Chapter 18 - Lime, Portland Cement & Concrete Flashcards
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
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
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
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
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.
Chemical name for Limestone
Calcium carbonate
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)
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)
Quicklime
Calcium Oxide
A casutic substance
reacts with water to create calcium hydrate (aka hydrated lime/slaked lime)
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
What is this substance in concrete
Hydrated Lime/Quicklime
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
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
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.
Amorphous Silica
Silicon dioxide (SiO2)
Noncrystiline ( ie. glassy)
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.
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
What is the main ingredient in Volcanic Ash
microscopic silica (with a small percentage of microscopic alumina)
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
What is most soil and rock made out of?
oxides of silicon and aluminum called silica and alumina
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
Chemistry of Lime:
Calcination of Limestone
Limestone —Heat—> lime + Carbon Dioxide
CaCO3 —Heat—> CaO + CO2
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
Chemistry of Lime:
Carbonation of Hydrated Lime
Ca(OH)2 + CO2 —-> CaCO3 + H2O
Hydrated Lime + Carbon Dioxide —> Calcium Carbonate + Water
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
What is a commonly used present pozzolana
fly ash
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
Size dirrerance between Fly Ash and Portland Cement Particles
Fly ash is less than 20 μm.
Portland Cemelt is 45 μm
μm
Micrometer
Millionth of a meter
0.001 mm
What is silica fume
- A form of contemporary pozzolana
- A waste product from the silicon industry
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
Why is portland cement used more than Pozzolana?
Portland cement is a mutch beter hyrdaulic cement
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
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
Types of Lime Used In Construction
High Calcium Limestone - 95% calcium carbonate
Dolmitic Limestone - 60-80% calcium carbonate
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
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
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
Types of Lime
Type N (Normal)
Type S (Special)
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
Use of Air Entrainments in Lime
Air Entrainments increase the resistance of lime mortar againsted the freeze thaw affect, but decreases its strength
How is Air Entrained Lime Designated?
- With an A suffix
- ie Type SA and Type NA lime
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)
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
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.
Uses of Lime (Construction)
Masonry Mortar
Plaster & Stucco
Soil Stabilization
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
How is modern Portalnd Cement different than the original 1800s formula
They are virtually identical
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
Clay (defined)
Clay consits of oxides of silica, alumina and iron oxide
Shale (defined)
Shale is a higly condensed form of clay
Sequence of Manufacturing Portland Cement
- Qauary limestone
- Crush limestone into 5/8” particles
- Store raw materials into silos (Crushed limestone, clay/shale, sand, bauxite, iron ore)
- Mix raw materials and grind to a fine powder in a grinding mill
- Powerfull fans move the powder from the grinding mill to a dust collector
- Material is then taken to storage silos
- 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
- Clinkers are cooled in a clinker cooler and and moved into silos
- From the silos they are mixed in with small amounts of gypsum stored in an adjacent silo to control the setting properties
- Clinker and gypsum are sent to a rotaing grinding mill and ground down and blended into portland cement; 45 um particles
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
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
Types of Portland Cement
Type I through Type V
Type I Portland Cement
General-purpose
Used when there is no special requirement
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
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
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
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
Type I/II
Meets the requirements of Type I (general use) and Type II (moderate-sulfate and low-heat-of hydration)
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
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%
Properties of Ailite in Portland Cement
Hydrates rapidly
Is responsible for inital set and early strength (from 1 - 7 days)
Properties of Belite in portland cement
Hydrates slowly and contributes to later strength gains (+28 days)
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)
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
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
