chap_02

CHAPTER 2

Portland, Blended, and Other Hydraulic Cements

Portland cements are hydraulic cements composedprimarily of hydraulic calcium silicates (Fig. 2-1) that setand harden by reacting chemically with water. This chem-ical reaction is called hydration. When the paste (cement,air, and water) is added to aggregates (sand and gravel,crushed stone, or other granular material) it acts as anadhesive and binds the aggregates together to form astonelike mass, concrete, the worlds most versatile andmost widely used construction material.

Hydration begins as soon as cement comes in contactwith water. This chemical reaction produces cementhydrates, a product of hydration, which form on the sur-face of each cement particle. These cement hydrates grad-ually grow and spread until they interlock with othersattached to adjacent cement particles or adhere to othernearby substances. This ongoing hydration process resultsin progressive stiffening, hardening and strength develop-ment. Hydration continues as long as moisture and tem-perature conditions are favourable (curing) and space forhydration products is available.

The stiffening of concrete can be recognized by a loss ofworkability that usually occurs within three hours ofmixing, but is dependent upon the composition and fine-ness of the cement, the admixtures, the mixture propor-tions, and the temperature conditions. Subsequently, the

concrete sets and becomes hard. Most of the hydration andstrength development take place within the first month ofconcretes life cycle, but they continue, though more slowly,for a long time with adequate moisture and temperature;continuous strength increases exceeding 30 years have beenrecorded (Washa and Wendt 1975 and Wood 1992).

THE BEGINNING OF AN INDUSTRYEarly builders used clay to bind stones together into a solidstructure for shelter and protection. The oldest concrete dis-covered so far dates from around 7000 BC and was found in1985 when a concrete floor was uncovered during the con-struction of a road at Yiftah El in Galilee, Israel. It consistedof a lime concrete, made from burning limestone to producequicklime, which when mixed with water and stone, hard-ened to form concrete (Brown 1996 and Auburn 2000).

A cementing material was used between the stoneblocks in the construction of the Great Pyramid at Giza inAncient Egypt around 2500 BC. Some reports say it was alime mortar while others say the cementing material wasmade from burnt gypsum. By 500 BC, the art of makinglime-based mortar arrived in Ancient Greece. The Greeksused lime-based materials as a binder between stone andbrick and as a rendering material over porous limestonescommonly used in the construction of their temples andpalaces.

Examples of early Roman concrete have been founddating back to 300 BC. The very word concrete is derivedfrom the Latin word concretus meaning grown togetheror compounded. The Romans perfected the use of pozzolanas a cementing material. Sometime during the second cen-tury BC the Romans quarried a volcanic ash near Pozzuoli,thinking it was sand, they mixed it with lime and found themixture to be much stronger than they had produced pre-viously. This discovery was to have a significant effect onconstruction as the material was not sand, but a fine vol-canic ash containing silica and alumina, which combinedchemically with the lime to produce what became knownas pozzolanic cement. This material was used by builders of

Fig. 2-1. Portland cement is a fine powder that when mixedwith water becomes the glue that holds aggregates togetherin concrete. (IMG12628)

21

HOMEPAGE

portland cement and the first to have his product patented.However, in 1845, I. C. Johnson, of White and Sons,Swanscombe, England, claimed to have burned the cementraw materials with unusually strong heat until the mass wasnearly vitrified, producing a portland cement as we nowknow it. This cement became the popular choice during themiddle of the 19th century and was exported from Englandto various parts of the world. Production also began inBelgium, France, and Germany about the same time andexport of these products from Europe to North Americabegan about 1865.

Natural cement producers in northeastern UnitedStates produced the first portland cement in North Americain 1871 at a plant near Coplay, Pennsylvania. The firstimports of portland cement into Canada date back to 1877.Canadian producers of natural cement recognized the supe-riority of portland cement and made a determined effort tocompete by converting existing facilities to produce theproven material for local consumption. In 1889, C. B. Wright& Sons, Hull, Quebec, became the first producer of portlandcement in Canada. Almost at the same time Napanee CementWorks, Napanee, Ontario came on line producing portlandcement. This was followed shortly after by the construction oftwo new plants for the production of portland cement, one atShallow Lake, near Owen Sound, Ontario, and one atLongue Pointe, east of Montreal, Quebec. These four plantsare credited with much of the pioneer work in the develop-ment of the portland cement industry in Canada. The firstportland cement plant in western Canada was built by theCanadian Pacific Railway Company in Vancouver in 1893.

In 1900, cement production in Canada totaled 73,072tons (51,122 tons of portland cement and 21,950 tons of nat-ural rock cement (Canada Department of Mines 1920). Onehundred years later in 2000, there were 16 plants thatproduced a total of 12.8 million tonnes of cement in 15 loca-tions across Canada.

In the industrys early days each producer made port-land cement according to their own specifications. The firststandard was established in 1916 by the Canadian Societyfor Civil Engineering. Taking over the job for the develop-ment of standards, the Canadian Standards Association(CSA) produced its first standard for hydraulic cement in1922. All subsequent cement standards, including the cur-rent standard, A5-98, have been developed by CSA.

MANUFACTURE OF PORTLAND CEMENTBy definition, portland cement is a product obtained bypulverizing clinker consisting essentially of hydraulic cal-cium silicates to which various forms of calcium sulphate,limestone, water, and processing additions may be addedat the option of the manufacturer.

Unlike cement manufactured to meet ASTM specification C 150, Standard Specification for PortlandCement, the Canadian Standards Associations Technical Committee on Hydraulic Cement and

the famous Roman walls, aqueducts and other historicstructures including the Theatre at Pompeii (seating 20,000spectators), the Colosseum and the Pantheon in Rome.Pozzolan seems to have been ignored during the MiddleAges when building practices were much less refined thanearlier and the quality of cementing materials deteriorated.The practice of burning lime and the use of pozzolan wasnot introduced again until the 1300s.

Efforts to determine why some limes possesshydraulic properties while those made from essentiallypure limestones do not were not made until the 18th cen-tury. John Smeaton, often referred to as the father of civilengineering in England, concentrated his work in thisfield. He found that an impure, soft limestone, containingclay minerals made the best hydraulic cement. This com-bined with a pozzolan, imported from Italy, was used inhis project to rebuild the Eddystone Lighthouse in theEnglish Channel, southwest of Plymouth England. Theproject took three years to complete and began operationin 1759; it was recognized as a significant accomplish-ment in the development of the cement industry. A numberof discoveries followed as efforts within a growing naturalcement industry were now directed to the production of aconsistent quality material.

The difference between a hydraulic lime and naturalcement is a function of the temperature attained duringcalcination. Furthermore, a hydraulic lime can hydrate in alump form, whereas natural cements must be crushedand finely ground before hydration can take place. Naturalcement is stronger than hydraulic lime but weaker thanportland cement. Records indicate that lime and hydrauliccement were first produced in Canada as early as 1830 to1840 at a plant in Hull, Quebec.

The development of portland cement was the result ofpersistent investigation by science and industry to producea superior quality natural cement. The invention of port-land cement is generally credited to Joseph Aspdin, anEnglish mason. In 1824, he obtained a patent for his prod-uct, which he named portland cement because when set,

it resembled thecolour of the natu-ral limestone quar-ried on the Isle ofPortland in theEnglish Channel(Fig. 2-2) (Aspdin1824). The namehas endured and isused throughoutthe world, withmany manufactur-ers adding theirown trade or brandnames.

Aspdin wasthe first to pre-scribe a formula for

22

Design and Control of Concrete Mixtures EB101

Fig. 2-2. Isle of Portland quarry stone(after which portland cement wasnamed) next to a cylinder of modernconcrete. (IMG12472)

Supplementary Materials recognizes carbonate additionsfor some portland cements. At the option of the manufac-turer, a maximum of 5% addition of limestone is permittedfor Type 10, Normal portland cement, and for Type 30,High-early-strength portland cement. The limestone addi-tion must be of a quality suitable for the manufacture ofportland cement clinker.

Materials used in the manufacture of portland cementmust contain appropriate proportions of calcium, silica,alumina, and iron components. During manufacture,analyses of all materials are made frequently to ensure auniformly high quality cement.

While the operations of all cement plants are basicallythe same, no flow diagram can adequately illustrate allplants. There is no typical portland cement manufacturingplant; every plant has significant differences in layout,equipment, or general appearance (Fig. 2-3).

Selected rawmaterials (Table 2-1)are transported fromthe quarry (Fig. 2-4),crushed (Fig. 2-5),milled, and propor-tioned so that theresulting mixture hasthe desired chemicalcomposition. Theraw materials aregenerally a mixtureof calcareous (cal-cium oxide) mate-rial, such as lime-stone, chalk or shells,and an argillaceous(silica and alumina)material such as clay,shale, or blast-fur-nace slag. Either adry or a wet processis used (Fig. 2-6). Inthe dry process,grinding and blend-ing are done withdry materials. In the wet process, the grinding and blendingoperations are done with the materials mixed with water ina slurry form. In other respects, the dry and wet processesare very much alike. Fig. 2-7 illustrates important techno-logical developments that can improve significantly theproductivity and energy efficiency of dry-process plants.

After blending, the ground raw material is fed into theupper end of a kiln (Fig. 2-8). The raw mix passes throughthe kiln at a rate controlled by the slope and rotationalspeed of the kiln. Burning fuel (powdered coal, new or

23

Chapter 2 Portland, Blended, and Other Hydraulic Cements

Fig. 2-3. Aerial view of a cement plant. (IMG12442)

Fig. 2-5. Quarry rock is trucked to theprimary crusher. (IMG12436)

Fig. 2-4. Limestone, a primary rawmaterial providing calcium in makingcement, is quarried near the cementplant. (IMG12437)

Table 2-1. Sources of Raw Materials Used in Manufacture of Portland CementCalcium Iron Silica Alumina SulphateAlkali waste Blast-furnace flue dust Calcium silicate Aluminum-ore refuse* AnhydriteAragonite* Clay* Cement rock Bauxite Calcium sulphateCalcite* Iron ore* Clay* Cement rock Gypsum*Cement-kiln dust Mill scale* Fly ash Clay*Cement rock Ore washings Fullers earth Copper slagChalk Pyrite cinders Limestone Fly ash*Clay Shale Loess Fullers earthFullers earth Marl* GranodioriteLimestone* Ore washings LimestoneMarble Quartzite LoessMarl* Rice-hull ash Ore washingsSeashells Sand* Shale*Shale* Sandstone SlagSlag Shale* Staurolite

SlagTraprock

Note: Many industrial byproducts have potential as raw materials for the manufacture of portland cement.*Most common sources.

Clin

ker

Gyp

sum

Lim

esto

ne

Sand

Clay

Iron

ore

Lim

esto

ne

Sand

Clay

Iron

ore

3. Burning changes raw mix chemically into cement clinker.

Raw mix is kiln burned topartial fusion

Rotating kilnFan Dust bin

Dust collector

Materials arestored separately

Coal, oil, gas,or other fuel

Clinker and gypsum conveyedto grinding mills

Clinker

Clinker coolerAir

Gypsum

ToKKiillnn

Grinding mill

Oversize

Fines

Materials areproportioned

4. Clinker with gypsum is ground into portland cement and shipped.

Clin

ker

Gyp

sum

Airseparator Dust

collector

Cementpump Bulk storage Bulktruck

Bulkcar

Boxcar

TruckPackagingmachine

2. Raw materials are ground to powder and blended.

Raw materialsare proportioned

Dustcollector

Hot airfurnace

To pneumatic pump

Raw

mix

Fine

s

Dry mixing andblending silos

Ground rawmaterial storage

AirGrinding mill

To air separator

Overs

ize

Too Kiln

DDrryyyy

PPrrrroo

cceeee

ssss

OR

2. Raw materials are ground, mixed with water to form slurry, and blended.


Grinding mill

Wateraddedhere

Oversize

Too Killn

WWeeee

ttPP

rrrroocc

eeeess

ss

Slurrypumps

Slur

ry

Fine

s

Vibratingscreen

Slurry is mixed and blended Storage basinsSlurrypump

Drilling rigOverburden

To Crusher

To vib

rating

scree

n

Primary crusher

Limestone

Raw materials consist ofcombinations of limestone,cement rock, and shale, clay, sand, or iron ore

Shale

Secondary crusher

1. Stone is first reduced to 125 mm size, then to 20 mm, and stored.

Raw materials conveyedto grinding mills

Each raw materialis stored separately

Fig. 2-6. Steps in the traditional manufacture of portland cement.

24



Roller mill To pneumatic pump

Discharge

Raw

mixDust

collector

Dry mixing andblending silos

Ground rawmaterial storage

Topreheater

Air

2. Raw materials are ground to powder and blended.

Lim

esto

ne

Sand

Clay

Iron

ore

Feed

High-pressure grinding rolls(optional, usually used inconjunction with a ball mill)

Raw material

Detail of roller mill, which combines crushing, grinding,drying, and classifying in one vertical unit

Productdischargeport

Classifierblade

Gas intake port

Hot gas fromkiln, preheateror cooler

Feed sproutGrinding roller

3. Burning changes raw mix chemically into cement clinker. Note four-stage preheater, flash furnaces, and shorter kiln.

Hot gases from preheater or clinker cooler to raw mill

Raw material feed

Preheater. Hot gases from kiln heatraw feed and provide about 40%calcination before feed enters kiln

Some installations include a FlashFurnace that provides about 85% to 95%calcination before feed enters kiln

Tertiary air duct

Rotating kilnFan Dust bin

Dust collector

Materials arestored separately

Clinker and gypsum conveyedto grinding mills

Clinker

Clinker coolerAir

Gypsum

Exhaustgas

FanSecondaryAir

Ambientair

Grinding mill

Air

Solids

Cementpump Bulk storage Bulktruck

Bulkcar

Boxcar

TruckPackagingmachine

Milldischarge

Finished cementproduct to silo

Primary air frommill air sweep

Bucketelevatorto separator

Separator rejects(tails) return to millClinker

and gypsum

Highefficiencydustcollector

Materials areproportioned

Twin high-pressure rollpress to precrush clinkerentering the ball mill(optional)

High efficiencyseparator

Mill productand air

Cementproductand airto dustcollector

4. Clinker with gypsum is ground into portland cement and shipped.

Clin

ker

Gyp

sum

Drilling rigOverburden

To Crusher

To vib

rating

scree

n

Primary crusher

Limestone

Raw materials consist ofcombinations of limestone,cement rock, and shale, clay, sand, or iron ore

Shale

Secondary crusher

1. Stone is first reduced to 125 mm size, then to 20 mm, and stored.

Raw materials conveyedto grinding mills

Each raw materialis stored separately

Fig. 2-7. Steps in the modern dry-process manufacture of portland cement.

25


TYPES OF PORTLAND CEMENTAll portland and blended cements are hydrauliccements. Hydraulic cement is the broad term todescribe cements that set and harden by react-ing chemically with water and are capable ofdoing so under water. They also stay hard andmaintain their stability under water. Portlandcements are used in all aspects of concrete con-struction. Different types of portland cement aremanufactured to meet the various physical andchemical requirements needed for specificpurposes. In Canada, portland cements aremanufactured to meet the specifications ofthe Canadian Standards Association (CSA)Standard A5. Five types of portland cementare covered in CSA A5 and are identified asfollows:

Type 10 Normal portland cementType 20 Moderate portland cement*Type 30 High-early-strength portland

cementType 40 Low-heat of hydration portland

cementType 50 Sulphate-resistant portland

cement

Portland cements specified and used in the UnitedStates normally meet the requirements of ASTM C 150,Standard Specification for Portland Cement. ASTM Standardsare by far the most widely referenced and used specifica-tions for cement and other concrete related materials.ASTM C 1157, Performance Specification for HydraulicCements, provides for six types of portland cement, and arediscussed under Other Hydraulic Cements later in thischapter.

ASTM C 150 provides for eight types of portlandcement and uses Roman numeral designations as follows:

Type I NormalType IA Normal, air-entrainingType II Moderate sulphate resistanceType IIA Moderate sulphate resistance, air-

entrainingType III High early strengthType IIIA High early strength, air-entrainingType IV Low heat of hydrationType V High sulphate resistance

ASTM C 150 cement Types I, II, III, IV, and V are essen-tially the same as CSA A5 Types 10 through 50, respec-tively except for the allowance of up to 5% limestoneaddition in Type 10 and Type 30 cements.

*Moderate with respect to the heat of hydration or sulphate resistance.

recycled oil, gas, rubber tires, and by-product fuel) isforced into the lower end of the kiln where temperatures of1400C to 1550C change the raw material chemically intocement clinker, grayish-black pellets predominantly thesize of marbles (Fig. 2-9). Fig. 2-10 shows the clinker pro-duction process from raw feed to the final product.

The clinker iscooled and thenpulverized. Duringthis operation asmall amount ofgypsum (Fig. 2-11)is added to regulatethe setting time ofthe cement and toimprove shrinkageand strength de-velopment proper-ties (Lerch 1946 andTang 1992). In thegrinding mill clink-er is ground so finethat nearly all of itpasses through a 45m sieve. This ex-tremely fine graypowder is portlandcement (Fig. 2-1).

26


Fig. 2-8. Rotary kiln (furnace) for manufacturing portland cement clinker.Inset view inside the kiln. (IMG12307, IMG12435)

Fig. 2-11. Gypsum, a source of sul-phate, is interground with portlandclinker to form portland cement. Ithelps control setting, drying shrin-kage properties, and strength devel-opment. (IMG12489)

Fig. 2-9. Portland cement clinker isformed by burning calcium and sil-iceous raw materials in a kiln. Thisparticular clinker is about 20 mm indiameter. (IMG12434)

BKerkhoffVideo


27

H2O

H2O

CO2 CO2

CO2

To 700CRaw materialsare free-flowingpowder

700-900CPowderis stillfree-flowing

1150-1200CParticles startto becomesticky

1350-1450CAgglomerationand layering ofparticles continueas material fallson top of eachother.

Cooling

1200-1350CAs particles start toagglomerate, theyare held togetherby the liquid.The rotation ofthe kiln initiatescoalescing ofagglomerates andlayering of particles.

Upon cooling, theC3A and C4AFcrystallize in theliquid phase.Lamellarstructureappears inbelitecrystals

Belite crystalsdecreasein amount,increasein size.Aliteincreasesin sizeand amount.

Above 1250C,liquid phaseis formed.Liquid allowsreactionbetweenbelite andfree CaO toform alite.

When calcinationis complete,temperatureincreasesrapidly.Small belitecrystalsform fromcombinationof silicates and CaO.

Wateris lost.Dehydratedclay re-crystallizes

As calcination continues,free limeincreasesReactive silicacombines withCaO to beginforming C2S.Calcinationmaintainsfeed temperature at 850C.

Angular alite crystals

Round belite crystals

Free CaO

Clay particleLimestone particle

Cross-section view of kiln Nodulization process Clinkering reactionsParticles are solid.No reaction between particles.

Reactions start happeningbetween solid particles.

Particles are still solid.

Capillary forces of the liquid keepparticles together.

Clinker nodules remainunchanged duringcooling

Nodules will form withsufficient liquid.

Insufficientliquid will resultin dusty clinker.

Fig. 2-10. Process of clinker production from raw feed to the final product (Hills 2000).

A detailed review of the five types of portland cementscovered in CSA Standard A5, Portland Cement, follows:

Type 10Type 10 portland cement is a general-purpose cement suit-able for all uses where the special properties of other typesare not required. Its uses in concrete include pavements,floors, reinforced concrete buildings, bridges, tanks, reser-voirs, pipe, masonry units, and precast concrete products(Fig. 2-12).

Type 20 Type 20 portland cement is used where precaution againstmoderate sulphate attack is important. It is used in normalstructures or elements exposed to soil or ground waterswhere sulphate concentrations are higher than normalbut not unusually severe (see Table 2-2 and Figs. 2-13 to

28


Table 2.2 Requirements for Concrete Subjected to Sulphate Attack*Minimum Maximum

Water-soluble specified 56 day water-to- Cementingsulphate (SO4) Sulphate (SO4) compressive cementing Air materials

Class of Degree of in soil in groundwater strength, materials content to beexposure exposure sample, % samples, mg/L MPa ratio category used**

S-1 Very severe Over 2.0 Over 10,000 35 0.40 2 50S-2 Severe 0.20 to 2.0 1500 to 10,000 32 0.45 2 50S-3 Moderate 0.10 to 0.20 150 to 1500 30 0.50 2 20E, 40, or 50E

* For seawater exposure refer to CSA A23.1 Clause 15. Where supplementary cementing materials are used, the owner may specify other test ages. The owner shall specify the minimum 28-day compressive strength. For steel-troweled interior slabs on grade subject to sulphate attack but not freeze thaw, air entrainment is not required.

** When combinations of portland cement and supplementary cementing materials are used, they shall have been proven, to the satisfactionof the owner, to produce concrete resistant to the exposure conditions under consideration.

Cementing material combinations with equivalent performance may be used (Refer to CSA A23.1 Clauses 3.2, 3.3, and 3.4). Type 20E cement with moderate sulphate resistance (Refer to CSA A23.1 Clause 3.1.2).

Note: Type 50E cement shall not be used in reinforced concrete exposed to both chlorides and sulphates. Refer to CSA A 23.1 Clause 15.4.See CSA Test Methods A23.2-2B and A23.2-3B for test methods to determine sulphate ion content.

Source: CSA Standard A23.1

Fig. 2-12. Typical uses for normal or general use cements include(across, top left to bottom right) highway pavements, floors, bridges,and buildings. (IMG12488, IMG12487, IMG12486, IMG12485)

0 2 4 6 8 10 12 14 16Age, years

1

2

3

4

5

Visu

al ra

ting

ASTM Type V (Type 50)w/c = 0.37ASTM Type II (Type 20)w/c = 0.38ASTM Type I (Type 10)w/c = 0.39

Cement content = 390 kg/m3

0 2 4 6 8 10 12 14 16Age, years

1

2

3

4

5

Visu

al ra

ting

w/c = 0.38w/c = 0.47w/c = 0.68

Fig. 2-13. (top) Performance of concretes made with differentcements in sulphate soil. Type II (20) and Type V (50) cementshave lower C3A contents that provide improved sulphate re-sistance. (bottom) Improved sulphate resistance results fromlow water-to-cementing materials ratios as demonstrated overtime for concrete beams exposed to sulphate soils in a wettingand drying environment. Shown are average values forconcretes containing a wide range of cementing materials,including cement Types I, II, V (10, 20, 50), blended cements,pozzolans, and slags. See Fig. 2-15 for rating illustration and adescription of the concrete beams (Stark 2002).

2-15). Type 20 cement has moderate sulphate resistantproperties because it contains no more than 7.5% tri-calcium aluminate (C3A).

Sulphates in moist soil or water may enter the concreteand develop expansive reactions with the hydrated C3A,resulting in expansion, scaling, and cracking of concrete.Some sulphate compounds, such as magnesium sulphate,directly attack calcium silicate hydrate. Wetting and dryingin a sulphate environment aggravates the formation of sul-phate salts or compounds that have sufficient crystalliza-tion pressure to disrupt cement paste.

Use of Type 20 cement must be accompanied by theuse of a low water to cementing materials ratio and lowpermeability to control sulphate attack. Fig. 2-13 illustratesthe improved sulphate resistance of a Type 20 (Type II)cement over a Type 10 (Type I) cement.

Concrete exposed to seawater is often made with Type20 cement. Seawater contains significant amounts of sul-phates and chlorides. Although sulphates in seawater arecapable of attacking concrete, the presence of chloridesinhibits the expansive reaction that is characteristic of sul-phate attack. Calcium sulphoaluminate (ettringite) andother sulphate compounds, the reaction products of sul-phate attack, are more soluble in a chloride solution andmore readily leach out of the concrete, thus resulting in lessdestructive expansion. This is the major factor explainingobservations from a number of sources that the perform-ance of concretes in seawater with portland cementshaving C3A contents as high as 10%, and sometimesgreater, have shown satisfactory durability, providing thepermeability of the concrete is low and the reinforcing steelhas adequate cover (Zhang, Bremner, and Malhotra 2003).

Type 20 cements specially manufactured to meet themoderate heat option of CSA A5 will generate less heat at aslower rate than Type 10 cement. The requirement of mod-erate heat of hydration can be specified at the option of thepurchaser. If heat-of-hydration maximums are specified,

29


Fig. 2-14. Moderate sulphate resistant cements and high sulphate resistant cements improve the sulphate resistance of concrete elements,such as (left to right) slabs on ground, pipe, and concrete posts exposed to high-sulphate soils. (IMG12484, IMG12483, IMG12482)

Fig. 2-15. Specimens used in the outdoor sulphate test plotin Sacramento, California, are 150 x 150 x 760-mm beams. Acomparison of ratings is illustrated: (top) a rating of 5 for 12-year old concretes made with Type V (50) cement and awater-to-cement ratio of 0.65; and (bottom) a rating of 2 for16-year old concretes made with Type V (50) cement and awater-to-cement ratio of 0.39 (Stark 2002).(IMG12481, IMG12480)

Type 40 Type 40 portland cement is used where the rate andamount of heat generated from hydration must be mini-mized. It develops strength at a slower rate than othercement types. Type 40 cement is intended for use in mas-sive concrete structures, such as large gravity dams, wherethe temperature rise resulting from heat generated duringhardening must be minimized (Fig. 2-16). Type 40 cementis generally only available by specific request for large proj-ects.

Type 50 Type 50 portland cement is used in concrete exposed tosevere sulphate actionprincipally where soils or ground-waters have a high sulphate content (Figs. 2-13 to 2-15). Itgains strength more slowly than Type 10 cement. Table 2-2lists sulphate concentrations requiring the use of Type 50cement. The high sulphate resistance of Type 50 cement isattributed to a low tricalcium aluminate content, not morethan 3.5%. Use of a low water to cementing materials ratioand low permeability are critical to the performance of anyconcrete exposed to sulphates. Even Type 50 cement con-crete cannot withstand a severe sulphate exposure if theconcrete has a high water to cementing materials ratio (Fig.2-15 top). Type 50 cement, like other portland cements, isnot resistant to acids and other highly corrosive sub-stances. The chemical and physical requirements for Type50 cement are given in CSA A5.

White Cement White portland cement is a true portland cement that dif-fers from gray cement chiefly in colour. It is made to con-form to the specifications of CSAA5 (ASTM C 150), usuallyType 10 or Type 30; the manufacturing process is controlled

this cement can be used in structures of considerable mass,such as large piers, large foundations, and thick retainingwalls (Fig. 2-16). Its use will reduce temperature rise andtemperature related cracking, which is especially impor-tant when concrete is placed in warm weather.

Type 30 Type 30 portland cement provides high strengths at anearly period, usually a week or less. It is chemically andphysically similar to Type 10 cement, except that its par-ticles have been ground finer. It is used when forms needto be removed as soon as possible or when the structuremust be put into service quickly. In cold weather its usepermits a reduction in the length of the curing period (Fig.2-17). Although higher-cement content mixes of Type 10cement can be used to gain high early strength, Type 30may provide it easier and more economically.

30


Fig. 2-16. Moderate heat and low heat cements minimize heatgeneration in massive elements or structures such as (left) verythick bridge supports, and (right) dams. Hoover dam, shownhere, used a Type 40 cement to control temperature rise.IMG12479, IMG12478)

Fig. 2-17. High early strength cements are used where early concrete strength is needed, such as in (left to right) cold weatherconcreting, fast track paving to minimize traffic congestion, and rapid form removal for precast concrete.(IMG12350, IMG12477, IMG12476)

so that the finished product will be white. White portlandcement is made of selected raw materials containing negli-gible amounts of iron and magnesium oxidesthe sub-stances that give cement its gray colour. White portlandcement is used primarily for architectural purposes such asprecast curtain walls and facing panels, terrazzo surfaces,stucco, cement paint, tile grout, and decorative concrete(Fig. 2-18). Its use is recommended wherever white orcoloured concrete, grout, or mortar is desired.

BLENDED HYDRAULIC CEMENTSBlended cements are used in all aspects of concrete con-struction in the same manner as portland cements.Blended cements can be used as the only cementing mate-rial in concrete or they can be used in combination withother supplementary cementing materials added at theconcrete plant. Blended cements are often designed to beused in combination with local pozzolans and slags. If ablended cement or portland cement is used alone or incombination with added pozzolans or slags, the concreteshould be tested for strength, durability, and other proper-ties required in project specifications (PCA 1995 andDetwiler, Bhatty, and Bhattacharja 1996).

Blended hydraulic cements are produced by inti-mately and uniformly intergrinding or blending two ormore types of fine materials. The primary materials areportland cement, ground granulated blast-furnace slag, flyash, silica fume, calcined clay, and other pozzolans,hydrated lime, and preblended cement combinations ofthese materials (Fig. 2-19). Blended hydraulic cementsmanufactured in Canada conform to the requirements ofCSA Standard A362 Blended Hydraulic Cement. In UnitedStates blended cements are covered under ASTM C 595,Specification For Blended Hydraulic Cements, and ASTM C1157, Performance Specification for Hydraulic Cement.

Blended hydraulic cement as defined by CSA A362 isa product consisting of a mixture of portland cement andone or more of granulated blast-furnace slag, fly ash, orsilica fume to which no processing additions have been

made except as permitted and noted in Clause 3.2 of theStandard.

The four types of blended hydraulic cementsaddressed in CSA A362 are:

Portland blast-furnace slag cement (S)Portland fly ash cement (F)Portland silica fume cement (SF)Ternary blend cement

These blended products are produced by either of thefollowing methods or a combination of both: (a) by inter-grinding portland cement clinker and blast-furnace slag,fly ash, or silica fume; or (b) by blending portland cementand finely ground granulated blast-furnace slag, fly ash, orsilica fume.

Blended hydraulic cements may develop lower earlycompressive strengths than the corresponding portlandcement. This effect is more pronounced as the proportionof slag or fly ash is increased. When a portland silica fumecement is used, experience indicates that early strengths

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Fig. 2-19. Blended cements CSA A362 (ASTM C 595 andASTM C 1157) use a combination of portland cement orclinker and gypsum blended or interground with pozzolans,slag, or fly ash. Shown is blended cement (centre)surrounded by (right and clockwise) clinker, gypsum,portland cement, fly ash, slag, silica fume, and calcined clay.(IMG12473)

Fig. 2-18. White portland cement is used in white or light-coloured architectural concrete, ranging from (left to right) terrazzo forfloors shown here with white cement and green granite aggregate (IMG12475), to decorative and structural precast and cast-in-place elements (68981), to building exteriors. The far right photograph shows a white precast concrete building housing theASTM Headquarters in West Conshohocken, Pennsylvania. Photo courtesy of ASTM.


are frequently higher than the strength of the correspon-ding portland cement.

The nomenclature and naming practice used forblended cements is as follows:

TE-A/B where

T = the equivalent performance to Type 10, 20, 30, 40,or 50 portland cement;

E = an indication that the cement has equivalent per-formance for the physical properties specified inCSA A362, Table 2;

A = the predominant supplementary material; andB = the secondary supplementary material, only spe-

cified in a ternary blend.Examples:

10E-S is a portland blast furnace slag cement having anequivalent performance to that of a Type 10 portlandcement.

40E-F is a portland fly ash cement having an equivalentperformance to that of a Type 40 portland cement.

50E-S/SF is a ternary blend cement having an equivalentperformance to that of a Type 50 portland cement with slagbeing the predominant supplementary cementing materialand silica fume the secondary supplementary cementingmaterial.

Portland Blast-Furnace Slag CementPortland blast-furnace slag cement, Type 10E-S, 20E-S,30E-S, 40E-S, or 50E-S, is a product consisting of portlandcement and finely ground, granulated blast-furnace slag inwhich the slag content is greater than 0 and less than 70%of the total mass. Blast-furnace slag, also known as ironblast-furnace slag, is the nonmetallic product, consistingessentially of silicates and alumino-silicates of calcium andother bases, that is developed in a molten condition simul-taneously with iron in a blast furnace. Granulation of theslag is achieved by immersing the molten slag in water orpelletizing the molten slag to produce a high percentage ofglass (a process called vitrification).

Portland Fly Ash CementPortland fly ash cement, Type 10E-F, 20E-F, 30E-F, 40E-F, or50E-F, is a product consisting of portland cement and flyash in which the fly ash content is greater than 0 and lessthan 40% of the total mass. Fly ash is the finely dividedresidue that results from the combustion of pulverized coaland which is carried from the combustion chamber of afurnace by the exhaust gases.

Portland Silica Fume CementPortland silica fume cement, Type 10E-SF, 20E-SF, 30E-SF,40E-SF, or 50E-SF, is a product consisting of portlandcement and silica fume in which the silica fume contentdoes not exceed 10% of the total mass. Silica fume is the

finely divided residue resulting from the production of sil-icon, ferro-silicon, or other silicon-containing alloys that iscarried from the burning surface area of an electric-arc fur-nace by exhaust gases. In some cases purchasers mayrequest silica fume contents in excess of 10% for specificapplications such as shotcrete. Cements manufactured tofulfill such requests are beyond the scope of CSA A362,Blended Hydraulic Cement.

Ternary Blended CementTernary blended cement, Type 10E-A/B, 20E-A/B, 30E-A/B, 40E-A/B, or 50E-A/B, is a product consisting of port-land cement and a combination of two of the following:finely granulated blast-furnace slag, fly ash, or silica fume.The total supplementary cementing material content isgreater than 0 and less than or equal to 70% of the totalmass; the slag content must be less than 70% of the totalmass, the fly ash content less than 40% of the total mass;and the silica fume content less than 10% of the total mass.

OTHER HYDRAULIC CEMENTSThe 1990s saw the creation of the worlds first performancespecification for hydraulic cementsASTM C 1157,Performance Specification for Hydraulic Cements. This specifi-cation is designed generically for hydraulic cement toinclude portland cement, modified portland cement, andblended hydraulic cement. Cements meeting the require-ments of C 1157 meet physical performance test require-ments, as opposed to prescriptive restrictions oningredients or cement chemistry as found in other cementspecifications. ASTM C 1157 provides for six types ofhydraulic cement as follows:

Type GU General useType HE High early strengthType MS Moderate sulphate resistanceType HS High sulphate resistanceType MH Moderate heat of hydrationType LH Low heat of hydration

In addition, these cements can also have an Option RLow Reactivity with Alkali-Reactive Aggregates speci-fied to help control alkali-silica reactivity. For example,Type GU-R would be a general use hydraulic cement withlow reactivity with alkali-reactive aggregates.

When specifying a C 1157 cement, the specifier usesthe nomenclature of hydraulic cement, portlandcement, modified portland cement or blendedhydraulic cement along with a type designation. Forexample, a specification may call for a Hydraulic CementType GU, a Blended Hydraulic Cement Type MS, or aPortland Cement Type HS. If a type is not specified, thenType GU is assumed.

ASTM C 1157 defines a blended cement as havingmore than 15% mineral additive and a modified portlandcement as containing up to 15% mineral additive. The min-

32

33


Table 2-3. Applications for Commonly Used CementsApplications*

Moderate Moderate Resistance toCement General heat of High early Low heat of sulphate High sulphate alkali-silica

specification purpose hydration strength hydration resistance resistance reactivity (ASR)**CSA A5 10 20 30 40 20 50

ASTM C 150 I II III IV II VLow alkali option

CSA A362 10E-S 20E-S 30E-S 40E-S 20E-S 50E-S10E-F 20E-F 30E-F 40E-F 20E-F 50E-F

10E-SF 20E-SF 30E-SF 40E-SF 20E-SF 50E-SFTernary Ternary Ternary Ternary Ternary Ternary10E-A/B 20E-A/B 30E-A/B 40E-A/B 20E-A/B 50E-A/B

Low

ASTM C 595 IS IS(MH) P(LH) IS(MS)reactivity

IP IP(MH) IP(MS)option

I(PM) I(PM)(MH) P(MS)I(SM) I(SM)(MH) I(PM)(MS)S, P I(SM)(MS)

Performancestandard

ASTM C 1157 GU MH HE LH MS HS Option Rhydraulic cements***

* Check the local availability of specific cements as all cements are not available everywhere. ** The option for low reactivity with ASR susceptible aggregates can be applied to the cement types in the columns to the left.

*** For ASTM C 1157 cements, the nomenclature of hydraulic cement, portland cement, air-entraining portland cement, modified portland cement, orblended hydraulic cement is used with the type designation.

used in the same manner as Type 20 portland cement(Fig. 2-14). Like Type 20, Type MS cement concrete must bemade with a lower water-cementing materials ratio to pro-vide sulphate resistance.

Type HSType HS cement is used in concrete exposed to severe sul-phate actionprincipally where soils or ground watershave a high sulphate content (see Table 2-2). It is used inthe same manner as Type 50 portland cement (Fig. 2-14).

Type MHType MH cement is used where the concrete needs to havea moderate heat of hydration and a controlled temperaturerise. Type MH cement is used in the same manner as amoderate heat Type 20 portland cement (Fig. 2-16).

Type LHType LH cement is used where the rate and amount of heatgenerated from hydration must be minimized. It developsstrength at a slower rate than other cement types. Type LHcement is intended for use in massive concrete structureswhere the temperature rise resulting from heat generatedduring hardening must be minimized. It is used in thesame manner as Type 40 portland cement (Fig. 2-16).

Table 2-3 provides a matrix of commonly usedcements and where they are used in concrete construction.

eral additive usually prefixes the modified portlandcement nomenclature, for example, slag-modified port-land cement.

ASTM C 1157 also allows a strength range to be speci-fied from a table in the standard. If a strength range is notspecified, only the minimum strengths apply. Strengthranges are rarely applied in the United States.

A detailed review of ASTM C 1157 cements follows:

Type GUType GU is a general-purpose cement suitable for all useswhere the special properties of other types are notrequired. Its uses in concrete include pavements, floors,reinforced concrete buildings, bridges, pipe, precast con-crete products, and other applications where Type 10 isused (Fig. 2-12).

Type HEType HE cement provides high strengths at an early age,usually a week or less. It is used in the same manner asType 30 portland cement (Fig. 2-17).

Type MSType MS cement is used where precaution against moder-ate sulphate attack is important, as in drainage structureswhere sulphate concentrations in ground waters are higherthan normal but not unusually severe (see Table 2-2). It is

Air-Entraining Portland CementsSpecifications for three types of air-entraining portlandcement (Types IA, IIA, and IIIA) are given in ASTM C 150.They correspond in composition to ASTM Types I, II, andIII, respectively, except that small quantities of air-entrain-ing material are interground with the clinker during man-ufacture. These cements produce concrete with improvedresistance to freezing and thawing. Such concrete containsminute, well-distributed, and completely separated airbubbles. Air entrainment for most concrete is achievedthrough the use of an air-entraining admixture, rather thanthrough the use of air-entraining cements. Air-entrainingcements are available only in certain areas. Air-entrainingcements are not covered by CSA and are not manufacturedin Canada.

MODIFIED PORTLAND CEMENTSThe term modified portland cement usually refers to ablended cement containing mostly portland cement alongwith a small amount of mineral additive. However, somelocal areas have modified portland cements that do not con-tain a mineral additive. The modification merely refers to aspecial property that cement has or a cement that has thecharacteristics of more than one type of portland cement.

HYDRAULIC SLAG CEMENTS(Cementitious Hydraulic Slag)Hydraulic slag cements are like other cements that set andharden by a chemical interaction with water. Concretemade with hydraulic slag cement is used for the sameapplications as concrete made with other hydrauliccements. Hydraulic slag cement (defined by CSA asCementitious Hydraulic Slag) is the product obtained bypulverizing a granulated blast-furnace slag that possesseshydraulic properties, and to which various forms of cal-cium sulphate and processing additions may be added atthe option of the manufacturer. The blast-furnace slag usedis the nonmetallic product, consisting essentially of sili-cates and alumino-silicates of calcium and other bases,which is developed in a molten condition simultaneouslywith iron in a blast furnace. When the molten blast-furnaceslag is chilled rapidly, a glassy granular material is formedwhich is known as granulated blast-furnace slag. Com-bining cementitious hydraulic slag with water producesessentially the same binding material (calcium silicatehydrate) that portland cement alone makes when com-bined with water. Cementitious Hydraulic Slag conformsto CSA Standard A363.

SPECIAL CEMENTSSpecial cements are produced for particular applications. Anumber of the other special cements described, althoughnot covered by CSA, have been used for specific applica-tions throughout the country. Table 2-4 summarizes anumber of special cements and their applications.

Masonry CementsMasonry cement is manufactured in Canada and coveredby CSA Standard A8, Masonry Cement. Masonry cementsare hydraulic cements designed for use in mortar formasonry construction (Fig. 2-20). They are a mixture ofportland cement, air entraining materials, and plasticizingmaterials (such as limestone or hydrated or hydrauliclime), together with other materials introduced to enhanceone or more properties such as setting time, workability,water retention, and durability. These materials are propor-tioned and packed at a cement plant under controlled con-ditions to assure uniformity of performance.

Masonry cements meet the requirements of CSA A8(ASTM C 91), which classifies them as Type N masonrycement and Type S masonry cement.

Type N masonry cement is for use in the preparationof Type N masonry mortar, or with the use of portlandcement additions it is capable of producing Type S mortar asspecified in CSA Standard A179, Mortar and Grout for UnitMasonry.

Type S masonry cement is for use in the preparation ofType S masonry mortar as specified in CSA A179, withoutthe use of portland cement additions.

The workability, strength, and colour of masonrycements stay at a high level of uniformity because of man-ufacturing controls. In addition to mortar for masonry con-struction, masonry cements are used for parging andportland cement based plaster (stucco) (Fig. 2-21) con-struction (see ASTM C 926). Masonry cement must never beused for making concrete.

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Fig. 2-20. Masonry cement and mortar cement are used tomake mortar to bond masonry units together. (IMG12471)

35


Fig. 2-21. Masonry cement and plastic cement are used to make plaster or stucco for commercial, institutional, and residential build-ings. Shown are a church and home with stucco exteriors. Inset shows a typical stucco texture. (IMG12470, IMG12469, 68805)

Table 2-4. Applications for Special CementsSpecial cements Type Application

White portland cements, ASTM C 150 I, II, III, V White or coloured architectural concrete, masonry, CSA A5 10 mortar, grout, plaster, and stuccoWhite masonry cements, ASTM C 91 M, S, N White or coloured mortar between masonry unitsCSA A8 N, SMasonry cements, ASTM C 91 M, S, N Mortar between masonry units,*CSA A8 N, S plaster, and stuccoMortar cements, ASTM C 1329 M, S, N Mortar between masonry unitsPlastic cements, ASTM C 1328 M, S Plaster and stucco**Expansive cements, ASTM C 845 E-1(K), E-1(M), E-1(S) Shrinkage compensating concreteOil-well cements, API-10 A, B, C, D, E, F, G, H Grouting wellsWaterproof cements Tile grout, paint, and stucco finish coatsRegulated-set cements Early strength and repair***Cements with functional General concrete construction needing specialadditions, see ASTM C 595 characteristics such as; water-reducing, retarding,and ASTM C 1157 air entraining, set control, and accelerating propertiesUltrafine cement Geotechnical grouting***Calcium aluminate cement Repair, chemical resistance, high

temperature exposuresMagnesium phosphate cement Repair and chemical resistanceGeopolymer cement General construction, repair, waste stabilizationEttringite cements Waste stabilizationSulphur cements Repair and chemical resistanceRapid hardening hydraulic cement VH, MR, GC General paving where very rapid (about 4 hours)

strength development is required

Mortar CementsMortar cements are hydraulic cements designed for usein mortar for masonry construction (Fig. 2-20). They con-sist of a mixture of portland cement or blended hydrauliccement and plasticizing materials together with othermaterials introduced to enhance one or more propertiessuch as setting time, workability, water retention anddurability. These components are proportioned at the

cement plant under controlled conditions to assure uni-formity of performance.

Mortar cements meet the requirements of ASTMC 1329, which also classifies mortar cements as Type N, TypeS, and Type M. A brief description of each type follows:

Type N mortar cements are used in ASTM C 270 TypeN and Type O mortars. They may also be used with port-land or blended cements to produce Type S and Type Mmortars.

* CSA portland cement Types 10, 20, 30 and ASTM Types I, II, and III and blended cement Types IS, IP, and I(PM) are also used in making mortar.** CSA portland cement Types 10, 20, 30 and ASTM Types I, II, and III and blended cement Types IP, I(SM) and I(PM) are also used in making plaster.

*** Portland and blended hydraulic cements are also used for these applications.

36


Type S mortar cements areused in ASTM C 270 Type Smortar. They may also be usedwith portland or blended ce-ments to produce Type M mortar.

Type M mortar cements areused in ASTM C 270 Type Mmortar without the addition ofother cements or hydrated lime.

Types N, S, and M generallyhave increasing levels of portlandcement and higher strength, TypeM having the highest strength.Type N is used most commonly.

The increased use of masonryin demanding structural applica-tions and high seismic areasresulted in the recent development of mortar cement.Mortar cement is similar to masonry cement in that it is afactory-prepared cement primarily used to producemasonry mortar. However, ASTM C 1329 places lowermaximum air content limits on mortar cement than per-mitted for masonry cements and ASTM C 1329 is the onlyASTM masonry material specification that includes bondstrength performance criteria.

The workability, strength, and colour of mortarcements stay at a uniform level because of manufacturingcontrols. In addition to mortar for masonry construction,mortar cements are also used for parging. Mortar cementmust never be used for making concrete.

Plastic Cements

Plastic cement is a hydraulic cement that meets therequirements of ASTM C 1328. It is used to make portlandcement-based plaster or stucco (see ASTM C 926) in theSouthwest and west coast area of the United States (Fig. 2-21). Plastic cements consist of a mixture of portland andblended hydraulic cement and plasticizing materials (suchas limestone, hydrated or hydraulic lime), together withmaterials introduced to enhance one or more propertiessuch as setting time, workability, water retention, and durability.

ASTM C 1328 defines separate requirements for aType M and a Type S plastic cement with Type M havinghigher strength requirements. The Uniform Building Code,UBC 25-1, does not classify plastic cement into differenttypes, but defines just one set of requirements which cor-respond to those of an ASTM C 1328 Type M plasticcement. When plastic cement is used, no lime or other plas-ticizer may be added to the plaster at the time of mixing.

The term plastic in plastic cement does not refer tothe inclusion of any organic compounds in the cement;rather, plastic refers to the ability of the cement to impartto the plaster a high degree of workability. Plaster madefrom this cement must remain workable for a long enoughtime for it to be reworked to obtain the desired densificationand texture. Plastic cement should not be used to make con-crete. For more information on the use of plastic cement andplaster, see Melander and Isberner (1996).

Finely-Ground Cements (Ultrafine Cements)Finely-ground cements, also called ultrafine cements, arehydraulic cements that are ground very fine for use ingrouting into fine soil or thin rock fissures (Fig. 2-22). Thecement particles are less than 10 m in diameter with 50%of particles less than 5 m. Blaine fineness often exceeds800 m2/kg. These very fine cements consist of portlandcement, ground granulated blast-furnace slag, and othermineral additives.

Expansive CementsExpansive cement is a hydraulic cement that expandsslightly during the early hardening period after setting. Itmust meet the requirements of ASTM C 845 in which it isdesignated as Type E-1. Currently, three varieties of expan-sive cement are recognized and have been designated as K,M, and S, which are added as a suffix to the type. TypeE-1(K) contains portland cement, anhydrous tetracalciumtrialuminosulphate, calcium sulphate, and uncombined cal-cium oxide (lime). Type E-1(M) contains portland cement,calcium aluminate cement, and calcium sulphate. Type E-1(S) contains portland cement with a high tricalcium alumi-nate content and calcium sulphate. Type E-1(K) is the mostreadily available expansive cement in North America.

Expansive cement may also be made of formulationsother than those mentioned. The expansive properties ofeach type can be varied over a considerable range. Type 10cement may be transformed into expansive cement by theaddition of an expansive admixture at the ready mix plant.

When expansion is restrained, for example by reinforc-ing steel, expansive cement concrete (also called shrinkagecompensating concrete) can be used to (1) compensate forthe volume decrease due to drying shrinkage, (2) inducetensile stress in reinforcement (post-tensioning), and (3) sta-bilize the long-term dimensions of post-tensioned concretestructures with respect to original design.

Fig. 2-22. (left) A slurry of finely ground cement and water can be injected into theground, as shown here, to stabilize in-place materials, to provide strength for foun-dations, or to chemically retain contaminants in soil. (IMG12468) Illustration (right) ofgrout penetration in soil.

One of the major advantages of using expansivecement in concrete is noted in (1) above; when you cancompensate for volume change due to drying shrinkageyou can control and reduce drying shrinkage cracks. Fig.2-23 illustrates the length change (early expansion anddrying shrinkage) history of shrinkage-compensating con-crete and conventional portland cement concrete. For moreinformation see Pfeifer and Perenchio (1973), Russell(1978), and ACI (1998).

Oil-Well CementsOil-well cements, used for oil-well grouting, often calledoil-well cementing, are usually made from portland ce-ment clinker or from blended hydraulic cements. Gener-ally they must be slow setting and resistant to hightemperatures and pressures. The American PetroleumInstitute Specification for Cements and Materials for WellCementing (API Specification 10A) includes requirementsfor eight classes of oil-well cements (Classes A through H)and three grades (Grades Oordinary, MSRmoderatesulphate resistant, and HSRhigh sulphate resistant).Each class is applicable for use at a certain range of welldepths, temperatures, pressures, and sulphate environ-ments. The petroleum industry also uses conventionaltypes of portland cement with suitable cement-modifiers.Expansive cements have also performed adequately aswell cements.

Cements with Functional AdditionsFunctional additions can be interground with cementclinker to beneficially change the properties of hydrauliccement. These additions must meet the requirements ofASTM C 226 or C 688. ASTM C 226 addresses air-entrain-

37


0.10

0.08

0.06

0.04

0.02

0

-0.02

-0.04

-0.06

Leng

th c

hang

e, p

erce

nt

0 7 50 100 150 200Time, days

Moist-cured for 7 days, followed byair drying at 23CRestrained by reinforcing steel, p=0.35%

Shrinkage-compensatingconcrete

Portland cementconcrete

Fig. 2-23. Length-change history of shrinkage compensatingconcrete containing Type E-1(S) cement and Type I (Type 10)portland cement concrete (Pfeifer and Perenchio 1973).

ing additions. ASTM C 688 addresses the following typesof additions: water-reducing, retarding, accelerating, waterreducing and retarding, water reducing and accelerating,and set control additions. Cement specifications ASTM C595 and C 1157 allow functional additions. These cementscan be used for normal or special concrete construction,grouting, and other applications.

Water-Repellent CementsWater-repellent cement, sometimes called waterproofedcement, is usually made by adding a small amount ofwater-repellent additive such as stearate (sodium, alu-minum, or other) to cement clinker during its final grind-ing (Lea 1971). Manufactured in either white or graycolour, it reduces capillary water transmission under littleto no pressure but does not stop water-vapor transmission.It is used in tile grouts, paint, and stucco finish coats.

Regulated-Set CementsRegulated-set cement is a calcium fluoroaluminatehydraulic cement that can be formulated and controlled toproduce concrete with setting times from a few minutes toan hour and with corresponding rapid early strengthdevelopment (Greening and others 1971). It is a portland-based cement with functional additions that can be manu-factured in the same kiln used to manufactureconventional portland cement. Regulated-set cementincorporates set control and early-strength-developmentcomponents. Final physical properties of the resulting con-crete are in most respects similar to comparable concretesmade with portland cement.

Geopolymer CementsGeopolymer cements are inorganic hydraulic cements thatare based on the polymerization of minerals (Davidovits,Davidovits and James 1999). The term more specificallyrefers to alkali-activated alumino-silicate cements, alsocalled zeolitic cements. They have been used in generalconstruction, high-early strength applications, and wastestabilization. These cements do not contain organic poly-mers or plastics.

Ettringite CementsEttringite cements are calcium sulphoaluminate cementsthat are specially formulated for particular uses, such asthe stabilization of waste materials (Klemm 1998). Theycan be formulated to form large amounts of ettringite tostabilize particular metallic ions within the ettringite struc-ture. Ettringite cements have also been used in rapid set-ting applications, including use in coal mines. Also seeprevious discussion on Expansive Cements.

Sulphur CementsSulphur cement is used to make sulphur cement concretefor repairs and chemically resistant applications. Sulphurcement melts at temperatures between 113C and 121C.Sulphur concrete is maintained at temperatures around130C during mixing and placing. The material gainsstrength quickly as it cools and is resistant to acids andaggressive chemicals. Sulphur cement does not containportland or hydraulic cement.

Rapid Hardening CementsRapid hardening, high-early strength, hydraulic cement isused in construction applications, such as fast-trackpaving, where fast strength development is needed (designor load carrying strength in less than three hours). Thesecements often use calcium sulphoaluminate to obtain earlystrength. They are classified as Types VH (very high-earlystrength), MR (middle range high-early strength), and GC(general construction).

SELECTING AND SPECIFYING CEMENTSWhen specifying cements for a project, be sure to check theavailability of cement types and allow the specifications tobe flexible in cement selection. Cements with special prop-erties should not be required unless special characteristicsare necessary. In addition, the use of supplementarycementing materials should not inhibit the use of any par-ticular portland or blended cement. The project specifica-tions should focus on the needs of the concrete structureand allow use of a variety of materials to accomplish thoseneeds. A typical specification may call for portland cementsmeeting CSA A5 (ASTM C 150 or C 1157) or for blendedcements meeting CSA A362 (ASTM C 595 or C 1157).

If no special properties (such as low-heat generationor sulphate attack) are required, all general use cementsshould be allowed. See Tables 2-3 and 2-4 for guidance onusing different cements.

Availability of CementsSome types of cement may not be readily available in allareas of Canada. Before specifying a type of cement, itsavailability should be determined.

CSAA5 Type 10 (ASTM C 150 Type I) portland cementis usually carried in stock and is furnished when there isnot a specific type of cement specified. Type 20 (Type II)cement is usually available where moderate sulphateresistance is needed. Type 30 (Type III) cement and whitecement are usually available in most areas. Type 40 (TypeIV) cement is manufactured only when specified for par-ticular projects (massive structures like dams) and there-fore is usually not readily available. Type 50 (Type V)cement is only readily available in particular parts ofCanada where it is needed to resist high sulphate environ-ments. Masonry cement is available in most areas.

Calcium Aluminate CementsCalcium aluminate cement is not portland cement-based.It is used in special applications for early strength gain(design strength in one day), resistance to high tempera-tures, and resistance to sulphates , weak acids, and seawa-ter. Portland cement and calcium aluminate cementcombinations have been used to make rapid setting con-cretes and mortars. Typical applications for calcium alumi-nate cement concrete include: chemically resistant, heatresistant and corrosion resistant industrial floors, refrac-tory castables; and repair applications. Standards address-ing these cements include British Standard BS 915-2 orFrench Standard NF P15-315.

The hydrates responsible for the rapid hardening andearly strength gain change over time, resulting in a loss ofstrength. This process, called conversion, always occurs.The process involves the conversion of the less stablehexagonal calcium aluminate hydrate (CAH10) to stablecubic tricalcium aluminate hydrate (C3AH6), hydrous alu-mina (AH3), and water. With time and particular moistureconditions and temperatures, this conversion causes a 53%decrease in volume of hydrated material. However, thisinternal volume change occurs without a dramatic alter-ation of the overall dimensions of a concrete element,resulting in increased paste porosity and decreased com-pressive strength. At low water-cement ratios, there isinsufficient space for all the calcium aluminate to react andform CAH10. The water released from conversion reactswith more calcium aluminate, partially compensating forthe effects of conversion. The design of durable concreteusing this type of cement must therefore be based on long-term performance, not on the high but transient strengthsthat can occur initially.

Long-term compressive strengths of 40 MPa are typi-cal for properly designed calcium aluminate cement con-crete. Higher strengths can be obtained with limestonecoarse aggregate, as compared with some other aggre-gates, which do not perform as well. For this reason it isrecommended that calcium aluminate cement not be usedfor certain types of construction, such as prestressed con-crete. Based on these facts, concrete should be propor-tioned with a total water (including water absorbed by theaggregate) to cement ratio of not more than 0.40 and witha minimum cement content of 400 kg/m3. Because of even-tual conversion, calcium aluminate cement is often used innonstructural applications and used with caution (or not atall) in structural applications (Taylor 1997).

Magnesium Phosphate CementsMagnesium phosphate cement is a rapid setting, earlystrength gain cement. It is usually used for special applica-tions, such as repair of pavements and concrete structuresor for resistance to certain aggressive chemicals. It does notcontain portland cement.

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If a given type is not available, comparable results fre-quently can be obtained with one of the available types.For example, high-early-strength concrete can be made byusing mixtures with higher Type 10 cement contents andlower water-cementing materials ratios. Also, the effects ofheat of hydration can be minimized by using lean mixes,smaller placing lifts, artificial cooling, or by adding a poz-zolan to the concrete.

Blended cements are available in most parts ofCanada; however, certain types of blended cement maynot be available in all areas. When blended cements arerequired but are not available, similar properties may beobtained by adding pozzolans [CSA A23.5 (ASTM C 618)]or finely ground granulated blast-furnace slag [CSA A23.5(ASTM C 989)] to the concrete at a ready mix plant usingnormal portland cement. Like any concrete mixture, thesemixes should be tested for time of set, strength gain, dura-bility, and other properties prior to use in construction.

Drinking Water ApplicationsConcrete has demonstrated decades of safe use in drinkingwater applications. Materials in contact with drinking watermust meet special requirements to control elements enteringthe water supply. Some localities may require that cementand concrete meet the special requirements of the AmericanNational Standards Institute/National Sanitation Founda-tion standard ANSI/NSF 61, Drinking Water System Compo-nentsHealth Effects. ANSI/NSF 61 is being adopted toassure that products such as pipe, coatings, process media,and plumbing fittings are safe for use in public drinkingwater systems. Cement is used in drinking water systemcomponents such as pipe and tanks, and therefore, is subjectto testing under Standard 61. Kanare (1995) outlines thespecifications and testing program required to certifycement for drinking water applications. Kanare and West(1993) and PCA (1992) address elements that can leach fromcement and concrete. Consult the local building code orlocal officials to determine if National Sanitation Foundationcertified cements are required for water projects such as con-crete pipe and concrete tanks (Fig. 2-24).

European Cement SpecificationsIn some instances, projects in Canada designed by engi-neering firms from other countries refer to cement stan-dards other than those in CSA or ASTM. For example, theEuropean cement standard (EN 197-1, -2, 2000) sometimesappears on project specifications. EN 197 cement TypesCEM I, II, III, IV, and V do not correspond to the cementtypes in CSA A5 (ASTM C 150), nor can a CSA cement besimply used in place of an EN specified cement withoutthe designers approval. CEM I is a portland cement andCEM II through V are blended cements. EN 197 also hasstrength classes and ranges (32.5, 42.5, and 52.5 MPa).There is no direct equivalency between CSA and othercement standards because of different test methods anddifferent limits on required properties. EN 197 cements arenot available in Canada and therefore the best approach isto inform the designer as to what cements are locally avail-able and ask for a change in the project specifications toallow a CSA cement.

CHEMICAL COMPOUNDS ANDHYDRATION OF PORTLAND CEMENTDuring the burning operation in the manufacture of port-land cement clinker, calcium combines with the other com-ponents of the raw mix to form four principal compoundsthat make up 90% of cement by mass. Gypsum (4% to 6%),or other calcium sulphate source, and grinding aids arealso added upon grinding. Cement chemists use the fol-lowing chemical shorthand (abbreviations) to describecompounds:

A= Al2O3, C=CaO, F= Fe2O3, H=H2O, M=MgO, S= SiO2,and = SO3.

The term phase can also be used to describe thecompounds of clinker. Following are the four primarycompounds in portland cement, their approximate chemi-cal formulas, and abbreviations:

Tricalcium silicate 3CaOSiO2 = C3SDicalcium silicate 2CaOSiO2 = C2STricalcium aluminate 3CaOAl2O3 = C3ATetracalcium

aluminoferrite 4CaOAl2O3Fe2O3 = C4AF

Following are the forms of calcium sulphate, their approx-imate chemical formulas, and abbreviations:

Anhydrous calciumsulphate CaSO4 = CaOSO3 = C

Calcium sulphatedihydrate (gypsum) CaSO42H2O =

CaOSO32H2O = CH2Calcium sulphate

hemihydrate CaSO41/2 H2O =CaOSO31/2 H2O = CH1/2

39

Fig. 2-24. Concrete has demonstrated decades of safe use indrinking water applications such as concrete tanks. (IMG12467)

BKerkhoffVideo


Gypsum is the predominant source of sulphate foundin cement.

C3S and C2S in clinker are also referred to as alite andbelite, respectively. Alite constitutes 50% to 70% of the clink-er, whereas belite accounts for only 15% to 30%. Aluminatecompounds constitute about 5% to 10% of the clinker andferrite compounds 5% to 15% (Taylor 1997). These andother compounds may be observed and analyzed throughthe use of microscopical techniques (see ASTM C 1356, Fig.2-25, and Campbell 1999).

In the presence of water, these compounds hydrate(chemically combined with water) to form new com-pounds that are the infrastructure of hardened cementpaste in concrete (Fig. 2-26). The calcium silicates, C3S andC2S, hydrate to form the compounds calcium hydroxide

and calcium silicate hydrate (archaically called tobermoritegel). Hydrated portland cement contains 15% to 25% cal-cium hydroxide and about 50% calcium silicate hydrate bymass. The strength and other properties of hydratedcement are due primarily to calcium silicate hydrate (Fig.2-27). C3A reacts with water and calcium hydroxide toform tetracalcium aluminate hydrate. C4AF reacts withwater to form calcium aluminoferrite hydrate. C3A, sul-phates (gypsum, anhydrite, or other sulphate source), andwater combine to form ettringite (calcium sulphoalumi-nate hydrate), monosulphoaluminate, and other relatedcompounds. These basic compound transformations areshown in Table 2-5. Brunauer (1957), Copeland and others(1960), Lea (1971), Powers and Brownyard (1947), Powers(1961), and Taylor (1997) addressed the pore structure and

40

Fig. 2-25. (left) Polished thin-section examination of portland clinker shows alite (C3S) as light, angular crystals. The darker,rounded crystals are belite (C2S). Magnification 400X. (right) Scanning electron microscope (SEM) micrograph of alite (C3S)crystals in portland clinker. Magnification 3000X. (IMG12466, IMG12465)

Fig. 2-26. Electron micrographs of (left) dicalcium silicate hydrate, (middle) tricalcium silicate hydrate, and (right) hydratednormal portland cement. Note the fibrous nature of the calcium silicate hydrates. Broken fragments of angular calcium hy-droxide crystallites are also present (right). The aggregation of fibres and the adhesion of the hydration particles is respon-sible for the strength development of portland cement paste. Reference (left and middle) Brunauer 1962 and (right) Copelandand Schulz 1962. (IMG12464, IMG12463, IMG12462)

BKerkhoffVideo

BKerkhoffVideo


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Table 2-5. Portland Cement Compound Hydration Reactions (Oxide Notation)2 (3CaOSiO2) + 11 H2O = 3CaO2SiO28H2O + 3 (CaOH2O)Tricalcium silicate Water Calcium silicate Calcium hydroxide

hydrate (C-S-H)2 (2CaOSiO2) + 9 H2O = 3CaO2SiO28H2O + CaOH2ODicalcium silicate Water Calcium silicate Calcium hydroxide

hydrate (C-S-H)3CaOAl2O3 + 3 (CaOSO32H2O) + 26 H2O = 6CaOAl2O33SO332H2OTricalcium aluminate Gypsum Water Ettringite2 (3CaOAl2O3) + 6CaOAl2O33SO332H2O + 4 H2O = 3 (4CaOAl2O3SO312H2O)Tricalcium aluminate Ettringite Water Calcium monosulphoaluminate3CaOAl2O3 + CaOH2O + 12 H2O = 4CaOAl2O313H2OTricalcium aluminate Calcium hydroxide Water Tetracalcium aluminate hydrate4CaO Al2O3Fe2O3 + 10 H2O + 2 (CaOH2O) = 6CaOAl2O3Fe2O312H2OTetracalcium Water Calcium hydroxide Calcium aluminoferrite hydratealuminoferrite

Note: This table illustrates only primary transformations and not several minor transformations. The composition of calcium silicate hydrate (C-S-H) is not stoichiometric (Tennis and Jennings 2000).

Porosity

Amou

nt

C-S-H

Ca(OH)2

C4(A, F)H13

Ettringite

Age: Minutes Hours Days0 5 30 7 2 6 7 2 7 28 90

Mono

sulphate

0

25

50

75

100

0 25 50 75 100Degree of hydration, %

Rel

ativ

e vo

lum

e, %

other

capillaryporosity

C-S-H

calciumhydroxideAFt andAFmcalciumsulphate

C4 AF

C3 A

C2S

C3S

Fig. 2-28. Relative volumes of the major compounds in the microstructure of hydrating portland cement pastes (left) as afunction of time (adapted from Locher, Richartz, and Sprung 1976) and (right) as a function of the degree of hydration asestimated by a computer model for a water to cement ratio of 0.50 (adapted from Tennis and Jennings 2000). Values are givenfor an average Type 10 (Type I) cement composition (Gebhardt 1995): C3S=55%, C2S=18%, C3A=10% and C4AF=8%. AFt andAFm includes ettringite (AFt) and calcium monosulphoaluminate (AFm) and other hydrated calcium aluminate compounds.See Table 2-5 for compound transformations.

Fig. 2-27. Scanning-electron micrographs of hardened cement paste at (left) 500X, and (right) 1000X. (IMG12461, IMG12460)


Dicalcium Silicate, C2S, hydrates and hardens slowlyand contributes largely to strength increase at agesbeyond one week.Tricalcium Aluminate, C3A, liberates a large amount ofheat during the first few days of hydration and hardening.It also contributes slightly to early strength development.Cements with low percentages of C3A are more resistant tosoils and waters containing sulphates.Tetracalcium Aluminoferrite, C4AF, is the product result-ing from the use of iron and aluminum raw materials toreduce the clinkering temperature during cement manu-facture. It hydrates rather rapidly but contributes very little

chemistry of cement paste. Fig. 2-28 shows estimates of therelative volumes of the compounds in hydrated portlandcement pastes.

A web-based computer model for hydration andmicrostructure development can be found at NIST (2001)[http://vcctl.cbt.nist.gov]. The Concrete MicroscopyLibrary (Lange and Stutzman 1999) provides a collection ofmicrographs of cement hydration and concrete athttp://www.cee.ce.uiuc.edu/lange/micro , 1999.

The approximate percentage of each compound can becalculated from a chemical oxide analysis (ASTM C 114) ofthe unhydrated cement as per ASTM C 150 (Bogue calcula-tions). Due to the inaccuracies of Bogue calculations, X-raydiffraction techniques can be used to more accurately deter-mine compound percentages (ASTM C 1365). Table 2-6shows typical elemental and compound composition andfineness for each of the principal types of portland cement.

Although elements are reported as simple oxides forstandard consistency, they are usually not found in thatoxide form in the cement. For example, sulphur from thegypsum is reported as SO3 (sulphur trioxide), however,cement does not contain any sulphur trioxide. The amountof calcium, silica, and alumina establish the amounts of theprimary compounds in the cement and effectively the prop-erties of hydrated cement. Sulphate is present to control set-ting, as well as drying shrinkage and strength gain (Tang1992). Minor and trace elements and their effect on cementproperties are discussed by Bhatty (1995) and PCA (1992).Present knowledge of cement chemistry indicates that theprimary cement compounds have the following properties:Tricalcium Silicate, C3S, hydrates and hardens rapidly andis largely responsible for initial set and early strength (Fig.2-29). In general, the early strength of portland cement con-crete is higher with increased percentages of C3S.

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Table 2-6. Chemical and Compound Composition and Fineness of Cements*Type of Chemical composition, % Potential compound composition,% Blaineportland Loss on fineness, cement SiO2 Al2O3 Fe2O3 CaO MgO SO3 Ignition, % Na2O eq C3S C2S C3A C4AF m2/kg

I (min-max) 18.7-22.0 4.7-6.3 1.6-4.4 60.6-66.3 0.7-4.2 1.8-4.6 0.6-2.9 0.11-1.20 40-63 9-31 6-14 5-13 300-421I (mean) 20.5 5.4 2.6 63.9 2.1 3.0 1.4 0.61 54 18 10 8 369II** (min-max) 20.0-23.2 3.4-5.5 2.4-4.8 60.2-65.9 0.6-4.8 2.1-4.0 0.0-3.1 0.05-1.12 37-68 6-32 2-8 7-15 318-480II** (mean) 21.2 4.6 3.5 63.8 2.1 2.7 1.2 0.51 55 19 6 11 377III (min-max) 18.6-22.2 2.8-6.3 1.3-4.9 60.6-65.9 0.6-4.6 2.5-4.6 0.1-2.3 0.14-1.20 46-71 4-27 0-13 4-14 390-644III (mean) 20.6 4.9 2.8 63.4 2.2 3.5 1.3 0.56 55 17 9 8 548IV (min-max) 21.5-22.8 3.5-5.3 3.7-5.9 62.0-63.4 1.0-3.8 1.7-2.5 0.9-1.4 0.29-0.42 37-49 27-36 3-4 11-18 319-362IV (mean) 22.2 4.6 5.0 62.5 1.9 2.2 1.2 0.36 42 32 4 15 340V (min-max) 20.3-23.4 2.4-5.5 3.2-6.1 61.8-66.3 0.6-4.6 1.8-3.6 0.4-1.7 0.24-0.76 43-70 11-31 0-5 10-19 275-430V (mean) 21.9 3.9 4.2 63.8 2.2 2.3 1.0 0.48 54 22 4 13 373White (min-max) 22.0-24.4 2.2-5.0 0.2-0.6 63.9-68.7 0.3-1.4 2.3-3.1 1.2-2.2 0.09-0.38 51-72 9-25 5-13 1-2 384-564White (mean) 22.7 4.1 0.3 66.7 0.9 2.7 1.6 0.18 63 18 10 1 482* Values represent a summary of combined statistics. Air-entraining cements are not included. For consistency in reporting, elements are

reported in a standard oxide form. This does not mean that the oxide form is present in the cement. For example, sulphur is reported as SO3,sulphur trioxide, but portland cement does not have sulphur trioxide present. Potential Compound Composition refers to ASTM C 150calculations using the chemical composition of the cement. The actual compound composition may be less due to incomplete or alteredchemical reactions.

** Includes fine grind cements. Adapted from PCA (1996) and Gebhardt (1995).

C3S

C3AC4AFOverall

C2S

0 20 40 60 80 100Age, days

100%

80%

60%

40%

20%

0%

Deg

ree o

f rea

ctio

n, %

by

mas

s

Fig. 2-29. Relative reactivity of cement compounds. Thecurve labeled overall has a composition of 55% C3S, 18%C2S, 10% C3A, and 8% C4AF, an average Type I (Type 10)cement composition (Tennis and Jennings 2000).

to strength. Most colour effects that make cement gray aredue to C4AF and its hydrates.

Calcium Sulphate, as anhydrite (anhydrous calciumsulphateC), gypsum (calciumsulphate dihydrateCH2), or hemihydrate, often called plaster of Paris or bas-sanite (calcium sulphate hemihydrateCH1/2) is addedto cement during final grind to provide sulphate to reactwith C3A to form ettringite (calcium sulphoaluminate).This controls the hydration of C3A. Without sulphate, acement would set rapidly. In addition to controlling settingand early strength gain, the sulphate also helps controldrying shrinkage and can influence strength through 28days.

In addition to the above primary cement compounds,numerous other lesser compound formulations also exist(PCA 1997, Taylor 1997, and Tennis and Jennings 2000).

Water (Evaporable and Nonevaporable)Water is a key ingredient of pastes, mortars, and concretes,as the phases in portland cement must chemically reactwith water to develop strength. The amount of wateradded to a mixture controls the durability as well. Thespace initially taken up by water in a cementitious mixtureis partially or completely replaced over time as the hydra-tion reactions proceed (Table 2-5). If more than about 35%water by mass of cementa water to cement ratio of 0.35is used, the porosity in the hardened material will remain,even after complete hydration. This is called capillaryporosity. Fig. 2-30 shows cement pastes with high and lowwater to cement ratios have equal masses after drying(evaporable water was removed). The cement consumedthe same amount of water in both pastes resulting in morebulk volume in the higher water-cement ratio paste. As thewater to cement ratio increases, the capillary porosityincreases, and the strength decreases. Also, transport prop-

43


erties such as permeability and diffusivity are increased,allowing detrimental chemicals to more readily attack theconcrete or reinforcing steel.

Water is found in cementing materials in severalforms. Free water is mixing water that has not reacted withthe cement pastes. Bound water is chemically combined inthe solid phases or physically bound to the solid surfaces.A reliable separation of the chemically-combined from thephysically-absorbed water is not possible. Therefore,Powers (1949) distinguished between evaporable andnonevaporable water. The non-evaporable water is theamount retained by a sample after it has been subjected toa drying procedure intended to remove all the free water(traditionally, by heating to 105C). Evaporable water wasoriginally considered to be free water, but it is now recog-nized that some bound water is also lost upon heating tothis temperature. All nonevaporable water is bound water,but the opposite is not true.

For complete hydration of portland cement, onlyabout 40% water (a water-to-cement ratio of 0.40) is needed.If a water to cement ratio greater than about 0.40 is used,the excess water not needed for cement hydration remainsin the capillary pores or evaporates. If a water-to-cementratio less than about 0.40 is used, some cement will remainunhydrated.

To estimate the degree of hydration of a hydratedmaterial, the nonevaporable water content is often used. Toconvert the measured nonevaporable water into degrees ofhydration, it is necessary to know the value of nonevap-orable water-to-cement ratio (wn/c) at complete hydration.Experimentally, this can be determined by preparing ahigh water-to-cement ratio cement paste (for example, 1.0)and continuously grinding while it hydrates in a rollermill. In this procedure, complete hydration of the cementwill typically be achieved after 28 days.

Alternatively, an estimate of the value of non-evaporable water-to-cement ratio (wn/c) at completehydration can be obtained from the potential Bogue com-position of the cement. Nonevaporable water contents forthe major compounds of portland cement are provided inTable 2-7. For a typical Type 10 cement, these coefficientswill generally result in a calculated wn/c for completelyhydrated cement somewhere between 0.22 and 0.25.

Fig. 2-30. Cement paste cylinders of equal mass and equalcement content, but mixed with different water-to-cementratios, after all water has evaporated from the cylinders. (IMG12302)

Table 2-7. Nonevaporable Water Contents for FullyHydrated Major Compounds of Cement

NonevaporableHydrated cement (combined) water content

compound (g water/g cement compound)C3S hydrate 0.24C2S hydrate 0.21C3A hydrate 0.40

C4AF hydrate 0.37Free lime (CaO) 0.33

PHYSICAL PROPERTIES OF CEMENTSpecifications for cement place limits on both its physicalproperties (performance) and often, chemical composition.An understanding of the significance of some of the phys-ical properties is helpful in interpreting results of cementtests. Tests of the physical properties of the cements shouldbe used to evaluate the properties of the cement, ratherthan the concrete. Cement specifications limit the proper-ties with respect to the type of cement. Cement should besampled in accordance with CSA A456.2-A1 (ASTM C183). During manufacture, cement is continuously moni-tored for its chemistry and the following properties:

Particle Size and FinenessPortland cement consists of individual angular particleswith a range of sizes, the result of pulverizing clinker in thegrinding mill (Fig. 2-31 top). Approximately 85% to 95% ofcement particles are smaller than 45 m, with the averageparticle around 15 m. Fig. 2-31 bottom illustrates the par-ticle size distribution for a portland cement. The overallparticle size distribution of cement is called fineness. Thefineness of cement affects heat released and the rate ofhydration. Greater cement fineness (smaller particle size)increases the rate at which cement hydrates and thus accel-

erates strength development. The effects of greater finenesson paste strength are manifested principally during thefirst seven days.

Cement fineness can be measured by a number ofmethods. One of the methods by which it is measured iscalled the Blaine air-permeability test (ASTM C 204Fig.2-32); it indirectly measures the surface area of the cementparticles per unit mass. Cements with finer particles havemore surface area in square metres per kilogram ofcement. The older use of square centimetres per gram forreporting fineness is now considered outdated. TheWagner turbidimeter test (ASTM C 115Fig. 2-32), canalso be used.

44


Cum

ulat

ive m

ass,

per

cent

100

80

60

40

20

0100 50 20 10 5 2 1 0.5

Equivalent spherical diameter, m

Typical partical sizedistribution curve for Type 10 or Type 20 cement

Fig. 2-31. (top) Scanning-electron micrograph of powderedcement at 1000X and (bottom) particle size distribution of aportland cement. (IMG12459)

Fig. 2-32. Blaine test apparatus (top) and Wagner turbi-dimeter (bottom) for determining the fineness of cement.Wagner fineness values are a little more than half of Blainevalues. (IMG12303, IMG12458)

In Canada fineness is measured by CSA Test MethodA 456.2-A3, Test Method for Determination of Cement Fine-ness by Wet-Sieving (ASTM C 430Fig. 2-33). The finenessis expressed as a percentage retained on the 45-m sieve.Electronic (x-ray or laser) particle size analyzers can also beused to test fineness (Fig. 2-34). Examples of Blaine finenessdata are given in Table 2-6.

ing cement testing, pastes are mixed to normal consistencyas defined by a penetration of 101 mm of the Vicat plung-er. see CSA A456.2-B1 (ASTM C 187) and Fig. 2-36.

Mortars are mixed toobtain either a fixedwater-cement ratio or toyield a flow within aprescribed range. Theflow is determined on aflow table as describedin CSA A456.3 (ASTMC 230), Fig. 2-37. Boththe normal consistency


SoundnessSoundness refers to the ability of a hardened paste to retainits volume. Lack of soundness or delayed destructive ex-pansion can be caused by excessive amounts of hard-burned free lime or magnesia. Most specifications forportland cement limit the magnesia (periclase) content andthe maximum expansion as measured by the autoclave-expansion test. Since adoption of the autoclave-expansion

chap_02

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