It will be fair to say that the Construction Industry is incomplete without construction material and that too “Cement.” It is the most widely used construction material. Cement is a folio, a substance utilized for development that sets, solidifies, and sticks to different materials to tie them together. Cement is rarely utilized all alone, but instead to bind with sand and gravel together. Cement blended in with fine aggregates produces mortar for brickwork, or with sand and gravel, produces concrete. Concrete is the most broadly involved material in the presence and is behind just water as the planet's most-polished off asset.
The historical backdrop of cementing material is just about as old as the history of engineering development. Some sort of cementing materials were utilized by Egyptians, Romans, and Indians in their old developments. It is believed that the early Egyptians generally utilized cementing materials, obtained by burning gypsum. The early Greeks and Romans used cementing materials obtained by burning limestone.
The process of manufacture of cement consists of grinding the raw materials, mixing them intimately in certain proportions depending upon their purity and composition, and burning them in a kiln at a temperature of about 1300 to 1500°C, at which temperature, the material sinters and partially fuses to form nodular shaped clinker. The clinker is cooled and ground to a fine powder with the addition of about 3 to 5% of gypsum. The product formed by using this procedure is Ordinary Portland Cement (OPC).
Cement exhibits different properties and characteristics depending upon their chemical compositions. By changing the fineness of grinding or the oxide composition, cement can be made to exhibit different properties. The use of additives, changing the chemical composition, and use of different raw materials have resulted in the availability of many types of cement to cater to the need of the construction industries for specific purposes.
Different Grades of Cement
- OPC Grade 43 (IS 8112:1989)
Used for general civil purposes like plastering, flooring up to M30 grade concrete, this type of cement can achieve compression strengths at 43 MPa and is widely available in the market. It is also used in the manufacture of precast items such as blocks, pipes, tiles, etc.
2. OPC Grade 53 (IS 12269:1987)
It is used for concrete grades higher than M30 for general purposes as well as building bridges, roads, multi-storeyed buildings, etc. Achieving a minimum compression strength of 53 MPa at 28 days, they are widely used in RCC and cement grouts
DIFFERENCES BETWEEN OPC GRADE 43 AND OPC GRADE 53
Both OPC Grade 43 and 53 are widely used in Indian markets and are readily available by leading brands such as UltraTech, Ambuja, ACC, etc. The major difference is that one finds it in their compression strengths. As the name suggests, OPC Grade 53 has more compression strength of 53 Mpa than that of OPC Grade 43 which has that of 43 Mpa in 28 days. Similarly, Grade 53 has better initial strength of 27 Mpa in 7 days whereas Grade 43 has 23 Mpa for the same duration.
Hence, Grade 43 Cement is used for plastering works, pathways, precast members, etc. whereas Grade 53 is used in RCC and prestressed. While Grade 53 cement comes with all these advantages over Grade 43 cement, it should be noted that Grade 53 cement is 2-3% costlier than Grade 43 ones and thus can be used in making structures where there are no heavy loading scenarios.
3. Portland Pozzolana Cement (PPC) (IS 1489:1981)
Portland Pozzolana cement is ordinary Portland cement intimately blended or interground with pozzolanic materials such as fly ash, calcined clay, rice husk ash, etc. Portland cement clinker is either interground or intimately blended with specified quantities of gypsum and pozzolanic materials to produce Portland Pozzolana cement. Pozzolanas by themselves do not have cementitious properties but react with calcium hydroxide in the presence of moisture at normal temperature to form compounds having cementitious properties. The concrete produced by using Portland Pozzolana cement has high ultimate strength, is more durable, resists wet cracking, thermal cracking, and has a high degree of cohesion and workability in concrete and mortar.
4. Portland Slag Cement (PSC) (IS 456:2015)
Slag cement is a hydraulic cement formed when granulated blast furnace slag (GGBFS) is ground to suitable fineness and is used to replace a portion of Portland cement. It is a recovered industrial by-product of an iron blast furnace. Molten slag diverted from the iron blast furnace is rapidly chilled, producing glassy granules that yield desired reactive cementitious characteristics when ground into cement fineness.
5. Sulphate Resisting Cement (SRC) (IS 12330:1988)
SRC is a type of Portland cement in which Tricalcium Aluminate (C3A) amount is less than 5% and the amount of C3A and calcium aluminoferrite (C4AF) together is less than 25%. It is used where the concrete structure faces the risk of being damaged by the high amount of sulphates found in its immediate environment. The use of SRC is recommended in places where the concrete is in contact with the soil, groundwater, and seawater, and/or exposed to the seacoast. In all these conditions, the concrete is exposed to attack from sulphates that are present in excessive amounts, which damages the structure.
DIFFERENCES BETWEEN OPC, PPC, PSC & SRC
In India, there are four types of cement available in the market; Ordinary Portland Cement (OPC), Portland Pozzolana Cement (PPC), Portland Slag Cement (PSC), and Sulphate Resisting Cement (SRC). All four of them can be used to construct buildings, big or small. PPC and SRC are also known as blended types of cement since fly ash and slag are mixed with cement respectively.
Typically, OPC is available in two grades in the market, 43 and 53. The grade indicates the compressive strength of the cement in N/mm2 at 28 days. Depending on the structural design, any one of them can be used for construction.
The difference between OPC and PPC is due to the addition of Pozzolana in the latter. The Pozzolana is a siliceous or siliceous and aluminous material. Fly ash sourced from thermal power plants is the most common source of Pozzolana. As per Indian Standards, 15 to 35% by weight of cement can be added as fly ash. The addition of fly ash gives better resistance to water in cement, has lower heat of hydration that improves workability, and has improved resistance to chemicals.
PSC is an intimately ground mixture of Portland cement clinker and granulated blast-furnace slag, either inter-ground or ground separately and blended together. Blast furnace slag can be obtained only from integrated steel plants. These plants are concentrated in the Eastern region of the country. Therefore their availability is more focussed on the Eastern zone in India. The slag added to the cement gives better workability, higher strength, better overall and chemical resistance.
The differences between PPC and PSC are marginally less. PSC is costlier than PPC but both of them are equally efficient for building homes. PSC is more preferred for constructions where water containing sulphates and chlorides are present as it can easily resist the effects of these chemicals and prevent chemical as well as weathering attacks on the cement.
The differences between SRC and OPC are only in the change in their chemical compositions. In SRC, Tricalcium Aluminate (C3A) is less than 5%. Higher C3A will make the cement more susceptible to adverse reactions with sulphates and make concrete deteriorate faster. With lower C3A, this reaction can be made slower and concrete can be made more durable.
CERTIFICATIONS AND TESTING OF CEMENT –
There are different types of cement and their respective chemical compositions available in India. Each type of cement has to be handled the way they are supposed to be and their mix proportions vary to various factors. Hence, the Bureau of Indian Standards (BIS) has some Indian Standard (IS) Codes for practice and reference for all types of cement and constructions. These IS codes include the Standardization in the field of all types of cement, pozzolana, testing sand, concrete, aggregates, instruments for cement and concrete testing, cement plant machinery and ferrocement concrete, reinforced concrete and prestressed concrete, test methods for concrete, concrete production and execution of concrete structures, performance requirements for structural concrete, non-traditional reinforcing materials for concrete structures and cement and lime. Below are some examples of the most commonly used IS Codes for construction practices in India.
IS 269:1989 Specification for ordinary Portland cement, 33 grade
IS 383:1970 Specification for coarse and fine aggregates from natural sources for concrete
IS 455:1989 Specification for Portland slag cement
IS 456:2000 Code of practice for plain and reinforced concrete
IS 457:1957 Code of practice for general construction of plain and reinforced concrete for dams and other massive structures
IS 516:1959 Method of test for the strength of concrete
IS 650:1991 Specification for standard sand for testing of cement
IS 1199:1959 Methods of sampling and analysis of concrete
IS 1343:1980 Code of practice for prestressed concrete
IS 1344:1981 Specification for calcined clay pozzolana
IS 1489(Part 1):1991 Specification for Portland pozzolana cement Part 1 Flyash based
IS 1489(Part 2):1991 Specification for Portland-pozzolana cement: Part 2 Calcined clay based
IS 1727:1967 Methods of test for pozzolanic materials
Based on these IS Codes, the BIS has also provided some standard tests on cement and their respective values. Reputed cement brands in India conduct these tests and compare the values with the respective IS Codes so that the buyer has no doubts about the quality of cement. Below are some common Laboratory Tests conducted on cement as per IS: 4031 - 1985
- Standard Consistency Test
- Initial and Final Setting Time Test
- Strength Test
- Soundness Test
Similarly, one can also send a sample of cement to laboratories for testing the quality and performance of cement. There are also on-site testing methods of cement which can be done by anyone to get a basic idea about the quality of cement. Some basic on-site tests on cement are provided below.
(a) Open the bag and take a good look at the cement. There should not be any visible lumps. The color of the cement should normally be greenish-grey.
(b) Thrust your hand into the cement bag. It must give you a cool feeling. There should not be any lump inside.
(c) Take a pinch of cement and feel-between the fingers. It should give a smooth and not a gritty feeling.
(d) Take a handful of cement and throw it on a bucket full of water, the particles should float for some time before they sink.
STORAGE OF CEMENT
Appropriate safety measures for the capacity of cement, for example, duration and place of capacity, game plan, climatic dampness content, and so forth are vital after the method involved with assembling and prior to involving it in the building site. Since the cement has a hygroscopic nature, the cement assimilates dampness from the climate effects and solidifies like stone which can't be utilized for constructional reasons. In this way, stockpiling of cement should be done with care.
Precautions to be taken care of while Storing Cement
- Moisture Content - The cement should be stored in such a way that it cannot expose to the atmosphere. So, airtight bags are used to pack the cement. If the cement is finely grained and is very good in quality, then it will absorb moisture vigorously. Hence, extra care should be taken for this type of cement and it is better to use it in its fresh stage. In any case, if it is exposed to the atmosphere, the presence of moisture content is to be tested. If the moisture content is more than 5% then it is not useful for the construction.
- Duration - It is preferred that the cement should not be stored for more than 3 months. However, if it is stored for more than 3 months the strength of cement should be tested before using it.
- Place of Storage - The bags of cement should not be stored in open places. Preferably specially designed storage sheds are good for cement storage. They can be used for longer periods. The main purpose of special design is to provide waterproof floors, roofs, and walls. The floor of the shed should be well above ground level. Small windows with airtight doors should be provided. Proper drainage should be provided inside and outside the shed to drain water in any case.
- Arrangement - A wooden platform of height 150 to 200 mm is prepared above the floor of the storage shed to avoid direct contact between the floors and cement bags. On the prepared wooden platform, the cement bags should be arranged one above the other which forms a stack of cement bags. Each stack should not consist not more than 10 bags of cement. The stack should not touch the walls of the shed and it should be considerably 300 mm away from the external walls. Each stack should be closely connected to avoid the circulation of air. To prevent collapsing of high stacks, a cross arrangement of bags one above the other is preferable. All the stacks are covered with a waterproof layer for long-term protection. Passage width of 900mm to 1000mm is provided between the stacks. The stack should consist of the same type of cement and for each stack date of placing should be noted to know their period of storage
- Withdrawal - When the time of use arrives, the Withdrawal of cement bags from stacks happens. The cement bags should be taken out in the First In First Out (FIFO) order. The bag first placed in the storage shed should be withdrawn first.
STORAGE OF CEMENT IN SILOS
At the large construction sites where a large quantity of cement is required, the cement is preferred to be stored in silos. In silos, the cement can be stored in bulk i.e. 12-50 tonnes, and that too under the ideal conditions. Silo is typically a welded steel cylindrical container. It is supported on four crossed braced legs and has a discharge outlet at the bottom. Moreover, it can also have some weighing arrangement at the bottom so as to get the required weight of cement in each batch. Cement is supplied in close tankers from the factory and pumped into these silos directly from these tankers. Scoring of cement in silos has the following advantages as compared to storing the stacks:
- The cost of bulk cement per ton is less than the bagged cement
- Unloading of cement through pumping arrangement directly into the silos is quite convenient and cheaper.
- Fewer precautions are to be observed.
- Less site space is required for any given quantity of cement
- As cement is delivered into the silos from the top and extracted from the bottom, the cement, which is received first, is always used first.
- The same silo can be reused for the other construction sites.
TOP CEMENT MANUFACTURERS IN INDIA –
UltraTech Cement Limited is the largest cement company in India and among the leading producers of cement globally. It is also the country’s largest manufacturer of white cement and Ready Mix Concrete. The company has a consolidated capacity* of 116.75 Million Tonnes Per Annum (MTPA) of grey cement. UltraTech Cement has 23 integrated plants, 1 clinkerisation unit, 26 grinding units, 7 bulk terminals, 1 white cement plant, 2 WallCare putty plants, and more than 100+ RMC plants – spanning India, UAE, Bahrain, and Sri Lanka. UltraTech Cement is also India's largest exporter of cement and clinker reaching out to meet demand in countries around the Indian Ocean, Africa, Europe, and the Middle East.
An established brand in India, Ambuja Cement is known for its high strength, high-performance Ordinary Portland Cement (OPC) and Pozzolana Portland Cement (PPC). OPC & PPC both are high-quality active hydraulic binders & are preferred brands in the market for all construction applications. The company currently has a manufacturing capacity of 29.65 million tonnes. Ambuja was the first to introduce 53-grade cement in the market. By benchmarking quality standards for the industry, Ambuja became the first cement company to receive the ISO 9002 quality certification.
ACC Limited (ACC) is a leading player in the Indian building materials space, with pan-India manufacturing and marketing presence. With 17 cement manufacturing units, 85 ready mix concrete plants, over 6,600 talented employees, a vast distribution network of 56,000 dealers & retailers, and a countrywide spread of sales offices, it contributes tremendously to the landscape of the country. From the Bhakra Nangal Dam in 1960 to the Mumbai-Pune Expressway, ACC cement is at the heart of iconic landmarks across the country.
Shree Cement is a company that cares for its customers and has served markets across India and the Middle East. Shree Cement has a consolidated Cement Production Capacity of 47.4 Million tonnes per annum (including overseas). Their operations span across India and the UAE with 4 integrated plants in India, 1 in UAE, and 9 Grinding Units. The company offers the top 3 types of cement in their range namely, OPC, PPC & PSC.
Founded by Mr. Jaidayal Dalmia in 1939, Dalmia Cement is one of India’s pioneering homegrown cement companies. The company operates a manufacturing capacity of 35.9 MnT per annum (MTPA), across 14 cement plants and grinding units which are spread across 10 states. With over 33,000 dealers and sub-dealers, the company presently services more than 22 states and is among the leading players in every region where it is present in. Dalmia Cement is the only company with at least one plant in each of the four key eastern states of West Bengal, Bihar, Jharkhand, and Odisha. The company offers a range of cement variants through its brand portfolio of three marquee brands: Dalmia Cement, Dalmia DSP, and Konark Cement. These brands are available as Portland Pozzolana Cement, Portland Slag Cement, Composite Cement, and Ordinary Portland Cement in select markets. Dalmia Cement is India’s largest manufacturer of slag cement and is a category leader in super-specialty cement used for oil wells, railway sleepers, and airstrips
Cement plays a key, yet regularly inconspicuous, a job in our lives. It is an adaptable and dependable development material with a wide scope of uses. Cement has replaced all other building materials, like clay and lime, which ruled high for hundreds of years, in construction from last century. It has the ability to hold the structure together. With these advantages and wide applications, cement is and will be a dominant construction material for the far future.