Cement is the most commonly used construction material that has both adhesion and cohesion properties due to which it can make bonding and bind particles of solid matter into a compact durable solid mass.
Cement is mainly classified into two categories on the basis hardening and setting mechanism.
- Hydraulic cement
- Non-hydraulic cement
Hydraulic cement: Hydraulic cement is a type of cement when mixed with water, it gets hardens due to the chemical reaction that occurs independently. Hydraulic cement sets in around 3 to 5 minutes when mixed with water.
Non- hydraulic cement: Non-hydraulic cement such as lime and gypsum plaster doesn’t harden when exposed to water. It should be kept dry in order to retain their strength, it takes substantially longer time to dry off. Non-hydraulic cement such as slaked lime hardens due to reaction of carbonation in the presence of carbon dioxide naturally present in the air.
Many Types of cement have been developed to suit different conditions such as:
Ordinary Portland cement (OPC)
This is the most common type of cement used in construction. It is manufactured by grinding clinker with the addition of a small quantity of gypsum, water and less than 1℅ air-entraining agents. Portland clinker consists of calcium silicate and is obtained by calcining to incipient fusion a predetermined and homogeneous mixture of materials mainly containing 59% – 64% lime (CaO) and 19% – 24% silica (SiO2) with 3% – 6% of alumina (Al2O3) and 1% – 4% iron oxide (Fe2O3).
The setting and hardening of cement after addition of water happens due to dissolution and reaction of its constituent. The calcium aluminate formed by the constituent is to set and harden the cement and then calcium trisilicate formed is responsible for early gain its strength during the first 48 hours. Calcium disilicate reacts slowly and responsible for strength at a later stage.
Portland Pozzolana Cement (PPC)
Portland pozzolana cement is manufactured either by grinding clinker and pozzolana or by blending Portland cement and fine pozzolana. The amount of pozzolana is 10-25%by weight of cement. This type of cement is suitable for waterfront structure or for marine structure as in dams, bridge piers and thick foundation where mass concrete is used, also used for sanitation system like Sewers. The pozzolana has no cementitious properties or less binding property but in the finely divided form with the presence of water can react with calcium hydroxide at a suitable temperature to form compounds having sufficient binding properties
Rapid Hardening Cement
Rapid hardening cement is manufactured similar to ordinary portland cement but contains high tricalcium silicate and finer grinding is done for the cement. This type of cement attains faster strength than ordinary Portland cement. It retains strength three-day strength of ordinary cement in one day. However, this type of cement is subjected to large shrinkage and water requirement for workability is high. The cost of rapid hardening cement is 10% higher than ordinary Portland cement. The concrete made with this type of cement is frost and freeze resistant as the concrete matures more quickly.
Extra Rapid Hardening Cement
Extra rapid hardening cement is manufacture by grinding Calcium Chloride with rapid hardening portland cement. The amount of calcium chloride is 2% by weight of cement. After adding water, a huge amount of heat is evolved within a short period of time along with hydration. So, this type of cement is perfect for concreting in cold weather. This type of cement has strength 25% more than the rapid hardening cement.
Portland Slag Cement
Portland slag cement is obtained by mixing Portland cement clinker, granulated blast furnace slag with gypsum in a suitable proportion and grinding it to a finer particle. It can also be manufactured by blending of Portland cement and finely ground granulated slag unlaid a mixing it thoroughly. Granulated slag is a non-metallic product consisting essentially of glass containing silicate and aluminium silicates of lime and other bases. This slag is obtained by processing of molten slag by rapidly chilling or quenching it with water or steam and air. This type of cement is generally developed to utilize the waste product obtained from blast furnaces.
Hydrophobic Portland cement
Hydrophobic cement is obtained by mixing ordinary Portland clinker with water repellent film-forming cement such as oleic acid, stearic acid. The water repellent film formed around each grain of cement reduces the rate of deterioration of the cement. These film will be broken at the time of mixing the cement with aggregate, allowing cement particles for normal hydration. However, these water repellent material allow a certain amount of air in the concrete, thereby increasing the workability.
Low heat Portland cement
Low heat Portland cement is manufactured in the same way as ordinary Portland cement. The only difference between them is the amount of compound like c3s and c3A are reduced whereas the amount of c2s is increased. This reduction of compounds retards the chemical action of hardening. This action makes this cement to gain strength at a slower rate. However, their ultimate strength is same as ordinary Portland cement.
Sulphate Resisting Portland cement
Generally, ordinary Portland cement is susceptible to the attack of sulphates. sulphate resisting Cement is developed to use where the soil is infected with sulphates. This type of cement contains a comparatively low amount of c3A and c4AF and high silica content. Sulphate resisting Portland cement is manufactured by grinding and intimately mixing together calcareous, silica, alumina and iron oxide bearing materials. The resultant clinker is grounded to produce the cement.
Quick Setting Cement
Quick setting cement is used for aggressive foundation conditions like where pumping is needed. This cement has a property to set fast. This property of cement is achieved by reducing the amount of gypsum at the time of clinker grinding. This type of cement is also used in some typical grouting operations.
High Alumina Cement
High alumina cement is manufactured from an aluminous and calcareous material either by sintering and grinding the resulting clinker i.e. fusing 40% bauxite, 40% lime and 25% iron oxide with a little of ferric oxide and silica, magnesia etc at a very high temperature. The total alumina content in this type of cement should not be less than 32%. The main ingredient is monocalcium aluminate which reacts together with water and forms dicalcium octahydrate hydro aluminate and aluminium oxide hydrate. The dicalcium octahydrate hydro aluminate gels consolidates and the hydration occurs which results in the crystallization of products. The rate of crystallization is high as compared to OPC which leads to a rapid gain of strength. The absence of c3A in this type of cement makes the resistance to sulphate attack. As this type of Cement is resistant to the action of seawater, sulphates, they are used as a refractory concrete in industries and widely used for precast concreting.