What is Grade of Concrete .Read More about Mix Design of concrete for better Strength & Durability of your Reinforced Concrete Structures.

What is Grade of Concrete .Read More about Mix Design of concrete for better Strength & Durability of your Reinforced Concrete Structures.

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What is Concrete:

It's mixture of  Cement,Sand, Aggregate , admixture with normal water to give Comprehensive strength at specified 7or 8 days Test.

What is Grade of Concrete:-

The grade of concrete varies greatly in accordance with the changing proportion of its constituent materials. The proportion and the ratio, in which the materials should be mixed together to obtain a certain grade of the concrete, has already been specified by IS 456:2000.

The above mixes given in the table are called Nominal Mix.

In the era of industrial and infrastructural developments, to cater the need for high strength concrete and overall improvement of the concrete properties, various high strength concrete has been introduced, taking it way more than M100.

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What is Mix Design
Due to the limitation of IS:456, a new procedure have been adopted in all around India, which is to properly design the mix, from the scratch, and thus finding the required ratio for that particular Concrete.
This is known as Mix Design of Concrete, which follows some certain principles, devised by IS:10262,2009. 
 Some of these factors have been mentioned following-
1. Grade of Cement
2. Size and shape (aggregates)
3. Grading Zone of Aggregate
4. Water absorption by the aggregate
5. The specific gravity of the materials
6. Type of Admixture added
7. Slump value of the concrete
8. W/C Ratio of concrete
9. Degree of supervision provided
10. Method of transportation of concrete
11. Concreting Methods(such as Tremie or underwater concreting).
1. . Target Mean Strength:
Before designing concrete Mix, the grade of the concrete, for which the design will be performed, should always be known beforehand. That is known as a characteristic strength of the concrete (in M45 concrete, the characteristic strength of the concrete is 45Mpa). From the characteristic strength, the target mean strength is found out, for that specific concrete, from the given formulae-
                       Target Mean Strength = Characteristic strength + t x s
Where, t is the tolerance factor which is equal to 1.65, taking 5% of the test results are expected to fall below it
And s is the standard deviation whose value can be found out of a separate grade of concrete, from “Standard Deviation chart” from any concrete book.

2.  Water-Cement Ratio:
After the Target Mean Strength has been found out, the water-cement ratio is being determined, either using the chart specified by IS:456,2000 on the basis of the Exposure condition and Grade of concrete or by using some experience used for the similar construction executed recently. W/C Ratio is one of the most important factors of the concrete,  which controls overall quality, as well as have a direct or indirect effect on different properties of concrete.
3. Water Content Determination:
After the W/C ratio has been determined, the amount of water required for mixing that specific grade of concrete may be found out through a chart, which is based on the size of aggregates used for making that concrete.
4. . Cement Content Determination:
After the required water content is determined, then from the water-cement ratio, and obtained water content, the cement content can easily be found out.
 W/C Ratio = Water Content/Cement Content
 5.Determining the amount of Course and fine aggregates:
The coarse and fine aggregates are then Determined. The weight of the coarse aggregate depends upon the size of the course Aggregates used and grading zones of the aggregate, namely, there are four grading zones of the aggregates, I, II, III and IV. The value can be found out from the respective charts in the” Design Mix” chapter of any concrete book. The value obtained from the chart is the volume of the coarse aggregate, per unit volume of total aggregates. After, the volume of the fine aggregates is found out by deducting the volume of course aggregate, from number 1.
6. Determination of Total volume of all the materials:
The volume of all the materials can be obtained from the following formulae-
          Volume= Weight obtained/specific gravity× 1/1000
If Admixture is used, then the volume of Admixture is also being determined. 

It can be determined by the following formulae-
         Volume= dosage of Admixture× Cement content× 1/1000
Considering the total volume of concrete produced as 1 cubic metre, the volume of cement, water, and Admixtures are determined. Then the remaining value is the volume of the total aggregates. By multiplying the volume of the total aggregates with the volume of the coarse and fine aggregates per unit volume of the aggregate, specific gravity of respective aggregates and the value 1000. 
7.  Taking out the ratio:
After the volume and weight of all the materials are found out, then the ratio of the respective materials are determined. It is generally done by making the value of the cement as 1 and dividing all the weight of elements by the weight of cement.
8. Preparation of trial mixes:
Generally,  6 samples of trial mixes are prepared to check the desired strength and all other properties. 

The second trial mix is done by constant w/c ratio of the first one, and varying water/Admixture content. Trial mix 3 and 4 is done by keeping the water content as preselected value and varying W/C ratio by 10 per cent.
 
The above  eight steps are  involved in the calculation of Mix Design.
 ****  Please note that a properly designed concrete mix offers around improvement of various characteristics, which not only resists all the loads expected on that concrete, it also offers greater stability throughout its lifespan as well as beyond the lifespan.

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Cement,sand, Stone aggregate, admixture, concrete, Concrete Technology, Mix proportion,mix design, samples, comprehensive strength, compression Strength of concrete in 28 days Test,IS 456:2000, trial mix,water content, cement content, Water Cement ratio, durability,long life