TN59

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TN59
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  This new edition of this Technical Note supersedesthe 1989 edition Hydraulic Cements – Properties and Characteristics  (TN 59) published by theCement and Concrete Association of Australia. Thesuperseded document was based on the then-current Australian Standards AS 1315 Portland Cement  and AS 1317 Blended Cement  which havesince been replaced by AS 3972—1997 Portland and Blended Cements  1 . This Technical Note takesaccount of this new Standard. 1INTRODUCTION ‘Cement’ is a generic term used to describe a widevariety of organic and inorganic binding agents. Themost widely used binding agents are those knownas hydraulic cements – finely ground inorganicmaterials which possess a strong hydraulic bindingaction, ie when mixed with water they harden togive a stable, durable product.There are many types of hydraulic cement andthis Technical Note discusses those available to theconstruction industry. 2FIELDS OF APPLICATION The main use for hydraulic cement is themanufacture of concrete. Some limits will be placedon the choice of concrete for a particular structure,eg by the construction techniques, the serviceconditions, the environment, and the structuralbehaviour of individual elements and the structure.Such constraints may make the use of a certain typeor types of cement more appropriate than others. 3PORTLAND AND BLENDED CEMENTS 3.1General Hydraulic cements produced in Australia fallbroadly into two categories: portland cements andblended cements. The latter are mixtures ofportland cement with other materials which eitherpossess cementitious properties of their own, egground granulated iron blastfurnace slags, or whichare pozzolanic in nature, ie they react with lime inthe presence of water to form cementitiouscompounds, eg fly ash and silica fume. Portlandand blended cements are manufactured in Australiato comply with the requirements of AS 3972 Portland and Blended Cements  1 . A number ofdifferent types of cements are covered by thisStandard. A summary of their physical and chemicalproperties specified in AS 3972 is given in Table 1 . 59 MAY 1998 Cements –oroperties andcharacteristics Cements – Properties and Characteristics S Guirguis BE(Hons) PhD MIEAust CPEng      T     E     C     H     N     I     C     A     L    n    o     t    e  AS 3972 is a performance based specification inwhich portland and blended cements are defined interms of their performance characteristics. As theraw materials used to produce portland andblended cements can vary widely from locality tolocality, the chemical composition of cements canalso vary quite widely. Nevertheless, with moderntechnology, from these diverse materials it ispossible to produce cements which have similarphysical characteristics. Hence, AS3972 specifiesonly those restrictions on chemical compositionwhich are necessary to ensure satisfactoryperformance, eg upper limits on the MgO and SO 3 contents to guard against excessive long-termvolumetric expansion of the hydrated cement paste. 3.2General Purpose Portland Cement – Type GP In keeping with world-wide practice, portlandcements complying with AS 3972 may contain up to5% mineral additions. Mineral additions are definedas being selected fly ash, slag, limestone containingmore than 80% calcium carbonate, or combinationsof these materials. Fly ash and slag are to complywith the requirements of AS3582.1 and AS3582.2respectively 3 .Thus portland cement is defined in AS 3972 as ahydraulic cement which is manufactured as ahomogenous product by grinding together portlandcement clinker and calcium sulfate, and which atthe discretion of the cement manufacturer maycontain up to 5% of mineral additions.General purpose portland cement is intendedfor use in most forms of concrete construction andshould be specified where the special properties ofthe other types, such as low heat of hydration, arenot required.As the raw materials used to produce portlandcements vary widely from location to location, Type GP cements may have a range of chemicalcompositions. The restrictions placed on thechemical and physical properties of Type GP cementby AS 3972 are those necessary to ensuresatisfactory performance as a general purposecement. 3.3General Purpose Blended Cement – Type GB Blended cement is defined in AS 3972 as a hydrauliccement containing portland cement and a quantitygreater than 5% of fly ash or slag or both and/or upto 10% silica fume. Fly ash, slag and silica fume areto comply with the requirements of the relevantparts of AS 3582 Supplementary Cementitious Materials for Use with Portland Cement  3 .General purpose blended cement is intended foruse in most forms of concrete construction wherethe special properties of other cement types are notrequired.By varying the proportions of portland cementand fly ash, slag, and silica fume in blended cementit is possible to produce cements with a fairly widerange of characteristics. In practice, however, thedifference in properties between Types GP and GB Page 2 Cements – Properties and Characteristics Table 1Summary of AS 3972 RequirementsCement typesAS 3972 Requirements * GPGBHELHSLSRChemical limitations Loss on ignitionreported if required – no limit is specifiedSulfuric anhydride SO 3 (max)%3.53.53.53.53.53.5MgOPortland cement clinker shall contain less than 4.5% Physical properties Setting timeMinimum (minutes)454545454545Maximum (hours)101010101010Soundness maximum (mm)555555Compressive strength minimum (MPa)3 days––20–––7 days25153010201528 days4030–303030Peak temperature rise maximum ˚(C)–––23––Drying shrinkage maximum (microstrain)28-day––––750–Sulfate expansion maximum (microstrain)16-week–––––900*Determined in accordance with the methods set out in AS 2350 Methods of Testing Portland and Blended Cements  2  may not be great, as both are formulated to be usedin general building construction.A possible exception to this are those Type GBcements containing silica fume, which are oftenintended to be used for particular applicationswhere high early strengths or specific durabilityrequirements are sought.Whilst the minimum strengths specified for TypeGB cement in AS 3972 are lower than those for TypeGP (in recognition of their generally lower rate ofstrength gain), it is not uncommon for their ultimatestrengths to equal or exceed those of Type GPcement, provided moisture is available (eg throughcuring) for a sufficient length of time Figure 1 .It should be noted that Type GB cementscontaining up to 10% silica fume would be expectedto have a different strength development curve tothat of other Type GB cements shown in Figure 1 . 3.4High Early Strength Cement – Type HE As the name implies, Type HE cement developsstrength more rapidly than Type GP or Type GBcements. Rapid strength development should not beconfused with rapid setting, the latter being the rateat which the cement paste loses its plasticity. Mostcements have somewhat similar setting times butmay have significantly different rates of strengthdevelopment.High early strength cement lends itself toapplications where rapid strength development isrequired, eg when formwork is to be removed earlyfor reuse, or where early strength is required sothat further construction can proceed. Rapidstrength development is usually accompanied by ahigher rate of heat evolution. Hence, Type HEcement should not be used in thick concretesections or in mass construction. On the otherhand, its use for construction under cold weatherconditions is beneficial.The typical strength development of concretemade with Type HE cement is shown in Figure 2 . 3.5Low Heat Cement – Type LH Type LH cement is intended for use where limitationof the heat of hydration (and hence the temperaturerise in the concrete) is necessary to avoidunacceptable thermal stresses, such as in massivestructures or in thick structural elements. Low heatcement may be a portland or a blended cementprovided it meets the requirements for temperaturerise specified in AS 3972 Table 1.Low heat characteristics are achieved byreducing the content of the more rapidly hydratingcompounds in cement or by blending with supple-mentary cementitious materials. This, generally,will result in a slower rate of strength development.Blended cements can have some inherentadvantages in minimising heat evolution because oftheir generally lower rates of strength gain.However, the ultimate strength of Type LHcement may be equivalent to, or higher than, thatfor other types of cement Figure 2 . 3.6Shrinkage Limited Cement – Type SL For many years, some major specifications inAustralia have recommended chemical compositionof cement as a means of controlling the shrinkageof cements to be used in concrete structures. Withinthe scope of AS 3972, a cement characterised interms of its shrinkage performance was required toreflect/cover the existing practice in some areasand applications.Type SL cement is intended for use whereemphasis is placed on drying shrinkage and crackcontrol in concrete structures (eg road pavementsand bridge structures). Type SL cement may be aportland or a blended cement provided it meets thedrying shrinkage limit specified in AS 3972 Table 1. 3.7Sulfate Resisting Cement – Type SR The relationship between the sulfate resistance ofportland cement and its tricalcium aluminate (C 3 A)content is well established. Portland cementcontaining less than 5% C 3 A is classified as sulfateresisting cement in many codes and standards forcement world-wide, including Australia until recently.Studieshaveshownthatcementspotentiallycontaining less calcium hydroxide on hydrationperform well in sulfate exposure, eg certainblended cements. A limit on C 3 A content for thesecements is neither appropriate nor applicable.Therefore, as a performance based specifi-cation,AS 3972 replaced the limit on C 3 A for sulfateresisting portland cement by a performance testand a performance limit (expansion limit) suitable Cements – Properties and Characteristics Page 3 ;; ;; ;; ;;; ;;;  ;;;;;;;;;;;;    %    O   F   2   8  -   D   A   Y   C   O   M   P   R   E   S   S   I   V   E   S   T   R   E   N   G   T   H AGE (days)20406080001 7 28 90100120140160Type GBType GP3 Figure 1: Typical development of concrete strengthwith age  for Type SR cement, being portland or blendedcement Table 1 .The formulation of Type SR, as a blendedcement, or as a portland cement with a low C 3 Acontent, may produce a cement having a lower rateof strength development at early age than, say, TypeGP cement Figure 2 . Hence, the minimum strengthrequirements in AS 3972 for Type SR cement arelower than those for Type GP cement Table 1 .Type SR cement is intended primarily for usewhere resistance to sulfates in solution is required.Type SR cement may be a portland or a blendedcement provided it meets the sulfate expansionlimit specified in AS 3972 Table 1. 4OTHER TYPES OF CEMENT 4.1General There is a continual growth in the types of cementavailable to the construction industry. Most of thesecements have limited uses and the output of themis very small.The following is a brief description of other typesof cement available in Australia (manufactured orimported) and their applications. 4.2Masonry Cement Masonry cement is intended mainly for use in mortarfor brick, stone and concrete block construction.It is a finely ground mixture of portland cementclinker, gypsum (calcium sulfate) and suitableinorganic materials such as hydrated lime,limestone and pozzolans. Air-entraining agents,water-reducers (plasticisers) and water-repellentsubstances, etc may also be incorporated.Masonry cement is produced to meet therequirements of Australian Standard AS 1316 Masonry Cement  .It is characterised by producing mortars of highworkability and high water retentivity, but whichhave lower strength and a lower rate of strengthdevelopment than portland cement mortar. Thesecharacteristics make masonry cement especiallysuitable for masonry work. It is unsuitable for anyform of structural concrete (plain, reinforced orprestressed). 4.3Off-white and White Portland Cement The grey colour of portland cement is due mainly tothe ferrite phase – tetracalcium aluminoferrite, C 4 AF.By lowering the iron content, off-white and whitecements can be produced. This is achieved by usingraw materials low in iron and manganese oxides.Because of more-costly raw materials and specialrequirements in manufacturing, off-white and whitecements are more expensive than the more widelyused grey portland cements.The composition of off-white and white cementsis characterised by relatively high C 3 A contents (9 to 15%) and low C 4 AF contents (1.5 to 2% for off-white and 0.3 to 0.4% for pure white cements).Off-white and white cements are used foraesthetic reasons. Since relatively high cementcontents are normal in this application, denseconcrete of low water-cement ratio, which arerequired properties for durability, can be obtained.However, due to the high C 3 A content of this type ofcement, it should not be used in low heat or sulfateresisting applications. Page 4 Cements – Properties and Characteristics    %    O   F   2   8  -   D   A   Y   C   O   M   P   R   E   S   S   I   V   E   S   T   R   E   N   G   T   H AGE (days)2040HEGPLHSLSRGBHEGPLHGB, SR, SL608000 1 7 28 901001201401603 Figure 2: Typical concrete strength development with age for various cements. Note: Types SR and SLcements may be portland or blended cements. If required, specific strength development data should be sought from the manufacturer.  There is no specific Australian Standard for thesetypes of cement, but off-white cement ismanufacturedin Australia to meet the requirementsfor Type GP, GB or HE cements in AS3972. Off-white and white cements imported into Australiaare generally required to comply with AS 3972 also. 4.4Coloured Cements Most coloured cements consist of cement andinorganic pigments interground or mixed together,although some are produced from clinkers having acharacteristic colour derived from the rawmaterials or the manufacturing process.In the production of coloured cements withpigments, the base is either grey cement (for darkcolours) or the more costly off-white or whitecement (for light colours).To be suitable for use with cements, pigmentsare required to be colour-fast under exposure tolight and weather and of a chemical compositionsuch that the pigment is neither affected by thecement, nor detrimental to its setting, hardening,and durability characteristics. Pigments should notcontain salts which may cause efflorescence. 4.5Oil-well Cement Oil-well cement is used in the petroleum industry togrout oil and gas wells. In these applications, thecement slurry must remain sufficiently fluid (attemperatures ranging from normal to about 200˚Cand under pressures ranging from atmospheric toabout 125 MPa) for the several hours needed topump it into position. It should then harden fairlyrapidly. It may also have to resist corrosiveconditions resulting from sulfur gases or waterscontaining dissolved salts.Oil-well cements are modified portland cementsthat are designed to serve this need. They consist ofcoarsely ground portland cement of low C 3 A content,with or without a retarder.The properties required of oil-well cements areset out in the American Petroleum InstituteStandard STD 10A API Specification for Oil-well Cements and Cement Additives  . They aresubdivided into six classes, each applicable to aspecified range of well depths, temperature andcorrosion conditions.Special methods of testing oil-well cements forthickening times and strength under conditions ofhigh temperature and pressure have beendeveloped and are covered by the AmericanPetroleum Institute Standard API RP-10B Recommended Practice for Testing Oil-Well Cements and Cement Additives  . 4.6High Alumina Cement (HAC) HAC is entirely different from portland cement in itschemical composition and in its characteristics. Thedifference is derived from the raw materials fromwhich it is made, principally bauxite and limestone.The product resulting from the chemicalcombination of these two materials is a cementhaving a high alumina (Al 2 O 3 ) content and a low lime(CaO) content as compared with portland cement. Insome literature, HAC is called ‘calcium aluminatecement’, but it is more commonly known as highalumina cement. It is imported into Australia.HAC is characterised by a very rapid rate ofstrength gain which results in very high earlystrengths and high rates of heat evolution. Thelatter characteristic allows hardening to take placeat relatively low temperatures but restricts HAC’suse in mass concrete or in other applications wherehigh rates of heat evolution may cause problems.HAC is resistant to attack by sulfates and sulfatesolutions, a property which, combined with its highearly strength, has led to its use in factory floorsand similar applications. It also finds application inrefractory concrete because of its resistance to veryhigh temperatures.However, HAC may suffer a substantial loss ofstrength in conditions which are both warm (above,say, 25˚C) and humid. Under these conditions, achemical process known as conversion takes place.During this process, some of the hydratedcompounds of the hardened cement paste convertto other compounds of smaller volume. This resultsin a cement paste with reduced strength. The rateat which conversion occurs depends on themoisture condition and temperature of the concrete.Where moisture is present and temperatures areabove 25˚C, the rate is fairly high. Water-cementratio also affects the rate of conversion; the greaterthe srcinal water-cement ratio, the faster the rateof conversion and the lower the converted strength.External chemical agents may also affect the rate ofconversion.Because of the possibility of conversion and lossin concrete strength, the use of HAC in warm humidenvironments should be approached with greatcaution. It should not be used in combination withother types of cement without first checking on theeffect of this on the properties and behaviour of thefresh and hardened concrete. Cements – Properties and Characteristics Page 5
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