1. How to calculate the expiry date of cement bags?
Every bag of cement has manufactured dates printed over them as shown below.
As you can see in the above image, the manufactured date of cement is printed as W48 DEC Y13.
Here, W stands for 👉 Week.
DEC stands for 👉 Month.
Y stands for 👉 Year.
W48 DEC Y13 means, the cement is manufactured on the 48th week of the year 2013 in the month of December. By observing the calendar (internet ), the 48th week is from Nov 25th to Dec1st of the year 2013.
We should add 3 months ( 90 days ) to the manufactured date, to get the expiry date of cement.
1st Dec 2013 + 90 days.
= 28th February 2014 will be the expiry date of cement.
So, it is OK to buy this bag of cement before 28th Feb of the year2014.
The other pattern of printing the manufactured date over the cement bags is as below.
As explained above, W, M, & Y stands for a week, month & year respectively.
Now the next question that comes to your mind is,
2. Why the expiry date of cement is set for the 3months from the manufactured date?
Cement is a chemically active material that absorbs moisture from the air to undergo a chemical reaction known as hydration. When the cement gets hydrated in the bag, it reduces the strength of the cement. Just by looking at the bag, we cannot conclude the amount of hydration of stored cement, and practically, it is not viable to test every bag of cement for its compressive strength.
By trial & error method, it is concluded that on average, the cement losses 20% of its original strength after 3 months from the date of manufacture. This 20% strength reduction is within the safety standards that we consider while designing the RCC structures.
So, the time limit for the expiry of the cement bag is set as 3 months from the manufactured date to maintain the safety & quality of the construction works.
For you 👇
3. Do every bag of cement lose the same amount of strength at the expiry date?
No. The reduction in the strength of the cement bags at a given time period depends upon,
1. Storage:
If the cement bags are stored according to the guidelines & procedure, the strength reduction will be minimized.
2. Season:
The moisture content present in the air will be more in the rainy season when compared to the summer season. So the strength reduction will be maximum on rainy days and when you buy the cement in the summer season, you may get the bags having a good level of strength nearer to 100%.
3. Type of cement :
The hydration rate of different types of cement is according to the constituents used while manufacturing them. So, the degree of loss in strength at the expiry date depends upon the type & grade of cement.
Cement is a common building material used by a wider public. The tests carried over the cement bags for their quality at an individual level are minimal. The expiry date is set after 3 months so that, the general public can select fresh cement bags, to maintain the construction quality.
4. What will be the strength reduction of cement bags with the age?
The table for the reduction in the strength of the cement for the given period of time is shown below.
|
Sl.
No.
|
Time period.
|
Strength
|
Decrease in
strength
|
|
1
|
Fresh
|
100%
|
0%
|
|
2
|
3 months
|
70 - 80%
|
20 - 30%
|
|
3
|
6 months
|
60 - 70%
|
30 - 40%
|
|
4
|
1 year
|
50 - 60%
|
40 - 50%
|
|
5
|
2 year
|
40 - 50%
|
50 - 60%
|
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