Cement Manufacturing, Properties, and Types
Cement Manufacturing Process
Cement is produced using limestone, rich in calcium oxides, and a silica-rich component like clay or blast furnace slag. These are mixed and heated in a rotary kiln, creating clinker, which contains:
- Dicalcium silicate
- Tricalcium aluminate
- Tricalcium silicate
- Tetracalcium ferroaluminate
Cement Properties
Specific Weight (Density)
The specific weight is the ratio of cement weight to its actual volume. It’s measured using a Chatelier flask, determining the displacement of liquid by 64 grams of cement.
Setting Time
The setting time is measured using a Vicat apparatus. A normal consistency is determined by a Tetmajer probe. The probe, weighing 300g with a 6mm tube, stops at the bottom of the pulp.
Cement Components
Pozzolan
Pozzolan is a silicon material that, when finely ground and mixed with water, acts as a binding agent.
Blast Furnace Slag
Blast furnace slag is a nonmetallic product from iron ore treatment.
Time Setting
This is the time between mixing cement with water and the paste losing plasticity. It’s measured using a Vicat needle. The ‘first setting’ occurs when a 1mm² needle, weighing 300 grams, stops 3mm from the bottom of the cement paste. The ‘end of setting’ is when the needle leaves no impression.
- Standard cement hardens: min 60 min, max 12 hours
- High-strength cement hardens: min 45 min, max 10 hours
Normal Consistency
Normal consistency is the water percentage that gives the cement paste a certain plasticity. It’s determined using a Tetmajer probe, a polished 1cm diameter shank weighing 300 grams. The test is done at 18-21°C, mixing 400 grams of cement with water for 5 minutes until homogeneous. The probe is applied without acquiring speed.
Types of Cement
Steel Cements
Steel cements consist of cement clinker, basic slag, and granulated blast furnace cast.
General Characteristics of Slag
Slag used in cement must:
- Come from blast furnaces processing iron ore.
- Be basic, with more basic elements than acidic ones.
- Be granular, cooled abruptly from the blast furnace.
Examples of Cement Types
Portland, Portland pozzolana, and Iron and Steel blast furnace slag are some examples.
Cement Classifications
- Portland Cement: Clinker with a low percentage of gypsum.
- Steel Cement: Clinker with basic slag and granulated blast furnace cast.
- Portland Steel Cement: Less than 30% granulated blast furnace slag.
- Steelmaker Cement: 30-75% granulated blast furnace slag.
- Pozzolanic Cement: Clinker, pozzolana, and gypsum.
- Portland Pozzolana Cement: Less than 30% pozzolan.
- Pozzolanic Cement: 30-50% pozzolan.
Concrete Density
The density of concrete is its mass divided by its volume, expressed in kg/m³ or kg/dm³ (kg/L).
Additives
Additives are products added to concrete to modify its properties in a planned and controlled manner.