Special cement are now manufactured for use in applications involving complex degradation, high temperature and pressure support properties. It is used in oil wells, railways and other industrial areas. The rapid urbanization, the rapid growth of infrastructure continue to increase demand and penetration of specialized cement for end-users. These types of cement stretch beyond construction to fulfil essential needs. These cement can be used at very high or very low temperatures. The different types of special cement as discussed below.
Oil – well cement
Oil-well cement is used for work in the drilling of oil wells that are subject to high temperatures and pressures. They usually consist of portland or pozzolanic cement (see below) with special organic retarders to prevent the cement from setting too quickly. Its main components include pozzolanic or Portland cement along with organic retarders. Oil-well Cement is used to provide a base ingredient in the slurry mix that is pumped into the interior metal section of the oil-well and forced back toward the surface from the base of the borehole making the production casing. Its features include thickening times controllable, excellent retarder response, integrity and durability, high sulfate resistance, consistent quality etc.
Railway sleeper Cement
These are manufactured as per specifications formulated by the Indian Railways for manufacturing concrete sleepers. It can withstand unfavorable climatic conditions, temperature, humidity, fungus or insect attack. Its properties include corrosion, high fineness enhances workability, and high early strength enables improved mass production cycle of concrete railway sleepers. The cement produces high resistance to lateral movement and is less prone to vertical and horizontal distortion. It offers strength to track and makes it suitable for holding shape at high speed. It can be used in high-rise buildings and marine structures where early strength is required.
It is a special cement that can be used with good results for a variety of conditions. It has been developed to produce concrete resistant to freeze-thaw action and to scaling caused by chemicals applied for severe frost and ice removal. In this cement, very small quantities of air-entraining materials are added as the clinker is ground during manufacturing. Concrete made with this cement contains tiny, well distributed and completely separated air bubbles. The bubbles are so small that there may be millions of them in a cubic foot of concrete. The air bubbles provide space for freezing water to expand without damaging the concrete. It is used for paving runways in airports.
Water repellent cement’
This type of cement is obtained by mixing finely ground cement clinker with gypsum and hydrophobizing additives. Its features include lower water absorption, greater frost resistance, and greater imperviousness to water than ordinary cement. Besides portland cement, cinder, alumina, and other kinds of cement can also be made water-repellent. It is suitable for reducing permeability in concrete tanks, reservoirs, sewerage works etc
High alumina cement
High alumina cement is obtained by fusing limestone and bauxite with small amounts of silicon oxide and titanium oxide at I500 C-1600 C in a rotary kiln, and then grinding the resulting products to fineness in the same method as that used of Portland cement. It is made by grinding alumina and calcareous material such as lime through sintering or fusing. It is heat resistant and is useful for industries dealing with high temperatures even direct fire. It offers high compressive strength and is very reactive. Also worth mentioning is its low frost action as there is more heat evolved during the setting process.
Given above are different types of special cement used for different special applications in India. These cements serve some specific functions such as altering the setting or hardening behavior of concrete, imparting superior workability, imparting water retention and plasticity to mortars etc.