45 Questions
What was the initial use of cement?
Making mortar
What led to the requirement for consistently higher standard material?
Use of cement for making concrete
In what year was the British standard specification for Portland cement first drawn up?
1904
What are the two main types of materials required for the manufacture of Portland cement?
Argillaceous and calcareous
What is the temperature range at which the material sinters and partially fuses to form clinker?
1300 to 1500°C
What is added to the clinker to form Portland cement?
Gypsum (3 to 5%)
What are the two processes of cement manufacture?
Wet and dry
What is fed into the rotary kiln?
Raw materials
What happens to the water in the mixture as it moves down the kiln?
It is driven off
What is the primary factor that influences the properties of cement?
Relative proportions of oxide compositions
What is the term used to describe the calculation of the potential composition of Portland cement?
Bogue Composition
Which of the following oxides is NOT a major compound in Portland cement?
Na2O
What is the formula for calculating the percentage of C3S in cement?
C3S = 4.07(CaO) – 7.60(SiO2) + 6.72(Al2O3) – 1.43(Fe2O3) – 2.85(SO3)
What is the purpose of R.H.Bogue's work in the context of cement?
To identify the major compounds present in cement
What are the oxides of sodium and potassium known as?
Alkalis
What is the term used to describe the four major compounds in Portland cement?
Bogue's Compounds
What is the purpose of the table showing the approximate oxide composition limits of ordinary Portland cement?
To provide a reference for oxide composition limits
What is the name of the process that occurs in the kiln at high temperature?
Clinkering
What is the purpose of reducing C3S and C3A in low-heat cement?
To reduce the heat of hydration
What is the characteristic of modified cement (Type II)?
Moderate heat generation and moderate strength gain
What is the effect of sulfates on ordinary Portland cement?
It leads to cracks and disruption due to expansion
What is the approximate volume increase of calcium sulphoaluminate?
227% of the original aluminates
What accelerates sulfate attack in ordinary Portland cement?
Alternating wetting and drying
What is the main characteristic of sulfate-resisting cement (Type V)?
Low C3A content and low C4AF content
What is the limit of C3A content in sulfate-resisting cement according to ASTM C 150-09?
5 per cent
What is the restriction on the sum of C4AF plus twice the C3A content in sulfate-resisting cement?
25 per cent
What is the limit of magnesia content in sulfate-resisting cement?
6 per cent
What is a pozzolanic material?
A material that reacts with calcium hydroxide to form compounds possessing cementitious properties
What is fly ash?
A waste material generated in thermal power stations when coal is used as fuel
What is an advantage of Portland Pozzolana Cement (PPC)?
It improves the pore size distribution and reduces microcracks
What is the purpose of electrostatic precipitator in thermal power stations?
To collect fly ash
What is the effect of pozzolanic action on soluble calcium hydroxide?
It converts it into insoluble cementitious products
What is the effect of PPC on permeability?
It improves permeability
How does PPC compare to OPC in terms of heat of hydration?
PPC generates less heat of hydration than OPC
What is a characteristic of Portland Pozzolana Cement?
It is finer than OPC
What is a condition for achieving higher long-term strength in PPC?
Presence of moisture
What is the primary role of tricalcium silicate (C3S) and dicalcium silicate (C2S) in cement?
To contribute to the strength of hydrated cement paste
What is the effect of C3A in cement?
It is undesirable and contributes little to the strength of cement
What is the purpose of C4AF in cement?
To accelerate the hydration of silicates
What happens when anhydrous cement is mixed with water?
It acquires adhesive property
What is the term for the chemical reactions between cement and water?
Hydration of cement
What is the nature of the reaction between cement and water?
Exothermic
What is the term for the heat liberated during the reaction of cement with water?
Heat of hydration
How does the rate of hydration of pure compounds vary?
It is faster in the early period and continues indefinitely at a decreasing rate
What is the significance of the hydration products formed during the reaction of cement and water?
They have cementing or adhesive value
Study Notes
Early Period of Cement
- In the early period, cement was used for making mortar only.
- Later, the use of cement was extended for making concrete.
Development of Standards
- Association of Engineers, Consumers, and Cement Manufacturers was established to specify standards for cement.
- German standard specification for Portland cement was drawn in 1877.
- British standard specification was first drawn up in 1904.
- The first ASTM specification was issued in 1904.
Manufacture of Portland Cement
- Raw materials required for manufacture of Portland cement are calcareous materials (limestone or chalk) and argillaceous material (shale or clay).
- Cement factories are established where these raw materials are available in plenty.
- The process of manufacture of cement consists of:
- Grinding the raw materials
- Mixing them intimately in certain proportions
- Burning them in a kiln at a temperature of about 1300 to 1500°C
- Cooling and grinding the clinker to fine powder with addition of about 3 to 5% of gypsum
Composition of Portland Cement
- The four compounds usually regarded as major compounds are:
- Tricalcium silicate (C3S)
- Dicalcium silicate (C2S)
- Tricalcium aluminate (C3A)
- Tetracalcium aluminoferrite (C4AF)
- The calculation of the potential composition of Portland cement is based on the work of R.H. Bogue and others, and is often referred to as "Bogue composition".
Hydration of Cement
- Anhydrous cement does not bind fine and coarse aggregate.
- The chemical reactions that take place between cement and water is referred to as hydration of cement.
- The quality, quantity, continuity, stability, and the rate of formation of the hydration products are important.
Heat of Hydration
- The reaction of cement with water is exothermic, liberating a considerable quantity of heat.
- Different compounds hydrate at different rates and liberate different quantities of heat.
- Low-heat evolution is achieved by reducing the contents of C3S and C3A which are the compounds evolving the maximum heat of hydration and increasing C2S.
Types of Cement
- Modified cement (Type II):
- Combines a somewhat higher rate of heat development with a rate of gain of strength similar to that of ordinary Portland cement.
- Recommended for use in structures where a moderately low heat generation is desirable or where moderate sulfate attack may occur.
- Sulfate-resisting cement (Type V):
- Has low C3A and comparatively low C4AF content.
- ASTM C 150-09 specification limits the C3A content to 5 per cent, and also restricts the sum of the content of C4AF plus twice the C3A content to 25 per cent.
- Portland Pozzolana cement (PPC):
- Has advantages such as:
- Economical due to replacement of costly clinker with cheaper pozzolanic material.
- Improved permeability due to conversion of soluble calcium hydroxide into insoluble cementitious products.
- Reduced heat of hydration.
- Improved pore size distribution and reduced microcracks at the transition zone.
- Higher long-term strength beyond a couple of months if enough moisture is available for continued pozzolanic action.
- Has advantages such as:
This quiz covers the early uses of cement, its extension to concrete, and the establishment of standard specifications for Portland cement by various associations and countries.
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