Chapter 18 - Lime, Portland Cement & Concrete Flashcards Preview

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Flashcards in Chapter 18 - Lime, Portland Cement & Concrete Deck (68):
1

Historical Background of Lime, Portland Cement & Concrete

- Until the middle of the 19th century, lime was the only cement available for use in masonry mortar, plaster, and concrete (whereas now, it is only a small component in mortar, stucco, whitewash, and soil stabilization).

- Portland Cement replaced lime in most usage and is the main ingredient in concrete

2

Thermal Properties of Quicklime

- 1 Btu is the amount of heat required to raise the temperature of 1 LB of water 1 degree F

- 1 lb of hydrated quicklime creates 450 Btu

- 450 Btus will raise the temp of 3.2 lb of water from 70 F to 212 F

3

Scumbag Uses of Quicklime

- British soldiers used quiklime in the war of 1217 by throwing it in thier faces to incapacitate them

- Criminals misused quicklime to dispose of bodies by buring them in quicklime and hydrated soil

4

What are Lime-Sand Mortars? 

When were they primarily used?

- A mortar where lime is a cement (binder) and sand is the filler

- Lime-Sand Mortars were used for thousands of years in masonry mortars (historic european buildings  & Egyptian Pyramids). 

- Lime-Sand Mortars were the only masonry morater until the advent of portland cement

5

What is lime made from

Limestone (aka calcium carbonate), the most abundant rocks on Earth's crust

Sedimentary rock

Limestone, composed mainly of skeletal fragments of marine organisms; trilobytes, coral, forams and molluscs. 

6

Chemical name for Limestone

Calcium carbonate

7

The process of creating lime from limestone

Calcining

Crushing limestone (calcium carbonate) into 2" rocks and heating to 1,800 deg F.

This endothermic reaction (ie heat is required to make it happen) of calcuim carbonate expels the carbon dioxide leaving carbon oxide (aka lime/quicklime)

8

Calcium Hydroxide

- Ca(OH)2

- The mixture of quicklime (calcium oxide: CaO) with water (dihydrogen monoxide: H20)

- Also called hydrated lime/slaked lime

- The mixture creates an exothermic reaction (ie heat is produced during the reaction)

9

Quicklime

Calcium Oxide

A casutic substance

reacts with water to create calcium hydrate (aka hydrated lime/slaked lime)

10

Packaging Of Hydrated Lime

- Hydrated Lime is generally used in powder form

- Created by hydrating quicklime (whose amount of water used to hydrate is much greater than needed for hydration reaction. Therefore, after hydration reaction, quicklime needs to evaporate/dry excess moisture). Allow to dry

- Crush in powder and package

11

What is this substance in concrete

Q image thumb

Hydrated Lime/Quicklime

12

Carbonation Of Lime

The hardening property of lime results from its ability to react with atmospheric carbon dioxide to create calcium carbonate.

Thus, the chemical reaction between lime with carbon dioxide returns lime it to its parent material, limestone

 

13

Carbination of masonry mortar

As the atmospheric carbon dioxide begins to react with lime-sand mortar in a wall, it converts the exposed area of the mortar into a hardened carbonite crust. This crust hinders further penetration of carbon dioxide into the interior volume of the mortar.

Is a slow reaction in large part because CO2 is a small part of air (4%)

- The cemnintg propoerty is more to do with the absorbtion of water in mortar by masonry than simple hardening; as water evaporated and the mortar shrinks, it draws the units toward itself. The tiny pores, pits, ans crevices on the surface, which get filled with mortar, add to the lime's cementing property 

14

Who Discovered the Pozzolanic Reaction and what was the basics of what they found?

Discovered by Romans in 1st or 2nd centry BC;

 

Romans found that in addition to lime being hardened by CO2 (which was already known), if also mixed with volcanic ash, the mixture (via the reaction to the amorphous silica), when used with sand and water, gave a mortar that set more quickly, was stronger, and more durrible than lime-sand mortar.

15

Amorphous Silica

Silicon dioxide (SiO2)

Noncrystiline ( ie. glassy)

16

What type of cement is created in the Pozzolanic Reaction? What are it's benefits?

mixing lime and volcanic ash with water produces a hydraulic cement, which is water resistant cement that does not disolve in water.

17

What is freelime and what does it do in water

Free lime is lime in absence of pozzolanic reaction.

It will gradualy disolive in water

18

What is the main ingredient in Volcanic Ash

microscopic silica (with a small percentage of microscopic alumina)

19

How is volcanic ash made?

- As volcanic lava jets out of the ground, the carbon in the rock and other organic matter is converted to carbon dioxide gas, which caries with it particles of rock that have melted and fused into glassy (amorphous) particles

- due to the pressure of the volcanic erupton, molten gas particles are converted to tiny beads of glass resulting in volcanic ash

20

What is most soil and rock made out of?

oxides of silicon and aluminum called silica and alumina

21

What is another name for Portland Cement and what gives volcanic ash its pozzolanic properties?

Pozzolanic matterial or simply pozzolana

 

It's both the microscopic size and amorphous nature of silica and alumina that give fly ash its pozzolanic prperties

22

Chemistry of Lime:

 

Calcination of Limestone

Limestone ---Heat---> lime + Carbon Dioxide

CaCO3 ---Heat---> CaO + CO2

 

23

Chemistry of Lime:

 

Hydration of Quicklime

Calcium Oxide + Water ----> Calcium Hydroxide + Heat

CaO + H2O ----> Ca(OH)2 + Heat 

Quicklime + Water  ----> Hydrated Lime (aka slaked lime) + Heat

24

Chemistry of Lime:

 

Carbonation of Hydrated Lime

Ca(OH)2 + CO2 ----> CaCO3 + H2O

Hydrated Lime + Carbon Dioxide ---> Calcium Carbonate + Water

25

Deffinition of Pozzolana

A meterial, when mixed with lime & water, converts the mixture into a hydraulic cement

Also, to qualify as pozzolana, the material must me extremly small (microscopic) and contain amorphious silica

26

What is a commonly used present pozzolana

fly ash

27

What is fly ash

A waste product from coal fired electricicity generating stations.

 

It is similar to volcanich ash, as it contains microscopic & amorphious silica

28

Size dirrerance between Fly Ash and Portland Cement Particles

Fly ash is less than 20  μm. 

Portland Cemelt is  45 μm

29

 μm

Micrometer

Millionth of a meter

0.001 mm

30

What is silica fume

 - A form of contemporary pozzolana

- A waste product from the silicon industry

31

What is the reaction between lime & pozzolana

- Creates a complex form of calcium silicate hydrate

- This calcium silicate hydrate is the main constituant prodced whn portland cement is mixed with water

32

Why is portland cement used more than Pozzolana?

Portland cement is a mutch beter hyrdaulic cement

33

Orgins of Roman Concrete & Mortar

Discovered lime from cooking & heating hearths which were made of limestone slabs

- The fire of the hearths calcinated the limestone and then the rain showers hydrated them

- Fly ash was readily avaialble as there were many active volcanoes at the time

- Pozzolan is derived from the town in southern Italy named Pozzali, a town in Naples which had many active volcanoes

34

Uses of Roman Concrete & Cement

- Was formed with two closely spaced stone or brick walls as a permanent formwork, of which many of the alls buil, the front face has crumbeled exposing the concrete

- Because thier cement was hydraulic, the mortar used in Roman concrete was also hyraulic

- Thus they build aquaducts to supply water (300 BC) and large structures such as the Pantheon (120 AD) using lime, volcanic ash, broken stone and water

35

Types of Lime Used In Construction

High Calcium Limestone - 95% calcium carbonate

Dolmitic Limestone - 60-80% calcium carbonate

36

Properties of Quicklime Extracted from Dolmitic Limestone

- Shares most of its properties with high calcium limestone in that they can both be calcinated into quicklime

- However, quicklime obtainied from dolmitic Limestone is calcium oxide cehmically combined with magnesium oxide

- CaO + MgO

37

Dolomic Limestone Vs High Calcium Limestone in terms of hydration

- Dolomic Limestone has an affinity to water, but does not hyrate as readily as Calcium Oxide alone as higher temperatures and pressures are generally needed to fully hydrate magnesium oxide

38

Why are unhydrated oxides in lime problemtic

- They are problematic because given the right temperature, pressure, and humidity they can hydrate abruptly well after construction is complete. Since the hydration of lime is an exothermic reaction, blistering an popping can occur

39

Types of Lime

Type N  (Normal)

Type S (Special)

40

Type S vs Type N Lime Characteristics

  • Type S hydrated lime has a maximum (8%) unhydrated oxides whereas Type N has no limit
  • Type S is more expensive than Type N
  • Has greater workablity and plasticity than Type N
  • Type S is the lime usually used in masonry mortar
  • Type S can be produced from either high calcium lime or dolometic lime, but in the US dolomitic lime is preffered it gives greater workability

41

Use of Air Entrainments in Lime

Air Entrainments increase the resistance of lime mortar againsted the freeze thaw affect, but decreases its strength

42

How is Air Entrained Lime Designated?

- With an A suffix

- ie Type SA and Type NA lime

43

Workability

Workability is a term used with referance to concrete, mortar and plaster.

With concrete it is somewhat measured by slump

With plaster and mortar there is no measurement like slump, but masons intuit what is preffered workablilty; mix will spread easily (ie a crunchy peanut butter on toast vs a creamy peanut butter)

44

Plasticity

Plasticity is related to workability

A measurable term with referances to mrotar and plaster mixes

- Workability is a combination of plasticity and water relativity

- Higher plasticity and water relativity is more workable

45

Uses of Lime (Nonconstruction)

  • Water purification in water-treatment plans due to its disinfecting properties and removes leads from water
  • Water softening
  • sewage sludge treatent
  • making of plastics and paints
  • etc.

 

46

Uses of Lime (Construction)

Masonry Mortar

Plaster & Stucco

Soil Stabilization

47

History of Portland Cement

  • Patented in 1825 by Joseph Aspidin, a britsh stone mason
  • Burnt finely ground limestone & clay in a kiln and found the resulting product was a hydraulic cement that set and gained strength more quickly than lime
  • Called it portland cement because the concrete it produced resembeled in color and strength to a highly sought after limestone quarried fromt he british Isle of Portland

48

How is modern Portalnd Cement different than the original 1800s formula

They are virtually identical

49

Raw Materials of Portland Cement

  • around 2/3 limestone
  • around 1/3 clay or shale
  • some amount of suplimental materials if the clay does not contain all requered elemaent alone; sand for silica, bauxite for alumina, and iron ore for iron

50

Clay (defined)

Clay consits of oxides of silica, alumina and iron oxide

51

Shale (defined)

Shale is a higly condensed form of clay

52

Sequence of Manufacturing Portland Cement 

  1. Qauary limestone
  2. Crush limestone into 5/8" particles
  3. Store raw materials into silos (Crushed limestone, clay/shale, sand, bauxite, iron ore)
  4. Mix raw materials and grind to a fine powder in a grinding mill
  5. Powerfull fans move the powder from the grinding mill to a dust collector
  6. Material is then taken to storage silos
  7. From powdered materail silos the material is taken to a kiln where it calcinates at the front end and moves the the hotter back end to coallese into 1/2" size clinkers
  8. Clinkers are cooled in a clinker cooler and and moved into silos
  9. From the silos they are mixed in with small amounts of gypsum stored in an adjacent silo to control the setting properties
  10. Clinker and gypsum are sent to a rotaing grinding mill and ground down and blended into portland cement; 45 um particles

 

53

Details about the rotary kiln in the production of Protland Cement

  • The kiln is the heart of the manufacturing process
  • The rotary kiln is the heaviest piece of rotating industrial equipment
  • It is a huge steel cylinder lined inside with refactory brick
  • The kiln is slightly sloped to allow the material to tumble forward by gravity
  • At the initial secttion of the kiln, the temp is 1800 degrees and allows calcium carbonate to convert to calcium oxide
  • At the backend the heat is more intense. The temp is 3400 degrees. Calcium oxide reacts with other raw materiasl to form complex calcium compunds. These materials become partially molten and coalese into 1/2" nodules called clinkers

 

 

54

Uses of Portland Cement

  • Most portland cement made is used in concrete for buildings, pavements, roads, bridges, and mdams
  • Other uses are in masonry mortars, plaster, stucco, and flooring

55

Types of Portland Cement

Type I through Type V

56

Type I Portland Cement

General-purpose 

Used when there is no special requirement

57

Type II Portland Cement

Moderate-Sulfate-resistant and low-heat-of hydration

combines the properties of type IV and Type V to a moderage degree

58

Type III Portland Cement

High-early-strength portland cement

Develops strenght at a faster rate in the initial stages but final strenght is the same as other types

Used in making precast concrete elements as economic factors require that the formwork for precast elements to be used as frequently as opossible. Thus these elements are usally cast one morning and removed the following morning

59

Type IV Portland Cement

Low-Heat-of-Hydration portland cement

Menat for use in massive concrete structures (dam walls or bridge piers), where the temperatures rise due to heat generated from hydration must be minimised

60

Type V Portland Cement

Sulfate-Resistant Portland Cement

Since portland cement can be advesrly affected by the presence of sulfer and can decompose into small fragments (spall). Type V is used when concrete i splced in soils and areas where groundwater have a high sulfer content 

61

Type I/II

Meets the requirements of Type I (general use) and Type II (moderate-sulfate and low-heat-of hydration)

62

Effects of particle size of Portland Cement

  • The finer the particles, the greater the surface area avaialble for water to coat cement particles
  • This increases the rate of hydration leading to higher early strenght of portland cement paste
  • Type III has the finet particle size

63

Composition of Portland Cement

Tricalcium Silicate (C3S) - alite - ~50%

Dicalcium Silicate (C2S) - belite - ~25%

Tricalcium Aluminate (C3A) - celite - ~5-12%

Tetracalcium-alumino-ferite (C4AF) - iron - up to 8%

64

Properties of Ailite in Portland Cement

Hydrates rapidly

Is responsible for inital set and early strength (from 1 - 7 days)

65

Properties of Belite in portland cement

Hydrates slowly and contributes to later strength gains (+28 days)

66

Properties of celite in Portland Cement

Liberates a great deal of the heat in the first few days and contribues somewhat in the intial strenfgth

Too much of it can reduce sulfate resistance (more spalling)

67

Properties of Iron in Portland Cement

Iron has little impact on portland cement properties but is necessary as a flux to reduce energy production durring production. A flux reduces the temperature at which the raw materials begin to coalese.

Iron and small amounts of maganese give concrete its color. White cement is made by reducing the iron ore and maganese

68

Properties of gypsum in Portland Cement

Increases the setting time of portland cement. Setting is the stifining (early hardening) of the mix (when it becomes semisolid