Stay updated on cement standards
Jagvir Goyal
Cement and steel being the two most important materials that govern the strength of a structure, remain under constant gaze of Bureau of Indian Standards. BIS keeps reviewing the specifications and parameters regarding these from time to time and revises the codal instructions for their properties and usage. Draft instructions are circulated among all prominent engineers for their opinion before adopting the changes and revising the codes. Recently, cement codes have undergone significant changes and it is important for a house builder to be in know of these.
Types of cement: There are 13 types of cement for which BIS has issued specifications and IS code numbers. Many of these cements are use specific. These include Rapid hardening cement, Portland slag cement, low heat Portland cement, Ordinary Portland Cement, Portland Pozzolana cement, High Alumina Cement, White Portland Cement and many others. Of these, only three types of cement are used by a house builder for his house. These are Ordinary Portland Cement, Portland Pozzolana Cement and White Portland cement.
IS Codes: The Ordinary Portland Cement when used by the house builders should conform to IS 269. The Portland Pozzolana Cement carries IS 1489 Part I mark. The White Portland Cement carries IS 8042 mark. Ordinary Portland Cement is commonly known as OPC and Portland Pozzolana cement is commonly known as PPC. White Portland Cement is commonly known as White cement. While the OPC and PPC are supplied in 50 kg bags, white cement is used only for some specific purposes in the house and thus its consumption in a house is very small. It is therefore purchased in 1 kg packs.
Grades: Earlier there used to be three grades of OPC. Now, as per latest revision of IS Code, there are five grades of OPC. These are 33 grade, 43 grade, 53 grade, 43 S grade and 53 S grade. There are no grades in PPC or in any other type of cement. 43 S grade and 53 S grade of cement are used in Railway Engineering for manufacture of sleepers. Here, S stands for Sleepers. OPC 33 grade, 43 grade and 53 grade cements are used for General purpose engineering such as building construction. The43 grade OPC is stronger than 33 grade cement and 53 grade cement is still stronger than 43 grade cement. Naturally, the tendency of the house builder is to opt for 53 grade cement to have a stronger structure.
Codes for cement grades: Earlier, there used to be three IS codes for different grades of OPC. For OPC 33 grade, the IS code was IS 269 and cement bags were marked with IS 269 mark. For 43 grade OPC, the IS code was IS 8112. The cement bags carrying IS 8112 mark were presumed to be having 43 grade cement. For 53 grade cement, IS code used to be IS 12269. All cement bags having 53 grade cement carried IS 12269 mark. In 2015, IS code for OPC has been revised and all grades of cement have been included in one IS code only. Now, all cement bags containing OPC are supposed to carry IS 269 mark only irrespective of grade of cement contained in it. Further, each bag will further mention whether it carries 33 grade cement or 43 grade cement or 53 grade cement. So don't look for IS 8112 mark or IS 12269 mark any more while buying cement. Rather, look for IS 269 mark only and further, the grade of cement as mentioned on the bag.
Why the grades: In all grades of Ordinary Portland Cement, same raw material is used. The difference between different grades of cement is due to the difference in proportion of raw materials in cement. Variation in proportion of raw materials in cement alters its physical properties and produces stronger varieties of cement, classified as 43 grade and 53 grade cement.
Types of PPC: There are two types of Portland Pozzolana cement or PPC. One type of cement contains fly ash as the pozzolana material. The other type of PPC contains calcined clay as pozzolana material. PPC containing fly ash has been given IS 1489 (Part 1) mark. PPC containing calcined clay has been given IS 1489 (Part II) mark. Use of different types of pozzolana materials alters physical and chemical properties of cement. In building work, fly ash based PPC is used. Thus, while choosing PPC for one's house, one should look for IS 1489 (Part 1) mark on the cement bags.
Strength values of OPC & PPC: As explained above, of the three grades of OPC, 53 grade is the strongest. Its strength is 530 kg per sq. cm. OPC 43 grade cement comes next. It has a strength of 430 kg per sq cm. OPC 33 grade has 330 kg per sq cm of strength. PPC is considered to have strength equivalent to that of OPC 33 grade cement. Therefore, its strength is 330 kg per sq cm. These are the minimum strength requirements for each grade and type of cement to win ISI mark. To be on safer side, the cement produced by cement manufacturers has much more strength than these minimum strength values. The buyer is therefore benefited on this account and gets better quality cement.
Choice: From the above details, it becomes clear that some grades of Ordinary Portland Cement carry better strength than PPC. Based on better strength, obvious choice of house builder shall, therefore, be 43 grade OPC or 53 grade OPC. Before finalising his choice, a house builder shall like to have a look at the difference in cost, presuming that 43 grade and 53 grade cement shall be much costlier than 33 grade cement or PPC. In actual, it is not so. There is not much difference in cost of different grades of cement. Thus a house builder shall like to easily finalise his choice as 43 grade cement or 53 grade cement.
Actual scene: Though a house builder will like to choose 43 grade or 53 grade cement for his house but actual picture is that these grades of cement are simply no more available in the market. Not only these, even 33 grade OPC is also not available in the market. Only PPC is available in the market and one is forced to choose it. Some dealers promise the house builders to provide OPC 43 grade or 53 grade cement to them by making a special request to the manufacturer to arrange cement of these grades for them but manufacturers agree to their request only if a large lot of OPC is demanded.
Availability of dry fly-ash from the thermal plants has attracted the cement manufacturers to produce more quantity of Portland Pozzolana Cement (PPC) and minimize the production Ordinary Portland Cement (OPC) as the manufacturing cost of PPC proves much lesser than that of OPC to them. This occurs because a substantial component of OPC clinker gets replaced with fly ash in PPC. The percentage rests somewhere between 15 to 35 per cent. Fly ash is freely available to the manufacturers from thermal plants. Though production cost is less, the market rate of both types of cement i.e. OPC and PPC is almost the same.
Important ingredient
Every house builder wants to choose the best type and brand of cement for construction of his house. Now, people have become aware of the grades of cement also. Many of the queries received are about the grade, type and brand of cement. A house builder wants to decide the best brand and grade and type of cement, fix up his dealer for supply of its lots as and when asked by him and free himself for other jobs related to the construction of his house. The decision, therefore, needs to be taken after thorough consideration.
Freshness of cement: The cement lot chosen should be as fresh as possible. The cement bags carry the week and year of manufacture marked on them. A house builder should try to buy a freshly arrived lot with dealer. Effort should be made to buy cement bags that are not more than two months old. Cement absorbs moisture from air and loses strength with time. In the latest IS code, Bureau of Indian standards has now made another provision that each bag of cement shall now carry the 'Best before Date' instruction. Earlier, no such instructions were given on cement bags. Now, a buyer can check the date of manufacture and 'best before date' instruction on the cement bags and buy the lot of cement accordingly.
The terms of choice
Keeping in view the latest revision in IS code by BIS and other details as explained in the article, one may go ahead to finalise his choice of cement as under:
- Look for OPC 43 grade cement or 53 grade cement, if available. If available, look for IS 269 mark on the bags along with grade of cement clearly mentioned on it.
- If OPC 43 grade or 53 Grade cement is not available, go ahead for buying PPC cement. In that case, look for IS 1489 Part I mark on the bags.
- Check the condition of cement bags. These must not be torn anywhere. The bags can be in jute or HDPE/PP or jute synthetic or multi-wall paper bags.
- Check the weight of Cement bags. See that net quantity of cement is 50 kg per bag, excluding the weight of bag.
- Most importantly, check the freshness of cement. Check the date of manufacture and newly introduced feature — 'Best before date'— on the bags.
The writer is Engineer-in-Chief, Civil Engineering Dept in a Punjab PSU
