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Materials > Cement > Flashcards

Cement Flashcards

1
Q

What percentage of CO2 emissions in modern concrete mixes is from its cement

A

60%

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2
Q

What percentage of CO2 emissions in Portland cement concrete mixes is from its cement

A

81%

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3
Q

What is lime and how is it made

A

calcium oxide, made from burning, at 900c, (calcinating) limestone, calcium carbonate

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4
Q

How does lime harden

A

First it reacts with water to become slake lime ,Ca(OH)2, then absorbs CO2 in the air to harden back into CaCO3.

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5
Q

What condition prevents lime from hardening and why

A

wet conditions because water is a product of the reaction (think equilibrium rules)

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6
Q

Is the hardening of lime quick or slow and why

A

It is slow because the CO2 has to penetrate the material and the CO2 concentration in air isn’t very high

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7
Q

Is lime strong

A

No

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8
Q

Why was the roman mortar and cement much stronger than the Greeks’

A

The used volcanic ash which contains aluminium oxide and silicon dioxide

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9
Q

How is Portland Cement made

A

limestone and clay heated to 1200 degrees celsius

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10
Q

What is belite

A

A calcium silicate hydrate phase, C2S

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11
Q

What is alite

A

A stronger calcium silicate hydrate phase, C3S that requires higher temperatures to form

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12
Q

What is the approximate percentages of alite and belite in modern day concrete

A

60 and 20 percent respectively

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13
Q

Why was the rotary kiln an improvement to the beehive kiln

A

Rotary kiln allowed continuous production rather than batch production

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14
Q

What is a hydraulic cement

A

A cement that sets (hardens) with water

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15
Q

How is OPC made and what is it made from

A

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

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16
Q

Where are cement plants typically located

A

At the limestone quarry

17
Q

What is the purpose of the heat exchangers in the cement production plant

A

They receive heat from the rotary kiln and reach up to 1000C so that the CaCO3 decomposes into CO2 and CaO

18
Q

Give the stages of the Cement production plant

A

Quarry, conveyor, crushing, heat exchanger, rotary kiln, clinker silo, gypsum and slag addition, grinding mill, bagged

19
Q

How is the clinker cooled down quickly after the rotary kiln

A

passed over a grate and ambient air is blasted from below

20
Q

What is the chemical name of gypsum and what does it do

A

Calcium sulphate and is used to retard the setting of cement

21
Q

What is a SCM

A

Supplementary Cementitious Material. A non clinkered solid reactive material used in cement. Limestone is a SCM

22
Q

what is C in clinker chemistry notation

A

CaO

23
Q

what is S in clinker chemistry notation

A

SiO2

24
Q

what is A in clinker chemistry notation

A

Al2O3

25
Q

what is F in clinker chemistry notation

A

Fe2O3

26
Q

what is H in clinker chemistry notation

A

H2O

27
Q

what is S^ in clinker chemistry notation

A

SO3

28
Q

What is clinker

A

An intermediate consisting of limestone and clay mixed together that has been crushed into powder on the scale of 10micrometers

29
Q

Why should one not use seawater for the cement in reinforced concrete

A

Contains chloride which causes corrosion

30
Q

Which is stronger C3S or C2S and why

A

C3S is stronger as it has more calcium so more calcium silicate hydrate can be formed

31
Q

Which reacts faster C3S or C2S

A

C3S

32
Q

When does the hydration of cement stop

A

When relative humidity is below 80%

33
Q

What is the general size of capillary pores

A

10-15micrometers in “diameter”

34
Q

What is the water to cement ratio of: high performance, normal and garden path concrete

A

0.3, 0.45, 0.6

35
Q

Why does having more water to cement decrease strength of concrete

A

More porosity (as space left behind by water is not filled) which is weak

36
Q

What can adding alkali to the cement do

A

Cause the reaction to happen much faster

Materials (15 decks)

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