Portland Cement: Composition and Manufacturing

• Portland Cement information
• Prepared by Engr. Jasmin G. Madayag

Learning Outcomes

• Identify the uses and properties of cement
• Familiarize yourself with property testing of cement based on ASTM standards

Portland Cement

• The term "Portland" originated in 1824 with English mason Joseph Aspdin
• Aspdin obtained a patent for his product and named it Portland Cement
• The cement blend produced concrete that resembled the color of natural limestone from the Isle of Portland in Europe
• William Aspdin, Joseph’s son, created the first cement containing alite, an impure form of tricalcium silicate

How Cement is Made

• Cement manufacturing involves processes like quarrying limestone, crushing, preheating, and using a kiln for clinker production
• Gypsum is added and grinding is used to achieve the final product
• Raw materials include limestone, chalk, or clay shale
• There are two manufacturing processes for cement: wet and dry

Flow Chart of Manufacturing OPC

• Raw materials are either Calcareous (Limestone OR Chalk) or Argillaceous (Clay OR Shale)
• There are two processes of manufacturing cement:
  • Wet Process: Raw Material to Crushers to Grinders to Wash Mill (Raw Material + 35% to 50% of water) to Slurry held in storage tanks/silos to Kiln (Calcination) to Clinkers to Addition of Gypsum to Grinders and ending with Ball mill cement packed in bags of 50 Kg
  • Dry Process: Raw Material to Crushers to Grinders to Compressed Air Blenders (Raw Material + 15% of water) to Flakes to Kiln(Calcination) to Clinkers to Addition of Gypsum to Grinders and ending with Ball mill cement packed in bags of 50 Kg

Portland Cement Production: Dry Process

• Calcareous and argillaceous raw materials are crushed with gyratory crushers into 2-5cm pieces separately
• Crushed materials are grinded into fine particles using a ball or tube mill
• After screening, each finely grinded material is stored in hoppers
• Powdered minerals are mixed in proportion to create a dry raw mix then stored in silos to be sent into a rotary kiln
• Raw materials are mixed in specific proportions to maintain the product's average composition

Portland Cement Production: Wet Process

• Raw materials are crushed, made into powdered form, and stored in silos
• Clay is washed to remove organic matter
• Powdered limestone and water-washed clay go to grinding mills to be mixed into a paste called slurry

Types of Portland Cement

• Different types of Portland cement are manufactured to meet different physical and chemical requirements
• American Society for Testing and Materials (ASTM) Designation C 150 provides specifications

Type I Portland Cement

• General purpose cement for uses where special properties of other types are not needed
• Avoid using where cement or concrete is subject to specific exposures like sulfate attack or high-heat from hydration
• Suitable for pavements, sidewalks, reinforced concrete buildings, bridges, railway structures, tanks, reservoirs, culverts, sewers, water pipes and masonry units

Type II Portland Cement

• Used where precaution against moderate sulfate attack is required such as in drainage structures
• Suited for sulfate concentrations in groundwaters higher than normal but not unusually severe
• Type II cement typically generates less heat at a slower rate than Type I
• Effective when used in structures of considerable mass, such as large piers, heavy abutments, and heavy retaining walls
• Reduces temperature rise, especially in warm-weather concrete placement

Type III Portland Cement

• A high-early strength product that provides strength at an early period, usually one week or less.
• Ideal when forms need to be removed quickly, or when the structure needs to be put into service quickly
• Its use in cold weather can reduce the controlled curing period
• Richer mixtures of Type I cement can be used to gain high early strength but Portland cement may provide that stronger, faster and cheaper

Type IV Portland Cement

• Low heat of hydration cement for use where the rate and amount of heat must be minimized
• Develops strength at a slower rate than Type I cement
• It is for use in massive concrete structures like large gravity dams, where temperature rise must be controlled during curing

Type V Portland Cement

• Considered a sulfate-resisting cement
• Used only in concrete exposed to severe sulfate action, or soils and groundwaters high in sulfate content

Properties of Portland Cement

Strength of Cement

• Flexural Strength
  • Measured using tensile strength in bending
  • The test involves a 40 x40 x 160 mm cement mortar beam, which is loaded at its center point until it fails
  • Standard test is ASTM C 348: Flexural Strength of Hydraulic Cement Mortars
• Compressive Strength

  • The most common strength test

  • A 50mm test specimen is subjected to a compressive load

  • Loading occurs between 20 and 80 seconds until the specimen fails

  • Standard tests for compressive strength:

    • AASHTO T 106
    • ASTM C 109: Compressive Strength of Hydraulic Cement Mortars (Using 50-mm or 2-in. Cube Specimens)
• Tensile Strength
  • A test that although was previously popular in the early years of cement production does not offer any useful information about the properties of cement today

Consistency of Cement

• Indicates the degree of stiffness
• The standard consistency of cement is between 26 and 33% by weight of dry cement
• Cement paste has standard consistency when a 10 mm plunger penetrates the paste to a distance of 5 to 7mm from the bottom of the Vicat mould
• Use the Vicat apparatus with the mould and its 10 mm diameter plunger for consistency testing

Setting Time of Cement

• Describes the stiffening of cement paste
• Cement sets and hardens when water is added
• Setting time varies depending on factors like fineness of cement, cement-water ratio, chemical content, and mixtures

Setting Times

• Initial set: describes when the paste begins to stiffen, about 30-45 minutes
• Final set: when the cement hardens and can sustain a load, occurs in under 10 hours
• Setting time can be an indicator of hydration rate
• Initial setting time should not be too low, and the final setting time should not be too high
• False set: abnormal premature stiffening of cement within minutes of mixing with water, but can be solved by remixing and adding more water
• Flash set: the rapid development of rigidity of freshly mixed cement paste with considerable heat, plasticity cannot be regained and the paste is permanently set

Hydration

• The reaction that happens when water is added is called hydration
• Hydration generates heat, which can affect the quality of the cement
• Generated heat can be useful in maintaining curing temperature during cold weather
• High heat generation can cause undesired stress in large structures
• Affected most by C3S and C3A present in cement, water-cement ratio, fineness and rate of curing

Bulk Density

• Cement has a variable range of density depending on the cement composition percentage
• Cement density is 62 to 78 pounds per cubic foot (994-1250 kg/m³)

Specific Gravity (Relative Density)

• Used in mixture proportioning calculations
• Portland cement has a specific gravity of 3.15, but other types of cement, such as Portland-blast-furnace-slag and Portland-pozzolan cement has a gravity of about 2.90

Standard test for Specific Gravity (Relative Density)

• AASHTO T 133 and ASTM C 188: Density of Hydraulic Cement