Types of Cement and their Uses in Concrete Construction
Cement exhibit different properties and characteristics depending upon their chemical composition. By changing the fineness of grinding or the oxide composition, cement can be made to exhibit different properties. Due to the extensive use of the cement, different types of cement for the compositions, as well as by varying the relative proportion of the oxide compositions, as well as by adding one or two more new minerals known as additives to the clinker at the time of grinding. The use of additives changes the chemical compositions of the cement and give different types of cement. Cement is classified as portland cement and non-portland cement. The distinction is mainly based on the method of manufacture.
Types of cement as listed below-
- Ordinary Portland cement
- Repaid hardening cement
- Sulphate resisting cement
- Quick setting cement
- Low heat cement
- Portland Pozzonland cement
- High strength cement
- High alumina cement.
Ordinary Portland cement -
It is the most common cement used in the construction industry. It has a low resistance to chemical attack and it has a medium rate of hardening. The chemical composition of ordinary Portland cement is lime, silica, alumina, iron oxide, magnesia, sulpher, trioxide, soda, and potash. Out of the total production of cement ordinary portland cement accounts for about 80 to 90 percent. The color of ordinary Portland cement is grey or greenish grey. It has a rate of strength development and rate of evolution of heat of hydration are medium. It has medium cracking resistance.
Rapid hardening cement –
This cement is similar to ordinary Portland cement. It develops strength rapidly so it is called as high early strength cement. It develops at the age of three days, the same strength as that is expected of ordinary Portland cement at seven days. The rapid rate of development of strength is due to the higher fineness of cement particles gives a greater surface area of the or action of water and higher C3S and lower C2S content. A higher fineness of cement particles gives a greater surface area for the action of water and higher C3S results in quicker hydration. It is used the or construction of important structures and underwater works. This cement contains a high percentage of cement. The lighter weight of rapid hardening cement and the shorter period of water curing make its use economical compared with the normal setting cement.
Sulphate Resisting Cement –
Ordinary Portland cement is not able to resist the attack of suphates. Sulph reacts with calcium hydroxide a calcium aluminate. The effect of this attack will result in the expansion and disruption of hydrated cement paste. This attack is known as Sulphate attack will greatly be accelerated in case of alternate wetting and drying as in case of marine structures.
To remedy the suphate attack, the use of cement with low C2A content is found to be effective. Such cement with low C3A and comparatively low C4AF content is known as sulphate resisting cement. This cement contains a high percentage of silicate. The sulphate resisting cement is used in the foundation and basement where the soil is infected with suphates. It is also used in case of construction of treatment works and also in the marine structures.
Quick Setting Cement –
This cement sets very early. This property is brought out by reducing the gypsum content at the time of clinker grinding. This cement is required to be mixed, placed and compacted very early. It is mostly used in underwater construction. It is not also useful for the purpose of grouting.
Low Heat Cement –
The hydration of cement is an exothermic action which produces a large quantity of heat during hydration. This heat of hydration results in cracks in the large body of concrete. So technologist produced a cement, which produces less amount of heat at a low rate during the process of hydration. This type of cement is evolved by reducing the contents of C3S and C3A which are the compounds evolving the maximum heat of hydration and increasing C2S.
The rate of evolution of heat will, therefore, be less and the evolution of heat will extend over a long period. Therefore, the feature of low heat cement is a slow rate of gain of strength, but the ultimate strength of low heat cement is the same as that of ordinary Portland cement. This cement used in mass concrete construction. Such as dam, retaining works, etc.
Portland Pozzolana Cement -
This cement is useful in marine and underwater constructions. Pozzoland is the name given to volcanic ashes which is chiefly a siliceous material. Pozzoland cement is prepared by mixing and grinding clinkers and pozzolana together. Pozzolana, Present in cement, reacts with the free lime liberated during hydration of cement and prevents disruption in concrete. The pozzolana constituent shall not be less than a percent and not more than percent by weight of Portland pozzolana cement. Portland pozzolana less heat of hydration and offers greater resistance to the attack of water than ordinary Portland cement.
High Strength Cement –
Certain works in the construction industry such as prestressed concrete, precast concrete requires high strength concrete. Thus construction industry requires a special type of ordinary Portland cement having a compressive strength much higher than the compressive strength specified for ordinary Portland cement. Cement having much higher strength than ordinary Portland cement is known as high strength ordinary Portland cement.
High Alumina Cement
It is manufactured by melting a mixture of bauxite and lime and lime and grinding them to a very fine powder. This cement contains 32% alumina. This cement is much costly. There is no expansion on the setting of this cement. It evolves much amount of heat in setting hence it should not be used in the massive concrete construction. It has the capability of resisting the action of acids and high temperature. The use of high alumina cement in restricted to works of furnaces and chemical plants.