Cement and Concrete Properties Quiz
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Questions and Answers

How does the type of cement influence the properties of concrete?

The type of cement affects the rate of hardening and durability of concrete.

What role does water play in the hydration process of cement?

Water participates in an exothermic chemical reaction during hydration, leading to setting and hardening of the cement.

In what ways does aggregate affect both fresh and hardened concrete?

Aggregate serves as a cheap, inert filler that influences the elastic properties and overall strength of fresh and hardened concrete.

How does porosity in cement paste impact its characteristics?

<p>Porosity affects workability in the fresh state and influences strength, stiffness, and density in the hardened state.</p> Signup and view all the answers

What are admixtures, and what purpose do they serve in concrete?

<p>Admixtures are small quantities of materials added to modify the properties of fresh and hardened concrete.</p> Signup and view all the answers

What are the primary products formed during the hydration of cement?

<p>The primary products are calcium silicate and calcium aluminate hydrates.</p> Signup and view all the answers

How does calcium hydroxide contribute to the properties of hardened cement?

<p>Calcium hydroxide helps buffer the pH of the water in the capillary pores at around pH 12.5.</p> Signup and view all the answers

What is the significance of gel porosity in hydrated cement?

<p>The gel porosity of hydrated cement is about 28% with a surface area of 200,000 m2/kg.</p> Signup and view all the answers

What role does curing play in the hydration of cement?

<p>Good curing ensures sufficient water remains for hydration to continue, enhancing strength and durability.</p> Signup and view all the answers

Explain the concept of 'autogenous healing' in concrete.

<p>Autogenous healing refers to the process where unhydrated cement can assist in healing cracks in concrete structures.</p> Signup and view all the answers

What is the initial surface area of cement before water is added, and how does it change?

<p>Before water is added, the surface area of the cement is approximately 350-450 m2/kg, which decreases after hydration.</p> Signup and view all the answers

Describe the heat evolution during the hydration process of Portland cement.

<p>The hydration process is exothermic, resulting in an initial peak in heat output followed by a dormant plateau.</p> Signup and view all the answers

What are the possible states of water held within the structure of hydrated cement?

<p>Water in hydrated cement can be either 'free' (evaporable) or chemically combined with the cement.</p> Signup and view all the answers

What are the two main property categories required for concrete in its fresh state?

<p>Cohesive and workable.</p> Signup and view all the answers

What is the time range that concrete is considered 'fresh' after mixing?

<p>2-10 hours.</p> Signup and view all the answers

List three properties that concrete must have in its hardened state.

<p>Strength, dimensional stability, and durability.</p> Signup and view all the answers

What role does the thixotropic property of cement paste play in the fresh concrete state?

<p>It allows the concrete mix to be compacted by vibration.</p> Signup and view all the answers

How does the hydration of Portland cement change the constituent volumes in concrete?

<p>It alters the volumes of water and hydration products over time.</p> Signup and view all the answers

What is meant by the term 'dimensional stability' in relation to hardened concrete?

<p>It refers to the material's elasticity, creep, and shrinkage properties.</p> Signup and view all the answers

Mention two aspects of durability that concrete must withstand.

<p>Weathering and chemical attack.</p> Signup and view all the answers

What is the significance of the elastic modulus in assessing concrete's properties?

<p>It measures the concrete's ability to deform elastically under load.</p> Signup and view all the answers

What does GGBS stand for and what is its nature in cementitious applications?

<p>GGBS stands for Ground Granulated Blast-furnace Slag and is semi-cementitious, capable of setting on its own.</p> Signup and view all the answers

What is the typical percentage range for blending GGBS with Portland cement?

<p>The typical blending range for GGBS with Portland cement is 10-90%.</p> Signup and view all the answers

What is the minimum combined mass percentage of reactive calcium oxide and reactive silicon dioxide required in CEM cement?

<p>At least 50%.</p> Signup and view all the answers

How do GGBS and PFA differ in their silica content according to the analysis provided?

<p>GGBS contains 36% SiO2, while PFA has a higher content at 48% SiO2.</p> Signup and view all the answers

What role does calcium sulfate play in the manufacture of cement?

<p>Calcium sulfate is added to control the setting behavior of cement.</p> Signup and view all the answers

What is the significance of the initial set time in cement strength classes?

<p>The initial set time should be greater than 60 minutes for strength classes up to 42.5 and greater than 45 minutes for classes 52.5 or higher.</p> Signup and view all the answers

What are the maximum allowable percentages of additives in cement mass?

<p>Total additives must not exceed 1.0% by mass, and organic additives must not exceed 0.5%.</p> Signup and view all the answers

What is microsilica characterized by in terms of its particle size and chemical composition?

<p>Microsilica has a very small particle size of 0.1 micron and contains over 90% amorphous SiO2.</p> Signup and view all the answers

What is the significance of aggregates in concrete production?

<p>Aggregates occupy about three-quarters of concrete's volume, significantly affecting its properties.</p> Signup and view all the answers

What role does microsilica play in concrete when used as a partial replacement for Portland cement?

<p>Microsilica provides nucleation sites for hydration compounds like Ca(OH)2 and CSH hydrates.</p> Signup and view all the answers

How do aggregate sources impact major construction projects?

<p>Several aggregate sources must be tested to ensure strength, durability, and non-reactivity.</p> Signup and view all the answers

According to the content, what is the effect of PFA on bleeding in concrete?

<p>PFA reduces bleeding in concrete, whereas GGBS can increase it at higher volumes.</p> Signup and view all the answers

What types of aggregates are primarily used in concrete production?

<p>Most aggregates come from natural sources, but recycled aggregates are also accepted.</p> Signup and view all the answers

What factors can influence the economics of concrete production?

<p>The choice and cost of aggregates can significantly influence production economics.</p> Signup and view all the answers

How does the density of PFA compare to that of GGBS and what is its implication for concrete mixtures?

<p>PFA has a lower relative density (2.0-2.3) compared to GGBS (2.9), which increases the volume of fine powder in the mix.</p> Signup and view all the answers

What are pozzolanic materials and their properties in cement?

<p>Pozzolanic materials can improve the physical properties of cement and may have latent hydraulic properties.</p> Signup and view all the answers

What are the primary raw materials required to manufacture Portland cement?

<p>The primary raw materials are calcium carbonate (CaCO3) and silica (SiO2), along with smaller quantities of alumina (Al2O3) and ferric oxide (Fe2O3).</p> Signup and view all the answers

At what temperatures does the process of calcining and sintering occur in the manufacture of Portland cement?

<p>Calcining occurs at 800°C, and sintering occurs at temperatures between 1300-1450°C.</p> Signup and view all the answers

What is the purpose of adding gypsum to Portland cement during the grinding process?

<p>Gypsum is added to control the setting time of the cement.</p> Signup and view all the answers

How is the major compound C3S significant in the context of Portland cement?

<p>C3S is significant because it generates the main early age strength of the cement during the first four weeks.</p> Signup and view all the answers

What is clinker in the context of Portland cement manufacturing?

<p>Clinker refers to the balls, up to 25mm in diameter, that are formed by the sintering of raw materials during cement production.</p> Signup and view all the answers

What happens to the raw meal containing carbonate and silicate during the cement manufacturing process?

<p>The raw meal is heated to drive off water and CO2, followed by sintering to fuse materials into clinker.</p> Signup and view all the answers

Explain the importance of compound composition over oxide composition in Portland cement.

<p>Compound composition is more important as small differences in oxide composition can lead to significant variations in the compound properties and resultant cement characteristics.</p> Signup and view all the answers

Why is it important to store Portland cement carefully and avoid contact with water?

<p>It is important because Portland cement is sensitive to moisture, which can adversely affect its quality and performance.</p> Signup and view all the answers

Flashcards

Water in Concrete

The amount of water in a concrete mix affects its workability and cohesion when fresh, and causes dimensional changes like shrinkage and creep in the hardened state.

Cement paste in Concrete

A thixotropic material that helps with cohesion and flow under vibration in its fresh state and becomes a hard, durable binder when hardened. However, it's dimensionally unstable, contributing to shrinkage and creep.

Aggregate in Concrete

Inert, cheap, and generally hard filler material in concrete. Its grading, shape, texture, type, and quality affect the elastic properties of both fresh and hardened concrete.

Porosity in Concrete

Air voids, water-filled capillary pores, and gel pores are all types of porosity in concrete. It affects workability and cohesion when fresh, and influences strength, stiffness, density, and frost resistance in the hardened state.

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Admixtures in Concrete

Small amounts added to concrete, typically less than 1% by weight of cement, to modify the properties of both fresh and hardened concrete.

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Concrete Strength

The ability of concrete to resist forces without breaking. Common types include compression, tension, and fatigue.

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Dimensional Stability

The change in size or shape of concrete over time due to factors like temperature, moisture, or applied loads.

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Durability

The ability of concrete to withstand various environmental conditions and resist degradation from factors like weather, chemicals, or salts.

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Fresh State

The time period within which the concrete mixture can be compacted and shaped before it begins to harden.

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Hardened State

The stage where concrete has hardened and gained its desired properties, such as strength and durability.

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Concrete Mixing

The process of mixing cement with water and aggregates to create concrete.

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Concreting Timescales

The time it takes for concrete to harden from the initial mixing to the final hardened state.

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Concrete Life-cycle

The time period from the extraction of materials to the construction and eventual lifespan of concrete structures.

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What is Portland cement?

A fine, powdery material produced by grinding clinker with gypsum, it's the key binder in concrete.

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What is clinker?

A material formed by sintering raw materials in a kiln at very high temperatures, it's the main component of Portland cement.

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What is sintering?

A process that transforms raw materials into clinker by firing them in a kiln at high temperatures.

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What are the major compounds used to produce Portland cement?

Calcium carbonate (CaCO3), silica (SiO2), alumina (Al2O3), and ferric oxide (Fe2O3), these minerals are the main ingredients of Portland cement.

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What are sources of calcium carbonate for cement production?

Limestone or chalk, these are sources of calcium carbonate, a key ingredient in Portland cement.

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What are sources of silica, alumina, and ferric oxide for cement production?

Clay or shale are sources of silica, alumina, and ferric oxide, essential minerals for the clinkering process.

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What is gypsum used for in cement production?

Gypsum is added to Portland cement to control the setting time, preventing it from setting too quickly.

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What are the main products formed during cement hydration?

Calcium silicate hydrates (CSH), these are the main products formed when Portland cement reacts with water, giving concrete its strength.

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C-S-H Gel

The primary bonding agent in cement paste, formed from a mixture of calcium silicate and calcium aluminate hydrates. It exists in a variety of forms, including fibers, flattened solids, and hollow branches, with dimensions typically ranging from 0.5 to 2 microns.

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Calcium Hydroxide Crystals

Hexagonal crystals of calcium hydroxide present in hardened cement paste. They play a crucial role in maintaining the pH of the porous water within the paste, keeping it around 12.5.

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Cement Hydration

The process by which cement reacts with water, forming hydrated compounds that bind the concrete together. It's an exothermic reaction, releasing heat.

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Concrete Durability

The ability of concrete to resist damage caused by environmental factors like weather, chemicals, and salts.

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Autogenous Healing

The process by which a crack in concrete is naturally sealed by the reaction of unhydrated cement particles with water that seeps into the crack.

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Unhydrated Cement

Unhydrated cement particles that remain within the concrete for long periods. They can contribute to autogenous healing and provide a reserve for future hydration.

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Heat Evolution in Cement Hydration

The rate of heat generated during the hydration process of cement. It typically shows a peak in heat output immediately after mixing, followed by a plateau, and then further gradual increases.

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What is Microsilica?

A by-product from silicon and ferro silicon alloy production, characterized by very fine particles, high silica content, and excellent pozzolanic properties.

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What is Silica Fume?

A very fine, reactive powder that acts as a pozzolan, enhancing the strength and durability of concrete.

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What is the particle size of Microsilica?

A material with a very small particle size, typically around 0.1 micron.

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What is the main component of Microsilica?

Microsilica has a high proportion of amorphous silicon, making it a strong pozzolanic material.

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How is Microsilica used in concrete?

It can be used to replace up to 10% of Portland cement by weight, enhancing concrete properties.

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How does Microsilica affect the hydration process?

It acts as a nucleation site for the formation of calcium hydroxide and CSH hydrates in concrete.

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What is GGBS?

The fine powder from grinding and drying a by-product of cement production, capable of setting on its own, but often blended with Portland cement.

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What are PFA and GGBS?

They are additions to concrete that improve its properties like strength, durability, and workability.

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CEM Cement Composition

The sum of the proportions of reactive calcium oxide (CaO) and reactive silicon dioxide (SiO2) in CEM cement must be at least 50% by mass, according to EN 196-2.

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Common Cement Types (EN 197)

A family of common cements categorized by European Standard EN 197, each type with specific properties and applications.

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Minor Constituents in Cement

Inorganic materials added to cement during manufacturing to enhance its handling and setting properties. Calcium sulfate is essential for controlling the setting time.

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Additives in Cement

Substances incorporated in cement to improve its production or final properties, but limited to 1% by weight of the cement.

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Aggregate Sourcing for Concrete

The process of testing multiple sources of aggregate for their suitability in large construction projects, focusing on strength, durability, and compatibility with cement.

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Recycled Aggregates in Concrete

The use of recycled materials in concrete production, particularly aggregates from diverse sources, following current BS EN standards.

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Aggregate Consumption in the UK

The high consumption rate of aggregates in the UK construction industry, emphasizing the importance of sustainable sourcing and efficient use.

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Study Notes

Concrete Technology

  • Concrete uses burnt rocks like limestone or gypsum to create inorganic bonding agents.
  • Ancient civilizations, including Egyptians, Mycenaean, and Minoan, used lime mortars, which involved heating calcium carbonate-bearing rocks.
  • Quicklime (calcium oxide, CaO) is produced by heating limestone, and reacts with water to form hydrated calcium hydroxide (Ca(OH)2), known as slaked lime.
  • Slaked lime binds sand, aggregates, and other materials to form mortar.
  • Mortar hardens through CO2 reaction with Ca(OH)2, forming calcium carbonate (CaCO3).
  • This process is slow and optimal at ambient relative humidity (50-70%).
  • Limitations of lime mortars include slow hardening and inability to harden under water, thus limiting their use in large marine structures.
  • Roman concrete (50BC-500AD) contained reactive silica (pozzolana) from volcanic tuff, forming calcium silicates, a hydraulic cement.
  • This Roman concrete allowed construction of large, durable structures (Colosseum, Pantheon).
  • Innovations included air entrainment using blood, waterproof concrete using fig polymers, and lightweight aggregates for structures.
  • Further advancements included Saxon concrete (500AD-1100AD), like Reading Abbey.
  • John Smeaton (1756) pioneered Portland cement by adding clay to limestone, used for Eddystone Lighthouse.
  • James Parker (1796) and Joseph Aspdin (1824) developed important processes for Portland cement production.

Concrete as a Composite Material

  • Concrete is a multi-level composite, mainly composed of coarse aggregate, fine aggregate, and cement paste.
  • Cement paste is a mixture of Portland cement, other cement replacements, and water.
  • The components vary in size from centimeters to angstroms.
  • Grading and proportions of constituents control concrete properties.
  • Coarse aggregate comprises natural gravel and crushed rock, while fine aggregate involves aggregates with sizes less than 5mm.
  • Cement paste consists of cementitious material (Portland cement, GGBS, PFA, and Microsilica) and water.
  • Proportions of constituents are defined by mass, weight ratios (e.g., water-cement ratio), or nominal proportions (e.g., 1:2:4 for cement:sand:aggregate ratios).

Role of Constituents

  • Portland Cement: Reacts with water to form cement paste, serving as an inorganic binder.
    • Various types exist (e.g., CEM I, CEM II).
    • Types and properties are dependent on oxide and compound composition.
  • Water: Crucial for hydration, which is the key chemical reaction that gives cement its strength.
  • Cement Paste: Forms a binder in concrete, affecting crucial properties like cohesion and flowability.
  • Aggregate: Economically crucial as a large part of a concrete structure, providing a base for strength.
  • Porosity: Characterized by air voids and water-filled pores affecting strength, stiffness and density.
  • Admixtures: Small quantities of materials modifying concrete's properties (e.g. air-entraining agents, setting accelerators).

Portland Cement

  • Portland cement clinker results from sintering precisely mixed raw materials (mainly CaO, SiO2, Al2O3, Fe2O3).
  • Raw materials are finely divided, intimately mixed and are homogenised..
  • Clinker is heated to produce (partially melt) and fuse into balls (typically 25 mm).
  • Grinding to powder, adding gypsum, and controlling setting time (by temperature and added components) are also crucial steps.
  • Chemical composition described by oxide or compound composition. Typical compounds are listed

Concrete Timescales and Life-Cycle

  • Concrete structures can last for centuries with proper design and maintenance.
  • Life cycles start with resource extraction and end with demolition/reuse/recycling.
  • Proper maintenance is key to ensure service life.

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ENG2100 Construction Materials Lecture Notes PDF

Description

This quiz explores the fundamental aspects of how the type of cement, water, and aggregates influence the properties of concrete. You'll learn about hydration processes, admixtures, and the effects of curing on concrete's performance. Test your knowledge about these essential components that contribute to the quality and durability of concrete.

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