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43 Grade of cement

43 Grade of cement :

        The 43 grade of cement is used for general civil construction works which is under normal expose(environmental) conditions. the average compressive strength of cement mortar attained after 28 days (6724 hours) in mega pascals (Mpa) of at least three mortar cubes of face area ( 50 cm squared) composed 1 part of cement and 3 parts of sand(conforming to IS 8112) by mass and P/4 (P is the percentage of water required to produce the past of standard consistence as per IS standards) + 3 percentage( of combined mass of cement plus sand )of water,prepared, stored and tested.

 The 43 grade opc is the most popular general-purpose cement in the country to day. the production of 43 grade opce is nearly 50% of the total production in the country.

43 Grade OPC are often used for the subsequent applications:

  •  General Civil Engineering construction work.
  •  RCC works(preferably where grade of concrete is up to M-30).
  •  Precast items such as blocks, tiles, pipes etc.
  •  Asbestos products such as sheets and pipes.
  •  Non-structural works such as plastering, flooring etc.

1.  33 grade of cement :

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53 Grade of cement

53 Grade of cement :

                                     The 53 grade of cement is used for general civil construction works which is under normal expose(environmental) conditions. the average compressive strength of cement mortar attained after 28 days (6724 hours) in mega pascals (Mpa) of at least three mortar cubes of face area ( 50 cm squared) composed 1 part of cement and 3 parts of sand(conforming to IS 12269) by mass and P/4 (P is the percentage of water required to produce the past of standard consistence as per IS standards) + 3 percentage( of combined mass of cement plus sand )of water,prepared, stored and tested.

                        53 Grade OPC is a higher strength cement to satisfy the requirements of the buyer for higher strength concrete. As per BIS requirements the minimum 28 days compressive strength of 53 Grade OPC shouldn't be less than 53 MPa. For certain specialized works, like pre-stressed concrete and certain items of precast concrete requiring consistently high strength concrete, 53 grade OPC is found very useful. 53 grades OPC produce higher-grade concrete at very economical cement content. In concrete mix design, for concrete M-20 and above grades a saving of 8 to 10 you look after cement may be achieved with the utilization of 53 grade OPC.


  • 53 Grade OPC will be used for the subsequent applications.

  • RCC works(Preferably where grade of concrete is M-25 and above)

  • Precast concrete items such as paving blocks, tiles building blocks etc.

  •  Pre-stressed concrete components

  • Runways, concrete Roads, Bridges etc.


2.  43 grade of cement :

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What are the Different Grades of the Cements

Different Grades of Cement 


Grades of cement :

                                      According to the Indian standards we have 3 different grades of cement. they are 33 grade,  43 grade,  53 grade cement. 

Cement was 1st discovered by an English brick layer Joseph Aspdin in 1824. He named it as Portland cement for the reason that the cement he discovered resembled the limestone found in Portland. Coming to the grades of cement the following discussion is OPC (ordinary Portland cement ) which is widely used in the construction fields.

33 grade of cement :

The 33 grade of cement is used for general civil construction works which is under normal expose(environmental) conditions. the average compressive strength of cement mortar attained after 28 days (6724 hours) in mega pascals (Mpa) of at least three mortar cubes of face area ( 50 cm squared) composed 1 part of cement and 3 parts of sand(conforming to IS 650:1966) by mass and P/4 (P is the percentage of water required to produce the past of standard consistence as per IS standards) + 3 percentage( of combined mass of cement plus sand )of water,prepared, stored and tested. 


                                               This cement is normally not used where high grade of concrete i.e.M-20 and above is required.This grade of cement is more useful for the mass concreting and plain cement concreting and can be used for plastering and single storied individual houses.The availability of higher grades of opc in the market impacts the usage of 33 grade opc. It is not used of the constructions where the speed progress required because the 33 grade cement won't attain the required strength to remove the shattering in 14 days or less due to this we will go for the higher grades.

2.  43 grade of cement :



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DESIGN MIX OF CONCRETE

Design mix:

As per the IS: 456-2000 the grade of concrete above the M-20 must and should be the design mix. And in the IS 456-2000 there is nothing mentioned about mix ratio 1:1:2 for M-25 grade of concrete. If we consider the ratio1:1:2 for M-20 then the cement content comes in the concrete matrix is 528 kg/m3.

Whereas IS: 456-2000 on the page 19 clause 8.2.4.2 mentioned that the cement content in the concrete not including fly ash and ground granulated blast furnace slag in excess of 450 kg/m3 should not be used in concert matrix unless special consideration has been given in the mix design. Otherwise increased risk of cracking due to drying shrinkage in thin sections, or to the early thermal cracking and to the increased risk of damage due to the alkali silica reactions.

The structural concrete surfaces is exposed to severe rain, alternate wetting and drying such as RCC overhead water tanks comes to severe exposure environment for which the minimum grade of concrete shall be M-30, and minimum cement content 320 kg/m3 and the maximum free W/C ratio is 0.45. 
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NOMINAL MIX DESIGN OF CONCRETE

NOMINAL MIX

                    The nominal mix proportions varies based on the zones of sand and size of the course aggregates, so its batter to get with the design mix, But the mix design of concrete cannot be used for any reason on the work for grades of M-20 or lower than the M-20. Generally we will go with the nominal mix where there is relatively unimportant works and simpler concrete works.In the nominal mix,all the ingredients which are prescribed and their proportions are specified.

                   
                        Therefore there is no scope for any deviation by the designer when the size of course aggregates and zone of sand is fixed. This Nominal mix concrete may be used for concrete of M-20 or lower than the M-20. IS: 456-2000 has recommended that the minimum grade of concrete shall not be less than M-20 in reinforced concrete work. The Nominal mixes can be used with the permission of engineer-in-charge for the important concrete works. Which however is likely to involve a higher cement content.

When the size of aggregate is 20mm and sand zone II is used than the mix proportions for the nominal mix are tabled below as per IS 456-2000

The table shown below is based on the sand zone II and the size of aggregates is 20mm
Grade
Max. quantity of dry Aggregates per 50 kg of cement
Fine Aggregate to Coarse Aggregate Ratio, by mass
Max. Quantity of water in litres
mix proportions
M-5
800
Generally 1:2 but may varies from 1:1.5 to 1:2.5
60
1:5:10
M-7.5
625
45
1:4:8
M-10
480
34
1:3:6
M-15
330
32
1:2:4
M-20
250
30
1:1.5:3


The Nominal mixes when the course aggregate is used with various sizes as per IS: 456-2000 and the fine aggregate is of Zone II as per IS: 383-1970.
Grade of Concrete
As per IS:383-1970 Maximum size of graded coarse aggregate
Mix Ratio by Weight
Max W/C Ratio
Max cement: Aggregate ratio by mass
Cement
Fine Aggregate
Coarse Aggregate
M-20
10
1 : 1.8 : 2.7
0.60
1.5
M-20
20
1 : 1.5 : 3.0
0.60
1.5
M-20
40
1 : 1.3 : 3.2
0.60
1.5








                     The above nominal mixes are worked out for Zone II of fine aggregate and the various sizes of course aggregate. As per IS: 383-1970 there are three more zones of sand. Therefore, the total nominal mixes shall be 10 for 12, 20 & 40 mm maximum size of coarse aggregate.
      
                   Thus, it seems to be that the nominal mixes doesn’t have a fix conventional proportions such as 1:1.5:3 or 1:2:4, but may vary according to maximum size of coarse aggregate and grading of fine aggregate and their zones. Hence the nominal mixes are also needed to be designed according to the sizes of aggregates available at site and the site conditions. However, the ultimate aim is to get the specified properties of concrete.
      
                The exposures of Indian Construction sites at most of the places are Moderate for which IS: 456-2000 specified the minimum grade of concrete for reinforced concrete should be M-25. Accordingly for durability aspects the structural concrete must not be below M-25 grade. The high strength benefits are obtained from M-25 should be taken into account in the design consideration of the concrete structure.
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CONCRETE MIX DESIGN for all grades OF CONCRETE


CONCRETE MIX DESIGN:

                   The strength is mainly influenced by the water/cement ratio, and the w/c ratio is almost independent of the parameters such as the properties of concrete with a compressive strength of the designed mix are influenced by the properties of aggregate in addition to that of water cement ratio. To obtain good strength, it is necessary to use the lowest possible w/c ratio which affects the workability of the mix. To design the any grade of concrete we require to follow these 11 steps as per IS: 10262: 2009


DATA FOR MIX PROPORTIONING

The following data are required for mix proportioning of a all grades of concrete:
1.           Grade designation
2.           Type of cement
3.           Target strength of mix proportion
4.           Maximum water-cement ratio
5.           Minimum cement content
6.           Workability
7.           Exposure conditions as per Table 4 and Table 5 of IS -456
8.           Maximum temperature of concrete at the time of placing
9.           Method of transporting and placing
10.      Type of aggregate
11.      Maximum cement content; and
12.      Whether an admixture shall or shall not be used and the type of admixture and the condition of usc.

Step 1: Grade designation

             First we need to conform grade of concrete. The grade of concrete is chosen based on the strength requirement and based on the place of work and loads coming on to the structures where this concrete is going to use. Basically we have 2 different mix

1.        Nominal mix
2.        Design mix

step 2: Type of cement

              The mix design depends on the bonding materials which are used in the concrete. In general we can adopt some special cementitious materials depends on the requirement and to adopt Echo-friendly concrete "like partial replacement of cement". 

The reaming steps explained in the design mix procedure to view the reaming steps  click on the above mix types
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STANDARD DEVIATION along with AN EXAMPLE

STANDARD DEVIATION :

Standard deviation for every grade of concrete shall be calculate separately. Because the value of standard deviation various based on the material used and batch mix. Based on the number of trials and based on the Indian standards.


standard deviation based on test strength of sample: 



1. Number of test results of samples - The total number of test strength of samples required to constitute an acceptable record for calculation of standard deviation shall be not less than 30, Attempts should be made to obtain from the 30 samples of motor cubes or concrete cubes (taken from site or laboratory) based on you requirement, as early as possible. When a mix is used for the first time.

2. In case of significant changes in concrete – when ever significant changes are made in the production of cement concrete batches (for example changes in the materials used, based on the mix Proportioning and equipment or technical control), the standard deviation value shall be calculated separately for such batches of concrete.

3. Standard deviation to be brought up-to date - The calculation of the standard
Deviation values shall be brought up-to-date after every change of mix proportioning. 



Assumed standard deviation:


When where sufficient test results for a particular grade of concrete are not available, then the value of standard deviation given in Table1 may be assumed for the proportioning of mix in the first instance. As soon as the results of samples are available, actual calculated standard deviation shall be used and the mix proportioned properly. However, when adequate past records for a similar grade exist and justify to the designer a value of standard deviation different from that shown in Table 1, it shall be permissible to use that value.

Table 1 Assumed Standard Deviation
(Clauses 3.2.1.2, A-3 and B-3)
 


Sl.No
Grade of Concrete
Characteristic compressive strength (N/mm2)
Assumed standard deviation (N/mm2)
1.
M10
10
3.5
2.
M15
15



3.
M20
20
4.0
4.
M25
25



5.
M30
30
6.0
6.
M35
35
7.
M40
40
8.
M45
45
9.
M50
50
10.
M55
55
 

NOTE - The above values correspond to the site control having proper storage of cement; weigh batching of all materials; controlled addition of water, regular checking of all materials. Aggregate grading and moisture content; and periodical checking of workability and strength. Where there is deviation from the above. Values given in the above table shall be increased by 1 N/mm2.


AN EXAMPLE:


When repeated no of samples gives different results, then we need to know how much widely the readings are spread. The spread of results tells us something about the uncertainty of a measurement. By knowing how large this results are spread. We can easily judge the quality of the measurement or set of measurements.The usual way to quantify spread is standard deviation. The standard deviation of a set of numbers shows us the values are how different the individual readings typically are from the average of the set. Mathematically standard deviation is stated as, the square root of deviations of all the result. This is denoted by σ.


The Standard deviation will be less if the quality control at site is good and most of the test results will be approximately equal to the mean value. If quality control is poor, then the test results will have much difference from the mean value and therefore, standard deviation will be higher.

 
CALCULATION:

Hera this table showing that the calculation of standard deviation for a Set of 30 Concrete Cube Test Results.

Sample number Crushing strength(mix let be X)Mpa Avg strength µ=∑X/n Deviation(X-µ) Square of Deviation(X-µ)2
1
43
42.167
0.83
0.6889
2
47
4.83
23.3289
3
49
6.83
46.6489
4
42
-0.167
0.027889
5
46
3.833
14.69189
6
45
2.833
8.025889
7
44
1.833
3.359889
8
41
-1.167
1.361889
9
40
-2.167
4.695889
10
38
-4.167
17.36389
11
37
-5.167
26.69789
12
39
-3.167
10.02989
13
35
-7.167
51.36589
14
36
-6.167
38.03189
15
48
5.83
33.9889
16
46
3.83
14.6689
17
47
4.83
23.3289
18
40
-2.167
4.695889
19
38
-4.167
17.36389
20
48
5.83
33.9889
21
43
0.83
0.6889
22
45
2.83
8.0089
23
44
1.83
3.3489
24
47
4.83
23.3289
25
37
-5.167
26.69789
26
39
-3.167
10.02989
27
36
-6.167
38.03189
28
42
-0.167
0.027889
29
43
0.83
0.6889
30
40
-2.167
4.695889
Total=1265 Total=489.9028
 
Average Strength, μ = 1265/30 = 42.167 MPa
Standard deviation = √[489.9/ (n-1)] = √(489.9/29) = 4.11 MPa

Where, n = Total number of samples

Coefficient of Variation = (Standard deviation/Average strength)*100
                                    = (4.11/42.167)*100
                                    = 9.79

If we consider less no. of samples that will increase standard deviation i.e. if we consider 20 samples then SD is 4.34 more in the no of samples means accurate in the SD
 


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