45 Questions
What is the primary property of cement?
Adhesive and cohesive properties
What is Portland cement primarily made of?
Calcareous material, alumina, and silica
What type of cements are used in making concrete?
Hydraulic cements
Who is attributed with the invention of Portland cement?
Joseph Aspdin
When did Joseph Aspdin take the patent for Portland cement?
21st October 1824
Why was Portland cement named as such?
Due to its resemblance to natural stone
What was the process used by Joseph Aspdin to create Portland cement?
Mixing limestone and clay, then calcining it in a furnace
What was the result of Joseph Aspdin's process of creating Portland cement?
A fine powder
How have ancient civilizations used cementing materials?
In their ancient constructions
What percentage of the material becomes liquid in the hottest part of the kiln?
20 to 30
What is the size range of the balls formed in the kiln?
3 to 25 mm
Why is gypsum added to the cooled clinker?
To prevent flash-setting of the cement
What is the main difference in water content between the wet and dry processes?
Wet process has 35-50% water, dry process has 12% water
What is a comparison between the wet and dry processes in terms of fuel consumption?
Dry process requires less fuel
What is an advantage of the dry process compared to the wet process?
It is more economic
What is a disadvantage of the dry process compared to the wet process?
It is less accurate to control mixing of raw materials
What are the main raw materials used in the manufacture of cement?
Lime, silica, alumina, and iron oxide
What is the final product of the kiln formed into balls?
Clinker
What is the primary factor that influences the properties of cement?
Proportions of oxide compositions
Who is credited with identifying the major compounds in Portland cement?
R.H. Bogue
What is the process called when the oxides combine at high temperature in the kiln?
Clinkering
What are the four major compounds in Portland cement?
C3S, C2S, C3A, C4AF
What is the name given to the calculation of the potential composition of Portland cement?
Bogue Composition
What are the two minor compounds of particular interest in Portland cement?
Na2O and K2O
What is the primary function of the kiln in cement production?
Combining the oxides at high temperature
What is the name given to the complex compounds formed in the kiln?
Bogue's Compounds
What are the oxides of sodium and potassium known as in Portland cement?
Alkalis
What is the primary characteristic of rapid-hardening Portland cement?
Higher early strength
What is the main difference between rapid-hardening and ordinary Portland cement?
Rate of hardening
Why should rapid-hardening Portland cement not be used in mass concrete construction?
It has a higher rate of heat development
What is the benefit of using rapid-hardening Portland cement in cold weather concrete?
It reduces the vulnerability of concrete to frost damage
What is the primary reason for using low heat Portland cement in mass concrete construction?
It has a lower rate of heat evolution
What is the main difference between rapid-hardening and low heat Portland cement?
Rate of heat development
What is the result of the higher fineness of rapid-hardening Portland cement?
It increases the strength at 10 to 20 hours
What is the recommended use of rapid-hardening Portland cement?
In all of the above
What is the main characteristic of ASTM Type III cements?
Higher fineness
What is the result of calcium hydroxide reacting with sulphates in soils or water?
Formation of calcium sulphate
What is the primary advantage of calcium hydroxide in concrete?
It resists the corrosion of reinforcements
What is the structure of hydrated cement at the macro level?
A two phase material
What is the transition zone in concrete?
The interfacial region between the particles of coarse aggregate and hardened cement paste
What is the effect of drying shrinkage or temperature variation on the transition zone?
It forms microcracks
What happens to the microcracks in the transition zone when the structure is loaded at high stress levels?
They propagate and form bigger cracks
Why does concrete fail at a lower stress level than the strength of bulk paste or aggregate?
Due to the presence of transition zone
What is the composition of fresh cement paste?
A plastic mass consisting of water and cement
What happens to the quantity of unhydrated cement in the paste with the lapse of time?
It decreases
Study Notes
Cement
- Cement is a material with adhesive and cohesive properties that bonds mineral fragments into a compact whole.
- Portland cement is made primarily from calcareous material, such as limestone or chalk, and from alumina and silica found as clay or shale.
Historical Background
- The history of cementing material is as old as the history of engineering construction.
- Egyptians, Romans, and Indians used cementing materials in their ancient constructions.
- Joseph Aspdin, a Leeds builder and bricklayer, patented Portland cement in 1824.
Manufacturing Process
- The manufacturing process involves mixing and grinding hard limestones and finely divided clay into a slurry, which is then calcined in a furnace.
- The mixture undergoes a series of chemical reactions, and the resulting clinker is interground with gypsum to prevent flash-setting.
- There are two main processes: wet process and dry process, which differ in the amount of water used and the heat required.
Chemical Composition of Portland Cement
- The raw materials used for the manufacture of cement consist mainly of lime, silica, alumina, and iron oxide.
- These oxides interact with each other in the kiln at high temperature to form more complex compounds.
- The relative proportions of these oxide compositions influence the properties of cement.
Bogue's Compounds
- The major compounds formed in the kiln are: C3S, C2S, C3A, and C4AF.
- The calculation of the potential composition of Portland cement is based on the work of R.H. Bogue.
Structure of Hydrated Cement
- Concrete is considered as a two-phase material: paste phase and aggregates phase.
- The transition zone, which is the interfacial region between the particles of coarse aggregate and hardened cement paste, is a plane of weakness.
- The transition zone develops microcracks due to drying shrinkage or temperature variation, which can lead to failure of bond.
Types of Portland Cement
- Rapid-hardening Portland cement (Type III) develops strength more rapidly and has a higher C3S content and a finer grinding of the cement clinker.
- Low heat Portland cement (Type IV) has a lower rate of heat evolution, making it suitable for mass concrete construction.
This quiz covers the basics of cement in concrete technology, including its characteristics and uses. It is designed for 2nd-year civil engineering students.
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