Portland Cement
Portland Cement Concrete: most widely used manufactured construction material in the world. Most important material in modern life. Consists of portland cement, aggregates, water, air voids, and admixtures.
There are many other different types of concrete, based on different cements. Portland cement concrete is so prevalent, that unless identified, it is assumed to be used primarily.
Portland cement is an instant glue (just add water) that bonds aggregates together to make portland cement concrete.
Production
Starts with two basic raw ingredients: a calcareous material and an argillaceous material.
Calcareous material: A calcium oxide, such as limestone, chalk, or oyster shells.
Argillaceous material: Combination of silica and alumina that can be obtained from clay, shale, and blast furnace slag.
These materials are crushed, and then stored in silos. The raw materials are passed through a grinding mill, using either a wet or dry process. The ground material is stored until it can be sent to the kiln.
Modern dry process cement plants use a heat recovery cycle to preheat the ground material, or feed stock, with the exhaust gas from the kiln.
Clinker: Raw materials melted at temperatures of 1400 C to 1650 C changing the raw materials into clinker. The clinker is cooled, stored, then ground into a fine powder. A small amount of gypsum is added to the clinker to regulate the setting time of the cement in the concrete.
Standard Sack: 94 lb, equal to 1 cubic ft. of loose cement when freshly packed.
Chemical Composition of Portland Cement:
1. Lime
2. Silica
3. Alumina
4. Iron Oxide
These raw materials interact in the kiln, forming complex chemical compounds. Calcination in the kiln restructures the molecular composition, producing four main compounds of:
1. Tricalcium Silicate
2. Dicalcium Silicate
3. Tricalcium Aluminate
4. Tetracalcium Aluminoferrite
Calcination: the conversion of metals into their oxides as a result of heating to a high temperature.
Fineness of Portland Cement
Fineness: Important property that must be carefully controlled. Because hydration starts at the surface of cement particles, the finer the cement particles, the larger the surface area and the faster the hydration.
Increases fineness beyond the requirements for a type of cement increases cost.
Maximum size of cement particles is 0.09 mm.
85%-95% of particles are smaller than 0.045 mm, and the average diameter is 0.01 mm.
1 kilogram of portland cement has approximately 7 trillion particles with a total surface area of about 300 to 400 sq. meters.
Fineness of cement is usually measured indirectly by measuring the surface area with the Blaine air permeability apparatus or the Wagner Turbidimeter apparatus.
Blaine Test: Surface area of the cement particles [in (sq. cm.)/g] is determined by measuring the air permeability of a cement sample and relating it to the air permeability of a standard material.
Wagner Turbidimeter: Determines the surface area by measuring the rate of sedimentation of cement suspended in kerosene.
The finer the cement particles, the slower the sedimentation.
Fineness also measured by determining the percent passing the 0.045 mm sieve.
Specific Gravity of Portland Cement
Specific Gravity: Needed for mixture proportioning calculations. Specific gravity of portland cement is 3.15.
Cement quantities are specified and measured by weight rather than volume.
Portland Cement Concrete: most widely used manufactured construction material in the world. Most important material in modern life. Consists of portland cement, aggregates, water, air voids, and admixtures.
There are many other different types of concrete, based on different cements. Portland cement concrete is so prevalent, that unless identified, it is assumed to be used primarily.
Portland cement is an instant glue (just add water) that bonds aggregates together to make portland cement concrete.
Production
Starts with two basic raw ingredients: a calcareous material and an argillaceous material.
Calcareous material: A calcium oxide, such as limestone, chalk, or oyster shells.
Argillaceous material: Combination of silica and alumina that can be obtained from clay, shale, and blast furnace slag.
These materials are crushed, and then stored in silos. The raw materials are passed through a grinding mill, using either a wet or dry process. The ground material is stored until it can be sent to the kiln.
Modern dry process cement plants use a heat recovery cycle to preheat the ground material, or feed stock, with the exhaust gas from the kiln.
Clinker: Raw materials melted at temperatures of 1400 C to 1650 C changing the raw materials into clinker. The clinker is cooled, stored, then ground into a fine powder. A small amount of gypsum is added to the clinker to regulate the setting time of the cement in the concrete.
Standard Sack: 94 lb, equal to 1 cubic ft. of loose cement when freshly packed.
Chemical Composition of Portland Cement:
1. Lime
2. Silica
3. Alumina
4. Iron Oxide
These raw materials interact in the kiln, forming complex chemical compounds. Calcination in the kiln restructures the molecular composition, producing four main compounds of:
1. Tricalcium Silicate
2. Dicalcium Silicate
3. Tricalcium Aluminate
4. Tetracalcium Aluminoferrite
Calcination: the conversion of metals into their oxides as a result of heating to a high temperature.
Fineness of Portland Cement
Fineness: Important property that must be carefully controlled. Because hydration starts at the surface of cement particles, the finer the cement particles, the larger the surface area and the faster the hydration.
Increases fineness beyond the requirements for a type of cement increases cost.
Maximum size of cement particles is 0.09 mm.
85%-95% of particles are smaller than 0.045 mm, and the average diameter is 0.01 mm.
1 kilogram of portland cement has approximately 7 trillion particles with a total surface area of about 300 to 400 sq. meters.
Fineness of cement is usually measured indirectly by measuring the surface area with the Blaine air permeability apparatus or the Wagner Turbidimeter apparatus.
Blaine Test: Surface area of the cement particles [in (sq. cm.)/g] is determined by measuring the air permeability of a cement sample and relating it to the air permeability of a standard material.
Wagner Turbidimeter: Determines the surface area by measuring the rate of sedimentation of cement suspended in kerosene.
The finer the cement particles, the slower the sedimentation.
Fineness also measured by determining the percent passing the 0.045 mm sieve.
Specific Gravity of Portland Cement
Specific Gravity: Needed for mixture proportioning calculations. Specific gravity of portland cement is 3.15.
Cement quantities are specified and measured by weight rather than volume.
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