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?

<p>Making mortar (C)</p> Signup and view all the answers

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

<p>1904 (D)</p> Signup and view all the answers

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

<p>Heat of Hydration (D)</p> 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?

<p>Calcium Silicate Hydrate (B)</p> Signup and view all the answers

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

<p>C2S (D)</p> Signup and view all the answers

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

<p>20 to 25 percent (A)</p> Signup and view all the answers

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

<p>Gets leached out (D)</p> Signup and view all the answers

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

<p>For hydraulic structures (D)</p> Signup and view all the answers

What is the nature of the hydration process over time?

<p>Slows down and continues indefinitely (A)</p> Signup and view all the answers

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

<p>It is required for the complete hydration of the cement. (A)</p> Signup and view all the answers

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

<p>The volume may be insufficient for all hydration products. (C)</p> Signup and view all the answers

What is the nominal diameter of gel pores as mentioned?

<p>3 nm (D)</p> Signup and view all the answers

How is setting different from hardening in cement paste?

<p>Setting refers to the paste losing plasticity. (D)</p> Signup and view all the answers

What causes a flash set in cement?

<p>Insufficient gypsum to control reactions. (D)</p> Signup and view all the answers

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

<p>15% (A)</p> Signup and view all the answers

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

<p>Capillary cavities form, making concrete porous. (A)</p> Signup and view all the answers

What is the initial setting time?

<p>Time from adding water until the paste loses plasticity. (D)</p> Signup and view all the answers

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

<p>Capillary pores (A)</p> Signup and view all the answers

What is the role of calcium hydroxide in concrete?

<p>It maintains a high pH value that resists corrosion. (B)</p> Signup and view all the answers

What is the transition zone in concrete?

<p>The interface between coarse aggregate particles and hardened cement paste. (D)</p> Signup and view all the answers

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

<p>85 to 90% (D)</p> Signup and view all the answers

What causes the transition zone to develop microcracks?

<p>Drying shrinkage or temperature variation. (C)</p> Signup and view all the answers

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

<p>The weakness of the transition zone. (C)</p> Signup and view all the answers

What happens to the unhydrated cement particles as time passes?

<p>They decrease in quantity while hydrates increase. (B)</p> Signup and view all the answers

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

<p>Unhydrated cement particles and water. (C)</p> Signup and view all the answers

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

<p>Chemical reactions during hydration. (C)</p> Signup and view all the answers

What is considered a disadvantage of calcium hydroxide in concrete?

<p>It reacts with sulphates and can cause deterioration. (D)</p> Signup and view all the answers

Flashcards

What is Cement?

A material that binds mineral fragments together, forming a solid mass. It has adhesive and cohesive properties.

Hydraulic Cement

The process of cement hardening due to chemical reactions with water. This happens even underwater, making it ideal for construction.

Who invented Portland cement?

The invention of Portland cement is attributed to Joseph Aspdin. He patented this cement in 1824, named after the resemblance of the hardened product to Portland stone.

Early Portland Cement

A fine powder produced by grinding calcined limestone and clay. This early form of cement primarily used for making mortar.

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Cement Standards Development

Organizations created to set standards for cement quality and ensure consistent performance in major construction projects.

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Heat of Hydration

The heat released during the chemical reaction of cement with water.

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Cement Hydration

A chemical reaction where cement combines with water, forming a solid mass that hardens over time.

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Rate of Hydration

A measure of how fast cement reacts with water. Different cement compounds react at different speeds.

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Calcium Silicate Hydrate (C-S-H)

The primary product formed during the hydration of cement, responsible for the strength and durability of concrete. It's a complex compound formed by the reaction of cement and water.

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Calcium Hydroxide (Ca(OH)2)

A by-product of cement hydration, it's soluble in water and can contribute to concrete's lack of durability, especially in structures exposed to water.

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Tricalcium Silicate (C3S)

The main compound responsible for the initial, rapid hardening of concrete. It reacts quickly with water, making it ideal for cold weather applications.

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Dicalcium Silicate (C2S)

A cement compound that reacts slowly with water, contributing to the long-term, sustained strength of concrete. It releases less heat of hydration, making it suitable for warm climates.

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Transition Zone

The region where hardened cement paste interfaces with aggregate particles in concrete. It's often a plane of weakness due to microcracks.

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Microcracks

These cracks, even smaller than a human hair, can form in the transition zone due to drying or temperature changes.

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Crack Propagation

Over time, microcracks can grow into bigger cracks, eventually leading to failure of the concrete's structure.

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Bond Strength

A measure of the resistance to cracking formed in the transition zone. A higher bond strength means less susceptibility to cracking.

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Calcium Sulfate Formation

A chemical reaction between calcium hydroxide and sulfates in soil or water, forming calcium sulfate, which can weaken cement.

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Corrosion Resistance

The ability of concrete to resist the rusting of steel reinforcement bars embedded within. This is due to the alkaline (high pH) nature of calcium hydroxide.

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Fresh Cement Paste

Fresh cement paste is a mixture of water and cement that hardens over time into a solid mass. This hardening involves chemical reactions between water and cement.

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Capillary Pores

Pores within hardened cement paste filled with water that doesn't contribute to hydration. These pores can affect the strength and durability of the concrete.

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Setting Time

The time it takes for cement paste to change from a fluid state to a rigid state, gaining some initial strength.

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Hardening Time

The time it takes for a set cement paste to gain strength and harden over time.

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Initial Setting Time

The time elapsed from adding water to the cement until the paste starts losing its plasticity.

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Final Setting Time

The time elapsed from adding water to the cement until the paste has completely lost its plasticity and set firm enough to resist pressure.

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Flash Set

Fast setting of cement caused by insufficient gypsum, leading to rapid stiffening.

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Gel Pores

Small, interconnected spaces within the cement paste that are filled with cement gel.

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Hydration

The chemical reaction of cement with water, creating a hardened mass.

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Water Requirements for Hydration

The percentage of water by weight of cement needed for complete hydration.

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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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Concrete Technology-I Past Paper 2022-2023 PDF

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.

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