Cement Chemistry and Manufacturing Quiz

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Questions and Answers

What is the primary benefit of C3S in Portland cement?

It hardens rapidly and provides high early strength. (correct)

It lowers the clinkering temperature.

It reduces chemical attack resistance.

It contributes to long-term strength.

Which compound contributes to strength increase at ages beyond one week?

C3S

C2S (correct)

C4AF

C3A

What effect does adding gypsum have on C3A in Portland cement?

It enhances sulfate resistance.

It accelerates hardening.

It reduces heat of hydration and slows setting. (correct)

It increases the proportion of C4AF.

Which chemical compound in Portland cement assists in reducing the clinkering temperature?

C4AF Signup and view all the answers

What is the proportion range of C4AF in Portland cement?

8-15% Signup and view all the answers

What is the purpose of slaking quick lime?

To convert it into a usable form for construction Signup and view all the answers

What is the temperature range during which complete dehydration occurs in the burning process?

400-500°C Signup and view all the answers

Which type of lime is produced by calcining pure calcium carbonate?

Quick lime Signup and view all the answers

What characterizes hydraulic lime compared to non-hydraulic lime?

It contains clay and hardens by internal reaction with water Signup and view all the answers

Which chemical reaction occurs during the dissociation of carbonates in the cement manufacturing process?

CaCO3 → CaO + CO2 Signup and view all the answers

Which of the following compounds is NOT formed during the compound formation stage?

Silicon dioxide (SiO2) Signup and view all the answers

Which of the following forms of hydrated lime is created by wet-slaking quick lime?

Milk of lime Signup and view all the answers

What is the primary process for preparing hydraulic lime?

Burning impure limestone containing clay Signup and view all the answers

What is the final product called after the raw materials have been fully burnt?

Clinker Signup and view all the answers

In which type of storage is cement most commonly stored after manufacturing?

Concrete silos Signup and view all the answers

What happens to slaked lime as it hardens?

It loses water and absorbs carbon dioxide from the air Signup and view all the answers

What is the specific gravity of quick lime?

3.40 Signup and view all the answers

What is an advantage of the wet process over the dry process in cement manufacturing?

Allows for easier blending of materials Signup and view all the answers

What is typically mixed with clinker to create Portland cement?

Gypsum Signup and view all the answers

Which form of hydrated lime is the result of adding just enough water to create a dry, fine powder?

Dry hydrate Signup and view all the answers

Which step is NOT part of the wet process of cement manufacturing?

Grinding of raw materials without water Signup and view all the answers

What is the primary use of Type I Portland cement?

In general-purpose applications without special properties Signup and view all the answers

Which type of Portland cement would you choose for structures of considerable mass?

Type II Moderate Portland cement Signup and view all the answers

What compound is formed from the hydration of tricalcium silicate and water?

Calcium silicate hydrate (C-S-H) Signup and view all the answers

Which type of Portland cement is specifically intended to achieve high early strength quickly?

Type III Portland cement Signup and view all the answers

What characteristic of Type IV Portland cement makes it suitable for specific applications?

Low heat of hydration Signup and view all the answers

When should Type I Portland cement be used?

In normal environmental conditions without severe climate changes Signup and view all the answers

What reaction occurs when tricalcium aluminate reacts with gypsum and water?

Production of ettringite Signup and view all the answers

Which type of Portland cement is likely to be used in cold weather applications?

Type IV Low Heat of Hydration Signup and view all the answers

What causes flash set in cement?

Rapid reaction between C3A and water Signup and view all the answers

Which factor does NOT contribute to unsoundness in cement?

Lower fineness of the cement Signup and view all the answers

What is measured in the Le Chatelier test?

Soundness of cement Signup and view all the answers

Which compound is known to hydrate at a rapid rate, affecting the heat of hydration?

C3A Signup and view all the answers

In the context of cement, what does the term 'fineness' refer to?

The surface area of the cement particles Signup and view all the answers

How does the total heat of hydration relate to the fineness of cement at later stages?

It has no effect Signup and view all the answers

What is the primary purpose of testing the compressive strength of cement?

To ensure structural integrity Signup and view all the answers

Which of the following is NOT a factor that affects the rate of heat evolution during hydration?

Time of setting Signup and view all the answers

What components make up lime mortar?

Lime, sand, and water Signup and view all the answers

Which mortar type offers the rapid development of strength?

Cement mortar Signup and view all the answers

Which property indicates the ease of handling mortar during construction?

Workability Signup and view all the answers

What is a major disadvantage of lime mortar compared to cement mortar?

Slow hardening Signup and view all the answers

Compo mortar is a combination of which components?

Cement, lime, and sand Signup and view all the answers

What effect does increasing the cement content have on cement mortar?

Increases all strength measures Signup and view all the answers

Which type of sand results in better workability for mortars?

Circular grain sand Signup and view all the answers

What must be used in mortar to ensure watertightness in damp conditions?

Cement Signup and view all the answers

Study Notes

Construction Materials - CENG 2092

Course name: Construction Materials
Course code: CENG 2092
University: Addis Ababa Science and Technology University
Year established: 2011

Chapter Two - Binders

Binders are substances used to bind inorganic and organic components.
Non-hydraulic binders only harden in the presence of air.
Hydraulic binders require water to harden.
Examples of binders:
- Lime
- Gypsum
- Portland cement.
- Mortar
- Bituminous (Asphalt)
- Synthetic

Binder Definition

Binders are substances used to bind inorganic and organic components.
Hydraulic binders are strong, hard, and/or flexible.
Binder action is usually due to chemical reactions during heating, mixing with water/other materials, or exposure to air.

Non-hydraulic Binders

Harden only in the presence of air.
Cannot set or harden in water.
Lime is the most common non-hydraulic binder.
Gypsum is a naturally occurring soft crystalline rock, also a non-hydraulic binder.
Hardening depends on combining with carbon dioxide (carbonation) to become limestone.

Hydraulic Binders

Require water to harden and develop strength.
Portland cement is the most common hydraulic binder.
Hydraulic binders are usually fine powders.

Lime

One of the oldest known cementing materials.
Found naturally as a rock of varying degrees of hardness.
Primarily composed of calcium oxide (CaO).
In its pure form, it associates with CO₂ to form CaCO₃ (white).
Often found mixed with impurities (CO₂, Fe₂O₃, MgCO₃).
Impurities determine color variation.
Generally a non-hydraulic binder but can be made hydraulic.
Production: Burning raw material limestone (CaCO₃) which produces CaO and CO₂.
Chalk and shell can contain over 98% CaCO₃.
Product type (hydraulic or non-hydraulic) depends on heat and slaking method.
Burning process occurs in either vertical shaft kilns or rotary kilns.

Lime Production - Vertical Shaft Kiln

Raw materials are fed at the top.
Finished product is drawn from the bottom opening.
Stages include preheating, calcining, and cooling.

Lime Production - Rotary Kiln

Rotating cylinder, inclined at 3-4 degrees to the horizontal.
Limestone is fed in at the back end. Fuel and combustion air are fed into the front end.
Product is discharged into a cooler.
Process includes coal feed/pulverized coal, firing fan, gear, air blower, dual fuel, gas/air, and lime cooler.

Classification of Lime

Commercial lime is classified into:
- Quick lime (caustic lime)
- Hydrated lime (slaked lime)
- Hydraulic lime

Quick Lime (A)

Obtained by calcining (burning) pure calcium carbonate.
White in color with a specific gravity of approximately 3.40.

Hydrated Lime (B)

Can't be used directly, needs to be mixed with water.
Reaction is called slaking, resulting in calcium hydroxide (Ca(OH)2), also called slaked lime or hydrated lime.
Forms of hydrated lime vary based on added water during slaking:
- Dry hydrate (dry-slaking)
- Milk of lime (wet-slaking)
- Lime putty

Hydraulic Lime (C)

Prepared by burning impure limestone that contains clay, producing compounds similar to Portland cement.
Hardening occurs through internal reaction with water.
Stronger but less plastic compared to non-hydraulic lime.
Manufacturing is similar to quick lime production, but a slightly higher temperature is required during burning.

Setting and Hardening of Lime

Slaked lime hardens by losing water and absorbing carbon dioxide from the air, transforming into calcium carbonate (CaCO₃) or limestone.

Uses of Lime

Construction material:
- Mortar (mixed with sand)
- Cement mortar (improves workability)
- Plaster
- Whitewash
- Lime concrete
- Clay soil stabilizer

Gypsum

Non-hydraulic binder that occurs naturally as a soft crystalline rock.
Easily scratched by a fingernail.
Naturally occurs as hydrated calcium sulfate (CaSO₄·2H₂O), generally 76% CaSO₄ and 24% H₂O.
Pure gypsum is known as alabaster (white translucent crystalline mineral).
Used in arts and building construction.
Easily turns into powder when heated.
Forms interlocking crystals when water is added to the powder.
Building gypsum is made of semi-hydrate gypsum from processing at 150-160°C.

Advantages of Gypsum as a Construction Material

Incombustibility
Superior surface finish
Good fire resistance
Resistance to insects
Low energy consumption during burning
Rapid drying

Major Shortcomings of Gypsum

Low strength in wet state
High creep under load

Plaster of Paris (A)

Produced by incompletely dehydrating pure gypsum, finely ground, at a somewhat lower temperature than 185°C.
This forms CaSO₄·½H₂O.
At higher temperatures (around 200°C), gypsum loses all water of crystallization and turns into a hydrated gypsum.
White powder with a specific gravity of 2.57.
Used for small patching jobs on plastered walls.
Excellent material for filling cracks, holes, and for painting/polishing wooden surfaces before painting.
Sets rapidly (5-10 minutes) from mixing with water to form a plastic paste.

Hard Finish Plaster (B)

Burning gypsum at a higher temperature than calcining cement plaster.
Treated with solutions, like alum and Glauber's salt (Na₂SO₄), results in a very hard plaster with a slow setting time.
Also known as anhydrous plaster or high-temperature gypsum derivative(CaSO₄· 2H₂O + High Heat = CaSO₄ + 2 H₂O).
May be polished to form a smooth surface for interior walls.

Uses of Gypsum

Wall plasters: gain half of their one-month strength in a day. Mortars of 1:1 proportions develop 80% of neat strength; 1:2 proportions generally have strength between one-half and two-thirds of neat strength. Gypsum to sand (1:3) sets in 2-32 hours, and 1.5-8 hours when mixed with wood fibers.
Plaster boards: made from thin layers of cardboard or wood cemented together with wall plaster. Stronger with the addition of sisal or coconut fibres. 10 kg/m² of plaster; 250 g/m² of fiber; very light and fire-resistant.
Non-load bearing gypsum partition blocks: solid or hollow, rectangular shape, straight and square edges; minimum compressive strength of 50 N/m².

Pyro-cell

Finely ground powder with an admixture. Forms gas upon mixing with water and expands the mixture to 3-4 times its original volume.
Hardens into a fire-resistant, light, cellular mass with good acoustical and insulating properties.

Cement

A binder used for concrete.
Dates back to 7000 BC, with a lime concrete floor found in Israel.
Portland cement was first patented in 1824, named after natural limestone quarried on the Isle of Portland (English Channel).
Primary components of raw materials: calcium, silica, alumina, iron.

Methods in Portland Cement Production

Dry process: Proportioned, ground, blended, and fed into the kiln.
Wet process: Adds water to the raw materials, grinding and blending in slurry form.

Portland Cement - Dry Process

Four main steps: treatment of raw materials, burning of the dry mix, grinding of the clinker, packaging, and storage.
Raw materials undergo crushing, drying, grinding, proportioning, and blending before burning in the kiln.
Finely powdered mixture (raw meal) is charged into a long, steel cylinder called a rotary kiln.

Portland Cement - Reactions During Burning

Complete dehydration: Water is driven off at low temperatures (about 400°C).
Dissociation of carbonate: Calcium carbonates dissociate at 800-900°C, forming calcium oxide and carbon dioxide.
Compound formation: Formation of compounds like tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), and tetracalcium aluminoferrite (C4AF).

Portland Cement - Grinding of Clinker

Completely burnt raw materials are converted into clinker lumps, drawn from the rotary kiln's lower end.

Portland Cement - Packing and Storage

Cement is typically stored in specially designed concrete storage tanks (silos).
It is drawn off mechanically and is commonly packaged in bags.
Dry mixing and blending method has less popularity than the wet process.

Portland Cement - Wet Process

Considered a better process for cement manufacture where a soft-variety limestone is the abundant raw material.
Steps in wet process:
- Preparation of slurry
- Burning or calcination
- Clinker grinding

Portland Cement - Clinker Production

Stages during clinker production
- Raw materials (at 700°C) are free-flowing
- Particles remain solid up to 700-900°C
- Nodulization: Solid particles; no reaction, Nodulization, particles stay solid as calcification continues
- Clinkering reactions: Formation of liquid phase; more heat is needed for various reactions
- Reactions happen at 1150-1200°C, particles become sticky, aglomerate, rotation initiates coalescing and layering of particles
- 1200-1350°C, capillary forces hold particles; small belite crystals forms, liquid phase; and reaction between belite and free CaO forms alite crystal formation.
- 1350-1450°C, Particles aglomerate, layer particles by falling, nodules form, and insufficient liquid produces dusty clinker. -Cooling causes C₃A and C₄AF crystallize, resulting in lamellar structure.

Chemical Compounds of Portland Cement

C₃S (tricalcium silicate): Highly desirable for its high early strength. Proportion ranges from 25-60%.
C₂S (dicalcium silicate): Hardens slowly, contributing to strength increase beyond one week. Proportion ranges from 13-50%.
C₃A (tricalcium aluminate): Generates a large amount of heat during hardening (first few days). Acting as a retarder and lowering heat of evolution when gypsum is added. Leads to calcium sulfoaluminate formation. Proportion ranges from 5-15%.
C₄AF (tetracalcium aluminoferrite): Decreases clinkering temperature to improve Portland cement manufacturing. Contributes little to strength, good resistance to chemical attack. Proportion ranges from 8-15%.

Summary of Portland Cement Clinker Characteristics

Table summarizing the properties (rate of hydration, strength, amount of heat liberated, and resistance to chemical attack), for each chemical compounds (C₃S, C₂S, C₃A, C₄AF)

Types of Portland Cement

IA (Normal): General purpose, used where special properties are not required.
II (Moderate): Suitable for structures needing moderate sulfate resistance or moderate heat of hydration (e.g., abutments, piers).
III (High Early Strength): Ideal for high early strength requirements, often used in quick construction.
IV (Low Heat): Intended for mass structures where low heat of hydration and slower strength development is needed (e.g., large concrete pour).
V (Sulfate Resisting): High sulfate resistance; for use where concrete is exposed to harsh sulfate conditions.
IA, IIA, IIIA: Improved resistance to freezing and thawing.

Other Types of Cement

Portland Pozzolana Cement (PPC): Blended with 20-30% by weight of pozzolanic material (e.g., a naturally occurring or artificial siliceous material) to get improved cementations properties.
Acid-resistant cement: Composed of acid-resistant aggregates and additives, increasing acid resistance from mixing with sodium silicate or soluble glass.
Blast furnace cement: Utilized slag from blast furnace, cheaper/economical, with nearly the same properties as ordinary cement, but unsuitable for dry arid zones; longer curing time.
Colored cement: Coloring via mineral pigments, the percentage usually varies from 5-10% but shouldn't exceed 10% for strength implications.
Expanding cement: Produced by adding an expanding medium to ordinary cement. Used for water-retaining structures and damaged concrete surfaces.
- Used in repairing damaged/cracked concrete surfaces.

Mortar

A mixture of sand or inert particles and a binding agent (typically cement and/or lime) with water added in predetermined ratios.
Mortar = Binder + Sand + H₂O

Mortar Uses

Jointing medium in masonry construction.
Wall plaster: even, smooth surfaces over construction.

Types of Mortar

Mud mortar: Soil and water.
Lime mortar: Lime, sand, water.
Cement mortar: Portland cement, sand, water.
Compo mortar: Combines lime and cement for improved properties.

Mortar Properties

Workability: Ease of transporting, placing, and finishing the mortar mix. Lime-sand mortars typically have better workability than cement-sand mortars.
Strength: Affected by ingredients, proportions, and curing method. Cement-sand mortars generally develop greater strength.
Water tightness: Portland cement mortars are often preferred for watertight applications due to their hydraulic properties. Strength and degree of water tightness increases with the density of the mix, keeping all other factors consistent.

Factors Affecting Mortar Properties

Mixing water amount
Binder properties
Cement content, fineness, and composition.
Sand characteristics and grading

Materials for Mortar

Binder: OPC, PPC, RHC, lime types.
Sand: Well graded, clean (free from dust, loam, clay, vegetable matter).

Mortar Proportioning/Recipe

Proportions vary based on application; e.g., Masonry cement, compo mortar, for plastering, etc.

Batching and Mixing

Accurately measuring components (cement by weight, sand by volume).
Specific volume measurements for different quantities in multiples of 35 liters. Standard boxes for mortar batching 40x35x25cm, 40x50x18cm.

Other Information (Miscellaneous)

Silt test (Jar test) for determining silt content of sand - 3mm or greater silt or 6%, then not suitable for mortar job.

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