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
