Cement

Cements in general are adhesive and cohesive materials which are capable of bonding together particles of solid matter into compact durable mass.
For civil engineering, cements containing compounds of lime as chief constituent to bind the fine and coarse aggregate particles together.

Portland cement is so named because a paste of 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/columns etc.
• Used in manufacturing of precast pipes, piles, etc.
• Important engineering structures e.g. bridges, culverts, dams, tunnels, etc.

Cement Compounds

• Cement consists of the following major compounds:
• Tricalcium silicate, C3S
• Dicalcium silicate, C2S
• Tricalcium aluminate, C3A
• Tetracalcium aluminoferrite, C4AF
• Gypsum, CSH2

Functions of ingredients of cement
                                                 Lime (CaO)

• It is the major constituent of cement . Its proportion is important.
• The excess makes the cement unsound and causes the cement to expand and disintegrate.
• In case of deficiency, the strength of cement is decreased and cement sets quickly.
• The right proportion makes cement sound and strong.
• Soundness of Cement: A term denoting freedom from expanding, contracting, cracking, or checking in setting of cement.

                                                      Silica (SiO2)

• It imparts strength to the cement due to formation of dicalcium silicate (2CaO SiO2 or C2S) and tricalcium silicate (3CaO SiO2 or C3S).
• Silica in excess provides greater strength to the cement but at the same time it prolongs its setting time.

                                                   Alumina (Al2O3)

• It imparts quick setting quality to the cement.
• It acts as a flux (rate of flow of energy) and lowers the clinkering temperature.
• Alumina in excess reduces the strength of cement.

                                                          Iron oxide (Fe2O3)

• It provides color, hardness and strength to cement.
• It also helps the fusion of raw materials during manufacture of cement.

               Harmful ingredient of cement

Alkali oxides (K2O and Na2O): if the amount of alkali oxides exceeds 1%, it leads to the failure of concrete made from that cement.

Magnesium oxide (MgO): if the content of MgO exceeds 5%, it causes cracks after mortar or concrete hardness.

                   Cement Manufacturing

Steps

• Grinding & mixing . Raw materials are ground and mixed in right proportions.
• Burning. Burning at 1300 to 1900oC and obtaining clinker from kilns.
• Grinding. Grinding of clinker to fine powder.

Processes

• Dry process. Dry mixing and grinding of constituents. Difficult for composition control, slow,.
• Wet process. Wet mixing and grinding into slurry which turns into clinker on burning in kiln. It is costly

                         Cement Properties

• Fineness: Size of cement particles; it can go from 60 to 1 micrometer (1 micrometer = thousandth of milimeter).
• Soundness: Change in volume of concrete after setting. It may cause cracks, distortion and disintegration of concrete.
• Setting time: Initial setting The time when the cement water paste attains a certain degree of hardness is known as initial setting time of cement. Final setting It is that stage at which cement water paste had attained sufficient strength and hardness. Final setting time of cement should not be more than 10 hours.
• Compressive strength of cement and sand mortar should not be less than
• 115 kg/cm2 after 3 days
• 175 kg/cm2 after 7 days

Hydration

• The chemical reaction between cement and water is known as hydration of cement.
• The reaction takes place between cement components (C4Af,C3A,C3S &C2S) and water.

Testing of Portland cement

• Fineness test
• Consistency test
• Setting time test
• Soundness test
• Tensile strength test
• Compressive strength test

Cement Types

• Portland Cement
• Ordinary Portland Cement (Type I)
• Rapid Hardening or High Early Strength Portland Cement (Type III)
• Low Heat Portland Cement (Type IV)
• Sulphate Resistant Portland Cement (Type V)
• Water Repellent Portland Cement
• Water Proof Portland Cement
• Air Entraining Portland Cement (Type I-A, II-A, III-A)
• Pozzolana Portland Cement

Other Varieties of Cement

• High Alumina Cement
• Quick Setting Cement
• Blast Furnace Slag Cement
• White Cement
• Colored Cement
• Expanding Cement
• Hydrophobic Cement