Cement Flashcards
What percentage of CO2 emissions in modern concrete mixes is from its cement
60%
What percentage of CO2 emissions in Portland cement concrete mixes is from its cement
81%
What is lime and how is it made
calcium oxide, made from burning, at 900c, (calcinating) limestone, calcium carbonate
How does lime harden
First it reacts with water to become slake lime ,Ca(OH)2, then absorbs CO2 in the air to harden back into CaCO3.
What condition prevents lime from hardening and why
wet conditions because water is a product of the reaction (think equilibrium rules)
Is the hardening of lime quick or slow and why
It is slow because the CO2 has to penetrate the material and the CO2 concentration in air isn’t very high
Is lime strong
No
Why was the roman mortar and cement much stronger than the Greeks’
The used volcanic ash which contains aluminium oxide and silicon dioxide
How is Portland Cement made
limestone and clay heated to 1200 degrees celsius
What is belite
A calcium silicate hydrate phase, C2S
What is alite
A stronger calcium silicate hydrate phase, C3S that requires higher temperatures to form
What is the approximate percentages of alite and belite in modern day concrete
60 and 20 percent respectively
Why was the rotary kiln an improvement to the beehive kiln
Rotary kiln allowed continuous production rather than batch production
What is a hydraulic cement
A cement that sets (hardens) with water
How is OPC made and what is it made from
Ordinary Portland Cement consists of 3/4 limestone and 1/4 clay and shale, heated up to 1450C. This forms a clinker which is then grinded into powder and then 4% gypsum is added
Where are cement plants typically located
At the limestone quarry
What is the purpose of the heat exchangers in the cement production plant
They receive heat from the rotary kiln and reach up to 1000C so that the CaCO3 decomposes into CO2 and CaO
Give the stages of the Cement production plant
Quarry, conveyor, crushing, heat exchanger, rotary kiln, clinker silo, gypsum and slag addition, grinding mill, bagged
How is the clinker cooled down quickly after the rotary kiln
passed over a grate and ambient air is blasted from below
What is the chemical name of gypsum and what does it do
Calcium sulphate and is used to retard the setting of cement
What is a SCM
Supplementary Cementitious Material. A non clinkered solid reactive material used in cement. Limestone is a SCM
what is C in clinker chemistry notation
CaO
what is S in clinker chemistry notation
SiO2
what is A in clinker chemistry notation
Al2O3
what is F in clinker chemistry notation
Fe2O3
what is H in clinker chemistry notation
H2O
what is S^ in clinker chemistry notation
SO3
What is clinker
An intermediate consisting of limestone and clay mixed together that has been crushed into powder on the scale of 10micrometers
Why should one not use seawater for the cement in reinforced concrete
Contains chloride which causes corrosion
Which is stronger C3S or C2S and why
C3S is stronger as it has more calcium so more calcium silicate hydrate can be formed
Which reacts faster C3S or C2S
C3S
When does the hydration of cement stop
When relative humidity is below 80%
What is the general size of capillary pores
10-15micrometers in “diameter”
What is the water to cement ratio of: high performance, normal and garden path concrete
0.3, 0.45, 0.6
Why does having more water to cement decrease strength of concrete
More porosity (as space left behind by water is not filled) which is weak
What can adding alkali to the cement do
Cause the reaction to happen much faster
