Different types of grades of concrete as per 456 : 2000 standard

This construction video tutorial from learning technology demonstrates the grades of concrete on the basis of IS 456 : 2000 standard. As per this standard the grades are categorized in three groups like ordinary concrete, standard concrete and high strength concrete. Here grades range from M10 to M80.

M10, M15 and M20 belong to Ordinary Concrete. M25, M30, M35, M40, M45, M50, M55 belong to Standard Concrete. M60, M65, M70, M75 and M80 belong to High Strength Concrete (HSC).

Here m denotes mix and number denotes characteristic compressive strength of 150 mm cube at 28 days in N/mm2 (Newton per millimeter square). It means if you take compressive test of a cube having dimensions 150 x 150 x 150 mm for 28 days, the value obtained is 10 N/mm2.

All these concrete grades are suitably for PCC work i.e. plain cement concrete work where rebar is not used.

Standard Concrete is generally used in 10 storied and higher buildings and super structures.

High strength concrete is mostly used for designing heavy structures.

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Published By

Rajib Dey

www.constructioncost.co

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The role of water in concrete

Water Cement Ratio signifies the ratio among the weight of water to the weight of cement applied in concrete mix.

Generally, water cement ratio remains under 0.4 to 0.6 with adherence to IS Code 10262 (2009) for nominal mix (M10, M15 …. M25)

The strength of concrete is directly impacted by the water cement ratio. It enhances the strength if employed in perfect ratio and if the ratio is improper, the strength will be reduced.

The importance of Water in Concrete

Concrete refers to a macro content. It comprises of micro constituents like cement, sand, fine aggregate & Coarse aggregate. With the purpose of obtaining high strength concrete to resist the desired compressive strength, it is required to set exact ratio of admixture to unite these materials.

The role of water is important here to accelerate this chemical process by adding 23%-25% of the cement volume. It produces 15% of water cement paste also called gel to fill the voids in the concrete.

Impact of too much water in concrete: If additional water is added more than the permissible limit of 23%, the strength of concrete will be significantly affected.

If the task of adding water is continued to improve the workability then the concrete contains lots of fluid materials where the aggregates will settle down. As soon as the water is evaporated it puts down lots of voids in concrete which influences the concrete strength.

But if the guidelines are followed to retain the strength of the concrete then it will change the concrete workability and makes it difficult to manage and place them.

Workability signifies the capacity of concrete to manage, convey and place devoid of any segregation. The concrete becomes perfectly workable if it can be easily dealt with, placed and transported devoid of any segregation at the time of being placed in construction site.

For this purpose, plasticisers & superplasticizers are utilized to enhance the workability by keeping the W/C Ratio unchanged.

In order to know how to work out water cement ratio, go through the following construction article www.civilology.com

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Published By
Rajib Dey
www.constructioncost.co
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Brief overview of concrete mix ratio

If cement is blended with sand, stone/aggregates and water, a paste will be developed and it can be applied to stick the building materials collectively. This paste is known as concrete.

The ration upon which the cement, sand, stones or aggregates are amalgamated, defines the strength of the concrete mix. Depending on these ratios, different types of concrete grades are accessible in the market. These concrete grades range from M10, M20, M30, M35, etc.

“M” denotes “mix”. Mix characterizes concrete with indicated ratios of cement, sand and aggregate. And the number after “M” denotes compressive strength of that concrete mix in N/mm2 after 28 days. As for instance, for M30 grade of concrete mix, its compressive strength after 28 days should have been 30 N/mm2.

Concrete mix ratio table

Given below, the standard chart table that displays different grades of concrete mix design together with their relevant ratios of cement, sand and aggregates required.

It is found that volume of sand is always retained half of that of aggregates in these standard mix designs. These proportions can be estimated and sustained with buckets or some other standard cubes which are easily utilized during the project. It is essential to keep up uniformity in each and every concrete mix produced throughout the entire project.

The site engineer/supervisor should take the responsibility to examine and implement it.

Water content ratio in concrete mix: The strength & adaptability of concrete is mainly dependent on water content. The adaptability of concrete (more fluid) will be increased with the higher quantity of water but it will decrease the concrete strength.

Contrarily, if the amount of water is low, adaptability of water will also be decreased. So, it becomes complicated to arrange such concrete in the structure. Required amount of water may differ for same volume of concrete for different grades of concrete. So, equilibrium should be maintained in the construction site throughout concrete mixing.

Video Source: Civil Engineering

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Published By
Rajib Dey
www.constructioncost.co
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