Portland Cement Quiz

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Questions and Answers

What type of material is Portland cement primarily made from?

Water and lime

Calcareous material and alumina (correct)

Clay and gypsum

Sand and gravel

Which type of cement is capable of setting and hardening under water?

Expansive cement

Non-hydraulic cement

Hydraulic cement (correct)

Air-entraining cement

Who is credited with the invention of Portland cement?

Thomas Telford

Joseph Aspdin (correct)

Isambard Kingdom Brunel

John Smeaton

What was the original use of cement before it was extended for making concrete?

Making mortar Signup and view all the answers

When was the first British standard specification for Portland cement drawn up?

1904 Signup and view all the answers

What is the term for the heat released during the reaction of cement with water?

Heat of Hydration Signup and view all the answers

Which product of hydration constitutes 50-60 percent of the volume of solids in a completely hydrated cement paste?

Calcium Silicate Hydrate Signup and view all the answers

Which compound hydrates comparatively slowly and contributes to the later strength of concrete?

C2S Signup and view all the answers

What percentage of the volume of solids in the hydrated paste does calcium hydroxide constitute?

20 to 25 percent Signup and view all the answers

What is an undesirable effect of the presence of calcium hydroxide in concrete?

Gets leached out Signup and view all the answers

In which situation is a higher percentage of C2S preferable in cement?

For hydraulic structures Signup and view all the answers

What is the nature of the hydration process over time?

Slows down and continues indefinitely Signup and view all the answers

What role does water play in the hydration of C3S and C2S compounds?

It is required for the complete hydration of the cement. Signup and view all the answers

What happens if less than 38% of water is used in the cement mix?

The volume may be insufficient for all hydration products. Signup and view all the answers

What is the nominal diameter of gel pores as mentioned?

3 nm Signup and view all the answers

How is setting different from hardening in cement paste?

Setting refers to the paste losing plasticity. Signup and view all the answers

What causes a flash set in cement?

Insufficient gypsum to control reactions. Signup and view all the answers

What percentage of gel water by weight is required for the formation of gel?

15% Signup and view all the answers

What happens if excess water is added to the cement mix?

Capillary cavities form, making concrete porous. Signup and view all the answers

What is the initial setting time?

Time from adding water until the paste loses plasticity. Signup and view all the answers

What type of pores are marked as 'C' in the simplified model of paste structure?

Capillary pores Signup and view all the answers

What is the role of calcium hydroxide in concrete?

It maintains a high pH value that resists corrosion. Signup and view all the answers

What is the transition zone in concrete?

The interface between coarse aggregate particles and hardened cement paste. Signup and view all the answers

What percentage of the hydrated paste consists of hydrates of various compounds after a month?

85 to 90% Signup and view all the answers

What causes the transition zone to develop microcracks?

Drying shrinkage or temperature variation. Signup and view all the answers

What is the main reason concrete fails at lower stress levels than expected?

The weakness of the transition zone. Signup and view all the answers

What happens to the unhydrated cement particles as time passes?

They decrease in quantity while hydrates increase. Signup and view all the answers

What is the primary composition of fresh cement paste shortly after mixing?

Unhydrated cement particles and water. Signup and view all the answers

What type of reaction is responsible for consuming some of the mixing water?

Chemical reactions during hydration. Signup and view all the answers

What is considered a disadvantage of calcium hydroxide in concrete?

It reacts with sulphates and can cause deterioration. Signup and view all the answers

Study Notes

What is Cement?

Cement is a material with adhesive and cohesive properties, bonding mineral fragments into a whole.
Portland cement is primarily made from calcareous materials (e.g., limestone, chalk) and alumina and silica (e.g., clay, shale).
Hydraulic cements set and harden under water through chemical reactions.

Historical Background

Cementing materials were used in ancient civilizations (Egyptians, Romans, Indians).
Joseph Aspdin, a Leeds builder, patented Portland cement in 1824.
The name "Portland" comes from its resemblance to a natural stone found in Portland, England.
Aspdin's process involved mixing, grinding, and calcining (heating) limestone and clay.
Cement was initially only used in mortar; later use expanded to include concrete.

Manufacture of Portland Cement

Raw materials: Limestone/chalk and shale/clay.
Processes: Raw material grinding, mixing in specific proportions, burning at high temperatures (1300-1500°C) to form clinker, cooling, and grinding to a fine powder. Gypsum is added.
Two processes : Wet and Dry
Wet process: Raw materials are mixed in water before feeding into the kiln.
Dry process: Raw materials are mixed dry before feeding into the kiln.

Chemical Composition of Portland Cement

Portland cement is primarily composed of oxides of Calcium, Silicon, Aluminium and Iron.
The relative proportions of these oxides affect cement properties.
Major compounds (Bogue compounds): Tricalcium silicate (C3S), Dicalcium silicate (C2S), Tricalcium aluminate (C3A), and Tetracalcium aluminoferrite (C4AF).

Hydration of Cement

Hydration: Chemical reaction between cement and water.
Hydration products (e.g., calcium silicate hydrate, calcium hydroxide) give cement its strength and properties.
Hydration is a gradual process.
Early hydration is quicker; later hydration is slower.
Heat of Hydration; The heat of hydration is related to the rate of hydration of different compounds.
Calcium silicate hydrates are the most important hydration products.
Calcium hydroxide is also a major product involved in the setting reaction.

Setting and Hardening of Cement

Setting: A change from a fluid to a solid state.
Initial setting time: When the paste starts losing plasticity.
Final setting time: When the paste completely loses plasticity.
Hardening: Continued strength development after setting.

Fineness of Cement

Fineness is crucial to hydration rate and strength development.
Finer cements have more surface area for hydration.

Soundness of Cement

Cement must not undergo significant volume changes after hardening.
Unsoundness can cause cracking.

Types of Portland Cement

Different types cater to various applications (e.g., ordinary, rapid hardening, low heat, sulfate resisting).
Variations relate to chemical composition and heat of hydration.
Some types are designed for specific environmental conditions.

Testing of Cement

Field tests help assess cement quality.
Laboratory tests provide detailed data.

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Description

Test your knowledge about Portland cement with this quiz. Discover key facts about its composition, historical uses, and important figures associated with its invention. Perfect for students of construction and civil engineering.