Queryasked by N.N. Chaudhari
Why 33/43/53 Grade of Cement? Why Not 30/40/50?
Solutionby Gharpedia
When we talk about the grade of cement, we often hear numbers like 33,43, and 53. This makes us wonder why cement grades are 33, 43, 53 and why not 30,40, and 50? Let us find out the secret behind these numbers.
Cement is classified as grade 33 cement, grade 43 cement, and grade 53 cement. These numbers – 33, 43, and 53 represent the compressive strength of the cement in Megapascals (MPa) or Newtons per millimetre square (N/mm²), measured after 28 days of curing. The test involves preparing cement mortar (a mixture of cement, sand, and water) and pouring this mortar into standard cube moulds of size 7.06cm × 7.06cm × 7.06cm. These cubes are allowed to cure under controlled laboratory conditions for 28 days. After curing, a compression test is conducted on the cubes. The results of this test determine the compressive strength of the cement, and consequently, its grade.
However, these strength values are not fixed or universal, unlike physical constants such as density or specific gravity. They are empirical values, meaning they are derived from practical experiments and can vary based on several factors such as:
- Change in the size of the testing cube mould.
- Change in the shape of the testing mould.
- Variation in testing methods.
- Difference in the number of curing days.
The empirical values of cement grades are derived after numerous tests and then standardised. This standardisation of cement grades ensures uniformity, quality control, and ease of selection for various construction projects.
Grading of Cement
Grading of cement is based on its minimum compressive strength. Importantly, this strength refers to the concrete or mortar made using the cement, not the cement alone. A particular grade of cement ensures that the resulting concrete or mortar achieves at least that much compressive strength. For example, a cement of Grade 33, when used to make concrete, results in concrete that can withstand a minimum compressive force of 33 MPa.
Although, Grades 33, 43, and 53 are similar in chemical composition, they differ in the grinding process. Higher grade cement is ground more finely during the final stages of production, resulting in greater durability and strength.
To conclude why grades of cement are 33,43,53 – the grades of cement: 33, 43, and 53 are based purely on its performance in compression tests. These grades are not 30, 40, or 50 because, after extensive testing and standardisation, the compressive strength of cement was found to be 33 MPa, 43 MPa, and 53MPa at 28 days of curing.
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