# Little-known Grade of Cement – How do they determine this? Underestimating grades have serious consequences for a student’s choice of university and their future.

Angela Rayner

Along with this underestimating grade of cement has serious consequences for a builder’s choice of building and their structural stability. Wait, builders have grades? Well no but cement sure does!

We can hear some of you asking “What is a grade of cement?”

A grade of cement is the sub-division done based on the compressive strength over the course of 28 days. While we say the grade of cement, it should be called the grade of Cement. Other cements like PPC are sub-divided based on different parameters.

Those who are new to this might even be asking what is OPC cement? Why are OPC and PPC graded in different ways?

## What is OPC cement?

OPC cement or Ordinary Pozzoland Cement is a type of cement that is made from argillaceous, calcareous, and gypsum. This is the most common type of cement that we can find virtually everywhere. This is because it is a jack of all trades of type of cement that scores average all across the board.

It has average strength, a medium amount of setting time, average hardness, and average flexibility. This type of cement is fine enough for most construction jobs and it has an average hydration rate and heat of hydration.

Since not every OPC cement is the same, it has been divided into three grades of cement.

## How is the grade of cement determined?

As we mentioned the grades of cement are based on its compressive strength on its 28th day. If you don’t know what compressive strength is, it is the resistance of an object to breaking under compression, which in our case is cement.

The compressive strength of cement is calculated using the following formula:

Compressive strength of a cement (c) = Load Applied (N) / Unit Area (MM sq)
= N/mm 2

As per IS 1489:1991, there are three grades of cement. They are OPC 33, OPC 43, and OPC 53. Each grade of cement has a different level of compressive strength which leads to each grade of cement having its unique features and uses. If this was not the case there would be no function for this division. Let’s see what they are.

The OPC 33 grade has a compressive strength of 33 Newton per Millimeter square on the 28th day from the time of application. But that being said, this is just the compressive strength on the 28th day. Before the 28th day, for cement to be graded they should meet the set requirement of compressive strength on the 3rd and 7th day as well.

This means that for cement to be considered as 33-Grade cement it needs to have a compressive strength of

• 16 Newton per Millimeter squared on the 3rd day
• 22 Newton per Millimeter squared on the 7th day
• 33 Newton per Millimeter squared on the 27th day

Along with this it also needs to have a fineness of 300 meters squared per Kilogram. Fineness is the property of cement that indicates the particle size of a cement per unit mass. Now that we know how cement is determined to be of 33 Grade, let’s quickly note down its property and uses.

• High workability
• Low heat of Hydration

Uses of OPC

• Plastering
• Brick Lining
• Tiling
• Used in areas that require compressive strength of above M 20 or 20 Newton per Milileter squared

It should also be noted that OPC 33 Grade cement is the cheapest grade of OPC cement.

The OPC 44 Grade has the Compressive Strength of 43 Newton per Millimeter squared on the 28th day from the day of application. As you may have guessed this cement is much tougher than the 33-grade cement. Similar to how a 33-grade cement, there is a requirement for cement to have a specific compressive strength on the 3rd, 7th, and 28th days. They are:

• 23 Newton per Millimeter squared on the 3rd day
• 33 Newton per Millimeter squared on the 7th day
• 43 Newton per Millimeter squared on the 27th day

As for the fineness, it needs to be 225 meters squared per Kilogram for this grade of OPC cement. As with the 33-grade cement, this grade of cement has its specific properties and area of use.

• Low Chloride Content
• Low corrosion of Steem reinforcement
• Good Workability with the Cement
• Initial Strength increase after 28 days
• Medium Heat of Hydration
• Moderate Sulphate Resistance

• In the preparation of RHC (Rapid Hardening Cement)
• For RCC (Reinforced Cement Concrete) and PCC (Plain Cement Concrete) works
• Construction of Bridges, Chimneys, Roads, Silos, etc
• Precast and Prestressed Concrete
• In constriction with grade acceptance of M30

The Price of OPC 43-Grade cement is higher than that of OPC 33-Grade but still lower than that of 53-Grade OPC cement

The compressive strength requirement for 53-Grade OPC cement is 53 Newton per Millimeter squared on the 28th day from the time of application. By now you should know that the grade of the cement is directly represented by its compressive strength on the 28th day. As with 33rd and 43rd-grade, it is also measured on the 3rd and 7th days as well. So basically a cement needs to have the following amount of compressive strength form from the day of application to be qualified as 53-Grade cement.

• 27 Newton per Millimeter squared on the 3rd day
• 37 Newton per Millimeter squared on the 7th day
• 53 Newton per Millimeter squared on the 27th day

Cement needs to have the fineness of 225 meter square per Kilogram along with the mentioned compressive strength for it to be considered as 53-Grade of cement. Its properties and functions are

• Sulphate Resistant
• Low Chloride
• Speedy Construction
• Shuttering Cost-saving caused by early removal
• Initial Strength continues to improve after 28 days

• Construction of Sleepers for railways, Pre-stressed Girders, Industrial Buildings, Roads and Runways
• Construction of RCC bridges
• RCC components like Beam, Columns, and Precast Concrete
• Precast Concrete
• Construction with the requirement of M25 and above concrete

The price of 53-Grade OPC cement is the highest among all of the OPC Cements. As a side note, if you want to be technical there are IS Codes of reference for them as well. They are: