Special cements are used to serve some specific functions in concrete and masonry construction. These functions can be altering the setting or hardening behavior of concrete, produce different architectural effects, enhance workability, impart water retention and plasticity of masonry, resist water penetration in walls or containment vessels, or reduces the cost of the cementing agent.
Thus, these special types of cement are used for specific requirements. Several special cements are now available to the concrete construction industry. Every kind of special cement gives a specific function in terms of application, performance, and durability.
These types of cement can be used at very high or very low temperatures. Among these, some special cement can also be used in acids. Special cement, such as silicate cement has a very high setting rate. Barium and strontium cement are resistant to radioactive radiation.
6 Special Types of Cements
Some of the special cement are described below:
1. Masonry Cement
For a long time, lime gauged with sand was used for mortar for laying brickwork. To increase the strength and rapidity of gaining strength, it became common practice to mix portland cement with the lime.
The usual proportion of cement: lime: sand can range from 1:1:6 for heavy loads to 1:3:12 for light loads. The cement sand mortars are too harsh, so lime is added for making the work easier. To avoid the necessity of mixing cement and lime, masonry cement are introduced.
The plasticity and workability of masonry cement are imparted by the limestone and air-entraining agent. The ease of working masonry cement & their water-retentive property increase their adhesion to bricks or other building units.
2. Oil Well Cement
In the process of drilling oil wells, oil well cement is used to fill the space between the steel lining tube and the wall of the well and also to grout up porous strata and to prevent water or gas from gaining access to oil-bearing strata.
This cement is subjected to very high pressure, and temperature may rise to 400 F. Thus, cement used must be capable of being pumped for up to about three years. It gets harden quickly after setting.
3. Expanding Cement
Expanding cement expands while hardening. Usually, concrete shrinks while hardening results in shrinkage cracks. So, this effect can be avoided by mixing expanding cement with regular cement in the concrete, which will neither shrink nor expand.
This cement can also be used in repairing work where the opened joint is filled with this cement so that after expansion, a tight joint is obtained.
4. Sorel Cement
Sorel cement is prepared by adding strong magnesium chloride to ground calcinated magnesia finely. Within 3-4 hours, it sets to a hard mass. The rate of hardening of the cement increases with the addition of 1.5% calcium chloride.
The advantage of sorel cement is its accelerated rate of setting, which is useful during cold weather.
5. Trief cement
Trief cement is practically the same blast furnace cement except that the blast furnace slag is ground wet and separate from cement. This cement has smaller shrinkage and smaller heat of evolution while setting than OPC.
6. High Alumina Cement
This cement is obtained by fusing limestone and bauxite with small amounts of silicon oxide and titanium oxide at 1500-1600C in a rotatory kiln & then grinding the resulting products to fineness in the same method as that used of portland cement.
The important components of high alumina cement are monocalcium aluminates, tricalcium pentaluminate, dicalcium silicate, and tetra calcium aluminoferrite.