Cement manufacturing is one of the biggest industries in the world. Due to its use in concrete and basically every civil structure, cement is the most important material in civil engineering.
Let us define what cement is:
Cement is a binder. It is a substance that can bind other materials together. For civil engineering, they are restricted to calcareous cements containing compounds of lime as chief constituent to bind the fine and coarse aggregate particles together. Its that simple (on the surface).
Portland cement is the most commonly used cement. It is named so because a paste of this cement with water, after it sets hard, resembles in color and hardness a Portland stone, a limestone quarried in Dorset (a county in South West England).
Uses of cement:
- Masonry work, plastering, pointing, joints for pipes & drains.
- Used in concrete for laying floors, roofs, constructing lintels, beams, stairs, pillars and columns etc.
- Used in manufacturing of precast pipes, piles, fencing posts etc.
- Important engineering structures e.g. bridges, culverts, dams, tunnels, etc.
Types of Portland cement:
- Rapid Hardening or High Early Strength Cement (Type III):
It gains strength faster than Ordinary Portland Cement (OPC). In 3 days, it develops 7 days strength of OPC with same water cement ratio. Its initial and final setting times are same as OPC. However, it contains more tri-calcium silicate (C3S) and emits more heat during setting, therefore unsuitable for mass concreting. It is lighter and costlier than OPC. Short curing period makes it economical. It is used for structures where immediate loading is required e.g. repair works.
- Extra Rapid Hardening Cement:
This type of cement is obtained by inter-grinding calcium Chloride (less 3 %). Its strength is 25% higher than rapid hardening cement at 1 or 2 days and 10 to 20 percent higher at 7 days.
- Quick Setting Cement:
It contains less percentage of Gypsum and ground much finer than OPC. It sets faster than OPC. The setting action is accelerated by adding small percentage of aluminum sulphate, during grinding. Initial setting time is 5 minutes and final setting time is 30 minutes. It is used for concreting in underwater or running water, war time, tunnels etc. Mixing and placing has to be faster to avoid initial setting prior to laying.
- Low Heat Cement:
Low percentage (5%) of tri-calcium silicate (C3S) and high (46%) of di-calcium silicate (C2S) is mixed to keep heat generation low. It has low lime content and less compressive strength. Initial setting time is one hour, and final setting time is 10 hours. It also has a very slow rate of developing strength. That is why it is not suitable for ordinary structures. Shuttering is required for long duration so cost will increase. Prolonged curing is required so structure utilization will be delayed.
- Sulphate Resistant Portland Cement:
Percentage of tricalcium aluminate (C3A) is kept below 5% which causes increased resisting power against sulphates. Heat developed is almost same as Low Heat Cement. Theoretically, it is an ideal cement. Costly manufacturing because of stringent composition requirements. It is used for structures likely to be damaged by severe alkaline conditions like bridges, culverts, canal lining, syphons, etc.
- Water Repellent Portland Cement:
It contains a small percentage of water-proofing material with the cement and is manufactured under the name “Aqua-Crete”. The cement is prepared with ordinary or rapid hardening cement and white cement. It is used in substances to check moisture penetration in basements etc. If this cement is used in concrete, considerable care is needed to avoid reduction in strength.
- Waterproof Portland cement:
It is prepared by mixing ordinary or rapid hardening cement and some percentage of a metal stearate (Ca, Al etc.) at the time of grinding. It is resistant to water and oil penetration. It is also resistant to acids, alkaline and salt discharged by industrial water. It is used for water retaining structure like oil storage tanks, reservoir, retaining walls, pool, small retention dam etc.
Other Varieties of Cement:
- Quick Setting Cement
- Blast Furnace Slag Cement
- White Cement
- Colored Cement
- Expanding Cement
- Hydrophobic Cement
- Air Entraining Portland Cement (Type I-A, II-A, III-A)
- Pozzolana Portland Cement
- High Alumina Cement