Suitability of Various Types of Cement and Its Grades?

Cement is a very popular and the oldest binding material in the world. There are various types of cement available nowadays. Each cement has special properties and therefore it is used under certain conditions.

A grade of cement indicates the strength of cement. The strength of cement is generally measured as compressive strength. The strength of cement is the most important of all the cement properties. Compressive strength is generally measured after 28 days of curing for a standard cube. Compressive strength measured in Mega pascal (Mpa) or in N/mm2.

Grades of cement available in the market:

i)  33 Grade OPC:

The 33-grade cement means that the compressive strength of the cement after 28 days is 33N/mm² when tested as per Indian Standards under standard conditions. This type of cement is used for general construction work under normal environmental conditions.

ii) 43 grade OPC:
• It is the most widely used general-purpose cement.
• For concrete grades up to M-30, precast elements.
• For marine structures but C3A should be between 5 – 8%.

iii) 53 grade OPC:
• For concrete grade higher than M-30, PSC works, bridge, roads, multistoried buildings, etc.
• For use in cold weather concreting.
• For marine structures but C3A should be between 5 – 8%.

iv) Portland Slag Cement (PSC) i.e. OPC + granulated slag: It gives low heat of hydration. The slag should be more than 50% and up to 70%. It is used for ;
• Marine and offshore structures- very high chloride and sulfate resistance. • Sewage disposal treatments works
• Water treatment plants
• Constructions that are expected to be attacked by dissolved chlorides and sulfate ions.
• Should be mainly used for all future structures.

v) Portland Pozzolana Cement: IS: 1489(part-I) – 1991 (using flyash):

• It gives low heat of hydration and reduces the leaching of calcium hydroxide. This cement should be used only after proper evaluation. This should be tested as per IS: 1489 (Pt I) – 1991. It is used for :
• hydraulic structures- dams, retaining walls
• Marine structures
• Mass concrete works- like bridge footings
• under aggressive conditions
• Masonry mortar and plastering.

vi) SRC- Sulphate Resisting Cement: (C3A < 3%) Sulphate Resisting Portland Cement is a type of Portland Cement in which the amount of tricalcium aluminate (C3A) is restricted to lower than 5% and 2C3A + C4AF lower than 25%. The SRC can be used for structural concrete wherever OPC or PPC or Slag Cement are usable under normal conditions.

The use of SRC is particularly beneficial in such conditions where the concrete is exposed to the risk of deterioration due to sulfate attack, for example, in contact with soils and groundwaters containing excessive amounts of sulfates as well as for concrete in seawater or exposed directly to the sea coast.

Conclusion:

Different types of cement for different Applications: Desirable to Construct foundations, sewage and waterworks in Sulphate resistant cement, RCC in 43 or 53 OPC, Plastering and masonry work in PPC.
It will optimize the cost and improve the quality of construction.

• Initial setting time: As per Indian standards, the minimum initial setting time is 30 minutes. Considering the hot weather conditions prevailing in India, it is all the more necessary to insist on a higher initial setting time for cement e.g. at least 60 minutes.
• Chemical properties: The chloride content is a very important requirement affecting the durability of concrete and is missing in IS specification.
• The fineness of cement: IS code provides for a minimum specific surface of 225M2 /Kg except for Portland Pozzolana Cement. Most of the Indian cement manufacturers resort to producing cement with increased fineness even higher than 300 presumably to improve the compressive strength of cement. This is not desirable in hot weather concreting. It is, therefore, necessary to lay down the upper limit of fineness while ordering cement or framing contract conditions for concrete works. The upper limit should be around 280.
• The heat of hydration: Heat of hydration should be specified for the types of cement for hot weather concreting it should be (i) 7 days <270 Kj/Kg and for 28 days >< 320Kj/Kg. For cold weather, it should be more.

Factors affecting the choice of cement: Following factors govern the choice of cement.

• Durability Characteristics
• Functional requirement – Deflection, crack width etc.
• Design parameters- Strength, fineness, setting time requirement, etc.
• Speed of construction- Time for construction etc.
• Environmental Conditions- Ground conditions, soluble salts, sulfates, Chemical plants, etc.