Portland Cement

Chapter 7

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ACI Definition

portland cement (n.) a cementitious productmade by heating raw materials containing oxides ofaluminum, silicon, and calcium to temperaturesapproaching 1500°C, then pulverizing the end productwith a small amount of gypsum.

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Limestone QuarryIsle of Portland, England

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Primary Ingredients

lime (CaO)  ‒ 61‐67%limestone, marble, chalk, marl, calcite, seashells, blast furnace slag

silica (SiO2)  ‒ 19‐23%clay, loess, shale, sand, sandstone, quartzite, fly ash, rice‐hull ash

alumina (Al2O3)  ‒ 2‐6%clay, loess, shale, bauxite, fly ash

iron oxide (Fe2O3)  ‒ 0‐6%clay, shale, iron ore, pyrite, blast furnace flue dust

Inside a Cement Kiln

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drying

Total time in kiln = 60‐90 minutes

400ºC1500ºC 800ºC

cooling

clinker

Inside a Cement Kiln

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3 2825

heatC

CaCO CaO CO

calcining

400ºC1500ºC 800ºC

cooling

clinker 1 ton of cement 1 ton of CO2

Inside a Cement Kiln

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sintering

C2Sforms

400ºC800ºC1500ºC

2 2 41200

2 heatC

CaO SiO Ca SiO

cooling

clinker

Inside a Cement Kiln

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sintering

C3Sforms

400ºC800ºC1500ºC

2 4 3 51250

heatC

CaO Ca SiO Ca SiO

cooling

clinker

Inside a Cement Kiln

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sintering

C3Aforms

400ºC800ºC1500ºC

2 3 3 2 613003 Ca Al Oheat

CCaO Al O

cooling

clinker

Inside a Cement Kiln

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C4AFforms

400ºC800ºC1500ºC

3 2 6 2 3 4 2 2 10CaO Ca Al O Fe O Ca Al Fe O

cooling

clinker

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Cement Phases

Dicalcium silicateC2S (2CaO∙SiO2)

Tricalcium silicateC3S (3CaO∙SiO2)

Tricalcium aluminateC3A (3CaO∙Al2O3)

Tetracalcium aluminoferriteC4AF (4CaO∙Al2O3∙Fe2O3)

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Cement Phases(Taken from Cement and Concrete by M.S.J. Gani)

Cement Phases

TricalciumSilicate

50%

DicalciumSilicate

25%

Tricalcium Aluminate

12%

Tetracalcium Aluminoferrite

8%

Gypsum4%

Other1%

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Typical Percentages by Weight(Mindess and Young, 1981)

Cement Composition

Characteristic C3S C2S C3A C4AFRate of hydration Med Slow Fast SlowHeat of hydration Med Low High LowEarly strength High Low Med LowUltimate strength High High Low LowSulfate resistance Good Good Poor Good

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Responsiblefor

Short‐termHardening

Responsiblefor

Long‐termHardening

Responsiblefor

InitialSetting

Setting = transformation of cement paste from fluid to gel to solid

Hardening = gain in strength after concrete gel has become a solid

Rate of Strength Gain

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Hydration Chemistry

2 4 2 2 2 22 4 3 2 3Ca SiO H O CaO SiO H O Ca OH

dicalciumsilicate

water

calcium silicate hydrate

calciumhydroxidecrystals

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Hydration Chemistry

3 4 2 2 2 22 6 3 2 3 3Ca SiO H O CaO SiO H O Ca OH

tricalciumsilicate

water

calcium silicate hydrate

calciumhydroxidecrystals

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Hydration Chemistry

CS H CSH CH

calciumsilicate

water

calcium silicate hydrate

calciumhydroxidecrystals

Hydration Chemistry

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C‐S‐HCH

Cement Composition

Type Name C3S C2S C3A C4AFI Normal 50 24 11 8II Modified 42 33 5 13III High early 60 13 9 8IV Low heat 26 50 5 12V Sulfate-resistant 40 40 3.5 9

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Table 7-3

Rate of Heat Generation

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Time (days)

Rate of Strength Gain

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Setting Time Factors

amount of C3Aamount of CaSO4cement fineness } cement type

Effects of Fineness

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Source: www.theconstructioncivil.com

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Setting Time Factors

amount of C3Aamount of CaSO4cement fineness

amount of mixing wateramount of sun/wind

ambient temperature } placing conditions

} cement type

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Hardening Factors

amount of C3S

amount of C2S

ambient temperature

ambient humidity } curing conditions

} cement type

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Effects of Water Loss

Relative effects of water lossduring the first three days on28-day compressive strength

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Effects of Water Loss

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Effects of Water Loss

Stored in laboratory air after 3 days

Stored in laboratory air after 7 days

Stored continuously in laboratory air

Figure 7‐2

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Effects of Temperature

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Effects of Temperature

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Effects of Steam-Curing

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Important Properties

Compressive Strength (of mortar cubes)

Tensile Strength (of mortar briquettes)

Relative Density (assume 3.15)

Setting Times (Initial and Final)

Fineness

Soundness (volume change)

Air Content (of mortar)