basic construction material may be due to its adaptability for a wide range of strength and workability. To achieve different strength requirements, it is the “Mix-design process” that makes the difference as the basic ingredients are same all the way.
Mix Design of Concrete is the process of deciding the proportions of the ingredients of concrete so as to be produced most economically, that would satisfy the desired properties of fresh and hardened concrete as well. In simpler words, the concrete should be well workable when fresh and the designed compressive strength as well as durability should be achieved at hardening.
The wide use of concrete as the basic construction material may be due to its adaptability for a wide range of strength and workability. To achieve different strength requirements, it is the “Mix-design process” that makes the difference as the basic ingredients are same all the way.
Very likely to other methods of Concrete Mix Design, Guidelines recommended by Bureau of Indian Standards for concrete mix design is based on certain empirical relations established through vast number of experiments conducted upon materials used in Indian conditions. IS: 10262 is the specified code to serve the purpose. This code came to being in the year 1982. So IS: 10262-1982 had been evolved to guide the concreting technology being followed at that period. But at present due to demand in high strength concrete and for economic production, use of supplementary materials has become essential. With the advanced technology a number of additives have been identified and are being used extensively now-a –days. These additives are not only enhancing the quality of concreting but also make the process economic and eco-friendly too.
So keeping these in view the necessary modifications were felt essential and the revised version of the code as IS: 10262-2009-“Concrete Mix Design-Guidelines” has met this in time. The revised version encourages use of supplementary cementitious materials and water reducing additives. Besides, being consistent with specifications of IS: 456-2000, necessary modifications have been made.
IS: 10262-1982 Vs IS: 10262-2009-The key modifications
i. Title of the Code
The modified title of the code itself makes the designer feel little flexible. i.e. “IS 10262-1982-Recommended guidelines for concrete mix design” modified as “IS 10262-2009-Concrete Mix proportioning Guidelines.”
i. Title of the Code
The modified title of the code itself makes the designer feel little flexible. i.e. “IS 10262-1982-Recommended guidelines for concrete mix design” modified as “IS 10262-2009-Concrete Mix proportioning Guidelines.”
ii. Strength & Durability
The 1982 version considers strength as the governing criteria for durability and so also for the mix design process.
The 1982 version considers strength as the governing criteria for durability and so also for the mix design process.
But according to the revised one strength may be a factor for acceptance but may not assures durability.
iii. Air Content
IS: 10262-1982 considers expected air content of 1% to 3% in the design process depending on the nominal maximum size of aggregates.
IS: 10262-1982 considers expected air content of 1% to 3% in the design process depending on the nominal maximum size of aggregates.
IS: 10262-2009 eliminates consideration of air content in the mix proportion calculation as it’s not of much significance.
iv. Water Cement Ratio
The old version suggested that selection of preliminary free w/c ratio may be adopted from established relationships presented in form of graph as generalized w/c ratio curves for different cement strengths. Accordingly six ready reference curves were there namely A to F for a wide range of cement strengths from 325kg/cm2 to 625kg/cm2. This selected w/c ratio is to be checked against limiting w/c ratio for durability.
The old version suggested that selection of preliminary free w/c ratio may be adopted from established relationships presented in form of graph as generalized w/c ratio curves for different cement strengths. Accordingly six ready reference curves were there namely A to F for a wide range of cement strengths from 325kg/cm2 to 625kg/cm2. This selected w/c ratio is to be checked against limiting w/c ratio for durability.
The revised version encourages establishing the relationships for actually used material. Otherwise it suggests to consider it from the specified table (Table-5) of IS: 456 for desired exposure condition as preliminary w/c ratio that has to be further checked for limiting value ensuring durability.
v. Measure of Workability
IS: 10262-1982 considers compaction factor as the measure of workability. In revised one, slump is considered as the measure of workability. Measurement of workability as slump is more convenient, widely used at sites and is better acceptable.
IS: 10262-1982 considers compaction factor as the measure of workability. In revised one, slump is considered as the measure of workability. Measurement of workability as slump is more convenient, widely used at sites and is better acceptable.
vi. Mineral Additives
The revised code provides guidelines for addition of supplementary cementitious additives. So additives like fly ash, silica fume, ground granulated blast furnace slag, rice husk ash etc. can be used in concrete mix provided the strength and durability requirement are met with.
The revised code provides guidelines for addition of supplementary cementitious additives. So additives like fly ash, silica fume, ground granulated blast furnace slag, rice husk ash etc. can be used in concrete mix provided the strength and durability requirement are met with.
So as per the revised code the concrete is no longer a four component system (cement, sand, coarse aggregates & water) as considered in the previous version, but it is much more.
vii. Calculation of water content
The quantity of water to be used plays a vital role in concrete mix design. Agreeing with the old guidelines, values of water content have been specified in terms of kg per cubic meter of concrete depending upon the nominal maximum size of aggregates which can be considered as starting selection point of water content.
The quantity of water to be used plays a vital role in concrete mix design. Agreeing with the old guidelines, values of water content have been specified in terms of kg per cubic meter of concrete depending upon the nominal maximum size of aggregates which can be considered as starting selection point of water content.
IS: 10262-2009 allows use of water reducers/ super plasticizers and also specifies the alteration in water content accordingly.
Further water adjustment was specified in terms of variation of compaction factor in the older version whereas the same has been remoulded in terms of slump variation (+3% for every 25mm slump over 50mm) in the revised one.
viii. Estimations of Coarse and Fine Aggregates
The 1982 publication specifies ratio of fine aggregates to all-in-aggregates from which coarse aggregates content can be derived.
The 1982 publication specifies ratio of fine aggregates to all-in-aggregates from which coarse aggregates content can be derived.
In revised one the volume of coarse aggregates per unit volume of total aggregates for different zones of fine aggregates and different maximum nominal size of aggregates has been tabulated from which the fine aggregates content has to be derived.
Further in the earlier guidelines necessary adjustments in sand content has been suggested depending on its grading zone, whereas the recent guidelines allow reduction in coarse aggregates content for better workability, provided other desired properties are satisfied.
ix. Miscellaneous
Besides the other points to be bolded are
• The standard is applicable for ordinary and standard grades of concrete.
• Various requirements have been modified in line with the requirements of IS: 456-2000-Plain and reinforced concrete-Code of practice.
• Other illustrations like trial mixes, numerical example etc have been reviewed and modified.
• An example illustrating mix proportioning with supplementary cementitious additive (fly ash) has been included.
Besides the other points to be bolded are
• The standard is applicable for ordinary and standard grades of concrete.
• Various requirements have been modified in line with the requirements of IS: 456-2000-Plain and reinforced concrete-Code of practice.
• Other illustrations like trial mixes, numerical example etc have been reviewed and modified.
• An example illustrating mix proportioning with supplementary cementitious additive (fly ash) has been included.
NUMERICAL EXAMPLE
Let’s consider a mix design with following design parameters.
Design Stipulations
Grade designation M25 (moderate exposure)
i.e. fck= 25 Mpa
Maximum nominal size of aggregates 20mm.
Sand conforming to Zone-II of IS: 383-1983
Degree of workability medium.
Let’s consider a mix design with following design parameters.
Design Stipulations
Grade designation M25 (moderate exposure)
i.e. fck= 25 Mpa
Maximum nominal size of aggregates 20mm.
Sand conforming to Zone-II of IS: 383-1983
Degree of workability medium.
Test Data
i. Cement used: PPC IS:1489
ii. Specific gravity of
Cement = 3.15
Fine Aggregates = 2.67
Coarse Aggregates = 2.78
i. Cement used: PPC IS:1489
ii. Specific gravity of
Cement = 3.15
Fine Aggregates = 2.67
Coarse Aggregates = 2.78
iii. Water absorption of
Fine Aggregates = 0.86%
Coarse Aggregates = 0.48%
Fine Aggregates = 0.86%
Coarse Aggregates = 0.48%
iv. Free surface moisture of
Fine Aggregates – nil
Coarse Aggregates – nil
Fine Aggregates – nil
Coarse Aggregates – nil
v. Grading of Aggregates (IS:383)
Fine Aggregates- Zone-II
Coarse Aggregates- nominal 20 mm size
Fine Aggregates- Zone-II
Coarse Aggregates- nominal 20 mm size
Design as per IS: 10262-1982
Target mean strength ft = fck +k.S
= 25 + 1.65 x 4.0 =31.6 Mpa
Target mean strength ft = fck +k.S
= 25 + 1.65 x 4.0 =31.6 Mpa
Selection of w/c ratio
28 day compressive strength of cement comes to be 543kg/cm2.
w/c ratio from curve E of figure.2 is 0.52.
Maximum w/c ratio from table 5 of IS: 456 is 0.5
Lets adopt w/c ratio = 0.5
Water & sand content
For 20mm nominal maximum size of aggregates water content is 186kg/m3 of concrete.
Fine Aggregates percentage of total aggregates by absolute volume = 35%
28 day compressive strength of cement comes to be 543kg/cm2.
w/c ratio from curve E of figure.2 is 0.52.
Maximum w/c ratio from table 5 of IS: 456 is 0.5
Lets adopt w/c ratio = 0.5
Water & sand content
For 20mm nominal maximum size of aggregates water content is 186kg/m3 of concrete.
Fine Aggregates percentage of total aggregates by absolute volume = 35%
Adjustment in water & sand content
Change in condition
|
Water adjustment ,%
|
Sand adjustment ,%
|
w/c ratio (-0.1)
|
0
|
2.0
|
Workability (+0.1 CF)
|
+3.0
|
0
|
Sand zone (Zone-II)
|
0
|
0
|
Total
|
+3%
|
-2%
|
Adjusted water content=186kg x 1.03 = 191.6 kg
Adjusted sand content = (35-2) %= 33%
Cement content calculation
w/c ratio = 0.5
Cement quantity = 191.6/ 0.5 = 383 kg.
Adjusted sand content = (35-2) %= 33%
Cement content calculation
w/c ratio = 0.5
Cement quantity = 191.6/ 0.5 = 383 kg.
Determination of Aggregates content
For 20mm nominal maximum size aggregates entrapped air as specified is 2%.
Total volume of ingredients excluding void per cubic meter of concrete designed = 0.98 m3.
For 20mm nominal maximum size aggregates entrapped air as specified is 2%.
Total volume of ingredients excluding void per cubic meter of concrete designed = 0.98 m3.
Total volume of aggregates = 0.98 – [(383/3.15) +191.6]/1000 = 0.667m3
Total mass of Fine Aggregates per m3 of concrete
= 0.667 x 2.67 x 0.33 x 1000 = 588 kg
Total mass of Coarse Aggregates per m3 of concrete
= 0.66 x 2.78 x (1-0.33) x 1000 = 1242 kg
= 0.667 x 2.67 x 0.33 x 1000 = 588 kg
Total mass of Coarse Aggregates per m3 of concrete
= 0.66 x 2.78 x (1-0.33) x 1000 = 1242 kg
Calculated proportions
Particulars
|
Qty. in kg/m3 of concrete
|
Mix Proportions by mass
|
Water
|
191.6
|
0.5
|
Cement
|
383
|
1
|
Sand
|
588
|
1.54
|
Coarse Aggregates
|
1242
|
3.24
|
Total
|
2405
|
Design as per IS: 10262-2009
Target mean strength ft= fck +k.S
= 25 + 1.65 x 4.0 =31.6 Mpa
Target mean strength ft= fck +k.S
= 25 + 1.65 x 4.0 =31.6 Mpa
Selection of w/c ratio
Maximum w/c ratio from table 5 of IS: 456 is s 0.5
Let’s adopt w/c ratio = 0.5
Water content
For 20mm nominal maximum size of aggregates and slump range 25mm to 50mm, water content is 186kg/m3 (Table 2) of concrete.
Cement content calculation
w/c ratio = 0.5
Cement quantity = 186/ 0.5 = 372 kg.
Determination of Coarse & Fine Aggregates Content
From table 3 of the standard, volume of Coarse Aggregates corresponding 20mm nominal maximum size aggregates and for Zone-II Fine Aggregates = 0.62%
Maximum w/c ratio from table 5 of IS: 456 is s 0.5
Let’s adopt w/c ratio = 0.5
Water content
For 20mm nominal maximum size of aggregates and slump range 25mm to 50mm, water content is 186kg/m3 (Table 2) of concrete.
Cement content calculation
w/c ratio = 0.5
Cement quantity = 186/ 0.5 = 372 kg.
Determination of Coarse & Fine Aggregates Content
From table 3 of the standard, volume of Coarse Aggregates corresponding 20mm nominal maximum size aggregates and for Zone-II Fine Aggregates = 0.62%
• Volume of concrete = 1m3
• Volume of cement = 372/3.15*1000 = 0.118m3
• Volume of water = 186/1000 = 0.186m3
• Volume of cement = 372/3.15*1000 = 0.118m3
• Volume of water = 186/1000 = 0.186m3
• Volume of all-in-aggregates
=1-(0.118+0.186) m = 0.696m3
=1-(0.118+0.186) m = 0.696m3
• Mass of Coarse Aggregates
=0.62 x 0.696 x 2.78 x 1000 =1200kg
=0.62 x 0.696 x 2.78 x 1000 =1200kg
• Mass of Fine Aggregates
= (1-0.62) x 0.696 x 2.67 x 1000 =706kg
= (1-0.62) x 0.696 x 2.67 x 1000 =706kg
Mix Proportion for Trial Mix No. I
Particulars
|
Qty. in kg/m3 of concrete
|
Mix Proportions by mass
|
Water
|
186
|
0.5
|
Cement
|
372
|
1
|
Sand
|
706
|
1.90
|
Coarse Aggregates
|
1200
|
3.22
|
Total
|
2464
|
The designed mixes can be graphically presented as following.
Discussion
i. During the 1980s the cements used were relatively of lower strengths. So the design following the old code results in more cement consumption.
ii. Allowance for mineral additives as per revised code makes the mix economic and also properties like strength and durability are enhanced.
iii. From the Numerical example it was observed that,
a. The Fine Aggregates content is appreciably higher, when designed as per the revised guidelines indicating the improved workability
b. Mix as per revised code yields better yield than that by older one, resulting a denser concrete.
However numerical interpretations are to be verified experimentally.
i. During the 1980s the cements used were relatively of lower strengths. So the design following the old code results in more cement consumption.
ii. Allowance for mineral additives as per revised code makes the mix economic and also properties like strength and durability are enhanced.
iii. From the Numerical example it was observed that,
a. The Fine Aggregates content is appreciably higher, when designed as per the revised guidelines indicating the improved workability
b. Mix as per revised code yields better yield than that by older one, resulting a denser concrete.
However numerical interpretations are to be verified experimentally.
References:
1. Indian Standard, IS:10262-1982-Recommended guidelines for concrete mix design.
2. Indian Standard, IS: 10262-2009-Concrete mix proportioning- Guidelines.
1. Indian Standard, IS:10262-1982-Recommended guidelines for concrete mix design.
2. Indian Standard, IS: 10262-2009-Concrete mix proportioning- Guidelines.
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